SpudFiles Wiki - User contributions [en]

Piston valve

2008-10-08T23:15:43Z

Pilgrimman: /* 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.

== 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 90<sup>o</sup>.

=== 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

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

[[category:valves]]

Pneumatic cannon

2008-05-04T21:10:45Z

Pilgrimman:

[[image:pneumatic ballvalve cannon.jpg|right|thumb|300px|Pneumatic ball valve cannon]]
A '''pneumatic cannon''' is a cannon powered by pressurized gas, usually air or CO2. They generally require a little more work to build than [[combustion cannon]]s, but using typical compressor pressures and a decent valve, they will outperform most combustion launchers of the same size.

==Basic Elements==

Pneumatic launchers consist of five basic elements:

*Compressed gas storage reservoir ([[chamber]] for short)
*Filling valve (bicycle [[Schrader valve]]s, [[quick disconnect]]s, etc.)
*Firing valve ([[ball valve]]s, [[sprinkler valve]]s, [[piston valve]]s, bolt-style valves(see piston valves) [[quick-exhaust valve]]s, and [[burst disk]]s are the most common)
*[[Barrel]]
*[[Pressure gauge]] (for safety & repeatable launches)

==Operation & Theory==

In order to fire, the operator loads a projectile into the barrel, fills the chamber with a compressed gas (see [[Pneumatic air sources]] for common filling methods), and activates the main valve thus dumping the air in the chamber to the barrel.

The expansion of the compressed gas propels the projectile down the barrel. The barrel length determines the amount of time the projectile has to accelerate and ultimately the velocity of the projectile.

Higher performance launchers use techniques such as:
* Faster valve opening times - see [[sprinkler valve modification]]
* Higher flow valves to maximize the airflow through the valve (Especially true for cannons with very long barrels)
* Using higher gas pressures.

Less common, but also effective in increasing power, some people will also use a gas with a higher speed of sound and particle speed (e.g. helium).

Efficiency of a cannon can be roughly determined by observing how much noise it makes when fired. A relatively quiet gun is often efficient, as there is little energy left over to create sound.

==Common types of launchers==

'''Ball Valve Launchers'''

Ball Valve Launchers release pressurized gas by way of a ball valve. These valves can be made of metal or plastic, and are available in many sizes and pressure ratings. Ball valves are simple to operate, and have very high flow. However, their opening times are comparitively long compared to other valves such as piston valves. Ball valves are typically used in simple designs, or on launchers with long barrels where large airflow is crucial. They can also be used as breech loaders, or venting ports on combustion cannons.

'''Sprinkler Valve Launchers'''

Sprinkler Valve Launchers release air using a commercially manufactured sprinkler valve. These valves are simple to use and install, but are designed to open slowly. This is due to their main application in water systems, to prevent water hammer from destroying the valve. Since air is being used, one can modify the valve to actuate faster, using a larger pilot valve, such as a blowgun, without fear of hammer effects. Sprinkler valves are the most cost-effective option if a design calls for moderate performance. However, their relatively low flow rates and number of internal bends cause the performance to reduce to roughly 60% of that of a piston valve of the same diameter. Sprinkler valves are typically rated to ~120 psig, but it is unadvisable to use them at this pressure, as they are designed for use with water.

'''Piston Valve/Diaphragm Launchers'''

[[Piston valve]] launchers use a [[piston]] in a valve that either seals against the barrel or chamber. Releasing air through the [[pilot valve]] will cause the remaining air to push the piston away from its sealing position and air will go out the barrel.

This is generally an efficient type of launcher, as the opening time is extremely fast and there is very little constriction of airflow in the actual valve. The only real loss of flow can be attributed to the bends inherent in the design that cause gasses to lose energy as they change direction.

A diaphragm launcher operates on the same principles as a piston valve. The only difference is that the piston cylinder is replaced by a flexible diaphragm that flexes towards the pilot valve to release air into the barrel. These valves open faster than piston valves, but have slightly lower flow rates. While piston valves require a bumper to protect the piston housing, diaphragm valves do not.

'''QEV launcher'''

[[QEV]] launchers use a similar principle as the [[Piston valve]] only these can be bought from the store. These valves open even faster than piston valves because their [[pilot volume]] is much lower, and the valve is commercially manufactured and optimized.

==Related Links==

Downloading the [[GGDT]] (Gas Gun Design Tool) is highly recommended to those interested in pneumatic launchers.

