SpudFiles Wiki - User contributions [en]

Chronograph

2011-05-29T07:12:32Z

Technician1002: Photo size fixed

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

Sample photo showing Audacity at the cannon discharge. The pre fire hiss of the pilot is shown followed by the piston valve opening. The muzzle blast is the portion with a heavy negative shift due to the pressure front of the muzzle blast.

[[File:Musket_discharge_799.png]]

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record valve opening times. Using more than 2 pickup coils provides the ability to measure changes in speed.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.

[[File:4_inch_coil_detail.jpg‎]]

Pick up coils on a 4 inch barrel for testing. Magnets are embedded in the shirt and ball projectiles.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

== High Speed Photography ==
With the introduction of consumer grade high speed cameras, high speed video is now a reality. With a known camera frame rate and a reference for how far the projectile moved between frames the speed can be calculated with speed = distance/time.

A variation to high speed video is a high speed strobe. This must be done in the dark to prevent overexposure with the long camera shutter time.

This composite was assembled from consecutive frames of the high speed video.
[[File:Tumblecomposite.jpg]]

[[Category:Tools]]

File:Musket discharge 799.png

2011-05-29T07:11:31Z

Technician1002: uploaded a new version of "File:Musket discharge 799.png": Audacity screenshot showing pre discharge pilot hiss. The downward swing is the main muzzle blast pressure wave.

Audacity file expanded on the muzzle blast of a piston cannon showing the pre fire pilot hiss.

File:Tumblecomposite.jpg

2011-05-29T07:06:51Z

Technician1002: uploaded a new version of "File:Tumblecomposite.jpg": Composite photo from high speed video

Composite photo from high speed video showing distance between frames

Chronograph

2011-05-29T06:41:24Z

Technician1002: /* High Speed Photography */

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

Sample photo showing Audacity at the cannon discharge. The pre fire hiss of the pilot is shown followed by the piston valve opening. The muzzle blast is the portion with a heavy negative shift due to the pressure front of the muzzle blast.

I'll fix the photo file size later.. Work in process.
[[File:Musket_discharge_799.png]]

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record valve opening times. Using more than 2 pickup coils provides the ability to measure changes in speed.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.

[[File:4_inch_coil_detail.jpg‎]]

Pick up coils on a 4 inch barrel for testing. Magnets are embedded in the shirt and ball projectiles.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

== High Speed Photography ==
With the introduction of consumer grade high speed cameras, high speed video is now a reality. With a known camera frame rate and a reference for how far the projectile moved between frames the speed can be calculated with speed = distance/time.

A variation to high speed video is a high speed strobe. This must be done in the dark to prevent overexposure with the long camera shutter time.

This composite was assembled from consecutive frames of the high speed video.
[[File:Tumblecomposite.jpg]]

[[Category:Tools]]

Chronograph

2011-05-29T06:37:05Z

Technician1002: /* Sound Based Homemade Chronograph */

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

Sample photo showing Audacity at the cannon discharge. The pre fire hiss of the pilot is shown followed by the piston valve opening. The muzzle blast is the portion with a heavy negative shift due to the pressure front of the muzzle blast.

I'll fix the photo file size later.. Work in process.
[[File:Musket_discharge_799.png]]

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record valve opening times. Using more than 2 pickup coils provides the ability to measure changes in speed.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.

[[File:4_inch_coil_detail.jpg‎]]

Pick up coils on a 4 inch barrel for testing. Magnets are embedded in the shirt and ball projectiles.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

== High Speed Photography ==
With the introduction of consumer grade high speed cameras, high speed video is now a reality. With a known camera frame rate and a reference for how far the projectile moved between frames the speed can be calculated with speed = distance/time.

This composite was assembled from consecutive frames of the high speed video.
[[File:Tumblecomposite.jpg]]

[[Category:Tools]]

Chronograph

2011-05-29T06:35:04Z

Technician1002: /* Sound Based Homemade Chronograph */

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

Sample photo showing Audacity at the cannon discharge. The pre fire hiss of the pilot is shown followed by the piston valve opening. The muzzle blast is the portion with a heavy positive and negative shift from the pressure front of the muzzle blast.

I'll fix the photo file size later.. Work in process.
[[File:Musket_discharge_799.png]]

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record valve opening times. Using more than 2 pickup coils provides the ability to measure changes in speed.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.

[[File:4_inch_coil_detail.jpg‎]]

Pick up coils on a 4 inch barrel for testing. Magnets are embedded in the shirt and ball projectiles.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

== High Speed Photography ==
With the introduction of consumer grade high speed cameras, high speed video is now a reality. With a known camera frame rate and a reference for how far the projectile moved between frames the speed can be calculated with speed = distance/time.

This composite was assembled from consecutive frames of the high speed video.
[[File:Tumblecomposite.jpg]]

[[Category:Tools]]

Chronograph

2011-05-29T06:33:29Z

Technician1002: /* Sound Based Homemade Chronograph */ Added Audacity screen shot.

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

Sample photo showing Audacity at the cannon discharge. The pre fire hiss of the pilot is shown followed by the piston valve opening. The muzzle blast is the portion with a heavy positive and negative shift from the pressure front of the muzzle blast.
[[File:Musket_discharge_799.png]]

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record valve opening times. Using more than 2 pickup coils provides the ability to measure changes in speed.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.

[[File:4_inch_coil_detail.jpg‎]]

Pick up coils on a 4 inch barrel for testing. Magnets are embedded in the shirt and ball projectiles.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

== High Speed Photography ==
With the introduction of consumer grade high speed cameras, high speed video is now a reality. With a known camera frame rate and a reference for how far the projectile moved between frames the speed can be calculated with speed = distance/time.

This composite was assembled from consecutive frames of the high speed video.
[[File:Tumblecomposite.jpg]]

[[Category:Tools]]

File:Musket discharge 799.png

2011-05-29T06:29:11Z

Technician1002: Audacity file expanded on the muzzle blast of a piston cannon showing the pre fire pilot hiss.

Audacity file expanded on the muzzle blast of a piston cannon showing the pre fire pilot hiss.

Chronograph

2011-05-29T06:08:29Z

Technician1002: /* Magnetic Based Homemade Chronograph */

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record valve opening times. Using more than 2 pickup coils provides the ability to measure changes in speed.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.

[[File:4_inch_coil_detail.jpg‎]]

Pick up coils on a 4 inch barrel for testing. Magnets are embedded in the shirt and ball projectiles.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

== High Speed Photography ==
With the introduction of consumer grade high speed cameras, high speed video is now a reality. With a known camera frame rate and a reference for how far the projectile moved between frames the speed can be calculated with speed = distance/time.

This composite was assembled from consecutive frames of the high speed video.
[[File:Tumblecomposite.jpg]]

[[Category:Tools]]

Chronograph

2011-05-29T06:03:25Z

Technician1002: /* High Speed Photography */

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record valve opening times. Using more than 2 pickup coils the ability to measure changes in speed is possible.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.

[[File:4_inch_coil_detail.jpg‎]]

Pick up coils on a 4 inch barrel for testing. Magnets are embedded in the shirt and ball projectiles.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

== High Speed Photography ==
With the introduction of consumer grade high speed cameras, high speed video is now a reality. With a known camera frame rate and a reference for how far the projectile moved between frames the speed can be calculated with speed = distance/time.

This composite was assembled from consecutive frames of the high speed video.
[[File:Tumblecomposite.jpg]]

[[Category:Tools]]

Chronograph

2011-05-29T06:01:52Z

Technician1002: /* High Speed Photography */

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record valve opening times. Using more than 2 pickup coils the ability to measure changes in speed is possible.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.

[[File:4_inch_coil_detail.jpg‎]]

Pick up coils on a 4 inch barrel for testing. Magnets are embedded in the shirt and ball projectiles.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

== High Speed Photography ==
With the introduction of consumer grade high speed cameras, high speed video is now a reality. With a known camera frame rate and a reference for how far the projectile moved between frames and the speed can be calculated.
This composite was assembled from consecutive frames of the high speed video.
Note this edit is a work in progress please be patient as I fix the photo.
[[File:Tumblecomposite.jpg]]

[[Category:Tools]]

Chronograph

2011-05-29T06:00:20Z

Technician1002: /* High Speed Photography */

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record valve opening times. Using more than 2 pickup coils the ability to measure changes in speed is possible.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.

[[File:4_inch_coil_detail.jpg‎]]

Pick up coils on a 4 inch barrel for testing. Magnets are embedded in the shirt and ball projectiles.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

== High Speed Photography ==
With the introduction of consumer grade high speed cameras, high speed video is now a reality. With a known camera frame rate and a reference for how far the projectile moved between frames and the speed can be calculated.
This composite was assembled from consecutive frames of the high speed video.
Note this edit is a work in progress please be patient as I fix the photo.
http://www.spudfiles.com/spud_wiki/images/d/d1/Tumblecomposite.jpg
[[Category:Tools]]

File:Tumblecomposite.jpg

2011-05-29T05:58:35Z

Technician1002: Composite photo from high speed video showing distance between frames

Composite photo from high speed video showing distance between frames

Chronograph

2011-05-29T05:53:49Z

Technician1002: Added High Speed Video to the list.

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record valve opening times. Using more than 2 pickup coils the ability to measure changes in speed is possible.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.

[[File:4_inch_coil_detail.jpg‎]]

Pick up coils on a 4 inch barrel for testing. Magnets are embedded in the shirt and ball projectiles.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

== High Speed Photography ==
With the introduction of consumer grade high speed cameras, high speed video is now a reality. With a known camera frame rate and a reference for how far the projectile moved between frames and the speed can be calculated.
This composite was assembled from consecutive frames of the high speed video.
Note this edit is a work in progress please be patient as I fix the photo.
http://www.spudfiles.com/forums/files/tumblecomposite1_171.jpg
[[Category:Tools]]

Chronograph

2010-12-22T06:55:07Z

Technician1002: /* Magnetic Based Homemade Chronograph */

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record valve opening times. Using more than 2 pickup coils the ability to measure changes in speed is possible.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.

[[File:4_inch_coil_detail.jpg‎]]

Pick up coils on a 4 inch barrel for testing. Magnets are embedded in the shirt and ball projectiles.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

[[Category:Tools]]

Chronograph

2010-12-22T06:44:40Z

Technician1002: /* Magnetic Based Homemade Chronograph */

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record opening times.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.

[[File:4_inch_coil_detail.jpg‎]]

Pick up coils on a 4 inch barrel for testing. Magnets are embedded in the shirt and ball projectiles.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

[[Category:Tools]]

Chronograph

2010-12-22T06:44:17Z

Technician1002: /* Magnetic Based Homemade Chronograph */

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record opening times.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.

[[File:4_inch_coil_detail.jpg‎]]
Pick up coils on a 4 inch barrel for testing. Magnets are embedded in the shirt and ball projectiles.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

[[Category:Tools]]

Chronograph

2010-12-22T06:43:52Z

Technician1002: Added magnetic pickup coil photos

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record opening times.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.

[[File:4_inch_coil_detail.jpg‎]]Pick up coils on a 4 inch barrel for testing. Magnets are embedded in the shirt and ball projectiles.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

[[Category:Tools]]

File:4 inch coil detail.jpg

2010-12-22T06:40:59Z

Technician1002: Test pick up coils on a 4 inch ABS barrel. A T shirt and foam ball have embeded magnets.

Test pick up coils on a 4 inch ABS barrel. A T shirt and foam ball have embeded magnets.

Quick Dump Valve

2010-12-18T01:24:26Z

Technician1002: /* The Quick Dump Valve */

'''Article Flag''' 
As an article relating to spudding hardware, this should be presented in a more neutral format - it currently reads like an advertisement. 
It should also be presented in a third person point of view, as newcomers won't be able to associate "I" or "Me" usefully. 
Flagged by [[User:Ragnarok|Ragnarok]] 20:32, 29 July 2009 (EDT)

== The Quick Dump Valve ==
[[Image:Wtooliepiston.png|frame|Toolie-style piston valve; A is barrel, B is sealing face, C is chamber, D is drive rod, E is piston, F is pilot volume, G is pilot valve.]]
The quick dump valve is a variation on a traditional barrel sealer piston valve. In the section on piston valves, various configurations are covered and the advantages and disadvantages of each. A quick dump valve may be used where the traditional valves shortcomings cause problems for the builder. It was noted in the piston valve section in the wiki that as a barrel sealer valve nears a 1:1 ratio, the pilot pressure needed to open the valve drops lower, and when they pop open, they do so with more force and speed. They become temperamental as the ratio approaches a 1:1 ratio as the force to start opening the valve drops. They tend to stick or are unable to vent the pilot low enough to fire it. As a result, piston valves that won't fire are a common problem.

The Quick Dump Valve or QDV was built to take advantage of close ratio piston valve advantages of speed while fixing the disadvantages of the temperamental nature of them failing to fire reliably or seal properly to build chamber pressure.

Spool valves are balanced design valves with several o rings that move past ports and are operated by the rings crossing ports to join some in the same segment or separate them. They are noted for the ability to switch high pressures with little force to operate the valve. Typical uses are the hydraulic controls on heavy machinery such as a backhoe. Normal spool valves have both ends of the valve rod at atmospheric pressure.

A QDV when closed has the appearance of a spool valve. The air source under pressure is sealed off in the chamber with an o ring on both sides of the port. What makes this different than a typical spool valve is when it is opened, the supply pressure is then applied to the end of the spool. This pressure provides a positive feedback to the spool so as it opens, the force opening it rapidly increases as supply pressure in the outlet port pushes on the piston.

Unlike a piston valve that uses pressure in a "Pilot" area to hold the valve closed, the QDV has no pressure on the pilot area of the piston to hold it closed. In this manner it is much like a spool control valve.

A video on the valve theory is posted here; [http://www.youtube.com/watch?v=No3nI07mlQo Youtube The Quick Dump Valve]

The first appearance of the Quick Dump Valve in an air cannon is covered in a contest for building t shirt launchers;
[http://inteltrailblazerschallenge.wikispaces.com/The+brag+zone IntelTrailBlazers Engineering Challenge]

The first mention of the valve on Spudfiles is in this thread.
[http://www.spudfiles.com/forums/interesting-new-valve-design-t17617.html Interesting New Valve Design]

This is a video of the T Shirt launcher in action. The team won the competition with this design.
[http://www.youtube.com/watch?v=9Klxqav_6NM Quick Reload T Shirt launcher]

Quick Dump valves can be constructed as either a coaxial design with the valve inside a chamber, or built inside a T for an external valve. Coaxial valves provide some of the best CV values possible.

[[Image:WikiOverview.jpg]]

The oldest is constructed with ABS. The valve is located in the breech of the chamber. The barrel is a long pipe that extended all the way though the chamber with ports cut into the pipe between the chamber and barrel. A plastic bag was stuffed into the barrel to highlight the ports for the photo. Otherwise they were too dark to see very well.

[[Image:ValvePorts1.JPG]]

This design works well. The drawbacks are the piston needs a rod shoved into the breech rope pull hole to reset the valve between shots and the design did not use floating o rings, so it pulls a little hard.

The piston is made from a piece of PVC pipe and a couple pipe caps and o rings. Any sturdy cylindrical object can be used that will hold the pressure and forces.

[[Image:CoreDetail.JPG]]

For safety on this design, it is very important to remember that shoving anything into the barrel does the same thing as pulling the rope. It opens the valve. ''' Never shove anything into this design of valve while it is under pressure.''' Load it and then add pressure.

The spudfiles page on the cannon is here;
[http://www.spudfiles.com/forums/abs-cellular-core-test-cannon-t17968.html ABS Cellular Core Test Cannon, also known as the apple cannon]
It was posted as a materials test discussion on using unrated plastic pipe in air cannons.

Later improvements to the design included using a rod instead of a rope to open and close the valve. The piston if permitted to slide freely on the rod can be made to operate quickly without having to accelerate the control trigger rod. In operation, when the rod is pushed in, a pin on the rod pushes the piston closed. To fire the rod is pulled back through the piston which retracts the pin behind the piston out of the piston travel area. Then a nut on the end of the rod pushes the front of the piston pulling it open triggering it. Once the valve cracks open, the air pressure between the piston and projectile pushes the valve open with the same pressure it applies to the projectile.

The valve can be relocated to the barrel end of the chamber.
This permits easy detachment of the barrel and the ability to attach various size barrels with minimum dead space.

A model of the T Shirt launcher shows the construction detail with the improvements. In Spudfiles, it is called the Marshmallow Cannon. It was built for a high speed marshmallow launching competition. With a removable and interchangeable barrel selection, it is easy to adapt to shooting gumballs, jawbreakers, batteries, tennis balls, and t shirts. With a 36 inch long t shirt barrel the 1 inch valve is able to toss shirts 200 feet.

The Spudfiles entry is here;
[http://www.spudfiles.com/forums/quick-dump-valve-t17858.html The Quick Dump Valve]
The spudfiles entry has links to a theory of operation video as well as more photos.

The tank as before is coaxial design with a valve body in the center. Unlike the earlier design, the barrel is removable and the valve is located at the barrel end of the chamber instead of the breech. The new design uses a rod to trigger and reset the valve.

[[Image:WikiTank.jpg]]

The valve core removed from the tank shows the piston with floating rings, rod, bumper, stopper, and trigger and reset pins.

[[Image:WikiVavleCoreAssy.jpg]]

A close up view of the piston shows the o rings fit loose in a floating O Ring design. The spudfiles page and linked videos show how this style of o ring installation lowers the friction in the valve.

[[Image:Piston_rings.jpg]]

The ports between the chamber and valve body can be seen inside the valve.

[[Image:WikiTankEnd.jpg]]

View of the assembled cannon with the tennis ball barrel. It tosses tennis balls 100 yards.

[[Image:Tennis_ball_barrel1.jpg]]

With high speed of operation and a high flow, the cannon is able to deliver high speeds. The photo is a 2X4 that was split with a couple jawbreakers.

[[Image:Split1a.JPG]]

Photos are copyright by Technician1002. Please ask before using elsewhere.

Piston valve

2010-12-18T01:22:06Z

Technician1002: Added Supah as an example

A '''piston valve''' is a [[pilot]] operated [[valve]]. It is very similar to a [[diaphragm valve]] in theory, but replaces it's flexible diaphragm with a rigid cylinder. There are 2 varieties; [[barrel]] sealing and [[chamber]] sealing.

== Barrel sealing valve ==

In a barrel sealing valve, the piston seals against the breech of the barrel. This is the most common piston valve design.

=== construction ===

The piston is often a well fitting cup-shaped object, such as a end cap. To provide a sealing face, a piece of rubber is attached, typically with a bolt. In the simplest case, equalization is accomplished by allowing the air to leak past the piston and into the chamber. Some people will machine their own pistons, in which case they often build [[O-ring]]s into them. With the O-rings, you need to make a small equalization hole; sometimes this is fancied up to be a homemade [[check valve]].

Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recommended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labeled "'''F'''" in the "use, barrel sealing" diagram.

These valves are often used on [[coaxial]]s and [[over/under]]s. In an over/under, the valve is built in a "T" fitting. The barrel is put co-axially through one end, the pilot and piston are put in the opposite one, and a chamber is connected to the perpendicular opening with a 90° elbow.

A commercially manufactured valve for spudding is the Mauler Valve.

=== Use ===
[[Image:Wpiston.PNG|frame|top=pressurized, bottom=firing]]
Operation:
#Air is added by filling behind the piston (C).
#The piston (E) slides forwards, and seals against the barrel (A). (Alternatively, one can use a spring to move the piston forwards, which allows one to fill [slowly at first, to allow the [[pressure]] to equalize] from the chamber.)
#More air is added, and leaks around the piston (or through a small equalization hole) and into the chamber (B), filling it to the desired pressure.
#The [[pilot valve]] (D) behind the piston is opened, the pressure in the pilot volume (C) drops, and the higher pressure in the chamber area pushes the piston away from the barrel.
#The air flows around from the chamber, and into the barrel, propelling the projectile.

=== Pilot Valves ===
There is a common misconception that a simple blowgun is enough to pilot large piston valves, 1.5" and above. This is not recommended as your cannon will have very bad performance or may not even function at all. For valves 1"-1.25" in diameter, a 1/4" ball valve is recommended. For valves between 1.5" and 2.5" a 1/2" or 3/4" ball valve is probably enough. Anything above that will benefit from a sprinkler valve or a 1" ball valve for a pilot valve. When it comes to pilot valves, bigger is always better.

== Chamber sealing piston valve ==

=== construction ===

The piston of a chamber-sealing piston valve has to seal on both the chamber port and to the pilot volume. This requires that the piston be machined with [[O-ring]]s. A small equalization hole is required; sometimes this is fancied up to be a homemade [[check valve]].

The piston is almost always housed in a "t" fitting.

Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recommended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labeled "'''F'''" in the "use, chamber sealing sealing" diagram.

These valves are often used on [[over/under]]s, as the flow is already turned around 90o.

A commercially manufactured valve for spudding is the Supah Valve.

=== Use ===
[[Image:Wcspiston.PNG|frame|top=pressurized, bottom=firing]]
Operation:
#Air is added by filling behind the piston (C).
#The piston (E) slides forwards, and seals against the barrel (A). (Alternatively, one can use a spring to move the piston forwards, which allows one to fill [slowly at first, to allow the [[pressure]] to equalize] from the chamber.)
#More air is added, and leaks through the equalization hole in the piston and into the chamber (B), filling it to the desired pressure.
#The [[pilot valve]] (D) behind the piston is opened, the pressure in the pilot volume (C) drops, and the higher pressure in the chamber area pushes the piston away from the chamber.
#The air flows out of the chamber, and into the barrel, propelling the projectile.

== Common traits ==

#The performance of these valves can be calculated with the [[GGDT]].
#If your valve [[honking|honks]], it is probably a good idea to invest in a better pilot valve, though this is more of a problem with barrel-sealing valves. Narrow ratio barrel sealers tend to be immune to honking due to the low pressure at which they crack open. A larger pilot volume on a narrow ratio barrel sealer can reduce pilot pressure rise from the piston moving into the plot space causing compression. With less compression, the valve will not re-close early due to the rapid drop in chamber pressure. This eliminates honking.
#In both cases, provided there is a good deal of space around the barrel, the full flow potential of the valve is realized when the piston has moved back 1/4th of the barrel's inside diameter (I.D./4). The derivation of this formula is as follows:

Given: A = Pi(R)^2
C = 2PiR
T = Piston travel
R = I.D. of barrel / 2

When the piston moves back, the smallest amount of area exposed is either the area of the circular cross section of the barrel or the area exposed by the piston, which is the side of a cylinder, the bases being the barrel and piston face. The optimal ratio of area exposed between the 2 spots is 1:1, which means the exposed areas should be the same. So one sets the equations A and CT equal, that is A = CT.

Pi(R)^2 = 2PiR(T)

Solving for "T" results in:

R/2 = T which, if one substitutes I.D./2 for R, results in:

I.D./4 = T

Many people choose to open larger to provide only one restriction to flow instead of 2 the same size in a row. This is done by allowing the valve to open fully unrestricted and then compress the bumper while opening further. This provides the fastest possible opening time by preventing the piston deceleration while still opening.

#Pneumatic actuation is not mandatory; mechanical means can be used to hold the valve shut, or open it, rather than using the force of the air.

***The following section submitted by Technician1002***

The operation of barrel sealing valves falls into 3 categories which is related to the dimensions of the barrel seal or seat to the piston outside diameter.

=== Large Ratio Piston Valve ===
When the ratio is large in a barrel sealer with either a large piston or small barrel, most of the force to open the valve is controlled by the differential of the chamber pressure and pilot area. As the valve opens, the small area that becomes exposed to the chamber as it opens contributes little to the opening speed. This large area ratio valve are noted for reliable operation as they have the ability to open pistons that don't slide well. Due to the pressure still in the pilot area as they open, as the chamber vents out the barrel, it is often faster than the pilot, so the force used to open the valve vanishes and the pilot pressure unable to keep up with the drop, forces the valve to close. If this repeats as the pilot vents, it is noticeable as honking. This class of valves include pistons with a 2:1 diameter ratio or more. A 2:1 diameter ratio is a 4:1 area ratio. These are not QEV valves because the area sealed by the piston is only 25% of the pilot area so when the valve opens the force change is small. It opens with the pilot at 3/4 the pressure of the chamber. When it opens and the pilot volume is reduced by the piston moving into the pilot space, the rise in pressure in the pilot prevents the piston from opening all the way, so opening speed is directly related to how much faster the pilot can vent over the rate the chamber vents out the barrel. A slow pilot equals a slow valve and may cause honking.

In a chamber sealer version where the valve seat seals against the chamber, they are fast as the pressure is released and more pressure presses on the larger exposed face of the piston. This style tends to have a fairly large dead space between the valve and projectile. In addition a large piston has a greater mass and as the piston moves, it requires a larger displacement using much of the chamber air energy. If the valve seat is small to use a smaller piston, the small orifice chokes the flow.

=== Small Ratio or QEV ===
As the ratio of the seat diameter to piston diameter is reduced, the area that the chamber is exposed to is reduced, to the point that the large area of the pilot is able to hold the piston closed until most of the pilot pressure is vented. Even when the pilot area is vented to a low pressure, the initial opening force is low because the area of the piston exposed to the chamber pressure is small as most of the face of the piston is exposed to no pressure in the barrel. This low opening force can cause many headaches with stuck pistons that sometimes fail to fire, and the equalization port may vent enough volume to prevent the pilot area from reaching a low enough pressure to open the valve. The lower the seat to diameter ratio; the lower the initial force the chamber can apply to open the valve, and the faster they snap open when they do get over the initial opening. This faster speed is due to the larger piston face exposed to the chamber pressure when the valve opens and the lower pressure in the pilot area. The lower pressure compresses less and provides less force on the back of the piston when it opens. The closer the ratio is to 1:1 the faster the avalanche, but the initial cracking open of the valve becomes slower as the initial opening force is lower and lower as you approach a 1:1 ratio.

One attractive feature of this valve is once it unseats and starts to open, the chamber pressure now acting on the face of the piston causes a large spike in opening force as the large barrel facing area is now exposed to the chamber pressure. This type of valve snaps open and is known as a Quick Exhaust Valve or QEV. This style valve is not prone to closing early and honking.

[[Image:MusketSeat.JPG ]]

The barrel sealer QEV piston valve has a large diameter seat in relation to the overall diameter of the piston.
A chamber sealer has a small seat in relation the the overall diameter so the force on the piston grows rapidly as the valve opens.

Chamber sealer valves have a disadvantage of needing a larger diameter piston for the same size valve seat as a barrel sealer. This adds mass and dead space between the valve piston and projectile. On the positive side, they are more reliable in opening and tend to have most of the opening acceleration early in the opening where it is needed. The drop in acceleration as the valve opens can increase the life expectancy of the valve as they compress the pilot area they slow before impact with the back of the breech.

=== 1:1 Ratio or QDV ===
If the ratio of the piston diameter is reduced to the diameter of the valve seat in a spool valve, then the valve won't open even when the pilot area is not under pressure. If the chamber is pressurized and no pressure is in the pilot area, the valve has the least back pressure of any of the piston valves and therefore the fastest opening when the valve is unseated by force. Even though the pilot area may half in volume as the piston moves into this space, the pressure rise from 1 atm to 2 atm is still less than the chamber force on the newly exposed face of the piston, so this piston will open fast regardless of the vent size or speed. This last category of piston valve is known as a Quick Dump Valve. To operate this valve in an air cannon, consideration must be made to mechanically move the piston and when the piston moves, the force will avalanche quickly as the piston face becomes exposed to the chamber pressure. For mechanical trigger the use a rope pull or a rod with a "sliding" piston are options to a spring or air start. The loose piston on a rope or rod provides speed as the core can accelerate freely when triggered. Decoupling the triggering mechanism from the piston prevents the trigger from adding to the moving mass of the piston. These valves are not subject to honking, but may "bounce" back closed after the shot by the pressure built up in the pilot area and bumper recoil after the chamber pressure is gone.

[[Image:QDV_parts.JPG]]

Assembled 1 inch QDV cannon and damaged can. Projectile was a 1 inch jawbreaker.
[[Image:Marshmallow_cannon.jpg]]

The quick dump valve has the piston OD the same size as the seat. It requires an external force to start it opening. It has no pilot pressure to hold it against a seat so it is often built with o rings on a piston. The valve cylinder can be built out of a pipe with ports cut in the side.

*[http://www.spudfiles.com/spud_wiki/index.php?title=Quick_Dump_Valve The Quick Dump Valve, by Technician1002.] Wiki page on the QDV

A video on the theory of the QDV cannon is here.
[http://www.youtube.com/watch?v=No3nI07mlQo The Quick Dump Valve]

=== O-Ring Considerations on a Piston Valve ===
To prevent stuck piston valves, consideration must be given to permit a good seal while not stopping movement.

To prevent stuck or hard to move pistons the o ring should not be compressed flat against the cylinder wall. Since movement is desirable, as well as a seal, we can design the piston to seal without needing to squeeze the o ring. The following video shows the theory fairly well.

[http://www.youtube.com/watch?v=BbDiZiRVrnk Youtube video on using o rings in air cannons]

At 4:20 in the video the force needed to move this piston is shown.