Pilot volume

2008-05-04T21:08:41Z

Pilgrimman: /* Pilot volume */

==Pilot volume==

'''Pilot Volume is the air that must be exausted so that the force due to the chamber air can push the piston back.'''

This means that the smaller the pilot volume, the faster your valve will open. Opening times can also be improved by a faster high-flow pilot valve.

Pilot volume

2008-05-04T21:08:26Z

Pilgrimman: /* Pilot volume */

==Pilot volume==
'''Pilot Volume is the air that must be exausted so that the force due to the chamber air can push the piston back.''

This means that the smaller the pilot volume, the faster your valve will open. Opening times can also be improved by a faster high-flow pilot valve.

Pneumatic cannon

2008-05-04T21:05:41Z

Pilgrimman: /* Common types of launchers */

[[image:pneumatic ballvalve cannon.jpg|right|thumb|300px|Pneumatic ball valve cannon]]
A '''pneumatic cannon''' is a cannon powered by pressurized gas, usually air or CO2. They generally require a little more work to build than [[combustion cannon]]s, but using typical compressor pressures of 120 psig or so and a decent valve, they will outperform most combustion launchers of the same size.

==Basic Elements==

Pneumatic launchers consist of five basic elements:

*Compressed gas storage reservoir ([[chamber]] for short)
*Filling valve (bicycle [[Schrader valve]]s, [[quick disconnect]]s, etc.)
*Firing valve ([[ball valve]]s, [[sprinkler valve]]s, [[piston valve]]s, bolt-style valves(see piston valves) [[quick-exhaust valve]]s, and [[burst disk]]s are the most common)
*[[Barrel]]
*[[Pressure gauge]] (for safety & repeatable launches)

==Operation & Theory==

In order to fire, the operator loads a projectile into the barrel, fills the chamber with a compressed gas (see [[Pneumatic air sources]] for common filling methods), and activates the main valve thus dumping the air in the chamber to the barrel.

The expansion of the compressed gas propels the projectile down the barrel. The barrel length determines the amount of time the projectile has to accelerate and ultimately the velocity of the projectile.

Higher performance launchers use techniques such as:
* Faster valve opening times - see [[sprinkler valve modification]]
* Higher flow valves to maximize the airflow through the valve (Especially true for cannons with very long barrels)
* Using higher gas pressures.

Less common, but also effective in increasing power, some people will also use a gas with a higher speed of sound and particle speed (e.g. helium).

Efficiency of a cannon can be roughly determined by observing how much noise it makes when fired. A relatively quiet gun is often efficient, as there is little energy left over to create sound.

==Common types of launchers==

'''Ball Valve Launchers'''

Ball Valve Launchers release pressurized gas by way of a ball valve. These valves can be made of metal or plastic, and are available in many sizes and pressure ratings. Ball valves are simple to operate, and have very high flow. However, their opening times are comparitively long compared to other valves such as piston valves. Ball valves are typically used in simple designs, or on launchers with long barrels where large airflow is crucial. They can also be used as breech loaders, or venting ports on combustion cannons.

'''Sprinkler Valve Launchers'''

Sprinkler Valve Launchers release air using a commercially manufactured sprinkler valve. These valves are simple to use and install, but are designed to open slowly. This is due to their main application in water systems, to prevent water hammer from destroying the valve. Since air is being used, one can modify the valve to actuate faster, using a larger pilot valve, such as a blowgun, without fear of hammer effects. Sprinkler valves are the most cost-effective option if a design calls for moderate performance. However, their relatively low flow rates and number of internal bends cause the performance to reduce to roughly 60% of that of a piston valve of the same diameter. Sprinkler valves are typically rated to ~120 psig, but it is unadvisable to use them at this pressure, as they are designed for use with water.

'''Piston Valve/Diaphragm Launchers'''

[[Piston valve]] launchers use a [[piston]] in a valve that either seals against the barrel or chamber. Releasing air through the [[pilot valve]] will cause the remaining air to push the piston away from its sealing position and air will go out the barrel.

This is generally an efficient type of launcher, as the opening time is extremely fast and there is very little constriction of airflow in the actual valve. The only real loss of flow can be attributed to the bends inherent in the design that cause gasses to lose energy as they change direction.

A diaphragm launcher operates on the same principles as a piston valve. The only difference is that the piston cylinder is replaced by a flexible diaphragm that flexes towards the pilot valve to release air into the barrel. These valves open faster than piston valves, but have slightly lower flow rates. While piston valves require a bumper to protect the piston housing, diaphragm valves do not.

'''QEV launcher'''

[[QEV]] launchers use a similar principle as the [[Piston valve]] only these can be bought from the store. These valves open even faster than piston valves because their [[pilot volume]] is much lower, and the valve is commercially manufactured and optimized.

==Related Links==

Downloading the [[GGDT]] (Gas Gun Design Tool) is highly recommended to those interested in pneumatic launchers.

Pneumatic cannon

2008-05-04T21:03:46Z

Pilgrimman: Added some common launcher info

[[image:pneumatic ballvalve cannon.jpg|right|thumb|300px|Pneumatic ball valve cannon]]
A '''pneumatic cannon''' is a cannon powered by pressurized gas, usually air or CO2. They generally require a little more work to build than [[combustion cannon]]s, but using typical compressor pressures of 120 psig or so and a decent valve, they will outperform most combustion launchers of the same size.

==Basic Elements==

Pneumatic launchers consist of five basic elements:

*Compressed gas storage reservoir ([[chamber]] for short)
*Filling valve (bicycle [[Schrader valve]]s, [[quick disconnect]]s, etc.)
*Firing valve ([[ball valve]]s, [[sprinkler valve]]s, [[piston valve]]s, bolt-style valves(see piston valves) [[quick-exhaust valve]]s, and [[burst disk]]s are the most common)
*[[Barrel]]
*[[Pressure gauge]] (for safety & repeatable launches)

==Operation & Theory==

In order to fire, the operator loads a projectile into the barrel, fills the chamber with a compressed gas (see [[Pneumatic air sources]] for common filling methods), and activates the main valve thus dumping the air in the chamber to the barrel.

The expansion of the compressed gas propels the projectile down the barrel. The barrel length determines the amount of time the projectile has to accelerate and ultimately the velocity of the projectile.

Higher performance launchers use techniques such as:
* Faster valve opening times - see [[sprinkler valve modification]]
* Higher flow valves to maximize the airflow through the valve (Especially true for cannons with very long barrels)
* Using higher gas pressures.

Less common, but also effective in increasing power, some people will also use a gas with a higher speed of sound and particle speed (e.g. helium).

Efficiency of a cannon can be roughly determined by observing how much noise it makes when fired. A relatively quiet gun is often efficient, as there is little energy left over to create sound.

==Common types of launchers==

'''Ball Valve Launchers'''

Ball Valve Launchers release pressurized gas by way of a ball valve. These valves can be made of metal or plastic, and are available in many sizes and pressure ratings. Ball valves are simple to operate, and have very high flow. However, their opening times are comparitively long compared to other valves such as piston valves. Ball valves are typically used in simple designs, or on launchers with long barrels where large airflow is crucial. They can also be used as breech loaders, or venting ports on combustion cannons.

'''Sprinkler Valve Launchers'''

Sprinkler Valve Launchers release air using a commercially manufactured sprinkler valve. These valves are simple to use and install, but are designed to open slowly. This is due to their main application in water systems, to prevent water hammer from destroying the valve. Since air is being used, one can modify the valve to actuate faster, using a larger pilot valve, such as a blowgun, without fear of hammer effects. Sprinkler valves are the most cost-effective option if a design calls for moderate performance. However, their relatively low flow rates and number of internal bends cause the performance to reduce to roughly 60% of that of a piston valve of the same diameter. Sprinkler valves are typically rated to ~120 psig, but it is unadvisable to use them at this pressure, as they are designed for use with water.

'''Piston Valve/Diaphragm Launchers'''

[[Piston valve]] launchers use a [[piston]] in a valve that either seals against the barrel or chamber. Releasing air through the [[pilot valve]] will cause the remaining air to push the piston away from its sealing position and air will go out the barrel.

This is generally an efficient type of launcher, as the opening time is extremely fast and there is very little constriction of airflow in the actual valve. The only real loss of flow can be attributed to the bends inherent in the design that cause gasses to lose energy as they change direction.

A diaphragm launcher operates on the same principles as a piston valve. the only difference is that the piston cylinder is replaced by a flexible diaphragm that flexes towards the pilot valve to release air into the barrel. These valves open faster than piston valves, but have slightly lower flow rates. While piston valves require a bumper to protect the piston housing, diaphragm valves do not.

'''QEV launcher'''

[[QEV]] launchers use a similar principle as the [[Piston valve]] only these can be bought from the store. These valves open even faster than piston valves because their [[pilot volume]] is much lower, and the valve is commercially manufactured and optimized.