Instead of having O rings in a groove that sit tight against the bottom of the groove and then are compressed by the cylinder, floating rings do not bottom out in the o ring groove. To seal, the pressure trying to blow past the ring seats it against the side of the o ring groove. Air that is able to get under the ring presses outward to apply pressure to the cylinder wall. As the pressure is increased, this force is increased so higher operating pressures make a tighter seal and a little higher friction to movement.

Floating piston rings fit loose in the grooves. The o ring is sized to be slightly larger than the cylinder diameter it slides inside.
This photo is of a 1 inch quick dump valve piston.
[[Image:Piston_rings.jpg]]

Here is a drawing showing the force of the pressure on the o ring to provide a tight seal.
[[Image:123_floatingpneumatic1.jpg]]

Source: RL Hudson O-Ring Design & Materials Guide. Used with permission.

[[category:valves]]

Piston valve

2010-12-18T01:20:52Z

Technician1002: Added Mauler as an example.

A '''piston valve''' is a [[pilot]] operated [[valve]]. It is very similar to a [[diaphragm valve]] in theory, but replaces it's flexible diaphragm with a rigid cylinder. There are 2 varieties; [[barrel]] sealing and [[chamber]] sealing.

== Barrel sealing valve ==

In a barrel sealing valve, the piston seals against the breech of the barrel. This is the most common piston valve design.

=== construction ===

The piston is often a well fitting cup-shaped object, such as a end cap. To provide a sealing face, a piece of rubber is attached, typically with a bolt. In the simplest case, equalization is accomplished by allowing the air to leak past the piston and into the chamber. Some people will machine their own pistons, in which case they often build [[O-ring]]s into them. With the O-rings, you need to make a small equalization hole; sometimes this is fancied up to be a homemade [[check valve]].

Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recommended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labeled "'''F'''" in the "use, barrel sealing" diagram.

These valves are often used on [[coaxial]]s and [[over/under]]s. In an over/under, the valve is built in a "T" fitting. The barrel is put co-axially through one end, the pilot and piston are put in the opposite one, and a chamber is connected to the perpendicular opening with a 90° elbow.

A commercially manufactured valve for spudding is the Mauler Valve.

=== Use ===
[[Image:Wpiston.PNG|frame|top=pressurized, bottom=firing]]
Operation:
#Air is added by filling behind the piston (C).
#The piston (E) slides forwards, and seals against the barrel (A). (Alternatively, one can use a spring to move the piston forwards, which allows one to fill [slowly at first, to allow the [[pressure]] to equalize] from the chamber.)
#More air is added, and leaks around the piston (or through a small equalization hole) and into the chamber (B), filling it to the desired pressure.
#The [[pilot valve]] (D) behind the piston is opened, the pressure in the pilot volume (C) drops, and the higher pressure in the chamber area pushes the piston away from the barrel.
#The air flows around from the chamber, and into the barrel, propelling the projectile.

=== Pilot Valves ===
There is a common misconception that a simple blowgun is enough to pilot large piston valves, 1.5" and above. This is not recommended as your cannon will have very bad performance or may not even function at all. For valves 1"-1.25" in diameter, a 1/4" ball valve is recommended. For valves between 1.5" and 2.5" a 1/2" or 3/4" ball valve is probably enough. Anything above that will benefit from a sprinkler valve or a 1" ball valve for a pilot valve. When it comes to pilot valves, bigger is always better.

== Chamber sealing piston valve ==

=== construction ===

The piston of a chamber-sealing piston valve has to seal on both the chamber port and to the pilot volume. This requires that the piston be machined with [[O-ring]]s. A small equalization hole is required; sometimes this is fancied up to be a homemade [[check valve]].

The piston is almost always housed in a "t" fitting.

Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recommended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labeled "'''F'''" in the "use, chamber sealing sealing" diagram.

These valves are often used on [[over/under]]s, as the flow is already turned around 90o.

=== Use ===
[[Image:Wcspiston.PNG|frame|top=pressurized, bottom=firing]]
Operation:
#Air is added by filling behind the piston (C).
#The piston (E) slides forwards, and seals against the barrel (A). (Alternatively, one can use a spring to move the piston forwards, which allows one to fill [slowly at first, to allow the [[pressure]] to equalize] from the chamber.)
#More air is added, and leaks through the equalization hole in the piston and into the chamber (B), filling it to the desired pressure.
#The [[pilot valve]] (D) behind the piston is opened, the pressure in the pilot volume (C) drops, and the higher pressure in the chamber area pushes the piston away from the chamber.
#The air flows out of the chamber, and into the barrel, propelling the projectile.

== Common traits ==

#The performance of these valves can be calculated with the [[GGDT]].
#If your valve [[honking|honks]], it is probably a good idea to invest in a better pilot valve, though this is more of a problem with barrel-sealing valves. Narrow ratio barrel sealers tend to be immune to honking due to the low pressure at which they crack open. A larger pilot volume on a narrow ratio barrel sealer can reduce pilot pressure rise from the piston moving into the plot space causing compression. With less compression, the valve will not re-close early due to the rapid drop in chamber pressure. This eliminates honking.
#In both cases, provided there is a good deal of space around the barrel, the full flow potential of the valve is realized when the piston has moved back 1/4th of the barrel's inside diameter (I.D./4). The derivation of this formula is as follows:

Given: A = Pi(R)^2
C = 2PiR
T = Piston travel
R = I.D. of barrel / 2

When the piston moves back, the smallest amount of area exposed is either the area of the circular cross section of the barrel or the area exposed by the piston, which is the side of a cylinder, the bases being the barrel and piston face. The optimal ratio of area exposed between the 2 spots is 1:1, which means the exposed areas should be the same. So one sets the equations A and CT equal, that is A = CT.

Pi(R)^2 = 2PiR(T)

Solving for "T" results in:

R/2 = T which, if one substitutes I.D./2 for R, results in:

I.D./4 = T

Many people choose to open larger to provide only one restriction to flow instead of 2 the same size in a row. This is done by allowing the valve to open fully unrestricted and then compress the bumper while opening further. This provides the fastest possible opening time by preventing the piston deceleration while still opening.

#Pneumatic actuation is not mandatory; mechanical means can be used to hold the valve shut, or open it, rather than using the force of the air.

***The following section submitted by Technician1002***

The operation of barrel sealing valves falls into 3 categories which is related to the dimensions of the barrel seal or seat to the piston outside diameter.

=== Large Ratio Piston Valve ===
When the ratio is large in a barrel sealer with either a large piston or small barrel, most of the force to open the valve is controlled by the differential of the chamber pressure and pilot area. As the valve opens, the small area that becomes exposed to the chamber as it opens contributes little to the opening speed. This large area ratio valve are noted for reliable operation as they have the ability to open pistons that don't slide well. Due to the pressure still in the pilot area as they open, as the chamber vents out the barrel, it is often faster than the pilot, so the force used to open the valve vanishes and the pilot pressure unable to keep up with the drop, forces the valve to close. If this repeats as the pilot vents, it is noticeable as honking. This class of valves include pistons with a 2:1 diameter ratio or more. A 2:1 diameter ratio is a 4:1 area ratio. These are not QEV valves because the area sealed by the piston is only 25% of the pilot area so when the valve opens the force change is small. It opens with the pilot at 3/4 the pressure of the chamber. When it opens and the pilot volume is reduced by the piston moving into the pilot space, the rise in pressure in the pilot prevents the piston from opening all the way, so opening speed is directly related to how much faster the pilot can vent over the rate the chamber vents out the barrel. A slow pilot equals a slow valve and may cause honking.

In a chamber sealer version where the valve seat seals against the chamber, they are fast as the pressure is released and more pressure presses on the larger exposed face of the piston. This style tends to have a fairly large dead space between the valve and projectile. In addition a large piston has a greater mass and as the piston moves, it requires a larger displacement using much of the chamber air energy. If the valve seat is small to use a smaller piston, the small orifice chokes the flow.

=== Small Ratio or QEV ===
As the ratio of the seat diameter to piston diameter is reduced, the area that the chamber is exposed to is reduced, to the point that the large area of the pilot is able to hold the piston closed until most of the pilot pressure is vented. Even when the pilot area is vented to a low pressure, the initial opening force is low because the area of the piston exposed to the chamber pressure is small as most of the face of the piston is exposed to no pressure in the barrel. This low opening force can cause many headaches with stuck pistons that sometimes fail to fire, and the equalization port may vent enough volume to prevent the pilot area from reaching a low enough pressure to open the valve. The lower the seat to diameter ratio; the lower the initial force the chamber can apply to open the valve, and the faster they snap open when they do get over the initial opening. This faster speed is due to the larger piston face exposed to the chamber pressure when the valve opens and the lower pressure in the pilot area. The lower pressure compresses less and provides less force on the back of the piston when it opens. The closer the ratio is to 1:1 the faster the avalanche, but the initial cracking open of the valve becomes slower as the initial opening force is lower and lower as you approach a 1:1 ratio.

One attractive feature of this valve is once it unseats and starts to open, the chamber pressure now acting on the face of the piston causes a large spike in opening force as the large barrel facing area is now exposed to the chamber pressure. This type of valve snaps open and is known as a Quick Exhaust Valve or QEV. This style valve is not prone to closing early and honking.

[[Image:MusketSeat.JPG ]]

The barrel sealer QEV piston valve has a large diameter seat in relation to the overall diameter of the piston.
A chamber sealer has a small seat in relation the the overall diameter so the force on the piston grows rapidly as the valve opens.

Chamber sealer valves have a disadvantage of needing a larger diameter piston for the same size valve seat as a barrel sealer. This adds mass and dead space between the valve piston and projectile. On the positive side, they are more reliable in opening and tend to have most of the opening acceleration early in the opening where it is needed. The drop in acceleration as the valve opens can increase the life expectancy of the valve as they compress the pilot area they slow before impact with the back of the breech.

=== 1:1 Ratio or QDV ===
If the ratio of the piston diameter is reduced to the diameter of the valve seat in a spool valve, then the valve won't open even when the pilot area is not under pressure. If the chamber is pressurized and no pressure is in the pilot area, the valve has the least back pressure of any of the piston valves and therefore the fastest opening when the valve is unseated by force. Even though the pilot area may half in volume as the piston moves into this space, the pressure rise from 1 atm to 2 atm is still less than the chamber force on the newly exposed face of the piston, so this piston will open fast regardless of the vent size or speed. This last category of piston valve is known as a Quick Dump Valve. To operate this valve in an air cannon, consideration must be made to mechanically move the piston and when the piston moves, the force will avalanche quickly as the piston face becomes exposed to the chamber pressure. For mechanical trigger the use a rope pull or a rod with a "sliding" piston are options to a spring or air start. The loose piston on a rope or rod provides speed as the core can accelerate freely when triggered. Decoupling the triggering mechanism from the piston prevents the trigger from adding to the moving mass of the piston. These valves are not subject to honking, but may "bounce" back closed after the shot by the pressure built up in the pilot area and bumper recoil after the chamber pressure is gone.

[[Image:QDV_parts.JPG]]

Assembled 1 inch QDV cannon and damaged can. Projectile was a 1 inch jawbreaker.
[[Image:Marshmallow_cannon.jpg]]

The quick dump valve has the piston OD the same size as the seat. It requires an external force to start it opening. It has no pilot pressure to hold it against a seat so it is often built with o rings on a piston. The valve cylinder can be built out of a pipe with ports cut in the side.

*[http://www.spudfiles.com/spud_wiki/index.php?title=Quick_Dump_Valve The Quick Dump Valve, by Technician1002.] Wiki page on the QDV

A video on the theory of the QDV cannon is here.
[http://www.youtube.com/watch?v=No3nI07mlQo The Quick Dump Valve]

=== O-Ring Considerations on a Piston Valve ===
To prevent stuck piston valves, consideration must be given to permit a good seal while not stopping movement.

To prevent stuck or hard to move pistons the o ring should not be compressed flat against the cylinder wall. Since movement is desirable, as well as a seal, we can design the piston to seal without needing to squeeze the o ring. The following video shows the theory fairly well.

[http://www.youtube.com/watch?v=BbDiZiRVrnk Youtube video on using o rings in air cannons]

At 4:20 in the video the force needed to move this piston is shown.

Instead of having O rings in a groove that sit tight against the bottom of the groove and then are compressed by the cylinder, floating rings do not bottom out in the o ring groove. To seal, the pressure trying to blow past the ring seats it against the side of the o ring groove. Air that is able to get under the ring presses outward to apply pressure to the cylinder wall. As the pressure is increased, this force is increased so higher operating pressures make a tighter seal and a little higher friction to movement.

Floating piston rings fit loose in the grooves. The o ring is sized to be slightly larger than the cylinder diameter it slides inside.
This photo is of a 1 inch quick dump valve piston.
[[Image:Piston_rings.jpg]]

Here is a drawing showing the force of the pressure on the o ring to provide a tight seal.
[[Image:123_floatingpneumatic1.jpg]]

Source: RL Hudson O-Ring Design & Materials Guide. Used with permission.

[[category:valves]]

Chronograph

2010-12-14T18:33:56Z

Technician1002: /* Magnetic Based Homemade Chronograph */

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record opening times.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.

[http://www.spudfiles.com/forums/files/web_4_inch_coil_detail_150.jpg]
Pick up coils on a 4 inch barrel for testing. Magnets are embedded in the shirt and ball projectiles.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

[[Category:Tools]]

Chronograph

2010-12-14T18:31:57Z

Technician1002: /* Magnetic Based Homemade Chronograph */

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record opening times.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.
[[File:http://www.spudfiles.com/forums/files/web_4_inch_coil_detail_150.jpg]]
Pick up coils on a 4 inch barrel for testing. Magnets are embedded in the shirt and ball projectiles.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

[[Category:Tools]]

Chronograph

2010-12-14T18:30:29Z

Technician1002: /* Magnetic Based Homemade Chronograph */

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record opening times.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.
[[http://www.spudfiles.com/forums/files/web_4_inch_coil_detail_150.jpg]]
Pick up coils on a 4 inch barrel for testing. Magnets are embedded in the shirt and ball projectiles.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

[[Category:Tools]]

Chronograph

2010-12-14T18:23:04Z

Technician1002: /* Magnetic Based Homemade Chronograph */

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

An advantage of magnetic is immunity from wadding, sabots, and muzzle condensation or blast causing detection errors in an optical gate. Another advantage is the ablility to measure speed inside a barrel or measure valve motion to record opening times.

Disadvantages include complexity in eliminating radio frequency interference, magnetic pickup from motors, transformers, etc and setting the gain correctly to prevent clipping or distortion of the signal. Another disadvantage is the need to use either a magnet in the projectile or use a bias magnetic field and a conductive projectile.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

[[Category:Tools]]

Chronograph

2010-12-14T18:16:08Z

Technician1002: Added Magnetic pickup

In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

== Magnetic Based Homemade Chronograph ==

When using magnetic pick up coils and either a magnetic projectile by embedding a small magnet or detecting a ferris or non ferris projectile by detecting a disturbance in a static magnetic field, the time to cross between the two pick up coils can accurately measure a passing projectile's speed. This was used by a Spudfiles member with multiple pickup coils on a plastic barrel to measure the projectile acceleration and fall off of acceleration for the purpose of optimization of a barrel length for maximum launch velocity. The signal from the pick up coils can be fed to a sound card for measurements the same way it is done for the home made optical pickup.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

[[Category:Tools]]

Flow coefficient

2010-12-14T01:42:04Z

Technician1002: reformatted.

The flow coefficient of a [[valve]] is a relative measure of its efficacy at allowing fluid flow. It describes the relationship between the [[pressure]] drop across an orifice and the corresponding flow rate.

There are two standards for valve CV. The most common is the volume in US gallons of water in one minute that will through a valve with a pressure drop of 1 psi across the valve.

The other standard is for compressible gas.

Wikipedia has the formulas for the CV of valves. The CV for gas flow is most often needed for flow calculations in spudding.

[http://en.wikipedia.org/wiki/Flow_coefficient] Wikipedia page on CV.

[[category:Concepts]]
[[category:Stubs]]

Flow coefficient

2010-12-14T01:40:02Z

Technician1002: updated CV to include the definition and standard for measurement. A link to the Wikipedia page is added.

The flow coefficient of a [[valve]] is a relative measure of its efficacy at allowing fluid flow. It describes the relationship between the [[pressure]] drop across an orifice and the corresponding flow rate.

There are two standards for valve CV. The most common is related to liquid flow and the volume of liquid that can pass the valve in Gallons per Minute for a 1 PSI pressure differential on the valve.

The other standard is for compressible gas.

Wikipedia has the formulas for the CV of valves. The CV for gas flow is most often needed for flow calculations in spudding.

Flow coefficient is the volume in US gallons of water in one minute that will through a valve with a pressure drop of 1 psi across the valve.

[http://en.wikipedia.org/wiki/Flow_coefficient] Wikipedia page on CV.

[[category:Concepts]]
[[category:Stubs]]

Piston valve

2010-12-13T18:23:20Z

Technician1002: Formatting

A '''piston valve''' is a [[pilot]] operated [[valve]]. It is very similar to a [[diaphragm valve]] in theory, but replaces it's flexible diaphragm with a rigid cylinder. There are 2 varieties; [[barrel]] sealing and [[chamber]] sealing.

== Barrel sealing valve ==

In a barrel sealing valve, the piston seals against the breech of the barrel. This is the most common piston valve design.

=== construction ===

The piston is often a well fitting cup-shaped object, such as a end cap. To provide a sealing face, a piece of rubber is attached, typically with a bolt. In the simplest case, equalization is accomplished by allowing the air to leak past the piston and into the chamber. Some people will machine their own pistons, in which case they often build [[O-ring]]s into them. With the O-rings, you need to make a small equalization hole; sometimes this is fancied up to be a homemade [[check valve]].

Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recommended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labeled "'''F'''" in the "use, barrel sealing" diagram.

These valves are often used on [[coaxial]]s and [[over/under]]s. In an over/under, the valve is built in a "T" fitting. The barrel is put co-axially through one end, the pilot and piston are put in the opposite one, and a chamber is connected to the perpendicular opening with a 90° elbow.

=== Use ===
[[Image:Wpiston.PNG|frame|top=pressurized, bottom=firing]]
Operation:
#Air is added by filling behind the piston (C).
#The piston (E) slides forwards, and seals against the barrel (A). (Alternatively, one can use a spring to move the piston forwards, which allows one to fill [slowly at first, to allow the [[pressure]] to equalize] from the chamber.)
#More air is added, and leaks around the piston (or through a small equalization hole) and into the chamber (B), filling it to the desired pressure.
#The [[pilot valve]] (D) behind the piston is opened, the pressure in the pilot volume (C) drops, and the higher pressure in the chamber area pushes the piston away from the barrel.
#The air flows around from the chamber, and into the barrel, propelling the projectile.

=== Pilot Valves ===
There is a common misconception that a simple blowgun is enough to pilot large piston valves, 1.5" and above. This is not recommended as your cannon will have very bad performance or may not even function at all. For valves 1"-1.25" in diameter, a 1/4" ball valve is recommended. For valves between 1.5" and 2.5" a 1/2" or 3/4" ball valve is probably enough. Anything above that will benefit from a sprinkler valve or a 1" ball valve for a pilot valve. When it comes to pilot valves, bigger is always better.

== Chamber sealing piston valve ==

=== construction ===

The piston of a chamber-sealing piston valve has to seal on both the chamber port and to the pilot volume. This requires that the piston be machined with [[O-ring]]s. A small equalization hole is required; sometimes this is fancied up to be a homemade [[check valve]].

The piston is almost always housed in a "t" fitting.

Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recommended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labeled "'''F'''" in the "use, chamber sealing sealing" diagram.

These valves are often used on [[over/under]]s, as the flow is already turned around 90o.

=== Use ===
[[Image:Wcspiston.PNG|frame|top=pressurized, bottom=firing]]
Operation:
#Air is added by filling behind the piston (C).
#The piston (E) slides forwards, and seals against the barrel (A). (Alternatively, one can use a spring to move the piston forwards, which allows one to fill [slowly at first, to allow the [[pressure]] to equalize] from the chamber.)
#More air is added, and leaks through the equalization hole in the piston and into the chamber (B), filling it to the desired pressure.
#The [[pilot valve]] (D) behind the piston is opened, the pressure in the pilot volume (C) drops, and the higher pressure in the chamber area pushes the piston away from the chamber.
#The air flows out of the chamber, and into the barrel, propelling the projectile.

== Common traits ==

#The performance of these valves can be calculated with the [[GGDT]].
#If your valve [[honking|honks]], it is probably a good idea to invest in a better pilot valve, though this is more of a problem with barrel-sealing valves. Narrow ratio barrel sealers tend to be immune to honking due to the low pressure at which they crack open. A larger pilot volume on a narrow ratio barrel sealer can reduce pilot pressure rise from the piston moving into the plot space causing compression. With less compression, the valve will not re-close early due to the rapid drop in chamber pressure. This eliminates honking.
#In both cases, provided there is a good deal of space around the barrel, the full flow potential of the valve is realized when the piston has moved back 1/4th of the barrel's inside diameter (I.D./4). The derivation of this formula is as follows:

Given: A = Pi(R)^2
C = 2PiR
T = Piston travel
R = I.D. of barrel / 2

When the piston moves back, the smallest amount of area exposed is either the area of the circular cross section of the barrel or the area exposed by the piston, which is the side of a cylinder, the bases being the barrel and piston face. The optimal ratio of area exposed between the 2 spots is 1:1, which means the exposed areas should be the same. So one sets the equations A and CT equal, that is A = CT.

Pi(R)^2 = 2PiR(T)

Solving for "T" results in:

R/2 = T which, if one substitutes I.D./2 for R, results in:

I.D./4 = T

Many people choose to open larger to provide only one restriction to flow instead of 2 the same size in a row. This is done by allowing the valve to open fully unrestricted and then compress the bumper while opening further. This provides the fastest possible opening time by preventing the piston deceleration while still opening.

#Pneumatic actuation is not mandatory; mechanical means can be used to hold the valve shut, or open it, rather than using the force of the air.

***The following section submitted by Technician1002***

The operation of barrel sealing valves falls into 3 categories which is related to the dimensions of the barrel seal or seat to the piston outside diameter.

=== Large Ratio Piston Valve ===
When the ratio is large in a barrel sealer with either a large piston or small barrel, most of the force to open the valve is controlled by the differential of the chamber pressure and pilot area. As the valve opens, the small area that becomes exposed to the chamber as it opens contributes little to the opening speed. This large area ratio valve are noted for reliable operation as they have the ability to open pistons that don't slide well. Due to the pressure still in the pilot area as they open, as the chamber vents out the barrel, it is often faster than the pilot, so the force used to open the valve vanishes and the pilot pressure unable to keep up with the drop, forces the valve to close. If this repeats as the pilot vents, it is noticeable as honking. This class of valves include pistons with a 2:1 diameter ratio or more. A 2:1 diameter ratio is a 4:1 area ratio. These are not QEV valves because the area sealed by the piston is only 25% of the pilot area so when the valve opens the force change is small. It opens with the pilot at 3/4 the pressure of the chamber. When it opens and the pilot volume is reduced by the piston moving into the pilot space, the rise in pressure in the pilot prevents the piston from opening all the way, so opening speed is directly related to how much faster the pilot can vent over the rate the chamber vents out the barrel. A slow pilot equals a slow valve and may cause honking.

In a chamber sealer version where the valve seat seals against the chamber, they are fast as the pressure is released and more pressure presses on the larger exposed face of the piston. This style tends to have a fairly large dead space between the valve and projectile. In addition a large piston has a greater mass and as the piston moves, it requires a larger displacement using much of the chamber air energy. If the valve seat is small to use a smaller piston, the small orifice chokes the flow.

=== Small Ratio or QEV ===
As the ratio of the seat diameter to piston diameter is reduced, the area that the chamber is exposed to is reduced, to the point that the large area of the pilot is able to hold the piston closed until most of the pilot pressure is vented. Even when the pilot area is vented to a low pressure, the initial opening force is low because the area of the piston exposed to the chamber pressure is small as most of the face of the piston is exposed to no pressure in the barrel. This low opening force can cause many headaches with stuck pistons that sometimes fail to fire, and the equalization port may vent enough volume to prevent the pilot area from reaching a low enough pressure to open the valve. The lower the seat to diameter ratio; the lower the initial force the chamber can apply to open the valve, and the faster they snap open when they do get over the initial opening. This faster speed is due to the larger piston face exposed to the chamber pressure when the valve opens and the lower pressure in the pilot area. The lower pressure compresses less and provides less force on the back of the piston when it opens. The closer the ratio is to 1:1 the faster the avalanche, but the initial cracking open of the valve becomes slower as the initial opening force is lower and lower as you approach a 1:1 ratio.

One attractive feature of this valve is once it unseats and starts to open, the chamber pressure now acting on the face of the piston causes a large spike in opening force as the large barrel facing area is now exposed to the chamber pressure. This type of valve snaps open and is known as a Quick Exhaust Valve or QEV. This style valve is not prone to closing early and honking.

[[Image:MusketSeat.JPG ]]

The barrel sealer QEV piston valve has a large diameter seat in relation to the overall diameter of the piston.
A chamber sealer has a small seat in relation the the overall diameter so the force on the piston grows rapidly as the valve opens.

Chamber sealer valves have a disadvantage of needing a larger diameter piston for the same size valve seat as a barrel sealer. This adds mass and dead space between the valve piston and projectile. On the positive side, they are more reliable in opening and tend to have most of the opening acceleration early in the opening where it is needed. The drop in acceleration as the valve opens can increase the life expectancy of the valve as they compress the pilot area they slow before impact with the back of the breech.

=== 1:1 Ratio or QDV ===
If the ratio of the piston diameter is reduced to the diameter of the valve seat in a spool valve, then the valve won't open even when the pilot area is not under pressure. If the chamber is pressurized and no pressure is in the pilot area, the valve has the least back pressure of any of the piston valves and therefore the fastest opening when the valve is unseated by force. Even though the pilot area may half in volume as the piston moves into this space, the pressure rise from 1 atm to 2 atm is still less than the chamber force on the newly exposed face of the piston, so this piston will open fast regardless of the vent size or speed. This last category of piston valve is known as a Quick Dump Valve. To operate this valve in an air cannon, consideration must be made to mechanically move the piston and when the piston moves, the force will avalanche quickly as the piston face becomes exposed to the chamber pressure. For mechanical trigger the use a rope pull or a rod with a "sliding" piston are options to a spring or air start. The loose piston on a rope or rod provides speed as the core can accelerate freely when triggered. Decoupling the triggering mechanism from the piston prevents the trigger from adding to the moving mass of the piston. These valves are not subject to honking, but may "bounce" back closed after the shot by the pressure built up in the pilot area and bumper recoil after the chamber pressure is gone.

[[Image:QDV_parts.JPG]]

Assembled 1 inch QDV cannon and damaged can. Projectile was a 1 inch jawbreaker.
[[Image:Marshmallow_cannon.jpg]]

The quick dump valve has the piston OD the same size as the seat. It requires an external force to start it opening. It has no pilot pressure to hold it against a seat so it is often built with o rings on a piston. The valve cylinder can be built out of a pipe with ports cut in the side.

*[http://www.spudfiles.com/spud_wiki/index.php?title=Quick_Dump_Valve The Quick Dump Valve, by Technician1002.] Wiki page on the QDV

A video on the theory of the QDV cannon is here.
[http://www.youtube.com/watch?v=No3nI07mlQo The Quick Dump Valve]

=== O-Ring Considerations on a Piston Valve ===
To prevent stuck piston valves, consideration must be given to permit a good seal while not stopping movement.

To prevent stuck or hard to move pistons the o ring should not be compressed flat against the cylinder wall. Since movement is desirable, as well as a seal, we can design the piston to seal without needing to squeeze the o ring. The following video shows the theory fairly well.

[http://www.youtube.com/watch?v=BbDiZiRVrnk Youtube video on using o rings in air cannons]

At 4:20 in the video the force needed to move this piston is shown.

Instead of having O rings in a groove that sit tight against the bottom of the groove and then are compressed by the cylinder, floating rings do not bottom out in the o ring groove. To seal, the pressure trying to blow past the ring seats it against the side of the o ring groove. Air that is able to get under the ring presses outward to apply pressure to the cylinder wall. As the pressure is increased, this force is increased so higher operating pressures make a tighter seal and a little higher friction to movement.

Floating piston rings fit loose in the grooves. The o ring is sized to be slightly larger than the cylinder diameter it slides inside.
This photo is of a 1 inch quick dump valve piston.
[[Image:Piston_rings.jpg]]

Here is a drawing showing the force of the pressure on the o ring to provide a tight seal.
[[Image:123_floatingpneumatic1.jpg]]

Source: RL Hudson O-Ring Design & Materials Guide. Used with permission.

[[category:valves]]

Piston valve

2010-12-13T18:20:59Z

Technician1002: /* Common traits */

A '''piston valve''' is a [[pilot]] operated [[valve]]. It is very similar to a [[diaphragm valve]] in theory, but replaces it's flexible diaphragm with a rigid cylinder. There are 2 varieties; [[barrel]] sealing and [[chamber]] sealing.

== Barrel sealing valve ==

In a barrel sealing valve, the piston seals against the breech of the barrel. This is the most common piston valve design.