==Related Links==

Downloading the [[GGDT]] (Gas Gun Design Tool) is highly recommended to those interested in pneumatic launchers.

Copper pipe

2008-04-29T03:27:14Z

Pilgrimman: /* Pros/Cons */

Copper pipe and fittings are rising in popularity as a spudgun construction material, particularly amongst UK based spudders, due to the rarity of pressure rated [[PVC]] in the country.

==Pros/Cons==

The primary advantages of copper pipe are that it is rated to much higher pressures than PVC, and has better failure characteristics due to it's high malleability preventing shattering. This makes it well suited for making high pressure [[pneumatic cannon]]s and [[hybrid cannon|hybrid]]s.
It is also typically internally very smooth and consistent, which combined with it's high rigidity makes it exceptional barrel material.
Copper pressure ratings have a safety factor of about 7.

The consistent internal diameter also makes it popular for construction of [[combustion cannon]] [[fuel meter]]s.

It is more expensive than PVC (especially larger dimensions) and considerably heavier, and is therefore mostly used for small caliber cannons (1" or less).

==Types & Use==

Copper pipe is usually joined by [[sweating]], using [[compression fitting]]s, or [[Copper epoxy]].
The latter two are slightly more expensive, but require minimal tools to use. Threaded fittings for copper pipe are usually made of brass.

Copper pipe comes in two tempers, annealed and drawn. Annealed copper pipe is very soft, and can usually be bent by hand. Drawn copper pipe is rigid, and will flex rather than bend (to a certain limit). Drawn pipe is the most useful in spudgun construction, since it will keep its shape and not get damaged easily. It is also rated to about twice the pressure as an annealed pipe of the same size.

==Safety==
Copper or Brass pipe/fittings should not be used with [[acetylene]] gas, as copper alloys can act as a catalyst to the explosive decomposition of the gas.

Due to it's relatively thin walled nature, potentially dangerous "sharp" ends can exist on pipe ends that have not been cleaned, and anybody using it should be aware of this.

Cutting of copper has a high attrition rate on rotary multi-tool abrasive discs, which will wear down at a high rate, and break apart regularly. Use of safety goggles is doubly recommended

[[category:construction materials]]

Index

2008-04-29T03:24:40Z

Pilgrimman: /* S */

This page is under construction, but should provide an '''alphabetical''' list of common spudding terms, as well as a note/definition about the term.

If you feel like it, start adding things.

==A==
ABS (Acrylonitrile Butadiene Styrene) - A plastic used in plumbing applications. More resistant to shock, low temperature, and chemicals, but difficult to find rated for pressure. Pressure rated ABS is legal for compressed gas applications.

==B==

Ballistics - The science of the motion of projectiles. Sometime divided into two sub-classes; "Internal Ballistics" is the motion of the projectile while it is still in the barrel, "External Ballistics" is the motion of the projectile after it has left the barrel.

[[Barrel]] - Present on all cannons. A barrel is a tube designed to allow the projectile to reach maximum velocity before the pressurized gas propelling it escapes to the atmosphere. Barrels also improve accuracy, and can be rifled to improve accuracy further.

BBMG - See [[BB machine gun]].

[[BB Machine Gun]] - Pneumatic gun designed to fire airsoft pellets or metal BBs at high rates of fire.

Bottled Gas - See [[Gas Bottle]]

[[Butane]] - A common fuel for combustion spud guns. Butane, a gas at room termperature and pressure, is readily available in disposable lighters.

==C==
[[Chamber]] - An element shared by all pressure based cannons, where either the pre-compressed air or flammable gas mixture is stored before firing.

[[Chronometer]] - 1. A device for measuring time. 2. A device for measuring the muzzle velocity of a gun. See also Chrony, muzzle velocity.

Chrony - A commercial device for measuring the muzzle velocity of a gun. Used for "real" guns, paintball guns, bows, and spud guns.

[[Combustion Cannon]] - A cannon that generates pressure by burning flammable gases.

[[Compressor]] - Motorized air pump.

[[Copper]] - Metal. Construction material.

==D==
[[DDT]] - Deflagration to Detonation Transistion. This very dangerous effect occurs when the flame front in a combustible gas mix exceeds the speed of sound in the gas - creating a super sonic shockwave and a very large pressure spike which may damage or destroy the [[chamber]].
It is very rare, and is only likely to occur in high mix [[Hybrid cannon]]s, or in combustion cannons with very long chambers.