=== construction ===

The piston is often a well fitting cup-shaped object, such as a end cap. To provide a sealing face, a piece of rubber is attached, typically with a bolt. In the simplest case, equalization is accomplished by allowing the air to leak past the piston and into the chamber. Some people will machine their own pistons, in which case they often build [[O-ring]]s into them. With the O-rings, you need to make a small equalization hole; sometimes this is fancied up to be a homemade [[check valve]].

Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recommended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labeled "'''F'''" in the "use, barrel sealing" diagram.

These valves are often used on [[coaxial]]s and [[over/under]]s. In an over/under, the valve is built in a "T" fitting. The barrel is put co-axially through one end, the pilot and piston are put in the opposite one, and a chamber is connected to the perpendicular opening with a 90° elbow.

=== Use ===
[[Image:Wpiston.PNG|frame|top=pressurized, bottom=firing]]
Operation:
#Air is added by filling behind the piston (C).
#The piston (E) slides forwards, and seals against the barrel (A). (Alternatively, one can use a spring to move the piston forwards, which allows one to fill [slowly at first, to allow the [[pressure]] to equalize] from the chamber.)
#More air is added, and leaks around the piston (or through a small equalization hole) and into the chamber (B), filling it to the desired pressure.
#The [[pilot valve]] (D) behind the piston is opened, the pressure in the pilot volume (C) drops, and the higher pressure in the chamber area pushes the piston away from the barrel.
#The air flows around from the chamber, and into the barrel, propelling the projectile.

=== Pilot Valves ===
There is a common misconception that a simple blowgun is enough to pilot large piston valves, 1.5" and above. This is not recommended as your cannon will have very bad performance or may not even function at all. For valves 1"-1.25" in diameter, a 1/4" ball valve is recommended. For valves between 1.5" and 2.5" a 1/2" or 3/4" ball valve is probably enough. Anything above that will benefit from a sprinkler valve or a 1" ball valve for a pilot valve. When it comes to pilot valves, bigger is always better.

== Chamber sealing piston valve ==

=== construction ===

The piston of a chamber-sealing piston valve has to seal on both the chamber port and to the pilot volume. This requires that the piston be machined with [[O-ring]]s. A small equalization hole is required; sometimes this is fancied up to be a homemade [[check valve]].

The piston is almost always housed in a "t" fitting.

Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recommended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labeled "'''F'''" in the "use, chamber sealing sealing" diagram.

These valves are often used on [[over/under]]s, as the flow is already turned around 90o.

=== Use ===
[[Image:Wcspiston.PNG|frame|top=pressurized, bottom=firing]]
Operation:
#Air is added by filling behind the piston (C).
#The piston (E) slides forwards, and seals against the barrel (A). (Alternatively, one can use a spring to move the piston forwards, which allows one to fill [slowly at first, to allow the [[pressure]] to equalize] from the chamber.)
#More air is added, and leaks through the equalization hole in the piston and into the chamber (B), filling it to the desired pressure.
#The [[pilot valve]] (D) behind the piston is opened, the pressure in the pilot volume (C) drops, and the higher pressure in the chamber area pushes the piston away from the chamber.
#The air flows out of the chamber, and into the barrel, propelling the projectile.

== Common traits ==

#The performance of these valves can be calculated with the [[GGDT]].
#If your valve [[honking|honks]], it is probably a good idea to invest in a better pilot valve, though this is more of a problem with barrel-sealing valves. Narrow ratio barrel sealers tend to be immune to honking due to the low pressure at which they crack open. A larger pilot volume on a narrow ratio barrel sealer can reduce pilot pressure rise from the piston moving into the plot space causing compression. With less compression, the valve will not re-close early due to the rapid drop in chamber pressure. This eliminates honking.
#In both cases, provided there is a good deal of space around the barrel, the full flow potential of the valve is realized when the piston has moved back 1/4th of the barrel's inside diameter (I.D./4). The derivation of this formula is as follows:

Given: A = Pi(R)^2
C = 2PiR
T = Piston travel
R = I.D. of barrel / 2

When the piston moves back, the smallest amount of area exposed is either the area of the circular cross section of the barrel or the area exposed by the piston, which is the side of a cylinder, the bases being the barrel and piston face. The optimal ratio of area exposed between the 2 spots is 1:1, which means the exposed areas should be the same. So one sets the equations A and CT equal, that is A = CT.

Pi(R)^2 = 2PiR(T)

Solving for "T" results in:

R/2 = T which, if one substitutes I.D./2 for R, results in:

I.D./4 = T

Many people choose to open larger to provide only one restriction to flow instead of 2 the same size in a row. This is done by allowing the valve to open fully unrestricted and then compress the bumper while opening further. This provides the fastest possible opening time by preventing the piston deceleration while still opening.

#Pneumatic actuation is not mandatory; mechanical means can be used to hold the valve shut, or open it, rather than using the force of the air.

***The following section submitted by Technician1002***

The operation of barrel sealing valves falls into 3 categories which is related to the dimensions of the barrel seal or seat to the piston outside diameter.

=== Large Ratio Piston Valve ===
When the ratio is large in a barrel sealer with either a large piston or small barrel, most of the force to open the valve is controlled by the differential of the chamber pressure and pilot area. As the valve opens, the small area that becomes exposed to the chamber as it opens contributes little to the opening speed. This large area ratio valve are noted for reliable operation as they have the ability to open pistons that don't slide well. Due to the pressure still in the pilot area as they open, as the chamber vents out the barrel, it is often faster than the pilot, so the force used to open the valve vanishes and the pilot pressure unable to keep up with the drop, forces the valve to close. If this repeats as the pilot vents, it is noticeable as honking. This class of valves include pistons with a 2:1 diameter ratio or more. A 2:1 diameter ratio is a 4:1 area ratio. These are not QEV valves because the area sealed by the piston is only 25% of the pilot area so when the valve opens the force change is small. It opens with the pilot at 3/4 the pressure of the chamber. When it opens and the pilot volume is reduced by the piston moving into the pilot space, the rise in pressure in the pilot prevents the piston from opening all the way, so opening speed is directly related to how much faster the pilot can vent over the rate the chamber vents out the barrel. A slow pilot equals a slow valve and may cause honking.

In a chamber sealer version where the valve seat seals against the chamber, they are fast as the pressure is released and more pressure presses on the larger exposed face of the piston. This style tends to have a fairly large dead space between the valve and projectile. In addition a large piston has a greater mass and as the piston moves, it requires a larger displacement using much of the chamber air energy. If the valve seat is small to use a smaller piston, the small orifice chokes the flow.

=== Small Ratio or QEV ===
As the ratio of the seat diameter to piston diameter is reduced, the area that the chamber is exposed to is reduced, to the point that the large area of the pilot is able to hold the piston closed until most of the pilot pressure is vented. Even when the pilot area is vented to a low pressure, the initial opening force is low because the area of the piston exposed to the chamber pressure is small as most of the face of the piston is exposed to no pressure in the barrel. This low opening force can cause many headaches with stuck pistons that sometimes fail to fire, and the equalization port may vent enough volume to prevent the pilot area from reaching a low enough pressure to open the valve. The lower the seat to diameter ratio; the lower the initial force the chamber can apply to open the valve, and the faster they snap open when they do get over the initial opening. This faster speed is due to the larger piston face exposed to the chamber pressure when the valve opens and the lower pressure in the pilot area. The lower pressure compresses less and provides less force on the back of the piston when it opens. The closer the ratio is to 1:1 the faster the avalanche, but the initial cracking open of the valve becomes slower as the initial opening force is lower and lower as you approach a 1:1 ratio.

One attractive feature of this valve is once it unseats and starts to open, the chamber pressure now acting on the face of the piston causes a large spike in opening force as the large barrel facing area is now exposed to the chamber pressure. This type of valve snaps open and is known as a Quick Exhaust Valve or QEV. This style valve is not prone to closing early and honking.

[[Image:MusketSeat.JPG ]]

The barrel sealer QEV piston valve has a large diameter seat in relation to the overall diameter of the piston.
A chamber sealer has a small seat in relation the the overall diameter so the force on the piston grows rapidly as the valve opens.

Chamber sealer valves have a disadvantage of needing a larger diameter piston for the same size valve seat as a barrel sealer. This adds mass and dead space between the valve piston and projectile. On the positive side, they are more reliable in opening and tend to have most of the opening acceleration early in the opening where it is needed. The drop in acceleration as the valve opens can increase the life expectancy of the valve as they compress the pilot area they slow before impact with the back of the breech.

=== 1:1 Ratio or QDV ===
If the ratio of the piston diameter is reduced to the diameter of the valve seat in a spool valve, then the valve won't open even when the pilot area is not under pressure. If the chamber is pressurized and no pressure is in the pilot area, the valve has the least back pressure of any of the piston valves and therefore the fastest opening when the valve is unseated by force. Even though the pilot area may half in volume as the piston moves into this space, the pressure rise from 1 atm to 2 atm is still less than the chamber force on the newly exposed face of the piston, so this piston will open fast regardless of the vent size or speed. This last category of piston valve is known as a Quick Dump Valve. To operate this valve in an air cannon, consideration must be made to mechanically move the piston and when the piston moves, the force will avalanche quickly as the piston face becomes exposed to the chamber pressure. For mechanical trigger the use a rope pull or a rod with a "sliding" piston are options to a spring or air start. The loose piston on a rope or rod provides speed as the core can accelerate freely when triggered. Decoupling the triggering mechanism from the piston prevents the trigger from adding to the moving mass of the piston. These valves are not subject to honking, but may "bounce" back closed after the shot by the pressure built up in the pilot area and bumper recoil after the chamber pressure is gone.

[[Image:QDV_parts.JPG]]

Assembled 1 inch QDV cannon and damaged can. Projectile was a 1 inch jawbreaker.
[[Image:Marshmallow_cannon.jpg]]

The quick dump valve has the piston OD the same size as the seat. It requires an external force to start it opening. It has no pilot pressure to hold it against a seat so it is often built with o rings on a piston. The valve cylinder can be built out of a pipe with ports cut in the side.

*[http://www.spudfiles.com/spud_wiki/index.php?title=Quick_Dump_Valve The Quick Dump Valve, by Technician1002.] Wiki page on the QDV

A video on the theory of the QDV cannon is here.
[http://www.youtube.com/watch?v=No3nI07mlQo The Quick Dump Valve]

=== O-Ring Considerations on a Piston Valve ===
To prevent stuck piston valves, consideration must be given to permit a good seal while not stopping movement.

To prevent stuck or hard to move pistons the o ring should not be compressed flat against the cylinder wall. Since movement is desirable, as well as a seal, we can design the piston to seal without needing to squeeze the o ring. The following video shows the theory fairly well.

[http://www.youtube.com/watch?v=BbDiZiRVrnk Youtube video on using o rings in air cannons]

At 4:20 in the video the force needed to move this piston is shown.

Instead of having O rings in a groove that sit tight against the bottom of the groove and then are compressed by the cylinder, floating rings do not bottom out in the o ring groove. To seal, the pressure trying to blow past the ring seats it against the side of the o ring groove. Air that is able to get under the ring presses outward to apply pressure to the cylinder wall. As the pressure is increased, this force is increased so higher operating pressures make a tighter seal and a little higher friction to movement.

Floating piston rings fit loose in the grooves. The o ring is sized to be slightly larger than the cylinder diameter it slides inside.
This photo is of a 1 inch quick dump valve piston.
[[Image:Piston_rings.jpg]]

Here is a drawing showing the force of the pressure on the o ring to provide a tight seal.
[[Image:123_floatingpneumatic1.jpg]]
Source: RL Hudson O-Ring Design & Materials Guide. Used with permission.

[[category:valves]]

Pilot

2010-12-13T18:10:19Z

Technician1002: Added larger pilot volume consideration for narrow ratio valves. Added small pilot and high flow for chamber sealers and wide ratio pistons.

A '''Pilot''' is the airspace behind the [[piston valve|piston]] or [[diaphragm valve|diaphragm]] in a [[valve]], which is vented to open the valve. For maximum performance, its volume should be small to provide fast response as well as being large enough to minimize compression of the pilot volume. Its is usually exhausted by means of a built-in [[solenoid]] or an external [[pilot valve]].

Considerations on deciding on the proper pilot volume includes the size of the pilot valve, the ratio of the piston being piloted, and the valve style, a barrel sealer or chamber sealer.

A barrel sealer piston valve with a large OD and a small seat diameter can provide a piston that acts much like a hydraulic valve where the speed of motion is directly related to the rate the pilot is vented. A small pilot volume and a large fast high flow pilot valve provides good performance with this style piston.

A chamber sealer piston requires a small pilot volume and high flow fast pilot to open them quickly. Sprinkler valve or other high flow fast pilots are recommended.

On a low leakage barrel sealer piston with a seat near the diameter of the piston in a barrel sealing configuration, high performance can be achieved with a smaller pilot valve such as a blowgun and a larger pilot volume to reduce compression of the pilot air volume when the piston opens. The narrow ratio pistons remain closed until the pilot pressure is very low due to the small area exposed to the chamber pressure while closed. This reduces the initial amount of air pressure in the pilot when the valve cracks open. When the valve pops open, with a larger pilot volume, the pressure rise in the pilot is low, so the piston pops open and remains open without requiring a large flow pilot. Low piston friction and low EQ bleed flow is required to get this high performance. Floating o ring seals are recommended for narrow ratio pistons. Too large of a pilot volume in this style of pilot arrangement does increase the time from when the trigger is pulled to when the pilot pressure is low enough to unseat the main piston. This time increases the amount of time the chamber has to bleed down through the piston EQ port into the pilot. A low flow EQ port is recommended as well as a moderate pilot volume to reduce pilot pressure rise as the piston opens.

See the section on piston valves for more information on piston valve configurations.

[[category:valves]]

Forum Stickies

2010-12-13T17:47:29Z

Technician1002: /* How-To Database */

==What Is A Sticky?==
A sticky is a topic on a forum that has been edited by a Moderator so that it will always show the 'stickied' topic at the top of the forum section it is posted in.

Topics are usually stickied for the main reason of them being extremely helpful to all members, new members in particular. The topics usually contain information unique to that topic and are very informative. By making the topic a sticky, it saves members from searching the forum for similar information. As the topic shows at the top of a particular forum section, members will always be able to find it and it will stand out to newer members.

==Spudfiles Stickies==
Below is a list of the current forum stickies on Spudfiles in there corresponding forum sections.

===Website Discussion===
*[http://www.spudfiles.com/forums/chatroom-requests-t15608.html Chatroom Requests.] Request members to enter the chatroom for an off-topic or spudgun related talk.
*[http://www.spudfiles.com/forums/posting-images-a-step-by-step-guide-t13190.html Posting images a step-by-step guide.] How to correctly post images in your posts on Spudfiles.
*[http://www.spudfiles.com/forums/spudfiles-extension-for-firefox-t11409.html Spudfiles extension for Firefox.] A useful toolbar for firefox made by a member of Spudfiles.
*[http://www.spudfiles.com/forums/parroting-t14472.html Parroting.] A topic by a Spudfiles Moderator on forum 'parroting'.

===General Spud Cannon Related===
*[http://www.spudfiles.com/forums/my-eye-accident-t15301.html My ~EYE~ Accident.] A topic about a spudgunning accident involving a member of Spudfiles
*[http://www.spudfiles.com/forums/newbie-help-t13096.html Newbie Help.] A topic compiling helpful links for new members.
*[http://www.spudfiles.com/forums/launcher-failure-analysis-log-t7483.html Launcher Failure Analysis Log.] A topic analysing various spudgun failures.
*[http://www.spudfiles.com/forums/spudfiles-member-map-t2639.html Spudfiles member map.] A map of some Spudfiles members worldwide.

===Pneumatic Cannon Discussion===
*[http://www.spudfiles.com/forums/the-sprinkler-valve-pdf-file-t16786.html The Sprinkler Valve.] A topic of compiled information on the spudder's most common pneumatic valve, the sprinkler valve.
*[http://www.spudfiles.com/forums/piston-valves-explained-visually-t8157.html Piston Valves Explained Visually.] Possibly one of the most well known and informative topic on Spudfiles. This topic shows how piston valves work using animation.
*[http://www.spudfiles.com/forums/sprinkler-valve-troubleshooting-guide-t8780.html Sprinkler Valve Troubleshooting.] Problem with your sprinkler valve? Read this sticky.
*[http://www.spudfiles.com/forums/how-much-co2-do-i-need-t7133.html How much co2 do I need?] This topic has information on how to determine how much CO2 is required for a given chamber size and pressure.
*[http://www.spudfiles.com/forums/read-this-before-posting-t2918.html Read this before posting!.] A warning message from a Moderator on posting.

===Combustion Cannon Discussion===
*[http://www.spudfiles.com/forums/sparker-reference-guide-t13030.html Sparker Reference Guide.] A helpful topic detailing some of the most common and uncommon ways of generating a spark in a spudgun.
*[http://www.spudfiles.com/forums/how-to-build-a-propane-meter-t7234.html How to build a propane meter.] Exactly that.

===Hybrid Cannon Discussion===
*[http://www.spudfiles.com/forums/hybrid-fueling-101-t13602.html Hybrid Fueling 101.] A great topic on how to accurately fuel your hybrid two different ways.

===BB/Airsoft/Pellet Gun Discussion===
*[http://www.spudfiles.com/forums/strafer-troubleshooting-guide-t8779.html Strafer Troubleshooting Guide.] Problem with your strafer? Read this sticky.

===Construction Materials/Ammo Discussion===
*[http://www.spudfiles.com/forums/ammo-ideas-t1724.html Ammo Ideas.] Got an idea for good spudgun ammo? Post it here. Please check first that you are not duplicating anything already previously said in the topic.
*[http://www.spudfiles.com/forums/golf-ball-barrel-faq-t5915.html Golf Ball Barrel FAQ.] All you need to know about golfball barrels being used with spudguns.

===Non-Spudgun Related Discussion===
*[http://www.spudfiles.com/forums/where-are-you-from-t12433.html Where are you?.] A Spudfiles poll detailing the locations of members who frequent the Spudfiles forum.
*[http://www.spudfiles.com/forums/the-meaning-of-this-section-t14449.html The meaning of this section.] Not quite the meaning of life, but still very important nonetheless.
*[http://www.spudfiles.com/forums/nsgrd-rules-and-guidelines-t11888.html NSGRD Rules and Guidelines.] Rules and guidelines specifically for the Non-Spudgun Related Dsicussion forum.
*[http://www.spudfiles.com/forums/rip-chewy-bill-vogt-memorial-t674.html RIP Chewy (Bill Vogt) -Memorial-.] A thread dedicated to the memory of member and moderator of the old Spudtech forum, Bill Vogt aka Chewy.
*[http://www.spudfiles.com/forums/viewtopic,p,158530.html#158530 Mug Shot Pics!!] Pictures of Spudfiles members.

===IPLA Discussion===
*[http://www.spudfiles.com/forums/uk-parts-locations-t3396.html UK - Parts Locations.] A thread to help spudders from the UK with finding spudgun supplies.
*[http://www.spudfiles.com/forums/australia-parts-locations-t3393.html Asutralia - Parts Locations.] Same as above, but for the Aussies.
*[http://www.spudfiles.com/forums/australia-meets-and-club-events-t3394.html Australia - Meets & Club Events.] A thread for Australian members to help organise spudgunning meets in Australia.
*[http://www.spudfiles.com/forums/uk-meets-and-club-events-t3395.html UK - Meets & Club Events.] A thread for UK members to help organise spudgunning meets in the UK.

===How-To Database===
*[http://www.spudfiles.com/forums/how-to-make-a-pneumatic-cannon-with-a-2-piston-valve-t10381.html How to make a pneumatic cannon with a 2" piston valve.] A topic with two different how-to's on making 2" piston valves.
*[http://www.spudfiles.com/forums/tutorial-making-a-small-o-ringed-piston-on-a-drill-press-t21740.html How to make a small piston on a drill press.] Step by step instructions to make a small plastic piston on a drill press.
*[http://www.spudfiles.com/forums/modding-a-sprinkler-valve-t305.html Modding a sprinkler valve.] How to mod a sprinkler valve tutorial.
*[http://www.spudfiles.com/forums/what-would-you-like-to-see-here-t5957.html What would you like to see here?] A thread about possible how-to's members could contribute to the forum.
*[http://www.spudfiles.com/forums/complete-plans-for-advanced-combustion-t4512.html Complete Plans for Advanced Combustion.] Plans on making an advanced combustion spudgun.

===Theories/Accessories Database===
*[http://www.spudfiles.com/forums/valve-cutaways-t273.html Valve Cutaways.] Pictures of different spudgunning valves cut in half.

==Important Spudfiles Announcements==
*[http://www.spudfiles.com/forums/posting-etiquette-t11887.html Posting Etiquette.] All the posting rules for the forum, differs from the actual forum rules.
*[http://www.spudfiles.com/forums/grammar-t1460.html Grammar.] A topic on why proper grammar is important on this forum.
*[http://www.spudfiles.com/forums/attention-comcast-cox-verizon-email-users-t16165.html Attention - Comcast/Cox/Verizon Email Users.] If you use Comcast/Cox/Verison email, read this announcement.
*[http://www.spudfiles.com/forums/caution-odd-advertisements-on-spudfiles-t16756.html Caution - Odd Advertisements On SpudFiles.] Seeing weird advertisements on Spudfiles? You probably have a virus, read this sticky.
*[http://www.spudfiles.com/forums/solvent-welding-course-recommended-for-all-t3009.html Solvent Welding Course Recommended For All.] Not sure if you are solvent welding your cannon correctly, or just want a free pen, take this solvent welding course. Highly recommended to insure a safe build.
*[http://www.spudfiles.com/forums/off-topic-and-non-spudgun-related-merged-t8929.html Off-Topic and Non-Spudgun Related Merged.] Outlining why the Off-Topic section was removed/merged.
*[http://www.spudfiles.com/forums/are-you-sure-your-post-belongs-here-t4360.html Are you SURE your post belongs here?] Before making a post in the How-To section, be sure to read this topic first.

Forum Stickies

2010-12-13T17:46:53Z

Technician1002: /* Pneumatic Cannon Discussion */

==What Is A Sticky?==
A sticky is a topic on a forum that has been edited by a Moderator so that it will always show the 'stickied' topic at the top of the forum section it is posted in.

Topics are usually stickied for the main reason of them being extremely helpful to all members, new members in particular. The topics usually contain information unique to that topic and are very informative. By making the topic a sticky, it saves members from searching the forum for similar information. As the topic shows at the top of a particular forum section, members will always be able to find it and it will stand out to newer members.

==Spudfiles Stickies==
Below is a list of the current forum stickies on Spudfiles in there corresponding forum sections.

===Website Discussion===
*[http://www.spudfiles.com/forums/chatroom-requests-t15608.html Chatroom Requests.] Request members to enter the chatroom for an off-topic or spudgun related talk.
*[http://www.spudfiles.com/forums/posting-images-a-step-by-step-guide-t13190.html Posting images a step-by-step guide.] How to correctly post images in your posts on Spudfiles.
*[http://www.spudfiles.com/forums/spudfiles-extension-for-firefox-t11409.html Spudfiles extension for Firefox.] A useful toolbar for firefox made by a member of Spudfiles.
*[http://www.spudfiles.com/forums/parroting-t14472.html Parroting.] A topic by a Spudfiles Moderator on forum 'parroting'.

===General Spud Cannon Related===
*[http://www.spudfiles.com/forums/my-eye-accident-t15301.html My ~EYE~ Accident.] A topic about a spudgunning accident involving a member of Spudfiles
*[http://www.spudfiles.com/forums/newbie-help-t13096.html Newbie Help.] A topic compiling helpful links for new members.
*[http://www.spudfiles.com/forums/launcher-failure-analysis-log-t7483.html Launcher Failure Analysis Log.] A topic analysing various spudgun failures.
*[http://www.spudfiles.com/forums/spudfiles-member-map-t2639.html Spudfiles member map.] A map of some Spudfiles members worldwide.

===Pneumatic Cannon Discussion===
*[http://www.spudfiles.com/forums/the-sprinkler-valve-pdf-file-t16786.html The Sprinkler Valve.] A topic of compiled information on the spudder's most common pneumatic valve, the sprinkler valve.
*[http://www.spudfiles.com/forums/piston-valves-explained-visually-t8157.html Piston Valves Explained Visually.] Possibly one of the most well known and informative topic on Spudfiles. This topic shows how piston valves work using animation.
*[http://www.spudfiles.com/forums/sprinkler-valve-troubleshooting-guide-t8780.html Sprinkler Valve Troubleshooting.] Problem with your sprinkler valve? Read this sticky.
*[http://www.spudfiles.com/forums/how-much-co2-do-i-need-t7133.html How much co2 do I need?] This topic has information on how to determine how much CO2 is required for a given chamber size and pressure.
*[http://www.spudfiles.com/forums/read-this-before-posting-t2918.html Read this before posting!.] A warning message from a Moderator on posting.

===Combustion Cannon Discussion===
*[http://www.spudfiles.com/forums/sparker-reference-guide-t13030.html Sparker Reference Guide.] A helpful topic detailing some of the most common and uncommon ways of generating a spark in a spudgun.
*[http://www.spudfiles.com/forums/how-to-build-a-propane-meter-t7234.html How to build a propane meter.] Exactly that.

===Hybrid Cannon Discussion===
*[http://www.spudfiles.com/forums/hybrid-fueling-101-t13602.html Hybrid Fueling 101.] A great topic on how to accurately fuel your hybrid two different ways.

===BB/Airsoft/Pellet Gun Discussion===
*[http://www.spudfiles.com/forums/strafer-troubleshooting-guide-t8779.html Strafer Troubleshooting Guide.] Problem with your strafer? Read this sticky.

===Construction Materials/Ammo Discussion===
*[http://www.spudfiles.com/forums/ammo-ideas-t1724.html Ammo Ideas.] Got an idea for good spudgun ammo? Post it here. Please check first that you are not duplicating anything already previously said in the topic.
*[http://www.spudfiles.com/forums/golf-ball-barrel-faq-t5915.html Golf Ball Barrel FAQ.] All you need to know about golfball barrels being used with spudguns.

===Non-Spudgun Related Discussion===
*[http://www.spudfiles.com/forums/where-are-you-from-t12433.html Where are you?.] A Spudfiles poll detailing the locations of members who frequent the Spudfiles forum.
*[http://www.spudfiles.com/forums/the-meaning-of-this-section-t14449.html The meaning of this section.] Not quite the meaning of life, but still very important nonetheless.
*[http://www.spudfiles.com/forums/nsgrd-rules-and-guidelines-t11888.html NSGRD Rules and Guidelines.] Rules and guidelines specifically for the Non-Spudgun Related Dsicussion forum.
*[http://www.spudfiles.com/forums/rip-chewy-bill-vogt-memorial-t674.html RIP Chewy (Bill Vogt) -Memorial-.] A thread dedicated to the memory of member and moderator of the old Spudtech forum, Bill Vogt aka Chewy.
*[http://www.spudfiles.com/forums/viewtopic,p,158530.html#158530 Mug Shot Pics!!] Pictures of Spudfiles members.

===IPLA Discussion===
*[http://www.spudfiles.com/forums/uk-parts-locations-t3396.html UK - Parts Locations.] A thread to help spudders from the UK with finding spudgun supplies.
*[http://www.spudfiles.com/forums/australia-parts-locations-t3393.html Asutralia - Parts Locations.] Same as above, but for the Aussies.
*[http://www.spudfiles.com/forums/australia-meets-and-club-events-t3394.html Australia - Meets & Club Events.] A thread for Australian members to help organise spudgunning meets in Australia.
*[http://www.spudfiles.com/forums/uk-meets-and-club-events-t3395.html UK - Meets & Club Events.] A thread for UK members to help organise spudgunning meets in the UK.

===How-To Database===
*[http://www.spudfiles.com/forums/how-to-make-a-pneumatic-cannon-with-a-2-piston-valve-t10381.html How to make a pneumatic cannon with a 2" piston valve.] A topic with two different how-to's on making 2" piston valves.
*[http://www.spudfiles.com/forums/modding-a-sprinkler-valve-t305.html Modding a sprinkler valve.] How to mod a sprinkler valve tutorial.
*[http://www.spudfiles.com/forums/what-would-you-like-to-see-here-t5957.html What would you like to see here?] A thread about possible how-to's members could contribute to the forum.
*[http://www.spudfiles.com/forums/complete-plans-for-advanced-combustion-t4512.html Complete Plans for Advanced Combustion.] Plans on making an advanced combustion spudgun.

===Theories/Accessories Database===
*[http://www.spudfiles.com/forums/valve-cutaways-t273.html Valve Cutaways.] Pictures of different spudgunning valves cut in half.

==Important Spudfiles Announcements==
*[http://www.spudfiles.com/forums/posting-etiquette-t11887.html Posting Etiquette.] All the posting rules for the forum, differs from the actual forum rules.
*[http://www.spudfiles.com/forums/grammar-t1460.html Grammar.] A topic on why proper grammar is important on this forum.
*[http://www.spudfiles.com/forums/attention-comcast-cox-verizon-email-users-t16165.html Attention - Comcast/Cox/Verizon Email Users.] If you use Comcast/Cox/Verison email, read this announcement.
*[http://www.spudfiles.com/forums/caution-odd-advertisements-on-spudfiles-t16756.html Caution - Odd Advertisements On SpudFiles.] Seeing weird advertisements on Spudfiles? You probably have a virus, read this sticky.
*[http://www.spudfiles.com/forums/solvent-welding-course-recommended-for-all-t3009.html Solvent Welding Course Recommended For All.] Not sure if you are solvent welding your cannon correctly, or just want a free pen, take this solvent welding course. Highly recommended to insure a safe build.
*[http://www.spudfiles.com/forums/off-topic-and-non-spudgun-related-merged-t8929.html Off-Topic and Non-Spudgun Related Merged.] Outlining why the Off-Topic section was removed/merged.
*[http://www.spudfiles.com/forums/are-you-sure-your-post-belongs-here-t4360.html Are you SURE your post belongs here?] Before making a post in the How-To section, be sure to read this topic first.

Forum Stickies

2010-12-13T17:45:58Z

Technician1002: /* Pneumatic Cannon Discussion */

==What Is A Sticky?==
A sticky is a topic on a forum that has been edited by a Moderator so that it will always show the 'stickied' topic at the top of the forum section it is posted in.

Topics are usually stickied for the main reason of them being extremely helpful to all members, new members in particular. The topics usually contain information unique to that topic and are very informative. By making the topic a sticky, it saves members from searching the forum for similar information. As the topic shows at the top of a particular forum section, members will always be able to find it and it will stand out to newer members.

==Spudfiles Stickies==
Below is a list of the current forum stickies on Spudfiles in there corresponding forum sections.

===Website Discussion===
*[http://www.spudfiles.com/forums/chatroom-requests-t15608.html Chatroom Requests.] Request members to enter the chatroom for an off-topic or spudgun related talk.
*[http://www.spudfiles.com/forums/posting-images-a-step-by-step-guide-t13190.html Posting images a step-by-step guide.] How to correctly post images in your posts on Spudfiles.
*[http://www.spudfiles.com/forums/spudfiles-extension-for-firefox-t11409.html Spudfiles extension for Firefox.] A useful toolbar for firefox made by a member of Spudfiles.
*[http://www.spudfiles.com/forums/parroting-t14472.html Parroting.] A topic by a Spudfiles Moderator on forum 'parroting'.

===General Spud Cannon Related===
*[http://www.spudfiles.com/forums/my-eye-accident-t15301.html My ~EYE~ Accident.] A topic about a spudgunning accident involving a member of Spudfiles
*[http://www.spudfiles.com/forums/newbie-help-t13096.html Newbie Help.] A topic compiling helpful links for new members.
*[http://www.spudfiles.com/forums/launcher-failure-analysis-log-t7483.html Launcher Failure Analysis Log.] A topic analysing various spudgun failures.
*[http://www.spudfiles.com/forums/spudfiles-member-map-t2639.html Spudfiles member map.] A map of some Spudfiles members worldwide.

===Pneumatic Cannon Discussion===
*[http://www.spudfiles.com/forums/the-sprinkler-valve-pdf-file-t16786.html The Sprinkler Valve.] A topic of compiled information on the spudder's most common pneumatic valve, the sprinkler valve.
*[http://www.spudfiles.com/forums/piston-valves-explained-visually-t8157.html Piston Valves Explained Visually.] Possibly one of the most well known and informative topic on Spudfiles. This topic shows how piston valves work using animation.
*[http://www.spudfiles.com/forums/tutorial-making-a-small-o-ringed-piston-on-a-drill-press-t21740.html How to make a small piston on a drill press.] Step by step instructions to make a small plastic piston on a drill press.
*[http://www.spudfiles.com/forums/sprinkler-valve-troubleshooting-guide-t8780.html Sprinkler Valve Troubleshooting.] Problem with your sprinkler valve? Read this sticky.
*[http://www.spudfiles.com/forums/how-much-co2-do-i-need-t7133.html How much co2 do I need?] This topic has information on how to determine how much CO2 is required for a given chamber size and pressure.
*[http://www.spudfiles.com/forums/read-this-before-posting-t2918.html Read this before posting!.] A warning message from a Moderator on posting.

===Combustion Cannon Discussion===
*[http://www.spudfiles.com/forums/sparker-reference-guide-t13030.html Sparker Reference Guide.] A helpful topic detailing some of the most common and uncommon ways of generating a spark in a spudgun.
*[http://www.spudfiles.com/forums/how-to-build-a-propane-meter-t7234.html How to build a propane meter.] Exactly that.

===Hybrid Cannon Discussion===
*[http://www.spudfiles.com/forums/hybrid-fueling-101-t13602.html Hybrid Fueling 101.] A great topic on how to accurately fuel your hybrid two different ways.

===BB/Airsoft/Pellet Gun Discussion===
*[http://www.spudfiles.com/forums/strafer-troubleshooting-guide-t8779.html Strafer Troubleshooting Guide.] Problem with your strafer? Read this sticky.

===Construction Materials/Ammo Discussion===
*[http://www.spudfiles.com/forums/ammo-ideas-t1724.html Ammo Ideas.] Got an idea for good spudgun ammo? Post it here. Please check first that you are not duplicating anything already previously said in the topic.
*[http://www.spudfiles.com/forums/golf-ball-barrel-faq-t5915.html Golf Ball Barrel FAQ.] All you need to know about golfball barrels being used with spudguns.

===Non-Spudgun Related Discussion===
*[http://www.spudfiles.com/forums/where-are-you-from-t12433.html Where are you?.] A Spudfiles poll detailing the locations of members who frequent the Spudfiles forum.
*[http://www.spudfiles.com/forums/the-meaning-of-this-section-t14449.html The meaning of this section.] Not quite the meaning of life, but still very important nonetheless.
*[http://www.spudfiles.com/forums/nsgrd-rules-and-guidelines-t11888.html NSGRD Rules and Guidelines.] Rules and guidelines specifically for the Non-Spudgun Related Dsicussion forum.
*[http://www.spudfiles.com/forums/rip-chewy-bill-vogt-memorial-t674.html RIP Chewy (Bill Vogt) -Memorial-.] A thread dedicated to the memory of member and moderator of the old Spudtech forum, Bill Vogt aka Chewy.
*[http://www.spudfiles.com/forums/viewtopic,p,158530.html#158530 Mug Shot Pics!!] Pictures of Spudfiles members.

===IPLA Discussion===
*[http://www.spudfiles.com/forums/uk-parts-locations-t3396.html UK - Parts Locations.] A thread to help spudders from the UK with finding spudgun supplies.
*[http://www.spudfiles.com/forums/australia-parts-locations-t3393.html Asutralia - Parts Locations.] Same as above, but for the Aussies.
*[http://www.spudfiles.com/forums/australia-meets-and-club-events-t3394.html Australia - Meets & Club Events.] A thread for Australian members to help organise spudgunning meets in Australia.
*[http://www.spudfiles.com/forums/uk-meets-and-club-events-t3395.html UK - Meets & Club Events.] A thread for UK members to help organise spudgunning meets in the UK.

===How-To Database===
*[http://www.spudfiles.com/forums/how-to-make-a-pneumatic-cannon-with-a-2-piston-valve-t10381.html How to make a pneumatic cannon with a 2" piston valve.] A topic with two different how-to's on making 2" piston valves.
*[http://www.spudfiles.com/forums/modding-a-sprinkler-valve-t305.html Modding a sprinkler valve.] How to mod a sprinkler valve tutorial.
*[http://www.spudfiles.com/forums/what-would-you-like-to-see-here-t5957.html What would you like to see here?] A thread about possible how-to's members could contribute to the forum.
*[http://www.spudfiles.com/forums/complete-plans-for-advanced-combustion-t4512.html Complete Plans for Advanced Combustion.] Plans on making an advanced combustion spudgun.

===Theories/Accessories Database===
*[http://www.spudfiles.com/forums/valve-cutaways-t273.html Valve Cutaways.] Pictures of different spudgunning valves cut in half.

==Important Spudfiles Announcements==
*[http://www.spudfiles.com/forums/posting-etiquette-t11887.html Posting Etiquette.] All the posting rules for the forum, differs from the actual forum rules.
*[http://www.spudfiles.com/forums/grammar-t1460.html Grammar.] A topic on why proper grammar is important on this forum.
*[http://www.spudfiles.com/forums/attention-comcast-cox-verizon-email-users-t16165.html Attention - Comcast/Cox/Verizon Email Users.] If you use Comcast/Cox/Verison email, read this announcement.
*[http://www.spudfiles.com/forums/caution-odd-advertisements-on-spudfiles-t16756.html Caution - Odd Advertisements On SpudFiles.] Seeing weird advertisements on Spudfiles? You probably have a virus, read this sticky.
*[http://www.spudfiles.com/forums/solvent-welding-course-recommended-for-all-t3009.html Solvent Welding Course Recommended For All.] Not sure if you are solvent welding your cannon correctly, or just want a free pen, take this solvent welding course. Highly recommended to insure a safe build.
*[http://www.spudfiles.com/forums/off-topic-and-non-spudgun-related-merged-t8929.html Off-Topic and Non-Spudgun Related Merged.] Outlining why the Off-Topic section was removed/merged.
*[http://www.spudfiles.com/forums/are-you-sure-your-post-belongs-here-t4360.html Are you SURE your post belongs here?] Before making a post in the How-To section, be sure to read this topic first.

Piston valve

2010-05-13T19:24:28Z

Technician1002: /* 1:1 Ratio or QDV */ Fixed dead link to QDV page

A '''piston valve''' is a [[pilot]] operated [[valve]]. It is very similar to a [[diaphragm valve]] in theory, but replaces it's flexible diaphragm with a rigid cylinder. There are 2 varieties; [[barrel]] sealing and [[chamber]] sealing.

== Barrel sealing valve ==

In a barrel sealing valve, the piston seals against the breech of the barrel. This is the most common piston valve design.

=== construction ===

The piston is often a well fitting cup-shaped object, such as a end cap. To provide a sealing face, a piece of rubber is attached, typically with a bolt. In the simplest case, equalization is accomplished by allowing the air to leak past the piston and into the chamber. Some people will machine their own pistons, in which case they often build [[O-ring]]s into them. With the O-rings, you need to make a small equalization hole; sometimes this is fancied up to be a homemade [[check valve]].

Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recommended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labeled "'''F'''" in the "use, barrel sealing" diagram.

These valves are often used on [[coaxial]]s and [[over/under]]s. In an over/under, the valve is built in a "T" fitting. The barrel is put co-axially through one end, the pilot and piston are put in the opposite one, and a chamber is connected to the perpendicular opening with a 90° elbow.

=== Use ===
[[Image:Wpiston.PNG|frame|top=pressurized, bottom=firing]]
Operation:
#Air is added by filling behind the piston (C).
#The piston (E) slides forwards, and seals against the barrel (A). (Alternatively, one can use a spring to move the piston forwards, which allows one to fill [slowly at first, to allow the [[pressure]] to equalize] from the chamber.)
#More air is added, and leaks around the piston (or through a small equalization hole) and into the chamber (B), filling it to the desired pressure.
#The [[pilot valve]] (D) behind the piston is opened, the pressure in the pilot volume (C) drops, and the higher pressure in the chamber area pushes the piston away from the barrel.
#The air flows around from the chamber, and into the barrel, propelling the projectile.

=== Pilot Valves ===
There is a common misconception that a simple blowgun is enough to pilot large piston valves, 1.5" and above. This is not recommended as your cannon will have very bad performance or may not even function at all. For valves 1"-1.25" in diameter, a 1/4" ball valve is recommended. For valves between 1.5" and 2.5" a 1/2" or 3/4" ball valve is probably enough. Anything above that will benefit from a sprinkler valve or a 1" ball valve for a pilot valve. When it comes to pilot valves, bigger is always better.

== Chamber sealing piston valve ==

=== construction ===

The piston of a chamber-sealing piston valve has to seal on both the chamber port and to the pilot volume. This requires that the piston be machined with [[O-ring]]s. A small equalization hole is required; sometimes this is fancied up to be a homemade [[check valve]].

The piston is almost always housed in a "t" fitting.

Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recommended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labeled "'''F'''" in the "use, chamber sealing sealing" diagram.

These valves are often used on [[over/under]]s, as the flow is already turned around 90o.

=== Use ===
[[Image:Wcspiston.PNG|frame|top=pressurized, bottom=firing]]
Operation:
#Air is added by filling behind the piston (C).
#The piston (E) slides forwards, and seals against the barrel (A). (Alternatively, one can use a spring to move the piston forwards, which allows one to fill [slowly at first, to allow the [[pressure]] to equalize] from the chamber.)
#More air is added, and leaks through the equalization hole in the piston and into the chamber (B), filling it to the desired pressure.
#The [[pilot valve]] (D) behind the piston is opened, the pressure in the pilot volume (C) drops, and the higher pressure in the chamber area pushes the piston away from the chamber.
#The air flows out of the chamber, and into the barrel, propelling the projectile.

== Common traits ==

#The performance of these valves can be calculated with the [[GGDT]].
#If your valve [[honking|honks]], it is probably a good idea to invest in a better pilot valve, though this is more of a problem with barrel-sealing valves.
#In both cases, provided there is a good deal of space around the barrel, the full flow potential of the valve is realized when the piston has moved back 1/4th of the barrel's inside diameter (I.D./4). The derivation of this formula is as follows:

Given: A = Pi(R)^2
C = 2PiR
T = Piston travel
R = I.D. of barrel / 2

When the piston moves back, the smallest amount of area exposed is either the area of the circular cross section of the barrel or the area exposed by the piston, which is the side of a cylinder, the bases being the barrel and piston face. The optimal ratio of area exposed between the 2 spots is 1:1, which means the exposed areas should be the same. So one sets the equations A and CT equal, that is A = CT.

Pi(R)^2 = 2PiR(T)

Solving for "T" results in:

R/2 = T which, if one substitutes I.D./2 for R, results in:

I.D./4 = T

Many people choose to open larger to provide only one restriction to flow instead of 2 the same size in a row. This is done by allowing the valve to open fully unrestricted and then compress the bumper while opening further. This provides the fastest possible opening time by preventing the piston deceleration while still opening.

#Pneumatic actuation is not mandatory; mechanical means can be used to hold the valve shut, or open it, rather than using the force of the air.

***The following section submitted by Technician1002***

The operation of barrel sealing valves falls into 3 categories which is related to the dimensions of the barrel seal or seat to the piston outside diameter.

=== Large Ratio Piston Valve ===
When the ratio is large in a barrel sealer with either a large piston or small barrel, most of the force to open the valve is controlled by the differential of the chamber pressure and pilot area. As the valve opens, the small area that becomes exposed to the chamber as it opens contributes little to the opening speed. This large area ratio valve are noted for reliable operation as they have the ability to open pistons that don't slide well. Due to the pressure still in the pilot area as they open, as the chamber vents out the barrel, it is often faster than the pilot, so the force used to open the valve vanishes and the pilot pressure unable to keep up with the drop, forces the valve to close. If this repeats as the pilot vents, it is noticeable as honking. This class of valves include pistons with a 2:1 diameter ratio or more. A 2:1 diameter ratio is a 4:1 area ratio. These are not QEV valves because the area sealed by the piston is only 25% of the pilot area so when the valve opens the force change is small. It opens with the pilot at 3/4 the pressure of the chamber. When it opens and the pilot volume is reduced by the piston moving into the pilot space, the rise in pressure in the pilot prevents the piston from opening all the way, so opening speed is directly related to how much faster the pilot can vent over the rate the chamber vents out the barrel. A slow pilot equals a slow valve and may cause honking.

In a chamber sealer version where the valve seat seals against the chamber, they are fast as the pressure is released and more pressure presses on the larger exposed face of the piston. This style tends to have a fairly large dead space between the valve and projectile. In addition a large piston has a greater mass and as the piston moves, it requires a larger displacement using much of the chamber air energy. If the valve seat is small to use a smaller piston, the small orifice chokes the flow.

=== Small Ratio or QEV ===
As the ratio of the seat diameter to piston diameter is reduced, the area that the chamber is exposed to is reduced, to the point that the large area of the pilot is able to hold the piston closed until most of the pilot pressure is vented. Even when the pilot area is vented to a low pressure, the initial opening force is low because the area of the piston exposed to the chamber pressure is small as most of the face of the piston is exposed to no pressure in the barrel. This low opening force can cause many headaches with stuck pistons that sometimes fail to fire, and the equalization port may vent enough volume to prevent the pilot area from reaching a low enough pressure to open the valve. The lower the seat to diameter ratio; the lower the initial force the chamber can apply to open the valve, and the faster they snap open when they do get over the initial opening. This faster speed is due to the larger piston face exposed to the chamber pressure when the valve opens and the lower pressure in the pilot area. The lower pressure compresses less and provides less force on the back of the piston when it opens. The closer the ratio is to 1:1 the faster the avalanche, but the initial cracking open of the valve becomes slower as the initial opening force is lower and lower as you approach a 1:1 ratio.

One attractive feature of this valve is once it unseats and starts to open, the chamber pressure now acting on the face of the piston causes a large spike in opening force as the large barrel facing area is now exposed to the chamber pressure. This type of valve snaps open and is known as a Quick Exhaust Valve or QEV. This style valve is not prone to closing early and honking.

[[Image:MusketSeat.JPG ]]

The barrel sealer QEV piston valve has a large diameter seat in relation to the overall diameter of the piston.
A chamber sealer has a small seat in relation the the overall diameter so the force on the piston grows rapidly as the valve opens.

Chamber sealer valves have a disadvantage of needing a larger diameter piston for the same size valve seat as a barrel sealer. This adds mass and dead space between the valve piston and projectile. On the positive side, they are more reliable in opening and tend to have most of the opening acceleration early in the opening where it is needed. The drop in acceleration as the valve opens can increase the life expectancy of the valve as they compress the pilot area they slow before impact with the back of the breech.

=== 1:1 Ratio or QDV ===
If the ratio of the piston diameter is reduced to the diameter of the valve seat in a spool valve, then the valve won't open even when the pilot area is not under pressure. If the chamber is pressurized and no pressure is in the pilot area, the valve has the least back pressure of any of the piston valves and therefore the fastest opening when the valve is unseated by force. Even though the pilot area may half in volume as the piston moves into this space, the pressure rise from 1 atm to 2 atm is still less than the chamber force on the newly exposed face of the piston, so this piston will open fast regardless of the vent size or speed. This last category of piston valve is known as a Quick Dump Valve. To operate this valve in an air cannon, consideration must be made to mechanically move the piston and when the piston moves, the force will avalanche quickly as the piston face becomes exposed to the chamber pressure. For mechanical trigger the use a rope pull or a rod with a "sliding" piston are options to a spring or air start. The loose piston on a rope or rod provides speed as the core can accelerate freely when triggered. Decoupling the triggering mechanism from the piston prevents the trigger from adding to the moving mass of the piston. These valves are not subject to honking, but may "bounce" back closed after the shot by the pressure built up in the pilot area and bumper recoil after the chamber pressure is gone.

[[Image:QDV_parts.JPG]]

Assembled 1 inch QDV cannon and damaged can. Projectile was a 1 inch jawbreaker.
[[Image:Marshmallow_cannon.jpg]]

The quick dump valve has the piston OD the same size as the seat. It requires an external force to start it opening. It has no pilot pressure to hold it against a seat so it is often built with o rings on a piston. The valve cylinder can be built out of a pipe with ports cut in the side.

*[http://www.spudfiles.com/spud_wiki/index.php?title=Quick_Dump_Valve The Quick Dump Valve, by Technician1002.] Wiki page on the QDV

A video on the theory of the QDV cannon is here.
[http://www.youtube.com/watch?v=No3nI07mlQo The Quick Dump Valve]

=== O-Ring Considerations on a Piston Valve ===
To prevent stuck piston valves, consideration must be given to permit a good seal while not stopping movement.

To prevent stuck or hard to move pistons the o ring should not be compressed flat against the cylinder wall. Since movement is desirable, as well as a seal, we can design the piston to seal without needing to squeeze the o ring. The following video shows the theory fairly well.

[http://www.youtube.com/watch?v=BbDiZiRVrnk Youtube video on using o rings in air cannons]

At 4:20 in the video the force needed to move this piston is shown.

Instead of having O rings in a groove that sit tight against the bottom of the groove and then are compressed by the cylinder, floating rings do not bottom out in the o ring groove. To seal, the pressure trying to blow past the ring seats it against the side of the o ring groove. Air that is able to get under the ring presses outward to apply pressure to the cylinder wall. As the pressure is increased, this force is increased so higher operating pressures make a tighter seal and a little higher friction to movement.

Floating piston rings fit loose in the grooves. The o ring is sized to be slightly larger than the cylinder diameter it slides inside.
This photo is of a 1 inch quick dump valve piston.
[[Image:Piston_rings.jpg]]

Here is a drawing showing the force of the pressure on the o ring to provide a tight seal.
[[Image:123_floatingpneumatic1.jpg]]
Source: RL Hudson O-Ring Design & Materials Guide. Used with permission.

[[category:valves]]

Good technical examples & articles

2010-05-13T19:21:05Z

Technician1002: /* Cannons */

This page is to be filled with the cannons generally considered good technical examples on the forums, or those that people just tend to like.
And the articles that are worth your reading time.

Obviously this page is under construction, somewhat subjective, and most definitely incomplete, but it's here to help a newbie get themselves well aligned with what spudding actually can be.

==VERY IMPORTANT RULE==
Most of these topics are fairly old. Please do not post in any topic that you are linked to from this page unless you have a VERY important technical question that is not answered anywhere in the thread.

Asking for plans in any one of these threads will cause you to become prematurely bald. If you are already bald, you don't want to know what becoming bald again after you are already bald does to you.

==ADDING TO THIS PAGE==

* Please put cannons in the right category, and '''alphabetically by user'''. (This is to prevent any "This cannon is better, so it should be higher up" edit wars.) Articles have no particular order of preference, but try and add them to the right category.
* Avoid adding a really recent cannon unless it's a very good example.
* Don't add your own cannons, because that's just big-headed. I know I ''(Ragnarok)'' did it, but I'm a self confessed hypocrite.

==Cannons==

'''Pneumatic'''
*[http://www.spudfiles.com/forums/t-t18733.html Old Bessy Sureshot, by AdiabaticManiak.] Not the most sophisticated cannon, but one of the few lever action ones.
*[http://www.spudfiles.com/forums/viewtopic,p,208016.html#208016 4.2 Inch Mortar, by biged.] A very well built replica WW2 mortar.
*[http://www.spudfiles.com/forums/t-t1342.html Sawn-off riot gun, by Brian the Brain.] A cannon that has inspired a great many people.
*[http://www.spudfiles.com/forums/t-t17312.html Mr Porter, by Brian the Brain.] What happens if a 2" porting piston valve and 500 psi come together.
*[http://www.spudfiles.com/forums/t-t17827.html Old Shatterhand, by Brian the Brain.] An exceptionally well made multi-shot hammer valve cannon.
*[http://www.spudfiles.com/forums/t-t7862.html S400, by Chaos.] Good looking, well built, and a good performer. 'Nuff said.
*[http://www.spudfiles.com/forums/t-t7899.html GB Semi, by Clide.] Self loading Golf ball gun. Good demonstration of a blowforward loader. Also notable for the HEAR valve.
*[http://www.spudfiles.com/forums/t-t14802.html Portable burst disk cartridges, by Davidvaini.]
*[http://www.spudfiles.com/forums/t-t12103.html SCTBDC, by DYI.] Big-ass pneumatic.
*[http://www.spudfiles.com/forums/t-t6455.html Mini Piston Gun, by ethal1222.] A good lesson in compact building.
*[http://www.spudfiles.com/forums/t-t6013.html Copperhead Prime, by Hotwired.] Good example of a simple, yet functional design that has inspired imitators.
*[http://www.spudfiles.com/forums/t-t10446.html 6mm Burst Disc Pneumatic, by Jackssmirkingrevenge.] Demonstration of the effectiveness of high pressure and a good valve.
*[http://www.spudfiles.com/forums/t-t7694.html RevoSemi, by Keep_it_Real.] A great example of a simple loader.
*[http://www.spudfiles.com/forums/t-t11453.html HEAL, by Ragnarok.] Because I'm a shameless self-promoter.
*[http://www.spudfiles.com/forums/t-t7093.html The SWAT, by schmanman.] Just a very large pneumatic.
*[http://www.spudfiles.com/forums/gorts-golf-bag-w-vids-contest-t3458.html Gort's Golf Bag, by sgort87.] A portable pneumatic cannon hidden inside a golf bag.
*[http://www.spudfiles.com/forums/t-t14348.html The Eclipse, by Solar.] One of the best produced cannons this forum has seen.
*[http://www.spudfiles.com/spud_wiki/index.php?title=Quick_Dump_Valve The Quick Dump Valve, by Technician1002.] An air valve that is mechanically triggered and reset for high reliability. Link fixed.
*[http://www.spudfiles.com/forums/t-t18846.html XM2, by wngovr.] Beautifully built cannon with an integral pump.

'''Combustion'''
*[http://www.spudfiles.com/forums/t-t174.html Revolver X, by Boogieman.] Well known combustion, good demonstration of speeding up shooting.
*[http://www.spudfiles.com/spudtech_archive/viewtopic.php?f=17&t=12971 57.5mm Oxymortar, by Caffeine.] One of the very early examples of machined cannons.
*[http://www.spudfiles.com/forums/t-t17090.html Small Pistol Grip Combustion, by CrashTestDummy II.] Demonstrating that simple cannons need not look it.
*[http://www.spudfiles.com/forums/t-t15766.html Mk2 Rotary barrelled Combustion, by Critical_Al.] Very well made "Rapid-fire" combustion.
*[http://www.spudfiles.com/forums/t-t4960.html Taternator II, by Dumbascii.] Taking combustion and just throwing overkill at it.
*[http://www.spudfiles.com/forums/t-t14319.html Wood Combustion, by Eddbot.] Not so serious, and not the world's best technical example, but worth a look, because most people like it.
*[http://www.spudfiles.com/forums/t-t17794.html The BL520, by jagerbond.] (Reviewed by PCGUY). A well thought out and built cannon from Spudfiles' sponsor.
*[http://www.spudfiles.com/forums/t-t16725.html The Gauntlet of Clara Ann, by Radiation.] For having one of the most grandiloquent cannon names on the forum.
*[http://www.spudfiles.com/forums/t-t7878.html Blue Flame III, by Sgort87.] Again, demonstrations of improving rate of fire.
*[http://www.spudfiles.com/forums/t-t6241.html Collapsible travel combustion, by Sgort87.] Neat concept for a telescoping cannon.
*[http://www.spudfiles.com/forums/t-t1575.html Proton Pack, by Sgort87.] Backpack based chamber, sometimes considered for a cannon design.
*[http://www.spudfiles.com/forums/t-t2736.html 12" Diameter bucket launcher, by Sgort87.] He does a lot of good combustions. Also, adventurous sizewise.
*[http://www.spudfiles.com/forums/t-t15211.html Triple Thunder cannons, by Starman.] Neatly built, well known and good performers - they had to make the list.

'''Hybrid'''
*[http://www.spudfiles.com/forums/t-t16882.html BACH, by Daccel.] Although not finished, this is one of the most viable methods to speed up hybrid operation.]
*[http://www.spudfiles.com/forums/t-t6822.html HPSCL, by DR.] Often known as the Gen-II tank, an early example (reposted here) of developments in hybrid fuelling.
*[http://www.spudfiles.com/forums/t-t9589.html Piston Hybrid, by Fnord.] A demonstration of an alternate hybrid valve.
*[http://www.spudfiles.com/forums/t-t7857.html FEAR, by Killjoy.] Just a big ass hybrid. Former holder of the spudgun velocity record.
*[http://www.spudfiles.com/forums/t-t15524.html HyGaC20, by Larda.] Current holder of spudgun velocity, and preignition mix pressure records. Also nice to look at.
*[http://www.spudfiles.com/forums/t-t17948.html The Cobra Venom, by Moonbogg.] A topic that documents the production of a high quality machined hybrid.

'''BBMG/Strafer'''
*[http://www.spudfiles.com/forums/t-t13762.html Deathray, by Brian the Brain.] Simplify, and add pressure.
*[http://www.spudfiles.com/forums/t-t12907.html RC-P240 Vortex cap BBMG, by Imortal87.] A good method of adding magazines to a BBMG.
*[http://www.spudfiles.com/forums/t-t10075.html 6mm Semi by Jackssmirkingrevenge.] Not so much a BBMG, but absolutely great for learning about blow forward loaders.
*[http://www.spudfiles.com/forums/t-t17845.html "I has full auto", by Jackssmirkingrevenge.] Jack finally builds a full auto pulsed BBMG after... I've forgotten. A long time, either way.
*[http://www.spudfiles.com/forums/t-t16441.html Ultimate Inline Mk IIIi, by Neospud.] Showing you how a BBMG should be done for practical field use.

'''Mini'''

*[http://www.spudfiles.com/forums/t-t7858.html Pneumatic Pengun, by Jackssmirkingrevenge.] For being one of the first examples of less ghetto minis.
*[http://www.spudfiles.com/forums/t-t18619.html Keychain Pengun, by jor2daje.] Nigh on minuscule, and with a mini pump
*[http://www.spudfiles.com/forums/t-t17102.html Mini Keychain, by jook13.] For being the first keychain spudgun.
*[http://www.spudfiles.com/forums/t-t17408.html 300 WinMag Coax, by jook13.] A gun... inside a bullet.

And thus we prove that success in Minis depends on a username starting with a J.

'''Other'''
*[http://www.spudfiles.com/forums/t-t13449.html 28.8kj Electrothermal cannon, by Larda.] Cannon powered by plasma. Somehow even more impressive than it sounds.

==Articles==

'''General Forum'''
*[http://www.spudfiles.com/forums/t-t14659.html A ''VERY'' worthwhile read on spudgunning and the forums.] A read of this will get you pretty up to date with the forum's workings.
*[http://www.spudfiles.com/forums/t-t16568.html A spudder's tale.] Not essential reading, but nice anyway.
*[http://www.spudfiles.com/forums/posting-images-a-step-by-step-guide-t13190.html Posting images a step-by-step guide.] How to post images on Spudfiles properly.
*[http://www.spudfiles.com/forums/rules.html Rules.] Main forum rules.
*[[The reasons behind the rules | Explanation of rules that sometimes raise questions.]]
*[http://www.spudfiles.com/forums/viewtopic,p,136508.html#136508 Posting Etiquette.] Posting rules for the Spudfiles forum, differs from the main forum rules.
*[[Why aren't my questions being answered?]] For if you've asked a question, but you're getting responses like "Do your own research".

'''Forum In-jokes'''
*[http://www.spudfiles.com/forums/t-t13069.html How to deal with frustration.] The famous *facepalmheaddeskcombo* explained.
*[http://www.spudfiles.com/forums/viewtopic,p,133222.html#133222 The Flaming Pink Elephant.] A metaphor for the forum's innuendo, as this is what it is as subtle as.
*[[Spudfiles Forum Jokes]] Worth a read, to help you gauge the forum's sense of humo(u)r before you misinterpret something.
*[[Tools redefined]]: What tools really are.

'''Safety'''
*[http://www.spudfiles.com/forums/t-t7783.html Things not to do.] A list of accidents people have had, and in many cases, how it could have been avoided.
*[http://www.spudfiles.com/forums/t-t15301.html A tale of shooting yourself in the face.] Again, more accidents.
*[http://www.spudfiles.com/forums/t-t11431.html Predicting if your cannon's recoil is likely to be dangerous.] It is inadvisable for a hand fired cannon to exceed 100 ft-lbs (135 J) of recoil, and even this will be unpleasant.

'''Construction'''
*[http://www.spudfiles.com/forums/t-t8157.html How piston valves work.] An explanation of what is arguably the best valve in spudding.
*[http://www.spudfiles.com/forums/t-t11866.html High pressure compressors.] How to adapt fridge parts into the spudder's high pressure solution.
*[http://www.spudfiles.com/forums/t-t2546.html A solution to rifling.] How to rifle a PVC barrel.
*[http://www.spudfiles.com/forums/t-t10381.html How to make a cannon with 2" piston valve.] How to make a 2" piston valve.
*[http://www.spudfiles.com/forums/t-t3009.html Solvent Welding Course.] An online course on how to solvent weld PVC correctly.
*[http://www.spudfiles.com/forums/t-t18108.html Suppressor Tutorial.] Quite a long video, but lots of information on suppressor (or silencer, if you must) construction.

'''Projectiles'''
*[http://www.spudfiles.com/forums/t-t16438.html A fairly interesting thread on projectile shape vs. drag.] It's a bit incoherent at times, but worth the study.
*[http://www.spudfiles.com/forums/t-t13477.html A theory on dart development.]

'''Aesthetics'''
* [http://www.spudfiles.com/forums/t-t15767.html Making a stock for your launcher?] This will be worth some reading.

Good technical examples & articles

2010-05-13T19:19:27Z

Technician1002: /* Cannons */

This page is to be filled with the cannons generally considered good technical examples on the forums, or those that people just tend to like.
And the articles that are worth your reading time.

Obviously this page is under construction, somewhat subjective, and most definitely incomplete, but it's here to help a newbie get themselves well aligned with what spudding actually can be.

==VERY IMPORTANT RULE==
Most of these topics are fairly old. Please do not post in any topic that you are linked to from this page unless you have a VERY important technical question that is not answered anywhere in the thread.

Asking for plans in any one of these threads will cause you to become prematurely bald. If you are already bald, you don't want to know what becoming bald again after you are already bald does to you.

==ADDING TO THIS PAGE==

* Please put cannons in the right category, and '''alphabetically by user'''. (This is to prevent any "This cannon is better, so it should be higher up" edit wars.) Articles have no particular order of preference, but try and add them to the right category.
* Avoid adding a really recent cannon unless it's a very good example.
* Don't add your own cannons, because that's just big-headed. I know I ''(Ragnarok)'' did it, but I'm a self confessed hypocrite.

==Cannons==

'''Pneumatic'''
*[http://www.spudfiles.com/forums/t-t18733.html Old Bessy Sureshot, by AdiabaticManiak.] Not the most sophisticated cannon, but one of the few lever action ones.
*[http://www.spudfiles.com/forums/viewtopic,p,208016.html#208016 4.2 Inch Mortar, by biged.] A very well built replica WW2 mortar.
*[http://www.spudfiles.com/forums/t-t1342.html Sawn-off riot gun, by Brian the Brain.] A cannon that has inspired a great many people.
*[http://www.spudfiles.com/forums/t-t17312.html Mr Porter, by Brian the Brain.] What happens if a 2" porting piston valve and 500 psi come together.
*[http://www.spudfiles.com/forums/t-t17827.html Old Shatterhand, by Brian the Brain.] An exceptionally well made multi-shot hammer valve cannon.
*[http://www.spudfiles.com/forums/t-t7862.html S400, by Chaos.] Good looking, well built, and a good performer. 'Nuff said.
*[http://www.spudfiles.com/forums/t-t7899.html GB Semi, by Clide.] Self loading Golf ball gun. Good demonstration of a blowforward loader. Also notable for the HEAR valve.
*[http://www.spudfiles.com/forums/t-t14802.html Portable burst disk cartridges, by Davidvaini.]
*[http://www.spudfiles.com/forums/t-t12103.html SCTBDC, by DYI.] Big-ass pneumatic.
*[http://www.spudfiles.com/forums/t-t6455.html Mini Piston Gun, by ethal1222.] A good lesson in compact building.
*[http://www.spudfiles.com/forums/t-t6013.html Copperhead Prime, by Hotwired.] Good example of a simple, yet functional design that has inspired imitators.
*[http://www.spudfiles.com/forums/t-t10446.html 6mm Burst Disc Pneumatic, by Jackssmirkingrevenge.] Demonstration of the effectiveness of high pressure and a good valve.
*[http://www.spudfiles.com/forums/t-t7694.html RevoSemi, by Keep_it_Real.] A great example of a simple loader.
*[http://www.spudfiles.com/forums/t-t11453.html HEAL, by Ragnarok.] Because I'm a shameless self-promoter.
*[http://www.spudfiles.com/forums/t-t7093.html The SWAT, by schmanman.] Just a very large pneumatic.
*[http://www.spudfiles.com/forums/gorts-golf-bag-w-vids-contest-t3458.html Gort's Golf Bag, by sgort87.] A portable pneumatic cannon hidden inside a golf bag.
*[http://www.spudfiles.com/forums/t-t14348.html The Eclipse, by Solar.] One of the best produced cannons this forum has seen.
*[http://www.spudfiles.com/spud_wiki/index.php?title=Quick_Dump_Valve The Quick Dump Valve, by Technician1002.] Edit; fixing and testing link. An air valve that is mechanically triggered and reset for high reliability.
*[http://www.spudfiles.com/forums/t-t18846.html XM2, by wngovr.] Beautifully built cannon with an integral pump.

'''Combustion'''
*[http://www.spudfiles.com/forums/t-t174.html Revolver X, by Boogieman.] Well known combustion, good demonstration of speeding up shooting.
*[http://www.spudfiles.com/spudtech_archive/viewtopic.php?f=17&t=12971 57.5mm Oxymortar, by Caffeine.] One of the very early examples of machined cannons.
*[http://www.spudfiles.com/forums/t-t17090.html Small Pistol Grip Combustion, by CrashTestDummy II.] Demonstrating that simple cannons need not look it.
*[http://www.spudfiles.com/forums/t-t15766.html Mk2 Rotary barrelled Combustion, by Critical_Al.] Very well made "Rapid-fire" combustion.
*[http://www.spudfiles.com/forums/t-t4960.html Taternator II, by Dumbascii.] Taking combustion and just throwing overkill at it.
*[http://www.spudfiles.com/forums/t-t14319.html Wood Combustion, by Eddbot.] Not so serious, and not the world's best technical example, but worth a look, because most people like it.
*[http://www.spudfiles.com/forums/t-t17794.html The BL520, by jagerbond.] (Reviewed by PCGUY). A well thought out and built cannon from Spudfiles' sponsor.
*[http://www.spudfiles.com/forums/t-t16725.html The Gauntlet of Clara Ann, by Radiation.] For having one of the most grandiloquent cannon names on the forum.
*[http://www.spudfiles.com/forums/t-t7878.html Blue Flame III, by Sgort87.] Again, demonstrations of improving rate of fire.
*[http://www.spudfiles.com/forums/t-t6241.html Collapsible travel combustion, by Sgort87.] Neat concept for a telescoping cannon.
*[http://www.spudfiles.com/forums/t-t1575.html Proton Pack, by Sgort87.] Backpack based chamber, sometimes considered for a cannon design.
*[http://www.spudfiles.com/forums/t-t2736.html 12" Diameter bucket launcher, by Sgort87.] He does a lot of good combustions. Also, adventurous sizewise.
*[http://www.spudfiles.com/forums/t-t15211.html Triple Thunder cannons, by Starman.] Neatly built, well known and good performers - they had to make the list.

'''Hybrid'''
*[http://www.spudfiles.com/forums/t-t16882.html BACH, by Daccel.] Although not finished, this is one of the most viable methods to speed up hybrid operation.]
*[http://www.spudfiles.com/forums/t-t6822.html HPSCL, by DR.] Often known as the Gen-II tank, an early example (reposted here) of developments in hybrid fuelling.
*[http://www.spudfiles.com/forums/t-t9589.html Piston Hybrid, by Fnord.] A demonstration of an alternate hybrid valve.
*[http://www.spudfiles.com/forums/t-t7857.html FEAR, by Killjoy.] Just a big ass hybrid. Former holder of the spudgun velocity record.
*[http://www.spudfiles.com/forums/t-t15524.html HyGaC20, by Larda.] Current holder of spudgun velocity, and preignition mix pressure records. Also nice to look at.
*[http://www.spudfiles.com/forums/t-t17948.html The Cobra Venom, by Moonbogg.] A topic that documents the production of a high quality machined hybrid.

'''BBMG/Strafer'''
*[http://www.spudfiles.com/forums/t-t13762.html Deathray, by Brian the Brain.] Simplify, and add pressure.
*[http://www.spudfiles.com/forums/t-t12907.html RC-P240 Vortex cap BBMG, by Imortal87.] A good method of adding magazines to a BBMG.
*[http://www.spudfiles.com/forums/t-t10075.html 6mm Semi by Jackssmirkingrevenge.] Not so much a BBMG, but absolutely great for learning about blow forward loaders.
*[http://www.spudfiles.com/forums/t-t17845.html "I has full auto", by Jackssmirkingrevenge.] Jack finally builds a full auto pulsed BBMG after... I've forgotten. A long time, either way.
*[http://www.spudfiles.com/forums/t-t16441.html Ultimate Inline Mk IIIi, by Neospud.] Showing you how a BBMG should be done for practical field use.

'''Mini'''

*[http://www.spudfiles.com/forums/t-t7858.html Pneumatic Pengun, by Jackssmirkingrevenge.] For being one of the first examples of less ghetto minis.
*[http://www.spudfiles.com/forums/t-t18619.html Keychain Pengun, by jor2daje.] Nigh on minuscule, and with a mini pump
*[http://www.spudfiles.com/forums/t-t17102.html Mini Keychain, by jook13.] For being the first keychain spudgun.
*[http://www.spudfiles.com/forums/t-t17408.html 300 WinMag Coax, by jook13.] A gun... inside a bullet.

And thus we prove that success in Minis depends on a username starting with a J.

'''Other'''
*[http://www.spudfiles.com/forums/t-t13449.html 28.8kj Electrothermal cannon, by Larda.] Cannon powered by plasma. Somehow even more impressive than it sounds.

==Articles==

'''General Forum'''
*[http://www.spudfiles.com/forums/t-t14659.html A ''VERY'' worthwhile read on spudgunning and the forums.] A read of this will get you pretty up to date with the forum's workings.
*[http://www.spudfiles.com/forums/t-t16568.html A spudder's tale.] Not essential reading, but nice anyway.
*[http://www.spudfiles.com/forums/posting-images-a-step-by-step-guide-t13190.html Posting images a step-by-step guide.] How to post images on Spudfiles properly.
*[http://www.spudfiles.com/forums/rules.html Rules.] Main forum rules.
*[[The reasons behind the rules | Explanation of rules that sometimes raise questions.]]
*[http://www.spudfiles.com/forums/viewtopic,p,136508.html#136508 Posting Etiquette.] Posting rules for the Spudfiles forum, differs from the main forum rules.
*[[Why aren't my questions being answered?]] For if you've asked a question, but you're getting responses like "Do your own research".

'''Forum In-jokes'''
*[http://www.spudfiles.com/forums/t-t13069.html How to deal with frustration.] The famous *facepalmheaddeskcombo* explained.
*[http://www.spudfiles.com/forums/viewtopic,p,133222.html#133222 The Flaming Pink Elephant.] A metaphor for the forum's innuendo, as this is what it is as subtle as.
*[[Spudfiles Forum Jokes]] Worth a read, to help you gauge the forum's sense of humo(u)r before you misinterpret something.
*[[Tools redefined]]: What tools really are.

'''Safety'''
*[http://www.spudfiles.com/forums/t-t7783.html Things not to do.] A list of accidents people have had, and in many cases, how it could have been avoided.
*[http://www.spudfiles.com/forums/t-t15301.html A tale of shooting yourself in the face.] Again, more accidents.
*[http://www.spudfiles.com/forums/t-t11431.html Predicting if your cannon's recoil is likely to be dangerous.] It is inadvisable for a hand fired cannon to exceed 100 ft-lbs (135 J) of recoil, and even this will be unpleasant.

'''Construction'''
*[http://www.spudfiles.com/forums/t-t8157.html How piston valves work.] An explanation of what is arguably the best valve in spudding.
*[http://www.spudfiles.com/forums/t-t11866.html High pressure compressors.] How to adapt fridge parts into the spudder's high pressure solution.
*[http://www.spudfiles.com/forums/t-t2546.html A solution to rifling.] How to rifle a PVC barrel.
*[http://www.spudfiles.com/forums/t-t10381.html How to make a cannon with 2" piston valve.] How to make a 2" piston valve.
*[http://www.spudfiles.com/forums/t-t3009.html Solvent Welding Course.] An online course on how to solvent weld PVC correctly.
*[http://www.spudfiles.com/forums/t-t18108.html Suppressor Tutorial.] Quite a long video, but lots of information on suppressor (or silencer, if you must) construction.

'''Projectiles'''
*[http://www.spudfiles.com/forums/t-t16438.html A fairly interesting thread on projectile shape vs. drag.] It's a bit incoherent at times, but worth the study.
*[http://www.spudfiles.com/forums/t-t13477.html A theory on dart development.]

'''Aesthetics'''
* [http://www.spudfiles.com/forums/t-t15767.html Making a stock for your launcher?] This will be worth some reading.

Good technical examples & articles

2010-05-13T19:16:12Z

Technician1002: /* Cannons */ Link died to a wikipage

This page is to be filled with the cannons generally considered good technical examples on the forums, or those that people just tend to like.
And the articles that are worth your reading time.

Obviously this page is under construction, somewhat subjective, and most definitely incomplete, but it's here to help a newbie get themselves well aligned with what spudding actually can be.

==VERY IMPORTANT RULE==
Most of these topics are fairly old. Please do not post in any topic that you are linked to from this page unless you have a VERY important technical question that is not answered anywhere in the thread.

Asking for plans in any one of these threads will cause you to become prematurely bald. If you are already bald, you don't want to know what becoming bald again after you are already bald does to you.

==ADDING TO THIS PAGE==

* Please put cannons in the right category, and '''alphabetically by user'''. (This is to prevent any "This cannon is better, so it should be higher up" edit wars.) Articles have no particular order of preference, but try and add them to the right category.
* Avoid adding a really recent cannon unless it's a very good example.
* Don't add your own cannons, because that's just big-headed. I know I ''(Ragnarok)'' did it, but I'm a self confessed hypocrite.

==Cannons==

'''Pneumatic'''
*[http://www.spudfiles.com/forums/t-t18733.html Old Bessy Sureshot, by AdiabaticManiak.] Not the most sophisticated cannon, but one of the few lever action ones.
*[http://www.spudfiles.com/forums/viewtopic,p,208016.html#208016 4.2 Inch Mortar, by biged.] A very well built replica WW2 mortar.
*[http://www.spudfiles.com/forums/t-t1342.html Sawn-off riot gun, by Brian the Brain.] A cannon that has inspired a great many people.
*[http://www.spudfiles.com/forums/t-t17312.html Mr Porter, by Brian the Brain.] What happens if a 2" porting piston valve and 500 psi come together.
*[http://www.spudfiles.com/forums/t-t17827.html Old Shatterhand, by Brian the Brain.] An exceptionally well made multi-shot hammer valve cannon.
*[http://www.spudfiles.com/forums/t-t7862.html S400, by Chaos.] Good looking, well built, and a good performer. 'Nuff said.
*[http://www.spudfiles.com/forums/t-t7899.html GB Semi, by Clide.] Self loading Golf ball gun. Good demonstration of a blowforward loader. Also notable for the HEAR valve.
*[http://www.spudfiles.com/forums/t-t14802.html Portable burst disk cartridges, by Davidvaini.]
*[http://www.spudfiles.com/forums/t-t12103.html SCTBDC, by DYI.] Big-ass pneumatic.
*[http://www.spudfiles.com/forums/t-t6455.html Mini Piston Gun, by ethal1222.] A good lesson in compact building.
*[http://www.spudfiles.com/forums/t-t6013.html Copperhead Prime, by Hotwired.] Good example of a simple, yet functional design that has inspired imitators.
*[http://www.spudfiles.com/forums/t-t10446.html 6mm Burst Disc Pneumatic, by Jackssmirkingrevenge.] Demonstration of the effectiveness of high pressure and a good valve.
*[http://www.spudfiles.com/forums/t-t7694.html RevoSemi, by Keep_it_Real.] A great example of a simple loader.
*[http://www.spudfiles.com/forums/t-t11453.html HEAL, by Ragnarok.] Because I'm a shameless self-promoter.
*[http://www.spudfiles.com/forums/t-t7093.html The SWAT, by schmanman.] Just a very large pneumatic.
*[http://www.spudfiles.com/forums/gorts-golf-bag-w-vids-contest-t3458.html Gort's Golf Bag, by sgort87.] A portable pneumatic cannon hidden inside a golf bag.
*[http://www.spudfiles.com/forums/t-t14348.html The Eclipse, by Solar.] One of the best produced cannons this forum has seen.
*[http://www.spudfiles.com/spud_wiki/index.php/Quick_Dump_Valve Quick Dump Valve by Technician1002.] Edit; Link appears to have gone bad. Investigating. An air valve that is mechanically triggered and reset for high reliability.
*[http://www.spudfiles.com/forums/t-t18846.html XM2, by wngovr.] Beautifully built cannon with an integral pump.

'''Combustion'''
*[http://www.spudfiles.com/forums/t-t174.html Revolver X, by Boogieman.] Well known combustion, good demonstration of speeding up shooting.
*[http://www.spudfiles.com/spudtech_archive/viewtopic.php?f=17&t=12971 57.5mm Oxymortar, by Caffeine.] One of the very early examples of machined cannons.
*[http://www.spudfiles.com/forums/t-t17090.html Small Pistol Grip Combustion, by CrashTestDummy II.] Demonstrating that simple cannons need not look it.
*[http://www.spudfiles.com/forums/t-t15766.html Mk2 Rotary barrelled Combustion, by Critical_Al.] Very well made "Rapid-fire" combustion.
*[http://www.spudfiles.com/forums/t-t4960.html Taternator II, by Dumbascii.] Taking combustion and just throwing overkill at it.
*[http://www.spudfiles.com/forums/t-t14319.html Wood Combustion, by Eddbot.] Not so serious, and not the world's best technical example, but worth a look, because most people like it.
*[http://www.spudfiles.com/forums/t-t17794.html The BL520, by jagerbond.] (Reviewed by PCGUY). A well thought out and built cannon from Spudfiles' sponsor.
*[http://www.spudfiles.com/forums/t-t16725.html The Gauntlet of Clara Ann, by Radiation.] For having one of the most grandiloquent cannon names on the forum.
*[http://www.spudfiles.com/forums/t-t7878.html Blue Flame III, by Sgort87.] Again, demonstrations of improving rate of fire.
*[http://www.spudfiles.com/forums/t-t6241.html Collapsible travel combustion, by Sgort87.] Neat concept for a telescoping cannon.
*[http://www.spudfiles.com/forums/t-t1575.html Proton Pack, by Sgort87.] Backpack based chamber, sometimes considered for a cannon design.
*[http://www.spudfiles.com/forums/t-t2736.html 12" Diameter bucket launcher, by Sgort87.] He does a lot of good combustions. Also, adventurous sizewise.
*[http://www.spudfiles.com/forums/t-t15211.html Triple Thunder cannons, by Starman.] Neatly built, well known and good performers - they had to make the list.

'''Hybrid'''
*[http://www.spudfiles.com/forums/t-t16882.html BACH, by Daccel.] Although not finished, this is one of the most viable methods to speed up hybrid operation.]
*[http://www.spudfiles.com/forums/t-t6822.html HPSCL, by DR.] Often known as the Gen-II tank, an early example (reposted here) of developments in hybrid fuelling.
*[http://www.spudfiles.com/forums/t-t9589.html Piston Hybrid, by Fnord.] A demonstration of an alternate hybrid valve.
*[http://www.spudfiles.com/forums/t-t7857.html FEAR, by Killjoy.] Just a big ass hybrid. Former holder of the spudgun velocity record.
*[http://www.spudfiles.com/forums/t-t15524.html HyGaC20, by Larda.] Current holder of spudgun velocity, and preignition mix pressure records. Also nice to look at.
*[http://www.spudfiles.com/forums/t-t17948.html The Cobra Venom, by Moonbogg.] A topic that documents the production of a high quality machined hybrid.

'''BBMG/Strafer'''
*[http://www.spudfiles.com/forums/t-t13762.html Deathray, by Brian the Brain.] Simplify, and add pressure.
*[http://www.spudfiles.com/forums/t-t12907.html RC-P240 Vortex cap BBMG, by Imortal87.] A good method of adding magazines to a BBMG.
*[http://www.spudfiles.com/forums/t-t10075.html 6mm Semi by Jackssmirkingrevenge.] Not so much a BBMG, but absolutely great for learning about blow forward loaders.
*[http://www.spudfiles.com/forums/t-t17845.html "I has full auto", by Jackssmirkingrevenge.] Jack finally builds a full auto pulsed BBMG after... I've forgotten. A long time, either way.
*[http://www.spudfiles.com/forums/t-t16441.html Ultimate Inline Mk IIIi, by Neospud.] Showing you how a BBMG should be done for practical field use.

'''Mini'''

*[http://www.spudfiles.com/forums/t-t7858.html Pneumatic Pengun, by Jackssmirkingrevenge.] For being one of the first examples of less ghetto minis.
*[http://www.spudfiles.com/forums/t-t18619.html Keychain Pengun, by jor2daje.] Nigh on minuscule, and with a mini pump
*[http://www.spudfiles.com/forums/t-t17102.html Mini Keychain, by jook13.] For being the first keychain spudgun.
*[http://www.spudfiles.com/forums/t-t17408.html 300 WinMag Coax, by jook13.] A gun... inside a bullet.

And thus we prove that success in Minis depends on a username starting with a J.

'''Other'''
*[http://www.spudfiles.com/forums/t-t13449.html 28.8kj Electrothermal cannon, by Larda.] Cannon powered by plasma. Somehow even more impressive than it sounds.

==Articles==

'''General Forum'''
*[http://www.spudfiles.com/forums/t-t14659.html A ''VERY'' worthwhile read on spudgunning and the forums.] A read of this will get you pretty up to date with the forum's workings.
*[http://www.spudfiles.com/forums/t-t16568.html A spudder's tale.] Not essential reading, but nice anyway.
*[http://www.spudfiles.com/forums/posting-images-a-step-by-step-guide-t13190.html Posting images a step-by-step guide.] How to post images on Spudfiles properly.
*[http://www.spudfiles.com/forums/rules.html Rules.] Main forum rules.
*[[The reasons behind the rules | Explanation of rules that sometimes raise questions.]]
*[http://www.spudfiles.com/forums/viewtopic,p,136508.html#136508 Posting Etiquette.] Posting rules for the Spudfiles forum, differs from the main forum rules.
*[[Why aren't my questions being answered?]] For if you've asked a question, but you're getting responses like "Do your own research".

'''Forum In-jokes'''
*[http://www.spudfiles.com/forums/t-t13069.html How to deal with frustration.] The famous *facepalmheaddeskcombo* explained.
*[http://www.spudfiles.com/forums/viewtopic,p,133222.html#133222 The Flaming Pink Elephant.] A metaphor for the forum's innuendo, as this is what it is as subtle as.
*[[Spudfiles Forum Jokes]] Worth a read, to help you gauge the forum's sense of humo(u)r before you misinterpret something.
*[[Tools redefined]]: What tools really are.

'''Safety'''
*[http://www.spudfiles.com/forums/t-t7783.html Things not to do.] A list of accidents people have had, and in many cases, how it could have been avoided.
*[http://www.spudfiles.com/forums/t-t15301.html A tale of shooting yourself in the face.] Again, more accidents.
*[http://www.spudfiles.com/forums/t-t11431.html Predicting if your cannon's recoil is likely to be dangerous.] It is inadvisable for a hand fired cannon to exceed 100 ft-lbs (135 J) of recoil, and even this will be unpleasant.

'''Construction'''
*[http://www.spudfiles.com/forums/t-t8157.html How piston valves work.] An explanation of what is arguably the best valve in spudding.
*[http://www.spudfiles.com/forums/t-t11866.html High pressure compressors.] How to adapt fridge parts into the spudder's high pressure solution.
*[http://www.spudfiles.com/forums/t-t2546.html A solution to rifling.] How to rifle a PVC barrel.
*[http://www.spudfiles.com/forums/t-t10381.html How to make a cannon with 2" piston valve.] How to make a 2" piston valve.
*[http://www.spudfiles.com/forums/t-t3009.html Solvent Welding Course.] An online course on how to solvent weld PVC correctly.
*[http://www.spudfiles.com/forums/t-t18108.html Suppressor Tutorial.] Quite a long video, but lots of information on suppressor (or silencer, if you must) construction.

'''Projectiles'''
*[http://www.spudfiles.com/forums/t-t16438.html A fairly interesting thread on projectile shape vs. drag.] It's a bit incoherent at times, but worth the study.
*[http://www.spudfiles.com/forums/t-t13477.html A theory on dart development.]

'''Aesthetics'''
* [http://www.spudfiles.com/forums/t-t15767.html Making a stock for your launcher?] This will be worth some reading.

Piston valve

2010-05-10T06:34:57Z

Technician1002: /* 1:1 Ratio or QDV */ Removed dead link to QDV page.

A '''piston valve''' is a [[pilot]] operated [[valve]]. It is very similar to a [[diaphragm valve]] in theory, but replaces it's flexible diaphragm with a rigid cylinder. There are 2 varieties; [[barrel]] sealing and [[chamber]] sealing.

== Barrel sealing valve ==

In a barrel sealing valve, the piston seals against the breech of the barrel. This is the most common piston valve design.

=== construction ===

The piston is often a well fitting cup-shaped object, such as a end cap. To provide a sealing face, a piece of rubber is attached, typically with a bolt. In the simplest case, equalization is accomplished by allowing the air to leak past the piston and into the chamber. Some people will machine their own pistons, in which case they often build [[O-ring]]s into them. With the O-rings, you need to make a small equalization hole; sometimes this is fancied up to be a homemade [[check valve]].

Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recommended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labeled "'''F'''" in the "use, barrel sealing" diagram.

These valves are often used on [[coaxial]]s and [[over/under]]s. In an over/under, the valve is built in a "T" fitting. The barrel is put co-axially through one end, the pilot and piston are put in the opposite one, and a chamber is connected to the perpendicular opening with a 90° elbow.

=== Use ===
[[Image:Wpiston.PNG|frame|top=pressurized, bottom=firing]]
Operation:
#Air is added by filling behind the piston (C).
#The piston (E) slides forwards, and seals against the barrel (A). (Alternatively, one can use a spring to move the piston forwards, which allows one to fill [slowly at first, to allow the [[pressure]] to equalize] from the chamber.)
#More air is added, and leaks around the piston (or through a small equalization hole) and into the chamber (B), filling it to the desired pressure.
#The [[pilot valve]] (D) behind the piston is opened, the pressure in the pilot volume (C) drops, and the higher pressure in the chamber area pushes the piston away from the barrel.
#The air flows around from the chamber, and into the barrel, propelling the projectile.

=== Pilot Valves ===
There is a common misconception that a simple blowgun is enough to pilot large piston valves, 1.5" and above. This is not recommended as your cannon will have very bad performance or may not even function at all. For valves 1"-1.25" in diameter, a 1/4" ball valve is recommended. For valves between 1.5" and 2.5" a 1/2" or 3/4" ball valve is probably enough. Anything above that will benefit from a sprinkler valve or a 1" ball valve for a pilot valve. When it comes to pilot valves, bigger is always better.

== Chamber sealing piston valve ==

=== construction ===

The piston of a chamber-sealing piston valve has to seal on both the chamber port and to the pilot volume. This requires that the piston be machined with [[O-ring]]s. A small equalization hole is required; sometimes this is fancied up to be a homemade [[check valve]].

The piston is almost always housed in a "t" fitting.

Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recommended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labeled "'''F'''" in the "use, chamber sealing sealing" diagram.

These valves are often used on [[over/under]]s, as the flow is already turned around 90o.

=== Use ===
[[Image:Wcspiston.PNG|frame|top=pressurized, bottom=firing]]
Operation:
#Air is added by filling behind the piston (C).
#The piston (E) slides forwards, and seals against the barrel (A). (Alternatively, one can use a spring to move the piston forwards, which allows one to fill [slowly at first, to allow the [[pressure]] to equalize] from the chamber.)
#More air is added, and leaks through the equalization hole in the piston and into the chamber (B), filling it to the desired pressure.
#The [[pilot valve]] (D) behind the piston is opened, the pressure in the pilot volume (C) drops, and the higher pressure in the chamber area pushes the piston away from the chamber.
#The air flows out of the chamber, and into the barrel, propelling the projectile.

== Common traits ==

#The performance of these valves can be calculated with the [[GGDT]].
#If your valve [[honking|honks]], it is probably a good idea to invest in a better pilot valve, though this is more of a problem with barrel-sealing valves.
#In both cases, provided there is a good deal of space around the barrel, the full flow potential of the valve is realized when the piston has moved back 1/4th of the barrel's inside diameter (I.D./4). The derivation of this formula is as follows:

Given: A = Pi(R)^2
C = 2PiR
T = Piston travel
R = I.D. of barrel / 2

When the piston moves back, the smallest amount of area exposed is either the area of the circular cross section of the barrel or the area exposed by the piston, which is the side of a cylinder, the bases being the barrel and piston face. The optimal ratio of area exposed between the 2 spots is 1:1, which means the exposed areas should be the same. So one sets the equations A and CT equal, that is A = CT.

Pi(R)^2 = 2PiR(T)

Solving for "T" results in:

R/2 = T which, if one substitutes I.D./2 for R, results in:

I.D./4 = T

Many people choose to open larger to provide only one restriction to flow instead of 2 the same size in a row. This is done by allowing the valve to open fully unrestricted and then compress the bumper while opening further. This provides the fastest possible opening time by preventing the piston deceleration while still opening.

#Pneumatic actuation is not mandatory; mechanical means can be used to hold the valve shut, or open it, rather than using the force of the air.

***The following section submitted by Technician1002***

The operation of barrel sealing valves falls into 3 categories which is related to the dimensions of the barrel seal or seat to the piston outside diameter.

=== Large Ratio Piston Valve ===
When the ratio is large in a barrel sealer with either a large piston or small barrel, most of the force to open the valve is controlled by the differential of the chamber pressure and pilot area. As the valve opens, the small area that becomes exposed to the chamber as it opens contributes little to the opening speed. This large area ratio valve are noted for reliable operation as they have the ability to open pistons that don't slide well. Due to the pressure still in the pilot area as they open, as the chamber vents out the barrel, it is often faster than the pilot, so the force used to open the valve vanishes and the pilot pressure unable to keep up with the drop, forces the valve to close. If this repeats as the pilot vents, it is noticeable as honking. This class of valves include pistons with a 2:1 diameter ratio or more. A 2:1 diameter ratio is a 4:1 area ratio. These are not QEV valves because the area sealed by the piston is only 25% of the pilot area so when the valve opens the force change is small. It opens with the pilot at 3/4 the pressure of the chamber. When it opens and the pilot volume is reduced by the piston moving into the pilot space, the rise in pressure in the pilot prevents the piston from opening all the way, so opening speed is directly related to how much faster the pilot can vent over the rate the chamber vents out the barrel. A slow pilot equals a slow valve and may cause honking.

In a chamber sealer version where the valve seat seals against the chamber, they are fast as the pressure is released and more pressure presses on the larger exposed face of the piston. This style tends to have a fairly large dead space between the valve and projectile. In addition a large piston has a greater mass and as the piston moves, it requires a larger displacement using much of the chamber air energy. If the valve seat is small to use a smaller piston, the small orifice chokes the flow.

=== Small Ratio or QEV ===
As the ratio of the seat diameter to piston diameter is reduced, the area that the chamber is exposed to is reduced, to the point that the large area of the pilot is able to hold the piston closed until most of the pilot pressure is vented. Even when the pilot area is vented to a low pressure, the initial opening force is low because the area of the piston exposed to the chamber pressure is small as most of the face of the piston is exposed to no pressure in the barrel. This low opening force can cause many headaches with stuck pistons that sometimes fail to fire, and the equalization port may vent enough volume to prevent the pilot area from reaching a low enough pressure to open the valve. The lower the seat to diameter ratio; the lower the initial force the chamber can apply to open the valve, and the faster they snap open when they do get over the initial opening. This faster speed is due to the larger piston face exposed to the chamber pressure when the valve opens and the lower pressure in the pilot area. The lower pressure compresses less and provides less force on the back of the piston when it opens. The closer the ratio is to 1:1 the faster the avalanche, but the initial cracking open of the valve becomes slower as the initial opening force is lower and lower as you approach a 1:1 ratio.

One attractive feature of this valve is once it unseats and starts to open, the chamber pressure now acting on the face of the piston causes a large spike in opening force as the large barrel facing area is now exposed to the chamber pressure. This type of valve snaps open and is known as a Quick Exhaust Valve or QEV. This style valve is not prone to closing early and honking.

[[Image:MusketSeat.JPG ]]

The barrel sealer QEV piston valve has a large diameter seat in relation to the overall diameter of the piston.
A chamber sealer has a small seat in relation the the overall diameter so the force on the piston grows rapidly as the valve opens.

Chamber sealer valves have a disadvantage of needing a larger diameter piston for the same size valve seat as a barrel sealer. This adds mass and dead space between the valve piston and projectile. On the positive side, they are more reliable in opening and tend to have most of the opening acceleration early in the opening where it is needed. The drop in acceleration as the valve opens can increase the life expectancy of the valve as they compress the pilot area they slow before impact with the back of the breech.

=== 1:1 Ratio or QDV ===
If the ratio of the piston diameter is reduced to the diameter of the valve seat in a spool valve, then the valve won't open even when the pilot area is not under pressure. If the chamber is pressurized and no pressure is in the pilot area, the valve has the least back pressure of any of the piston valves and therefore the fastest opening when the valve is unseated by force. Even though the pilot area may half in volume as the piston moves into this space, the pressure rise from 1 atm to 2 atm is still less than the chamber force on the newly exposed face of the piston, so this piston will open fast regardless of the vent size or speed. This last category of piston valve is known as a Quick Dump Valve. To operate this valve in an air cannon, consideration must be made to mechanically move the piston and when the piston moves, the force will avalanche quickly as the piston face becomes exposed to the chamber pressure. For mechanical trigger the use a rope pull or a rod with a "sliding" piston are options to a spring or air start. The loose piston on a rope or rod provides speed as the core can accelerate freely when triggered. Decoupling the triggering mechanism from the piston prevents the trigger from adding to the moving mass of the piston. These valves are not subject to honking, but may "bounce" back closed after the shot by the pressure built up in the pilot area and bumper recoil after the chamber pressure is gone.

[[Image:QDV_parts.JPG]]

Assembled 1 inch QDV cannon and damaged can. Projectile was a 1 inch jawbreaker.
[[Image:Marshmallow_cannon.jpg]]

The quick dump valve has the piston OD the same size as the seat. It requires an external force to start it opening. It has no pilot pressure to hold it against a seat so it is often built with o rings on a piston. The valve cylinder can be built out of a pipe with ports cut in the side.

A video on the theory of the QDV cannon is here.
[http://www.youtube.com/watch?v=No3nI07mlQo The Quick Dump Valve]

=== O-Ring Considerations on a Piston Valve ===
To prevent stuck piston valves, consideration must be given to permit a good seal while not stopping movement.

To prevent stuck or hard to move pistons the o ring should not be compressed flat against the cylinder wall. Since movement is desirable, as well as a seal, we can design the piston to seal without needing to squeeze the o ring. The following video shows the theory fairly well.

[http://www.youtube.com/watch?v=BbDiZiRVrnk Youtube video on using o rings in air cannons]

At 4:20 in the video the force needed to move this piston is shown.

Instead of having O rings in a groove that sit tight against the bottom of the groove and then are compressed by the cylinder, floating rings do not bottom out in the o ring groove. To seal, the pressure trying to blow past the ring seats it against the side of the o ring groove. Air that is able to get under the ring presses outward to apply pressure to the cylinder wall. As the pressure is increased, this force is increased so higher operating pressures make a tighter seal and a little higher friction to movement.

Floating piston rings fit loose in the grooves. The o ring is sized to be slightly larger than the cylinder diameter it slides inside.
This photo is of a 1 inch quick dump valve piston.
[[Image:Piston_rings.jpg]]

Here is a drawing showing the force of the pressure on the o ring to provide a tight seal.
[[Image:123_floatingpneumatic1.jpg]]
Source: RL Hudson O-Ring Design & Materials Guide. Used with permission.

[[category:valves]]

Quick Dump Valve

2009-08-18T10:14:48Z

Technician1002: /* The Quick Dump Valve */

'''Article Flag''' 
As an article relating to spudding hardware, this should be presented in a more neutral format - it currently reads like an advertisement. 
It should also be presented in a third person point of view, as newcomers won't be able to associate "I" or "Me" usefully. 
Flagged by [[User:Ragnarok|Ragnarok]] 20:32, 29 July 2009 (EDT)

== The Quick Dump Valve ==

The quick dump valve is a variation on a traditional barrel sealer piston valve. In the section on piston valves, various configurations are covered and the advantages and disadvantages of each. A quick dump valve may be used where the traditional valves shortcomings cause problems for the builder. It was noted in the piston valve section in the wiki that as a barrel sealer valve nears a 1:1 ratio, the pilot pressure needed to open the valve drops lower, and when they pop open, they do so with more force and speed. They become temperamental as the ratio approaches a 1:1 ratio as the force to start opening the valve drops. They tend to stick or are unable to vent the pilot low enough to fire it. As a result, piston valves that won't fire are a common problem.

The Quick Dump Valve or QDV was built to take advantage of close ratio piston valve advantages of speed while fixing the disadvantages of the temperamental nature of them failing to fire reliably or seal properly to build chamber pressure.

Spool valves are balanced design valves with several o rings that move past ports and are operated by the rings crossing ports to join some in the same segment or separate them. They are noted for the ability to switch high pressures with little force to operate the valve. Typical uses are the hydraulic controls on heavy machinery such as a backhoe. Normal spool valves have both ends of the valve rod at atmospheric pressure.

A QDV when closed has the appearance of a spool valve. The air source under pressure is sealed off in the chamber with an o ring on both sides of the port. What makes this different than a typical spool valve is when it is opened, the supply pressure is then applied to the end of the spool. This pressure provides a positive feedback to the spool so as it opens, the force opening it rapidly increases as supply pressure in the outlet port pushes on the piston.

Unlike a piston valve that uses pressure in a "Pilot" area to hold the valve closed, the QDV has no pressure on the pilot area of the piston to hold it closed. In this manner it is much like a spool control valve.

A video on the valve theory is posted here; [http://www.youtube.com/watch?v=No3nI07mlQo Youtube The Quick Dump Valve]

The first appearance of the Quick Dump Valve in an air cannon is covered in a contest for building t shirt launchers;
[http://inteltrailblazerschallenge.wikispaces.com/The+brag+zone IntelTrailBlazers Engineering Challenge]

The first mention of the valve on Spudfiles is in this thread.
[http://www.spudfiles.com/forums/interesting-new-valve-design-t17617.html Interesting New Valve Design]

This is a video of the T Shirt launcher in action. The team won the competition with this design.
[http://www.youtube.com/watch?v=9Klxqav_6NM Quick Reload T Shirt launcher]

Quick Dump valves can be constructed as either a coaxial design with the valve inside a chamber, or built inside a T for an external valve. Coaxial valves provide some of the best COF values possible.

[[Image:WikiOverview.jpg]]

The oldest is constructed with ABS. The valve is located in the breech of the chamber. The barrel is a long pipe that extended all the way though the chamber with ports cut into the pipe between the chamber and barrel. A plastic bag was stuffed into the barrel to highlight the ports for the photo. Otherwise they were too dark to see very well.

[[Image:ValvePorts1.JPG]]

This design works well. The drawbacks are the piston needs a rod shoved into the breech rope pull hole to reset the valve between shots and the design did not use floating o rings, so it pulls a little hard.

The piston is made from a piece of PVC pipe and a couple pipe caps and o rings. Any sturdy cylindrical object can be used that will hold the pressure and forces.

[[Image:CoreDetail.JPG]]

For safety on this design, it is very important to remember that shoving anything into the barrel does the same thing as pulling the rope. It opens the valve. ''' Never shove anything into this design of valve while it is under pressure.''' Load it and then add pressure.

The spudfiles page on the cannon is here;
[http://www.spudfiles.com/forums/abs-cellular-core-test-cannon-t17968.html ABS Cellular Core Test Cannon, also known as the apple cannon]
It was posted as a materials test discussion on using unrated plastic pipe in air cannons.

Later improvements to the design included using a rod instead of a rope to open and close the valve. The piston if permitted to slide freely on the rod can be made to operate quickly without having to accelerate the control trigger rod. In operation, when the rod is pushed in, a pin on the rod pushes the piston closed. To fire the rod is pulled back through the piston which retracts the pin behind the piston out of the piston travel area. Then a nut on the end of the rod pushes the front of the piston pulling it open triggering it. Once the valve cracks open, the air pressure between the piston and projectile pushes the valve open with the same pressure it applies to the projectile.

The valve can be relocated to the barrel end of the chamber.
This permits easy detachment of the barrel and the ability to attach various size barrels with minimum dead space.

A model of the T Shirt launcher shows the construction detail with the improvements. In Spudfiles, it is called the Marshmallow Cannon. It was built for a high speed marshmallow launching competition. With a removable and interchangeable barrel selection, it is easy to adapt to shooting gumballs, jawbreakers, batteries, tennis balls, and t shirts. With a 36 inch long t shirt barrel the 1 inch valve is able to toss shirts 200 feet.

The Spudfiles entry is here;
[http://www.spudfiles.com/forums/quick-dump-valve-t17858.html The Quick Dump Valve]
The spudfiles entry has links to a theory of operation video as well as more photos.

The tank as before is coaxial design with a valve body in the center. Unlike the earlier design, the barrel is removable and the valve is located at the barrel end of the chamber instead of the breech. The new design uses a rod to trigger and reset the valve.

[[Image:WikiTank.jpg]]

The valve core removed from the tank shows the piston with floating rings, rod, bumper, stopper, and trigger and reset pins.

[[Image:WikiVavleCoreAssy.jpg]]

A close up view of the piston shows the o rings fit loose in a floating O Ring design. The spudfiles page and linked videos show how this style of o ring installation lowers the friction in the valve.

[[Image:Piston_rings.jpg]]

The ports between the chamber and valve body can be seen inside the valve.

[[Image:WikiTankEnd.jpg]]

View of the assembled cannon with the tennis ball barrel. It tosses tennis balls 100 yards.

[[Image:Tennis_ball_barrel1.jpg]]

With high speed of operation and a high flow, the cannon is able to deliver high speeds. The photo is a 2X4 that was split with a couple jawbreakers.

[[Image:Split1a.JPG]]

Photos are copyright by Technician1002. Please ask before using elsewhere.

Quick Dump Valve

2009-08-10T21:17:35Z

Technician1002: /* The Quick Dump Valve */

'''Article Flag''' 
As an article relating to spudding hardware, this should be presented in a more neutral format - it currently reads like an advertisement. 
It should also be presented in a third person point of view, as newcomers won't be able to associate "I" or "Me" usefully. 
Flagged by [[User:Ragnarok|Ragnarok]] 20:32, 29 July 2009 (EDT)

== The Quick Dump Valve ==

The quick dump valve is a variation on a traditional barrel sealer piston valve. In the section on piston valves, various configurations are covered and the advantages and disadvantages of each. A quick dump valve may be used where the traditional valves shortcomings cause problems for the builder. It was noted in the piston valve section in the wiki that as a barrel sealer valve nears a 1:1 ratio, the pilot pressure needed to open the valve drops lower, and when they pop open, they do so with more force and speed. They become temperamental as the ratio approaches a 1:1 ratio as the force to start opening the valve drops. They tend to stick or are unable to vent the pilot low enough to fire it. As a result, piston valves that won't fire are a common problem.

The Quick Dump Valve or QDV was built to take advantage of close ratio piston valve advantages of speed while fixing the disadvantages of the temperamental nature of them failing to fire reliably or seal properly to build chamber pressure.

Spool valves are balanced design valves with several o rings that move past ports and are operated by the rings crossing ports to join some in the same segment or separate them. They are noted for the ability to switch high pressures with little force to operate the valve. Typical uses are the hydraulic controls on heavy machinery such as a backhoe. Normal spool valves have both ends of the valve rod at atmospheric pressure.

A QDV when closed has the appearance of a spool valve. The air source under pressure is sealed off in the chamber with an o ring on both sides of the port. What makes this different than a typical spool valve is when it is opened, the supply pressure is then applied to the end of the spool. This pressure provides a positive feedback to the spool so as it opens, the force opening it rapidly increases as supply pressure in the outlet port pushes on the piston.

Unlike a piston valve that uses pressure in a "Pilot" area to hold the valve closed, the QDV has no pressure on the pilot area of the piston to hold it closed. In this manner it is much like a spool control valve.

A video on the valve theory is posted here; [http://www.youtube.com/watch?v=No3nI07mlQo Youtube The Quick Dump Valve]

The first appearance of the Quick Dump Valve in an air cannon is covered in a contest for building t shirt launchers;
[http://inteltrailblazerschallenge.wikispaces.com/The+brag+zone IntelTrailBlazers Engineering Challenge]

The first mention of the valve on Spudfiles is in this thread.
[http://www.spudfiles.com/forums/interesting-new-valve-design-t17617.html Interesting New Valve Design]

This is a video of the T Shirt launcher in action. The team won the competition with this design.
[http://www.youtube.com/watch?v=9Klxqav_6NM Quick Reload T Shirt launcher]

Quick Dump valves can be constructed as either a coaxial design with the valve inside a chamber, or built inside a T for an external valve. I prefer the coaxial designs myself for the best COF values possible.

[[Image:WikiOverview.jpg]]

The oldest is constructed with ABS. The valve is located in the breech of the chamber. The barrel is a long pipe that extended all the way though the chamber with ports cut into the pipe between the chamber and barrel. A plastic bag was stuffed into the barrel to highlight the ports for the photo. Otherwise they were too dark to see very well.

[[Image:ValvePorts1.JPG]]

This design works well. The drawbacks are the piston needs a rod shoved into the breech rope pull hole to reset the valve between shots and the design did not use floating o rings, so it pulls a little hard.

The piston is made from a piece of PVC pipe and a couple pipe caps and o rings. Any sturdy cylindrical object can be used that will hold the pressure and forces.

[[Image:CoreDetail.JPG]]

For safety on this design, it is very important to remember that shoving anything into the barrel does the same thing as pulling the rope. It opens the valve. ''' Never shove anything into this design of valve while it is under pressure.''' Load it and then add pressure.

The spudfiles page on the cannon is here;
[http://www.spudfiles.com/forums/abs-cellular-core-test-cannon-t17968.html ABS Cellular Core Test Cannon, also known as the apple cannon]
It was posted as a materials test discussion on using unrated plastic pipe in air cannons.

Later improvements to the design included using a rod instead of a rope to open and close the valve. The piston if permitted to slide freely on the rod can be made to operate quickly without having to accelerate the control trigger rod. In operation, when the rod is pushed in, a pin on the rod pushes the piston closed. To fire the rod is pulled back through the piston which retracts the pin behind the piston out of the piston travel area. Then a nut on the end of the rod pushes the front of the piston pulling it open triggering it. Once the valve cracks open, the air pressure between the piston and projectile pushes the valve open with the same pressure it applies to the projectile.

The valve can be relocated to the barrel end of the chamber.
This permits easy detachment of the barrel and the ability to attach various size barrels with minimum dead space.

A model of the T Shirt launcher shows the construction detail with the improvements. In Spudfiles, it is called the Marshmallow Cannon. It was built for a high speed marshmallow launching competition. With a removable and interchangeable barrel selection, it is easy to adapt to shooting gumballs, jawbreakers, batteries, tennis balls, and t shirts. With a 36 inch long t shirt barrel the 1 inch valve is able to toss shirts 200 feet.

The Spudfiles entry is here;
[http://www.spudfiles.com/forums/quick-dump-valve-t17858.html The Quick Dump Valve]
The spudfiles entry has links to a theory of operation video as well as more photos.

The tank as before is coaxial design with a valve body in the center. Unlike the earlier design, the barrel is removable and the valve is located at the barrel end of the chamber instead of the breech. The new design uses a rod to trigger and reset the valve.

[[Image:WikiTank.jpg]]

The valve core removed from the tank shows the piston with floating rings, rod, bumper, stopper, and trigger and reset pins.

[[Image:WikiVavleCoreAssy.jpg]]

A close up view of the piston shows the o rings fit loose in a floating O Ring design. The spudfiles page and linked videos show how this style of o ring installation lowers the friction in the valve.

[[Image:Piston_rings.jpg]]

The ports between the chamber and valve body can be seen inside the valve.

[[Image:WikiTankEnd.jpg]]

View of the assembled cannon with the tennis ball barrel. It tosses tennis balls 100 yards.

[[Image:Tennis_ball_barrel1.jpg]]

With high speed of operation and a high flow, the cannon is able to deliver high speeds. The photo is a 2X4 that was split with a couple jawbreakers.

[[Image:Split1a.JPG]]

Photos are copyright by Technician1002. Please ask before using elsewhere.

Good technical examples & articles

2009-08-10T21:12:55Z

Technician1002: /* Cannons */

This page is to be filled with the cannons generally considered good technical examples on the forums, or those that people just tend to like.
And the articles that are worth your reading time.

Obviously this page is under construction, somewhat subjective, and most definitely incomplete, but it's here to help a newbie get themselves well aligned with what spudding actually can be.

==VERY IMPORTANT RULE==
Most of these topics are fairly old. Please do not post in any topic that you are linked to from this page unless you have a VERY important technical question that is not answered anywhere in the thread.

Asking for plans in any one of these threads will cause you to become prematurely bald. If you are already bald, you don't want to know what becoming bald again after you are already bald does to you.

==ADDING TO THIS PAGE==

* Please put cannons in the right category, and '''alphabetically by user'''. (This is to prevent any "This cannon is better, so it should be higher up" edit wars.) Articles have no particular order of preference, but try and add them to the right category.
* Avoid adding a really recent cannon unless it's a very good example.
* Don't add your own cannons, because that's just big-headed. I know I ''(Ragnarok)'' did it, but I'm a self confessed hypocrite.

==Cannons==

'''Pneumatic'''
*[http://www.spudfiles.com/forums/t-t18733.html Old Bessy Sureshot, by AdiabaticManiak.] Not the most sophisticated cannon, but one of the few lever action ones.
*[http://www.spudfiles.com/forums/viewtopic,p,208016.html#208016 4.2 Inch Mortar, by biged.] A very well built replica WW2 mortar.
*[http://www.spudfiles.com/forums/t-t1342.html Sawn-off riot gun, by Brian the Brain.] A cannon that has inspired a great many people.
*[http://www.spudfiles.com/forums/t-t17312.html Mr Porter, by Brian the Brain.] What happens if a 2" porting piston valve and 500 psi come together.
*[http://www.spudfiles.com/forums/t-t17827.html Old Shatterhand, by Brian the Brain.] An exceptionally well made multi-shot hammer valve cannon.
*[http://www.spudfiles.com/forums/t-t7862.html S400, by Chaos.] Good looking, well built, and a good performer. 'Nuff said.
*[http://www.spudfiles.com/forums/t-t7899.html GB Semi, by Clide.] Self loading Golf ball gun. Good demonstration of a blowforward loader. Also notable for the HEAR valve.
*[http://www.spudfiles.com/forums/t-t14802.html Portable burst disk cartridges, by Davidvaini.]
*[http://www.spudfiles.com/forums/t-t12103.html SCTBDC, by DYI.] Big-ass pneumatic.
*[http://www.spudfiles.com/forums/t-t6455.html Mini Piston Gun, by ethal1222.] A good lesson in compact building.
*[http://www.spudfiles.com/forums/t-t6013.html Copperhead Prime, by Hotwired.] Good example of a simple, yet functional design that has inspired imitators.
*[http://www.spudfiles.com/forums/t-t10446.html 6mm Burst Disc Pneumatic, by Jackssmirkingrevenge.] Demonstration of the effectiveness of high pressure and a good valve.
*[http://www.spudfiles.com/forums/t-t7694.html RevoSemi, by Keep_it_Real.] A great example of a simple loader.
*[http://www.spudfiles.com/forums/t-t11453.html HEAL, by Ragnarok.] Because I'm a shameless self-promoter.
*[http://www.spudfiles.com/forums/t-t7093.html The SWAT, by schmanman.] Just a very large pneumatic.
*[http://www.spudfiles.com/forums/gorts-golf-bag-w-vids-contest-t3458.html Gort's Golf Bag, by sgort87.] A portable pneumatic cannon hidden inside a golf bag.
*[http://www.spudfiles.com/forums/t-t14348.html The Eclipse, by Solar.] One of the best produced cannons this forum has seen.
*[http://www.spudfiles.com/spud_wiki/index.php/Quick_Dump_Valve Quick Dump Valve by Technician1002.] An air valve that is mechanically triggered and reset for high reliability.
*[http://www.spudfiles.com/forums/t-t18846.html XM2, by wngovr.] Beautifully built cannon with an integral pump.

'''Combustion'''
*[http://www.spudfiles.com/forums/t-t174.html Revolver X, by Boogieman.] Well known combustion, good demonstration of speeding up shooting.
*[http://www.spudfiles.com/spudtech_archive/viewtopic.php?f=17&t=12971 57.5mm Oxymortar, by Caffeine.] One of the very early examples of machined cannons.
*[http://www.spudfiles.com/forums/t-t17090.html Small Pistol Grip Combustion, by CrashTestDummy II.] Demonstrating that simple cannons need not look it.
*[http://www.spudfiles.com/forums/t-t15766.html Mk2 Rotary barrelled Combustion, by Critical_Al.] Very well made "Rapid-fire" combustion.
*[http://www.spudfiles.com/forums/t-t4960.html Taternator II, by Dumbascii.] Taking combustion and just throwing overkill at it.
*[http://www.spudfiles.com/forums/t-t14319.html Wood Combustion, by Eddbot.] Not so serious, and not the world's best technical example, but worth a look, because most people like it.
*[http://www.spudfiles.com/forums/t-t17794.html The BL520, by jagerbond.] (Reviewed by PCGUY). A well thought out and built cannon from Spudfiles' sponsor.
*[http://www.spudfiles.com/forums/t-t16725.html The Gauntlet of Clara Ann, by Radiation.] For having one of the most grandiloquent cannon names on the forum.
*[http://www.spudfiles.com/forums/t-t7878.html Blue Flame III, by Sgort87.] Again, demonstrations of improving rate of fire.
*[http://www.spudfiles.com/forums/t-t6241.html Collapsible travel combustion, by Sgort87.] Neat concept for a telescoping cannon.
*[http://www.spudfiles.com/forums/t-t1575.html Proton Pack, by Sgort87.] Backpack based chamber, sometimes considered for a cannon design.
*[http://www.spudfiles.com/forums/t-t2736.html 12" Diameter bucket launcher, by Sgort87.] He does a lot of good combustions. Also, adventurous sizewise.
*[http://www.spudfiles.com/forums/t-t15211.html Triple Thunder cannons, by Starman.] Neatly built, well known and good performers - they had to make the list.

'''Hybrid'''
*[http://www.spudfiles.com/forums/t-t16882.html BACH, by Daccel.] Although not finished, this is one of the most viable methods to speed up hybrid operation.]
*[http://www.spudfiles.com/forums/t-t6822.html HPSCL, by DR.] Often known as the Gen-II tank, an early example (reposted here) of developments in hybrid fuelling.
*[http://www.spudfiles.com/forums/t-t9589.html Piston Hybrid, by Fnord.] A demonstration of an alternate hybrid valve.
*[http://www.spudfiles.com/forums/t-t7857.html FEAR, by Killjoy.] Just a big ass hybrid. Former holder of the spudgun velocity record.
*[http://www.spudfiles.com/forums/t-t15524.html HyGaC20, by Larda.] Current holder of spudgun velocity, and preignition mix pressure records. Also nice to look at.
*[http://www.spudfiles.com/forums/t-t17948.html The Cobra Venom, by Moonbogg.] A record of the production of a high quality machined hybrid.

'''BBMG/Strafer'''
*[http://www.spudfiles.com/forums/t-t13762.html Deathray, by Brian the Brain.] Simplify, and add pressure.
*[http://www.spudfiles.com/forums/t-t12907.html RC-P240 Vortex cap BBMG, by Imortal87.] A good method of adding magazines to a BBMG.
*[http://www.spudfiles.com/forums/t-t10075.html 6mm Semi by Jackssmirkingrevenge.] Not so much a BBMG, but absolutely great for learning about blow forward loaders.
*[http://www.spudfiles.com/forums/t-t17845.html "I has full auto", by Jackssmirkingrevenge.] Jack finally builds a full auto pulsed BBMG after... I've forgotten. A long time, either way.
*[http://www.spudfiles.com/forums/t-t16441.html Ultimate Inline Mk IIIi, by Neospud.] Showing you how a BBMG should be done for practical field use.

'''Mini'''

*[http://www.spudfiles.com/forums/t-t7858.html Pneumatic Pengun, by Jackssmirkingrevenge.] For being one of the first examples of less ghetto minis.
*[http://www.spudfiles.com/forums/t-t18619.html Keychain Pengun, by jor2daje.] Nigh on minuscule, and with a mini pump
*[http://www.spudfiles.com/forums/t-t17102.html Mini Keychain, by jook13.] For being the first keychain spudgun.
*[http://www.spudfiles.com/forums/t-t17408.html 300 WinMag Coax, by jook13.] A gun... inside a bullet.

And thus we prove that success in Minis depends on a username starting with a J.

'''Other'''
*[http://www.spudfiles.com/forums/t-t13449.html 28.8kj Electrothermal cannon, by Larda.] Cannon powered by plasma. Somehow even more impressive than it sounds.

==Articles==

'''General Forum'''
*[http://www.spudfiles.com/forums/t-t14659.html A ''VERY'' worthwhile read on spudgunning and the forums.] A read of this will get you pretty up to date with the forum's workings.
*[http://www.spudfiles.com/forums/t-t16568.html A spudder's tale.] Not essential reading, but nice anyway.
*[http://www.spudfiles.com/forums/posting-images-a-step-by-step-guide-t13190.html Posting images a step-by-step guide.] How to post images on Spudfiles properly.
*[http://www.spudfiles.com/forums/rules.html Rules.] Main forum rules.
*[[The reasons behind the rules | Explanation of rules that sometimes raise questions.]]
*[http://www.spudfiles.com/forums/viewtopic,p,136508.html#136508 Posting Etiquette.] Posting rules for the Spudfiles forum, differs from the main forum rules.
*[[Why aren't my questions being answered?]] For if you've asked a question, but you're getting responses like "Do your own research".

'''Forum In-jokes'''
*[http://www.spudfiles.com/forums/t-t13069.html How to deal with frustration.] The famous *facepalmheaddeskcombo* explained.
*[http://www.spudfiles.com/forums/viewtopic,p,133222.html#133222 The Flaming Pink Elephant.] A metaphor for the forum's innuendo, as this is what it is as subtle as.
*[[Spudfiles Forum Jokes]] Worth a read, to help you gauge the forum's sense of humo(u)r before you misinterpret something.
*[[Tools redefined]]: What tools really are.

'''Safety'''
*[http://www.spudfiles.com/forums/t-t7783.html Things not to do.] A list of accidents people have had, and in many cases, how it could have been avoided.
*[http://www.spudfiles.com/forums/t-t15301.html A tale of shooting yourself in the face.] Again, more accidents.
*[http://www.spudfiles.com/forums/t-t11431.html Predicting if your cannon's recoil is likely to be dangerous.] It is inadvisable for a hand fired cannon to exceed 100 ft-lbs (135 J) of recoil, and even this will be unpleasant.

'''Construction'''
*[http://www.spudfiles.com/forums/t-t8157.html How piston valves work.] An explanation of what is arguably the best valve in spudding.
*[http://www.spudfiles.com/forums/t-t11866.html High pressure compressors.] How to adapt fridge parts into the spudder's high pressure solution.
*[http://www.spudfiles.com/forums/t-t2546.html A solution to rifling.] How to rifle a PVC barrel.
*[http://www.spudfiles.com/forums/t-t10381.html How to make a cannon with 2" piston valve.] How to make a 2" piston valve.
*[http://www.spudfiles.com/forums/t-t3009.html Solvent Welding Course.] An online course on how to solvent weld PVC correctly.
*[http://www.spudfiles.com/forums/t-t18108.html Suppressor Tutorial.] Quite a long video, but lots of information on suppressor (or silencer, if you must) construction.

'''Projectiles'''
*[http://www.spudfiles.com/forums/t-t16438.html A fairly interesting thread on projectile shape vs. drag.] It's a bit incoherent at times, but worth the study.
*[http://www.spudfiles.com/forums/t-t13477.html A theory on dart development.]

'''Aesthetics'''
* [http://www.spudfiles.com/forums/t-t15767.html Making a stock for your launcher?] This will be worth some reading.

Good technical examples & articles

2009-08-10T21:11:13Z

Technician1002: /* Cannons */

This page is to be filled with the cannons generally considered good technical examples on the forums, or those that people just tend to like.
And the articles that are worth your reading time.

Obviously this page is under construction, somewhat subjective, and most definitely incomplete, but it's here to help a newbie get themselves well aligned with what spudding actually can be.

==VERY IMPORTANT RULE==
Most of these topics are fairly old. Please do not post in any topic that you are linked to from this page unless you have a VERY important technical question that is not answered anywhere in the thread.

Asking for plans in any one of these threads will cause you to become prematurely bald. If you are already bald, you don't want to know what becoming bald again after you are already bald does to you.

==ADDING TO THIS PAGE==

* Please put cannons in the right category, and '''alphabetically by user'''. (This is to prevent any "This cannon is better, so it should be higher up" edit wars.) Articles have no particular order of preference, but try and add them to the right category.
* Avoid adding a really recent cannon unless it's a very good example.
* Don't add your own cannons, because that's just big-headed. I know I ''(Ragnarok)'' did it, but I'm a self confessed hypocrite.

==Cannons==

'''Pneumatic'''
*[http://www.spudfiles.com/forums/t-t18733.html Old Bessy Sureshot, by AdiabaticManiak.] Not the most sophisticated cannon, but one of the few lever action ones.
*[http://www.spudfiles.com/forums/viewtopic,p,208016.html#208016 4.2 Inch Mortar, by biged.] A very well built replica WW2 mortar.
*[http://www.spudfiles.com/forums/t-t1342.html Sawn-off riot gun, by Brian the Brain.] A cannon that has inspired a great many people.
*[http://www.spudfiles.com/forums/t-t17312.html Mr Porter, by Brian the Brain.] What happens if a 2" porting piston valve and 500 psi come together.
*[http://www.spudfiles.com/forums/t-t17827.html Old Shatterhand, by Brian the Brain.] An exceptionally well made multi-shot hammer valve cannon.
*[http://www.spudfiles.com/forums/t-t7862.html S400, by Chaos.] Good looking, well built, and a good performer. 'Nuff said.
*[http://www.spudfiles.com/forums/t-t7899.html GB Semi, by Clide.] Self loading Golf ball gun. Good demonstration of a blowforward loader. Also notable for the HEAR valve.
*[http://www.spudfiles.com/forums/t-t14802.html Portable burst disk cartridges, by Davidvaini.]
*[http://www.spudfiles.com/forums/t-t12103.html SCTBDC, by DYI.] Big-ass pneumatic.
*[http://www.spudfiles.com/forums/t-t6455.html Mini Piston Gun, by ethal1222.] A good lesson in compact building.
*[http://www.spudfiles.com/forums/t-t6013.html Copperhead Prime, by Hotwired.] Good example of a simple, yet functional design that has inspired imitators.
*[http://www.spudfiles.com/forums/t-t10446.html 6mm Burst Disc Pneumatic, by Jackssmirkingrevenge.] Demonstration of the effectiveness of high pressure and a good valve.
*[http://www.spudfiles.com/forums/t-t7694.html RevoSemi, by Keep_it_Real.] A great example of a simple loader.
*[http://www.spudfiles.com/forums/t-t11453.html HEAL, by Ragnarok.] Because I'm a shameless self-promoter.
*[http://www.spudfiles.com/forums/t-t7093.html The SWAT, by schmanman.] Just a very large pneumatic.
*[http://www.spudfiles.com/forums/gorts-golf-bag-w-vids-contest-t3458.html Gort's Golf Bag, by sgort87.] A portable pneumatic cannon hidden inside a golf bag.
*[http://www.spudfiles.com/forums/t-t14348.html The Eclipse, by Solar.] One of the best produced cannons this forum has seen.
*[http://www.spudfiles.com/spud_wiki/index.php/Quick_Dump_Valve Quick Dump Valve by Technician1002.] A reliable air valve that is mechanically triggered and reset for higher reliability than conventional piston valves.
*[http://www.spudfiles.com/forums/t-t18846.html XM2, by wngovr.] Beautifully built cannon with an integral pump.

'''Combustion'''
*[http://www.spudfiles.com/forums/t-t174.html Revolver X, by Boogieman.] Well known combustion, good demonstration of speeding up shooting.
*[http://www.spudfiles.com/spudtech_archive/viewtopic.php?f=17&t=12971 57.5mm Oxymortar, by Caffeine.] One of the very early examples of machined cannons.
*[http://www.spudfiles.com/forums/t-t17090.html Small Pistol Grip Combustion, by CrashTestDummy II.] Demonstrating that simple cannons need not look it.
*[http://www.spudfiles.com/forums/t-t15766.html Mk2 Rotary barrelled Combustion, by Critical_Al.] Very well made "Rapid-fire" combustion.
*[http://www.spudfiles.com/forums/t-t4960.html Taternator II, by Dumbascii.] Taking combustion and just throwing overkill at it.
*[http://www.spudfiles.com/forums/t-t14319.html Wood Combustion, by Eddbot.] Not so serious, and not the world's best technical example, but worth a look, because most people like it.
*[http://www.spudfiles.com/forums/t-t17794.html The BL520, by jagerbond.] (Reviewed by PCGUY). A well thought out and built cannon from Spudfiles' sponsor.
*[http://www.spudfiles.com/forums/t-t16725.html The Gauntlet of Clara Ann, by Radiation.] For having one of the most grandiloquent cannon names on the forum.
*[http://www.spudfiles.com/forums/t-t7878.html Blue Flame III, by Sgort87.] Again, demonstrations of improving rate of fire.
*[http://www.spudfiles.com/forums/t-t6241.html Collapsible travel combustion, by Sgort87.] Neat concept for a telescoping cannon.
*[http://www.spudfiles.com/forums/t-t1575.html Proton Pack, by Sgort87.] Backpack based chamber, sometimes considered for a cannon design.
*[http://www.spudfiles.com/forums/t-t2736.html 12" Diameter bucket launcher, by Sgort87.] He does a lot of good combustions. Also, adventurous sizewise.
*[http://www.spudfiles.com/forums/t-t15211.html Triple Thunder cannons, by Starman.] Neatly built, well known and good performers - they had to make the list.

'''Hybrid'''
*[http://www.spudfiles.com/forums/t-t16882.html BACH, by Daccel.] Although not finished, this is one of the most viable methods to speed up hybrid operation.]
*[http://www.spudfiles.com/forums/t-t6822.html HPSCL, by DR.] Often known as the Gen-II tank, an early example (reposted here) of developments in hybrid fuelling.
*[http://www.spudfiles.com/forums/t-t9589.html Piston Hybrid, by Fnord.] A demonstration of an alternate hybrid valve.
*[http://www.spudfiles.com/forums/t-t7857.html FEAR, by Killjoy.] Just a big ass hybrid. Former holder of the spudgun velocity record.
*[http://www.spudfiles.com/forums/t-t15524.html HyGaC20, by Larda.] Current holder of spudgun velocity, and preignition mix pressure records. Also nice to look at.
*[http://www.spudfiles.com/forums/t-t17948.html The Cobra Venom, by Moonbogg.] A record of the production of a high quality machined hybrid.

'''BBMG/Strafer'''
*[http://www.spudfiles.com/forums/t-t13762.html Deathray, by Brian the Brain.] Simplify, and add pressure.
*[http://www.spudfiles.com/forums/t-t12907.html RC-P240 Vortex cap BBMG, by Imortal87.] A good method of adding magazines to a BBMG.
*[http://www.spudfiles.com/forums/t-t10075.html 6mm Semi by Jackssmirkingrevenge.] Not so much a BBMG, but absolutely great for learning about blow forward loaders.
*[http://www.spudfiles.com/forums/t-t17845.html "I has full auto", by Jackssmirkingrevenge.] Jack finally builds a full auto pulsed BBMG after... I've forgotten. A long time, either way.
*[http://www.spudfiles.com/forums/t-t16441.html Ultimate Inline Mk IIIi, by Neospud.] Showing you how a BBMG should be done for practical field use.

'''Mini'''

*[http://www.spudfiles.com/forums/t-t7858.html Pneumatic Pengun, by Jackssmirkingrevenge.] For being one of the first examples of less ghetto minis.
*[http://www.spudfiles.com/forums/t-t18619.html Keychain Pengun, by jor2daje.] Nigh on minuscule, and with a mini pump
*[http://www.spudfiles.com/forums/t-t17102.html Mini Keychain, by jook13.] For being the first keychain spudgun.
*[http://www.spudfiles.com/forums/t-t17408.html 300 WinMag Coax, by jook13.] A gun... inside a bullet.

And thus we prove that success in Minis depends on a username starting with a J.

'''Other'''
*[http://www.spudfiles.com/forums/t-t13449.html 28.8kj Electrothermal cannon, by Larda.] Cannon powered by plasma. Somehow even more impressive than it sounds.

==Articles==

'''General Forum'''
*[http://www.spudfiles.com/forums/t-t14659.html A ''VERY'' worthwhile read on spudgunning and the forums.] A read of this will get you pretty up to date with the forum's workings.
*[http://www.spudfiles.com/forums/t-t16568.html A spudder's tale.] Not essential reading, but nice anyway.
*[http://www.spudfiles.com/forums/posting-images-a-step-by-step-guide-t13190.html Posting images a step-by-step guide.] How to post images on Spudfiles properly.
*[http://www.spudfiles.com/forums/rules.html Rules.] Main forum rules.
*[[The reasons behind the rules | Explanation of rules that sometimes raise questions.]]
*[http://www.spudfiles.com/forums/viewtopic,p,136508.html#136508 Posting Etiquette.] Posting rules for the Spudfiles forum, differs from the main forum rules.
*[[Why aren't my questions being answered?]] For if you've asked a question, but you're getting responses like "Do your own research".

'''Forum In-jokes'''
*[http://www.spudfiles.com/forums/t-t13069.html How to deal with frustration.] The famous *facepalmheaddeskcombo* explained.
*[http://www.spudfiles.com/forums/viewtopic,p,133222.html#133222 The Flaming Pink Elephant.] A metaphor for the forum's innuendo, as this is what it is as subtle as.
*[[Spudfiles Forum Jokes]] Worth a read, to help you gauge the forum's sense of humo(u)r before you misinterpret something.
*[[Tools redefined]]: What tools really are.

'''Safety'''
*[http://www.spudfiles.com/forums/t-t7783.html Things not to do.] A list of accidents people have had, and in many cases, how it could have been avoided.
*[http://www.spudfiles.com/forums/t-t15301.html A tale of shooting yourself in the face.] Again, more accidents.
*[http://www.spudfiles.com/forums/t-t11431.html Predicting if your cannon's recoil is likely to be dangerous.] It is inadvisable for a hand fired cannon to exceed 100 ft-lbs (135 J) of recoil, and even this will be unpleasant.

'''Construction'''
*[http://www.spudfiles.com/forums/t-t8157.html How piston valves work.] An explanation of what is arguably the best valve in spudding.
*[http://www.spudfiles.com/forums/t-t11866.html High pressure compressors.] How to adapt fridge parts into the spudder's high pressure solution.
*[http://www.spudfiles.com/forums/t-t2546.html A solution to rifling.] How to rifle a PVC barrel.
*[http://www.spudfiles.com/forums/t-t10381.html How to make a cannon with 2" piston valve.] How to make a 2" piston valve.
*[http://www.spudfiles.com/forums/t-t3009.html Solvent Welding Course.] An online course on how to solvent weld PVC correctly.
*[http://www.spudfiles.com/forums/t-t18108.html Suppressor Tutorial.] Quite a long video, but lots of information on suppressor (or silencer, if you must) construction.

'''Projectiles'''
*[http://www.spudfiles.com/forums/t-t16438.html A fairly interesting thread on projectile shape vs. drag.] It's a bit incoherent at times, but worth the study.
*[http://www.spudfiles.com/forums/t-t13477.html A theory on dart development.]

'''Aesthetics'''
* [http://www.spudfiles.com/forums/t-t15767.html Making a stock for your launcher?] This will be worth some reading.

Good technical examples & articles

2009-08-10T21:10:06Z

Technician1002: /* Cannons */

This page is to be filled with the cannons generally considered good technical examples on the forums, or those that people just tend to like.
And the articles that are worth your reading time.

Obviously this page is under construction, somewhat subjective, and most definitely incomplete, but it's here to help a newbie get themselves well aligned with what spudding actually can be.

==VERY IMPORTANT RULE==
Most of these topics are fairly old. Please do not post in any topic that you are linked to from this page unless you have a VERY important technical question that is not answered anywhere in the thread.

Asking for plans in any one of these threads will cause you to become prematurely bald. If you are already bald, you don't want to know what becoming bald again after you are already bald does to you.

==ADDING TO THIS PAGE==

* Please put cannons in the right category, and '''alphabetically by user'''. (This is to prevent any "This cannon is better, so it should be higher up" edit wars.) Articles have no particular order of preference, but try and add them to the right category.
* Avoid adding a really recent cannon unless it's a very good example.
* Don't add your own cannons, because that's just big-headed. I know I ''(Ragnarok)'' did it, but I'm a self confessed hypocrite.

==Cannons==

'''Pneumatic'''
*[http://www.spudfiles.com/forums/t-t18733.html Old Bessy Sureshot, by AdiabaticManiak.] Not the most sophisticated cannon, but one of the few lever action ones.
*[http://www.spudfiles.com/forums/viewtopic,p,208016.html#208016 4.2 Inch Mortar, by biged.] A very well built replica WW2 mortar.
*[http://www.spudfiles.com/forums/t-t1342.html Sawn-off riot gun, by Brian the Brain.] A cannon that has inspired a great many people.
*[http://www.spudfiles.com/forums/t-t17312.html Mr Porter, by Brian the Brain.] What happens if a 2" porting piston valve and 500 psi come together.
*[http://www.spudfiles.com/forums/t-t17827.html Old Shatterhand, by Brian the Brain.] An exceptionally well made multi-shot hammer valve cannon.
*[http://www.spudfiles.com/forums/t-t7862.html S400, by Chaos.] Good looking, well built, and a good performer. 'Nuff said.
*[http://www.spudfiles.com/forums/t-t7899.html GB Semi, by Clide.] Self loading Golf ball gun. Good demonstration of a blowforward loader. Also notable for the HEAR valve.
*[http://www.spudfiles.com/forums/t-t14802.html Portable burst disk cartridges, by Davidvaini.]
*[http://www.spudfiles.com/forums/t-t12103.html SCTBDC, by DYI.] Big-ass pneumatic.
*[http://www.spudfiles.com/forums/t-t6455.html Mini Piston Gun, by ethal1222.] A good lesson in compact building.
*[http://www.spudfiles.com/forums/t-t6013.html Copperhead Prime, by Hotwired.] Good example of a simple, yet functional design that has inspired imitators.
*[http://www.spudfiles.com/forums/t-t10446.html 6mm Burst Disc Pneumatic, by Jackssmirkingrevenge.] Demonstration of the effectiveness of high pressure and a good valve.
*[http://www.spudfiles.com/forums/t-t7694.html RevoSemi, by Keep_it_Real.] A great example of a simple loader.
*[http://www.spudfiles.com/forums/t-t11453.html HEAL, by Ragnarok.] Because I'm a shameless self-promoter.
*[http://www.spudfiles.com/forums/t-t7093.html The SWAT, by schmanman.] Just a very large pneumatic.
*[http://www.spudfiles.com/forums/gorts-golf-bag-w-vids-contest-t3458.html Gort's Golf Bag, by sgort87.] A portable pneumatic cannon hidden inside a golf bag.
*[http://www.spudfiles.com/forums/t-t14348.html The Eclipse, by Solar.] One of the best produced cannons this forum has seen.
*[http://www.spudfiles.com/forums/t-t18846.html XM2, by wngovr.] Beautifully built cannon with an integral pump.

'''Combustion'''
*[http://www.spudfiles.com/forums/t-t174.html Revolver X, by Boogieman.] Well known combustion, good demonstration of speeding up shooting.
*[http://www.spudfiles.com/spudtech_archive/viewtopic.php?f=17&t=12971 57.5mm Oxymortar, by Caffeine.] One of the very early examples of machined cannons.
*[http://www.spudfiles.com/forums/t-t17090.html Small Pistol Grip Combustion, by CrashTestDummy II.] Demonstrating that simple cannons need not look it.
*[http://www.spudfiles.com/forums/t-t15766.html Mk2 Rotary barrelled Combustion, by Critical_Al.] Very well made "Rapid-fire" combustion.
*[http://www.spudfiles.com/forums/t-t4960.html Taternator II, by Dumbascii.] Taking combustion and just throwing overkill at it.
*[http://www.spudfiles.com/forums/t-t14319.html Wood Combustion, by Eddbot.] Not so serious, and not the world's best technical example, but worth a look, because most people like it.
*[http://www.spudfiles.com/forums/t-t17794.html The BL520, by jagerbond.] (Reviewed by PCGUY). A well thought out and built cannon from Spudfiles' sponsor.
*[http://www.spudfiles.com/forums/t-t16725.html The Gauntlet of Clara Ann, by Radiation.] For having one of the most grandiloquent cannon names on the forum.
*[http://www.spudfiles.com/forums/t-t7878.html Blue Flame III, by Sgort87.] Again, demonstrations of improving rate of fire.
*[http://www.spudfiles.com/forums/t-t6241.html Collapsible travel combustion, by Sgort87.] Neat concept for a telescoping cannon.
*[http://www.spudfiles.com/forums/t-t1575.html Proton Pack, by Sgort87.] Backpack based chamber, sometimes considered for a cannon design.
*[http://www.spudfiles.com/forums/t-t2736.html 12" Diameter bucket launcher, by Sgort87.] He does a lot of good combustions. Also, adventurous sizewise.
*[http://www.spudfiles.com/spud_wiki/index.php/Quick_Dump_Valve Quick Dump Valve by Technician1002. A reliable air valve that is mechanically triggered and reset for higher reliability than conventional piston valves.
*[http://www.spudfiles.com/forums/t-t15211.html Triple Thunder cannons, by Starman.] Neatly built, well known and good performers - they had to make the list.

'''Hybrid'''
*[http://www.spudfiles.com/forums/t-t16882.html BACH, by Daccel.] Although not finished, this is one of the most viable methods to speed up hybrid operation.]
*[http://www.spudfiles.com/forums/t-t6822.html HPSCL, by DR.] Often known as the Gen-II tank, an early example (reposted here) of developments in hybrid fuelling.
*[http://www.spudfiles.com/forums/t-t9589.html Piston Hybrid, by Fnord.] A demonstration of an alternate hybrid valve.
*[http://www.spudfiles.com/forums/t-t7857.html FEAR, by Killjoy.] Just a big ass hybrid. Former holder of the spudgun velocity record.
*[http://www.spudfiles.com/forums/t-t15524.html HyGaC20, by Larda.] Current holder of spudgun velocity, and preignition mix pressure records. Also nice to look at.
*[http://www.spudfiles.com/forums/t-t17948.html The Cobra Venom, by Moonbogg.] A record of the production of a high quality machined hybrid.

'''BBMG/Strafer'''
*[http://www.spudfiles.com/forums/t-t13762.html Deathray, by Brian the Brain.] Simplify, and add pressure.
*[http://www.spudfiles.com/forums/t-t12907.html RC-P240 Vortex cap BBMG, by Imortal87.] A good method of adding magazines to a BBMG.
*[http://www.spudfiles.com/forums/t-t10075.html 6mm Semi by Jackssmirkingrevenge.] Not so much a BBMG, but absolutely great for learning about blow forward loaders.
*[http://www.spudfiles.com/forums/t-t17845.html "I has full auto", by Jackssmirkingrevenge.] Jack finally builds a full auto pulsed BBMG after... I've forgotten. A long time, either way.
*[http://www.spudfiles.com/forums/t-t16441.html Ultimate Inline Mk IIIi, by Neospud.] Showing you how a BBMG should be done for practical field use.

'''Mini'''

*[http://www.spudfiles.com/forums/t-t7858.html Pneumatic Pengun, by Jackssmirkingrevenge.] For being one of the first examples of less ghetto minis.
*[http://www.spudfiles.com/forums/t-t18619.html Keychain Pengun, by jor2daje.] Nigh on minuscule, and with a mini pump
*[http://www.spudfiles.com/forums/t-t17102.html Mini Keychain, by jook13.] For being the first keychain spudgun.
*[http://www.spudfiles.com/forums/t-t17408.html 300 WinMag Coax, by jook13.] A gun... inside a bullet.

And thus we prove that success in Minis depends on a username starting with a J.

'''Other'''
*[http://www.spudfiles.com/forums/t-t13449.html 28.8kj Electrothermal cannon, by Larda.] Cannon powered by plasma. Somehow even more impressive than it sounds.

==Articles==

'''General Forum'''
*[http://www.spudfiles.com/forums/t-t14659.html A ''VERY'' worthwhile read on spudgunning and the forums.] A read of this will get you pretty up to date with the forum's workings.
*[http://www.spudfiles.com/forums/t-t16568.html A spudder's tale.] Not essential reading, but nice anyway.
*[http://www.spudfiles.com/forums/posting-images-a-step-by-step-guide-t13190.html Posting images a step-by-step guide.] How to post images on Spudfiles properly.
*[http://www.spudfiles.com/forums/rules.html Rules.] Main forum rules.
*[[The reasons behind the rules | Explanation of rules that sometimes raise questions.]]
*[http://www.spudfiles.com/forums/viewtopic,p,136508.html#136508 Posting Etiquette.] Posting rules for the Spudfiles forum, differs from the main forum rules.
*[[Why aren't my questions being answered?]] For if you've asked a question, but you're getting responses like "Do your own research".

'''Forum In-jokes'''
*[http://www.spudfiles.com/forums/t-t13069.html How to deal with frustration.] The famous *facepalmheaddeskcombo* explained.
*[http://www.spudfiles.com/forums/viewtopic,p,133222.html#133222 The Flaming Pink Elephant.] A metaphor for the forum's innuendo, as this is what it is as subtle as.
*[[Spudfiles Forum Jokes]] Worth a read, to help you gauge the forum's sense of humo(u)r before you misinterpret something.
*[[Tools redefined]]: What tools really are.

'''Safety'''
*[http://www.spudfiles.com/forums/t-t7783.html Things not to do.] A list of accidents people have had, and in many cases, how it could have been avoided.
*[http://www.spudfiles.com/forums/t-t15301.html A tale of shooting yourself in the face.] Again, more accidents.
*[http://www.spudfiles.com/forums/t-t11431.html Predicting if your cannon's recoil is likely to be dangerous.] It is inadvisable for a hand fired cannon to exceed 100 ft-lbs (135 J) of recoil, and even this will be unpleasant.

'''Construction'''
*[http://www.spudfiles.com/forums/t-t8157.html How piston valves work.] An explanation of what is arguably the best valve in spudding.
*[http://www.spudfiles.com/forums/t-t11866.html High pressure compressors.] How to adapt fridge parts into the spudder's high pressure solution.
*[http://www.spudfiles.com/forums/t-t2546.html A solution to rifling.] How to rifle a PVC barrel.
*[http://www.spudfiles.com/forums/t-t10381.html How to make a cannon with 2" piston valve.] How to make a 2" piston valve.
*[http://www.spudfiles.com/forums/t-t3009.html Solvent Welding Course.] An online course on how to solvent weld PVC correctly.
*[http://www.spudfiles.com/forums/t-t18108.html Suppressor Tutorial.] Quite a long video, but lots of information on suppressor (or silencer, if you must) construction.

'''Projectiles'''
*[http://www.spudfiles.com/forums/t-t16438.html A fairly interesting thread on projectile shape vs. drag.] It's a bit incoherent at times, but worth the study.
*[http://www.spudfiles.com/forums/t-t13477.html A theory on dart development.]

'''Aesthetics'''
* [http://www.spudfiles.com/forums/t-t15767.html Making a stock for your launcher?] This will be worth some reading.

Quick Dump Valve

2009-08-06T22:55:00Z

Technician1002: /* The Quick Dump Valve */

'''Article Flag''' 
As an article relating to spudding hardware, this should be presented in a more neutral format - it currently reads like an advertisement. 
It should also be presented in a third person point of view, as newcomers won't be able to associate "I" or "Me" usefully. 
Flagged by [[User:Ragnarok|Ragnarok]] 20:32, 29 July 2009 (EDT)

== The Quick Dump Valve ==

The quick dump valve is a variation on a traditional barrel sealer piston valve. In the section on piston valves, various configurations are covered and the advantages and disadvantages of each. A quick dump valve may be used where the traditional valves shortcomings cause problems for the builder. It was noted in the piston valve section in the wiki that as a barrel sealer valve nears a 1:1 ratio, the pilot pressure needed to open the valve drops lower, and when they pop open, they do so with more force and speed. They become temperamental as the ratio approaches a 1:1 ratio as the force to start opening the valve drops. They tend to stick or are unable to vent the pilot low enough to fire it. As a result, piston valves that won't fire are a common problem.

The Quick Dump Valve or QDV was built to take advantage of close ratio piston valve advantages of speed while fixing the disadvantages of the temperamental nature of them failing to fire reliably or seal properly to build chamber pressure.

Spool valves are balanced design valves with several o rings that move past ports and are operated by the rings crossing ports to join some in the same segment or separate them. They are noted for the ability to switch high pressures with little force to operate the valve. Typical uses are the hydraulic controls on heavy machinery such as a backhoe. Normal spool valves have both ends of the valve rod at atmospheric pressure.

A QDV when closed has the appearance of a spool valve. The air source under pressure is sealed off in the chamber with an o ring on both sides of the port. What makes this different than a typical spool valve is when it is opened, the supply pressure is then applied to the end of the spool. This pressure provides a positive feedback to the spool so as it opens, the force opening it rapidly increases as supply pressure in the outlet port pushes on the piston.

Unlike a piston valve that uses pressure in a "Pilot" area to hold the valve closed, the QDV has no pressure on the pilot area of the piston to hold it closed. In this manner it is much like a spool control valve.

A video on the valve theory is posted here; [http://www.youtube.com/watch?v=No3nI07mlQo The Quick Dump Valve]

The first appearance of the Quick Dump Valve in an air cannon is covered in a contest for building t shirt launchers;
[http://inteltrailblazerschallenge.wikispaces.com/The+brag+zone IntelTrailBlazers Engineering Challenge]

The first mention of the valve on Spudfiles is in this thread.
[http://www.spudfiles.com/forums/interesting-new-valve-design-t17617.html Interesting New Valve Design]

This is a video of the T Shirt launcher in action. The team won the competition with this design.
[http://www.youtube.com/watch?v=9Klxqav_6NM Quick Reload T Shirt launcher]

Quick Dump valves can be constructed as either a coaxial design with the valve inside a chamber, or built inside a T for an external valve. I prefer the coaxial designs myself for the best COF values possible.

[[Image:WikiOverview.jpg]]

The oldest is constructed with ABS. The valve is located in the breech of the chamber. The barrel is a long pipe that extended all the way though the chamber with ports cut into the pipe between the chamber and barrel. A plastic bag was stuffed into the barrel to highlight the ports for the photo. Otherwise they were too dark to see very well.

[[Image:ValvePorts1.JPG]]

This design works well. The drawbacks are the piston needs a rod shoved into the breech rope pull hole to reset the valve between shots and the design did not use floating o rings, so it pulls a little hard.

The piston is made from a piece of PVC pipe and a couple pipe caps and o rings. Any sturdy cylindrical object can be used that will hold the pressure and forces.

[[Image:CoreDetail.JPG]]

For safety on this design, it is very important to remember that shoving anything into the barrel does the same thing as pulling the rope. It opens the valve. ''' Never shove anything into this design of valve while it is under pressure.''' Load it and then add pressure.

The spudfiles page on the cannon is here;
[http://www.spudfiles.com/forums/abs-cellular-core-test-cannon-t17968.html ABS Cellular Core Test Cannon, also known as the apple cannon]
It was posted as a materials test discussion on using unrated plastic pipe in air cannons.

Later improvements to the design included using a rod instead of a rope to open and close the valve. The piston if permitted to slide freely on the rod can be made to operate quickly without having to accelerate the control trigger rod. In operation, when the rod is pushed in, a pin on the rod pushes the piston closed. To fire the rod is pulled back through the piston which retracts the pin behind the piston out of the piston travel area. Then a nut on the end of the rod pushes the front of the piston pulling it open triggering it. Once the valve cracks open, the air pressure between the piston and projectile pushes the valve open with the same pressure it applies to the projectile.

The valve can be relocated to the barrel end of the chamber.
This permits easy detachment of the barrel and the ability to attach various size barrels with minimum dead space.

A model of the T Shirt launcher shows the construction detail with the improvements. In Spudfiles, it is called the Marshmallow Cannon. It was built for a high speed marshmallow launching competition. With a removable and interchangeable barrel selection, it is easy to adapt to shooting gumballs, jawbreakers, batteries, tennis balls, and t shirts. With a 36 inch long t shirt barrel the 1 inch valve is able to toss shirts 200 feet.

The Spudfiles entry is here;
[http://www.spudfiles.com/forums/quick-dump-valve-t17858.html The Quick Dump Valve]
The spudfiles entry has links to a theory of operation video as well as more photos.

The tank as before is coaxial design with a valve body in the center. Unlike the earlier design, the barrel is removable and the valve is located at the barrel end of the chamber instead of the breech. The new design uses a rod to trigger and reset the valve.

[[Image:WikiTank.jpg]]

The valve core removed from the tank shows the piston with floating rings, rod, bumper, stopper, and trigger and reset pins.

[[Image:WikiVavleCoreAssy.jpg]]

A close up view of the piston shows the o rings fit loose in a floating O Ring design. The spudfiles page and linked videos show how this style of o ring installation lowers the friction in the valve.

[[Image:Piston_rings.jpg]]

The ports between the chamber and valve body can be seen inside the valve.

[[Image:WikiTankEnd.jpg]]

View of the assembled cannon with the tennis ball barrel. It tosses tennis balls 100 yards.

[[Image:Tennis_ball_barrel1.jpg]]

With high speed of operation and a high flow, the cannon is able to deliver high speeds. The photo is a 2X4 that was split with a couple jawbreakers.

[[Image:Split1a.JPG]]

Photos are copyright by Technician1002. Please ask before using elsewhere.

File:Crown.JPG

2009-08-05T00:12:45Z

Technician1002: High res photo of heat crowned 2.5 inch barrel. Edge was heated and then shoved onto the top of a full 2 liter pop to form the crown.

High res photo of heat crowned 2.5 inch barrel. Edge was heated and then shoved onto the top of a full 2 liter pop to form the crown.

Piston valve

2009-08-01T00:48:20Z

Technician1002: /* O-Ring Considerations on a Piston Valve */

A '''piston valve''' is a [[pilot]] operated [[valve]]. It is very similar to a [[diaphragm valve]] in theory, but replaces it's flexible diaphragm with a rigid cylinder. There are 2 varieties; [[barrel]] sealing and [[chamber]] sealing.

== Barrel sealing valve ==

In a barrel sealing valve, the piston seals against the breech of the barrel. This is the most common piston valve design.

=== construction ===

The piston is often a well fitting cup-shaped object, such as a end cap. To provide a sealing face, a piece of rubber is attached, typically with a bolt. In the simplest case, equalization is accomplished by allowing the air to leak past the piston and into the chamber. Some people will machine their own pistons, in which case they often build [[O-ring]]s into them. With the O-rings, you need to make a small equalization hole; sometimes this is fancied up to be a homemade [[check valve]].

Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recommended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labeled "'''F'''" in the "use, barrel sealing" diagram.

These valves are often used on [[coaxial]]s and [[over/under]]s. In an over/under, the valve is built in a "T" fitting. The barrel is put co-axially through one end, the pilot and piston are put in the opposite one, and a chamber is connected to the perpendicular opening with a 90° elbow.

=== Use ===
[[Image:Wpiston.PNG|frame|top=pressurized, bottom=firing]]
Operation:
#Air is added by filling behind the piston (C).
#The piston (E) slides forwards, and seals against the barrel (A). (Alternatively, one can use a spring to move the piston forwards, which allows one to fill [slowly at first, to allow the [[pressure]] to equalize] from the chamber.)
#More air is added, and leaks around the piston (or through a small equalization hole) and into the chamber (B), filling it to the desired pressure.
#The [[pilot valve]] (D) behind the piston is opened, the pressure in the pilot volume (C) drops, and the higher pressure in the chamber area pushes the piston away from the barrel.
#The air flows around from the chamber, and into the barrel, propelling the projectile.

== Chamber sealing piston valve ==

=== construction ===

The piston of a chamber-sealing piston valve has to seal on both the chamber port and to the pilot volume. This requires that the piston be machined with [[O-ring]]s. A small equalization hole is required; sometimes this is fancied up to be a homemade [[check valve]].

The piston is almost always housed in a "t" fitting.

Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recommended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labeled "'''F'''" in the "use, chamber sealing sealing" diagram.

These valves are often used on [[over/under]]s, as the flow is already turned around 90o.

=== Use ===
[[Image:Wcspiston.PNG|frame|top=pressurized, bottom=firing]]
Operation:
#Air is added by filling behind the piston (C).
#The piston (E) slides forwards, and seals against the barrel (A). (Alternatively, one can use a spring to move the piston forwards, which allows one to fill [slowly at first, to allow the [[pressure]] to equalize] from the chamber.)
#More air is added, and leaks through the equalization hole in the piston and into the chamber (B), filling it to the desired pressure.
#The [[pilot valve]] (D) behind the piston is opened, the pressure in the pilot volume (C) drops, and the higher pressure in the chamber area pushes the piston away from the chamber.
#The air flows out of the chamber, and into the barrel, propelling the projectile.

== Common traits ==

#The performance of these valves can be calculated with the [[GGDT]].
#If your valve [[honking|honks]], it is probably a good idea to invest in a better pilot valve, though this is more of a problem with barrel-sealing valves.
#In both cases, provided there is a good deal of space around the barrel, the full flow potential of the valve is realized when the piston has moved back 1/4th of the barrel's inside diameter (I.D./4). The derivation of this formula is as follows:

Given: A = Pi(R)^2
C = 2PiR
T = Piston travel
R = I.D. of barrel / 2

When the piston moves back, the smallest amount of area exposed is either the area of the circular cross section of the barrel or the area exposed by the piston, which is the side of a cylinder, the bases being the barrel and piston face. The optimal ratio of area exposed between the 2 spots is 1:1, which means the exposed areas should be the same. So one sets the equations A and CT equal, that is A = CT.

Pi(R)^2 = 2PiR(T)

Solving for "T" results in:

R/2 = T which, if one substitutes I.D./2 for R, results in:

I.D./4 = T

Many people choose to open larger to provide only one restriction to flow instead of 2 the same size in a row. This is done by allowing the valve to open fully unrestricted and then compress the bumper while opening further. This provides the fastest possible opening time by preventing the piston deceleration while still opening.

#Pneumatic actuation is not mandatory; mechanical means can be used to hold the valve shut, or open it, rather than using the force of the air.

***The following section submitted by Technician1002***

The operation of barrel sealing valves falls into 3 categories which is related to the dimensions of the barrel seal or seat to the piston outside diameter.

=== Large Ratio Piston Valve ===
When the ratio is large in a barrel sealer with either a large piston or small barrel, most of the force to open the valve is controlled by the differential of the chamber pressure and pilot area. As the valve opens, the small area that becomes exposed to the chamber as it opens contributes little to the opening speed. This large area ratio valve are noted for reliable operation as they have the ability to open pistons that don't slide well. Due to the pressure still in the pilot area as they open, as the chamber vents out the barrel, it is often faster than the pilot, so the force used to open the valve vanishes and the pilot pressure unable to keep up with the drop, forces the valve to close. If this repeats as the pilot vents, it is noticeable as honking. This class of valves include pistons with a 2:1 diameter ratio or more. A 2:1 diameter ratio is a 4:1 area ratio. These are not QEV valves because the area sealed by the piston is only 25% of the pilot area so when the valve opens the force change is small. It opens with the pilot at 3/4 the pressure of the chamber. When it opens and the pilot volume is reduced by the piston moving into the pilot space, the rise in pressure in the pilot prevents the piston from opening all the way, so opening speed is directly related to how much faster the pilot can vent over the rate the chamber vents out the barrel. A slow pilot equals a slow valve and may cause honking.

In a chamber sealer version where the valve seat seals against the chamber, they are fast as the pressure is released and more pressure presses on the larger exposed face of the piston. This style tends to have a fairly large dead space between the valve and projectile. In addition a large piston has a greater mass and as the piston moves, it requires a larger displacement using much of the chamber air energy. If the valve seat is small to use a smaller piston, the small orifice chokes the flow.

=== Small Ratio or QEV ===
As the ratio of the seat diameter to piston diameter is reduced, the area that the chamber is exposed to is reduced, to the point that the large area of the pilot is able to hold the piston closed until most of the pilot pressure is vented. Even when the pilot area is vented to a low pressure, the initial opening force is low because the area of the piston exposed to the chamber pressure is small as most of the face of the piston is exposed to no pressure in the barrel. This low opening force can cause many headaches with stuck pistons that sometimes fail to fire, and the equalization port may vent enough volume to prevent the pilot area from reaching a low enough pressure to open the valve. The lower the seat to diameter ratio; the lower the initial force the chamber can apply to open the valve, and the faster they snap open when they do get over the initial opening. This faster speed is due to the larger piston face exposed to the chamber pressure when the valve opens and the lower pressure in the pilot area. The lower pressure compresses less and provides less force on the back of the piston when it opens. The closer the ratio is to 1:1 the faster the avalanche, but the initial cracking open of the valve becomes slower as the initial opening force is lower and lower as you approach a 1:1 ratio.

One attractive feature of this valve is once it unseats and starts to open, the chamber pressure now acting on the face of the piston causes a large spike in opening force as the large barrel facing area is now exposed to the chamber pressure. This type of valve snaps open and is known as a Quick Exhaust Valve or QEV. This style valve is not prone to closing early and honking.

[[Image:MusketSeat.JPG ]]

The barrel sealer QEV piston valve has a large diameter seat in relation to the overall diameter of the piston.
A chamber sealer has a small seat in relation the the overall diameter so the force on the piston grows rapidly as the valve opens.

Chamber sealer valves have a disadvantage of needing a larger diameter piston for the same size valve seat as a barrel sealer. This adds mass and dead space between the valve piston and projectile. On the positive side, they are more reliable in opening and tend to have most of the opening acceleration early in the opening where it is needed. The drop in acceleration as the valve opens can increase the life expectancy of the valve as they compress the pilot area they slow before impact with the back of the breech.

=== 1:1 Ratio or QDV ===
A new page dedicated to the QDV is here;
[http://www.spudfiles.com/spud_wiki/index.php/Quick_Dump_Valve Quick Dump Valve Piston]

If the ratio of the piston diameter is reduced to the diameter of the valve seat in a spool valve, then the valve won't open even when the pilot area is not under pressure. If the chamber is pressurized and no pressure is in the pilot area, the valve has the least back pressure of any of the piston valves and therefore the fastest opening when the valve is unseated by force. Even though the pilot area may half in volume as the piston moves into this space, the pressure rise from 1 atm to 2 atm is still less than the chamber force on the newly exposed face of the piston, so this piston will open fast regardless of the vent size or speed. This last category of piston valve is known as a Quick Dump Valve. To operate this valve in an air cannon, consideration must be made to mechanically move the piston and when the piston moves, the force will avalanche quickly as the piston face becomes exposed to the chamber pressure. For mechanical trigger the use a rope pull or a rod with a "sliding" piston are options to a spring or air start. The loose piston on a rope or rod provides speed as the core can accelerate freely when triggered. Decoupling the triggering mechanism from the piston prevents the trigger from adding to the moving mass of the piston. These valves are not subject to honking, but may "bounce" back closed after the shot by the pressure built up in the pilot area and bumper recoil after the chamber pressure is gone.

[[Image:QDV_parts.JPG]]

Assembled 1 inch QDV cannon and damaged can. Projectile was a 1 inch jawbreaker.
[[Image:Marshmallow_cannon.jpg]]

The quick dump valve has the piston OD the same size as the seat. It requires an external force to start it opening. It has no pilot pressure to hold it against a seat so it is often built with o rings on a piston. The valve cylinder can be built out of a pipe with ports cut in the side.

A video on the theory of the QDV cannon is here.
[http://www.youtube.com/watch?v=No3nI07mlQo The Quick Dump Valve]

=== O-Ring Considerations on a Piston Valve ===
To prevent stuck piston valves, consideration must be given to permit a good seal while not stopping movement.

To prevent stuck or hard to move pistons the o ring should not be compressed flat against the cylinder wall. Since movement is desirable, as well as a seal, we can design the piston to seal without needing to squeeze the o ring. The following video shows the theory fairly well.

[http://www.youtube.com/watch?v=BbDiZiRVrnk Youtube video on using o rings in air cannons]

At 4:20 in the video the force needed to move this piston is shown.

Instead of having O rings in a groove that sit tight against the bottom of the groove and then are compressed by the cylinder, floating rings do not bottom out in the o ring groove. To seal, the pressure trying to blow past the ring seats it against the side of the o ring groove. Air that is able to get under the ring presses outward to apply pressure to the cylinder wall. As the pressure is increased, this force is increased so higher operating pressures make a tighter seal and a little higher friction to movement.

Floating piston rings fit loose in the grooves. The o ring is sized to be slightly larger than the cylinder diameter it slides inside.
This photo is of a 1 inch quick dump valve piston.

[[Image:Piston_rings.jpg]]

Here is a drawing showing the force of the pressure on the o ring to provide a tight seal.

[[Image:123_floatingpneumatic1.jpg]]

Source: RL Hudson O-Ring Design & Materials Guide. Used with permission.

[[category:valves]]

File:123 floatingpneumatic1.jpg

2009-08-01T00:47:44Z

Technician1002: Source: RL Hudson O-Ring Design & Materials Guide. Used with permission.

Source: RL Hudson O-Ring Design & Materials Guide. Used with permission.

Piston valve

2009-08-01T00:45:11Z

Technician1002: /* O-Ring Considerations on a Piston Valve */

A '''piston valve''' is a [[pilot]] operated [[valve]]. It is very similar to a [[diaphragm valve]] in theory, but replaces it's flexible diaphragm with a rigid cylinder. There are 2 varieties; [[barrel]] sealing and [[chamber]] sealing.

== Barrel sealing valve ==

In a barrel sealing valve, the piston seals against the breech of the barrel. This is the most common piston valve design.

=== construction ===

The piston is often a well fitting cup-shaped object, such as a end cap. To provide a sealing face, a piece of rubber is attached, typically with a bolt. In the simplest case, equalization is accomplished by allowing the air to leak past the piston and into the chamber. Some people will machine their own pistons, in which case they often build [[O-ring]]s into them. With the O-rings, you need to make a small equalization hole; sometimes this is fancied up to be a homemade [[check valve]].

Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recommended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labeled "'''F'''" in the "use, barrel sealing" diagram.

These valves are often used on [[coaxial]]s and [[over/under]]s. In an over/under, the valve is built in a "T" fitting. The barrel is put co-axially through one end, the pilot and piston are put in the opposite one, and a chamber is connected to the perpendicular opening with a 90° elbow.

=== Use ===
[[Image:Wpiston.PNG|frame|top=pressurized, bottom=firing]]
Operation:
#Air is added by filling behind the piston (C).
#The piston (E) slides forwards, and seals against the barrel (A). (Alternatively, one can use a spring to move the piston forwards, which allows one to fill [slowly at first, to allow the [[pressure]] to equalize] from the chamber.)
#More air is added, and leaks around the piston (or through a small equalization hole) and into the chamber (B), filling it to the desired pressure.
#The [[pilot valve]] (D) behind the piston is opened, the pressure in the pilot volume (C) drops, and the higher pressure in the chamber area pushes the piston away from the barrel.
#The air flows around from the chamber, and into the barrel, propelling the projectile.

== Chamber sealing piston valve ==

=== construction ===

The piston of a chamber-sealing piston valve has to seal on both the chamber port and to the pilot volume. This requires that the piston be machined with [[O-ring]]s. A small equalization hole is required; sometimes this is fancied up to be a homemade [[check valve]].

The piston is almost always housed in a "t" fitting.

Because a piston is heavier and harder than a diaphragm, and PVC is somewhat brittle, it is recommended that a bumper of sorts is built into your pilot volume. Common bumpers include heavy-duty rubber hose, and such. This is labeled "'''F'''" in the "use, chamber sealing sealing" diagram.

These valves are often used on [[over/under]]s, as the flow is already turned around 90o.

=== Use ===
[[Image:Wcspiston.PNG|frame|top=pressurized, bottom=firing]]
Operation:
#Air is added by filling behind the piston (C).
#The piston (E) slides forwards, and seals against the barrel (A). (Alternatively, one can use a spring to move the piston forwards, which allows one to fill [slowly at first, to allow the [[pressure]] to equalize] from the chamber.)
#More air is added, and leaks through the equalization hole in the piston and into the chamber (B), filling it to the desired pressure.
#The [[pilot valve]] (D) behind the piston is opened, the pressure in the pilot volume (C) drops, and the higher pressure in the chamber area pushes the piston away from the chamber.
#The air flows out of the chamber, and into the barrel, propelling the projectile.

== Common traits ==

#The performance of these valves can be calculated with the [[GGDT]].
#If your valve [[honking|honks]], it is probably a good idea to invest in a better pilot valve, though this is more of a problem with barrel-sealing valves.
#In both cases, provided there is a good deal of space around the barrel, the full flow potential of the valve is realized when the piston has moved back 1/4th of the barrel's inside diameter (I.D./4). The derivation of this formula is as follows:

Given: A = Pi(R)^2
C = 2PiR
T = Piston travel
R = I.D. of barrel / 2

When the piston moves back, the smallest amount of area exposed is either the area of the circular cross section of the barrel or the area exposed by the piston, which is the side of a cylinder, the bases being the barrel and piston face. The optimal ratio of area exposed between the 2 spots is 1:1, which means the exposed areas should be the same. So one sets the equations A and CT equal, that is A = CT.

Pi(R)^2 = 2PiR(T)

Solving for "T" results in:

R/2 = T which, if one substitutes I.D./2 for R, results in:

I.D./4 = T

Many people choose to open larger to provide only one restriction to flow instead of 2 the same size in a row. This is done by allowing the valve to open fully unrestricted and then compress the bumper while opening further. This provides the fastest possible opening time by preventing the piston deceleration while still opening.

#Pneumatic actuation is not mandatory; mechanical means can be used to hold the valve shut, or open it, rather than using the force of the air.

***The following section submitted by Technician1002***

The operation of barrel sealing valves falls into 3 categories which is related to the dimensions of the barrel seal or seat to the piston outside diameter.

=== Large Ratio Piston Valve ===
When the ratio is large in a barrel sealer with either a large piston or small barrel, most of the force to open the valve is controlled by the differential of the chamber pressure and pilot area. As the valve opens, the small area that becomes exposed to the chamber as it opens contributes little to the opening speed. This large area ratio valve are noted for reliable operation as they have the ability to open pistons that don't slide well. Due to the pressure still in the pilot area as they open, as the chamber vents out the barrel, it is often faster than the pilot, so the force used to open the valve vanishes and the pilot pressure unable to keep up with the drop, forces the valve to close. If this repeats as the pilot vents, it is noticeable as honking. This class of valves include pistons with a 2:1 diameter ratio or more. A 2:1 diameter ratio is a 4:1 area ratio. These are not QEV valves because the area sealed by the piston is only 25% of the pilot area so when the valve opens the force change is small. It opens with the pilot at 3/4 the pressure of the chamber. When it opens and the pilot volume is reduced by the piston moving into the pilot space, the rise in pressure in the pilot prevents the piston from opening all the way, so opening speed is directly related to how much faster the pilot can vent over the rate the chamber vents out the barrel. A slow pilot equals a slow valve and may cause honking.

In a chamber sealer version where the valve seat seals against the chamber, they are fast as the pressure is released and more pressure presses on the larger exposed face of the piston. This style tends to have a fairly large dead space between the valve and projectile. In addition a large piston has a greater mass and as the piston moves, it requires a larger displacement using much of the chamber air energy. If the valve seat is small to use a smaller piston, the small orifice chokes the flow.

=== Small Ratio or QEV ===
As the ratio of the seat diameter to piston diameter is reduced, the area that the chamber is exposed to is reduced, to the point that the large area of the pilot is able to hold the piston closed until most of the pilot pressure is vented. Even when the pilot area is vented to a low pressure, the initial opening force is low because the area of the piston exposed to the chamber pressure is small as most of the face of the piston is exposed to no pressure in the barrel. This low opening force can cause many headaches with stuck pistons that sometimes fail to fire, and the equalization port may vent enough volume to prevent the pilot area from reaching a low enough pressure to open the valve. The lower the seat to diameter ratio; the lower the initial force the chamber can apply to open the valve, and the faster they snap open when they do get over the initial opening. This faster speed is due to the larger piston face exposed to the chamber pressure when the valve opens and the lower pressure in the pilot area. The lower pressure compresses less and provides less force on the back of the piston when it opens. The closer the ratio is to 1:1 the faster the avalanche, but the initial cracking open of the valve becomes slower as the initial opening force is lower and lower as you approach a 1:1 ratio.

One attractive feature of this valve is once it unseats and starts to open, the chamber pressure now acting on the face of the piston causes a large spike in opening force as the large barrel facing area is now exposed to the chamber pressure. This type of valve snaps open and is known as a Quick Exhaust Valve or QEV. This style valve is not prone to closing early and honking.

[[Image:MusketSeat.JPG ]]

The barrel sealer QEV piston valve has a large diameter seat in relation to the overall diameter of the piston.
A chamber sealer has a small seat in relation the the overall diameter so the force on the piston grows rapidly as the valve opens.

Chamber sealer valves have a disadvantage of needing a larger diameter piston for the same size valve seat as a barrel sealer. This adds mass and dead space between the valve piston and projectile. On the positive side, they are more reliable in opening and tend to have most of the opening acceleration early in the opening where it is needed. The drop in acceleration as the valve opens can increase the life expectancy of the valve as they compress the pilot area they slow before impact with the back of the breech.

=== 1:1 Ratio or QDV ===
A new page dedicated to the QDV is here;
[http://www.spudfiles.com/spud_wiki/index.php/Quick_Dump_Valve Quick Dump Valve Piston]

If the ratio of the piston diameter is reduced to the diameter of the valve seat in a spool valve, then the valve won't open even when the pilot area is not under pressure. If the chamber is pressurized and no pressure is in the pilot area, the valve has the least back pressure of any of the piston valves and therefore the fastest opening when the valve is unseated by force. Even though the pilot area may half in volume as the piston moves into this space, the pressure rise from 1 atm to 2 atm is still less than the chamber force on the newly exposed face of the piston, so this piston will open fast regardless of the vent size or speed. This last category of piston valve is known as a Quick Dump Valve. To operate this valve in an air cannon, consideration must be made to mechanically move the piston and when the piston moves, the force will avalanche quickly as the piston face becomes exposed to the chamber pressure. For mechanical trigger the use a rope pull or a rod with a "sliding" piston are options to a spring or air start. The loose piston on a rope or rod provides speed as the core can accelerate freely when triggered. Decoupling the triggering mechanism from the piston prevents the trigger from adding to the moving mass of the piston. These valves are not subject to honking, but may "bounce" back closed after the shot by the pressure built up in the pilot area and bumper recoil after the chamber pressure is gone.

[[Image:QDV_parts.JPG]]

Assembled 1 inch QDV cannon and damaged can. Projectile was a 1 inch jawbreaker.
[[Image:Marshmallow_cannon.jpg]]

The quick dump valve has the piston OD the same size as the seat. It requires an external force to start it opening. It has no pilot pressure to hold it against a seat so it is often built with o rings on a piston. The valve cylinder can be built out of a pipe with ports cut in the side.

A video on the theory of the QDV cannon is here.
[http://www.youtube.com/watch?v=No3nI07mlQo The Quick Dump Valve]

=== O-Ring Considerations on a Piston Valve ===
To prevent stuck piston valves, consideration must be given to permit a good seal while not stopping movement.

To prevent stuck or hard to move pistons the o ring should not be compressed flat against the cylinder wall. Since movement is desirable, as well as a seal, we can design the piston to seal without needing to squeeze the o ring. The following video shows the theory fairly well.

[http://www.youtube.com/watch?v=BbDiZiRVrnk Youtube video on using o rings in air cannons]

At 4:20 in the video the force needed to move this piston is shown.

Instead of having O rings in a groove that sit tight against the bottom of the groove and then are compressed by the cylinder, floating rings do not bottom out in the o ring groove. To seal, the pressure trying to blow past the ring seats it against the side of the o ring groove. Air that is able to get under the ring presses outward to apply pressure to the cylinder wall. As the pressure is increased, this force is increased so higher operating pressures make a tighter seal and a little higher friction to movement.

Floating piston rings fit loose in the grooves. The o ring is sized to be slightly larger than the cylinder diameter it slides inside.
This photo is of a 1 inch quick dump valve piston.

[[Image:Piston_rings.jpg]]

Here is a drawing showing the force of the pressure on the o ring to provide a tight seal.

[[Image:123_floatingpneumatic.jpg]]

Source: RL Hudson O-Ring Design & Materials Guide. Used with permission.

[[category:valves]]