[[Diaphragm valve]] - Related to [[Piston valve]]. Generally rarer, but often considered to open faster but have lower flow. Typically used in coaxial designs, and commercially manufactured as inline sprinkler valves.

Drain Waste Vent (DWV) - A designation by the NSF (National Sanitation Foundation) that means the item is approved for drain, waste, or venting applications. By nature, DWV does not require a pressure rating, but some DWV pipes are rated for pressure.

==E==
[[Epoxy]] - A combination of chemicals that form a bond much stronger than any glue. Often used for sealing leaks or during sprinkler valve modification. Some people have created very large parts of cannons from epoxy, as well as pistons.

==F==
Flame Front - The edge of a flame whose speed, in part, affects the power of the cannon it is powering. If the flame front exceeds the speed of sound, [[DDT]] occurs.

==G==
[[Gas Bottle]] - A metal cylinder filled with pressurized gases.

==H==
[[Hybrid Cannon]] - A cannon that uses a pre-compressed flammable gas mixture. The increased fuel + oxygen charge in the chamber substantially increases the pressure, temperature and energy in the chamber. Ignition is somewhat difficult, as spark length is roughly inversely proportional to pressure. Very powerful, but requires experience to successfully and safely implement.

==I==

[[Ignition source]] - Used to start the combustion reaction in a [[combustion cannon]] or [[Hybrid Cannon]]. Sources range from lantern sparkers, to piezoelectric grill ignitors, to ignition coils and camera flash circuits.

==J==

==K==

==L==
Lathe -

==M==

Mach - The speed of sound for a ''given set of environmental conditions''. The speed of sound changes with temperature and the nature of the fluid involved. For dry air at 15C, one Mach is equivalent to 340.3 m/s (1225 km/h, 761.2 mph, 1116 fps). At normal temperatures the small temperature dependence is usually ignored. At the elevated temperatures that exist in the chamber of a combustion gun, the speed of sound is significantly increased. At the adiabatic flame temperature of propane in air the speed of sound is increased by about 3-fold to ~990 m/s (3560 km/h, 2210 mph, 3250 fps).

MAPP - A bottled gas used in combustion or hybrid applications. MAPP has been experimentally determined to produce muzzle velocities 11% greater than those of propane.

Muzzle Knife - (Aka [[spud cutter]].) The sharpening of the muzzle of a barrel so that it will automatically cut a spud to the proper size for the barrel. Internal beveling of the muzzle can produce a better seal. See also [[spud cutter]].

==N==
Nitrogen - An inert gas with a lower molar mass than the average of air. This allows slightly higher particle speeds, and therefore, higher muzzle velocities.

NSF - National Sanitation Foundation. "NSF" is often printed on pipe, along with letters that designate what applications the pipe is NSF-approved for.

==O==
O-Ring - Often made of Neoprene or similar, these rings can seal thousands of pounds of pressure, but must be mounted very precisely for most applications, which often requires use of a lathe.

==P==
Piezoelectricity - A property of certain materials where the material can be mechanically stressed, and produce high voltage electric current. When electricity is applied to the crystal, it vibrates. This property is implemented in grill ignitors, which are commonly used as ignition sources in spud guns.

Pilot Valve - A valve whose purpose is to exhaust pilot air, thus triggering a larger main valve, or, in cases, another pilot valve.

[[Piston valve]] - A high power home-made valve which is generally considered to be second only to [[Burst disk]] valves in performance, but more practical to use. Releases air by rapidly exhausting the area behind the piston (pilot), thus causing the piston to be pushed backwards, and stop sealing the chamber from the barrel. See also: [[Diaphragm valve]]

[[Pneumatic Cannon]] - A cannon that uses pre-compressed air for power.

Potable Water (PW) - An NSF designation found on some plumbing pipe and fittings. Potable Water systems are pressurized, so, by nature, NSF-PW pipes are pressure rated.

[[Propane]] - A common fuel for combustion spud guns, as well as hybrid cannons.

[[PVC]] - Most common spudgun construction material. Gets brittle in cold weather, and may shatter if dropped or abused. Pressure rated PVC is easy to find in the U.S., although large diameter pipe is difficult to find. PVC is illegal for compressed gas applications.

==Q==
[[QEV]] - Quick Exhaust Valve. Essentially a pre-made [[piston valve|piston]] or [[diaphragm valve]]. These are quite hard to find, and are moderately expensive.

==R==

==S==

[[Safety]] - More important than even the spudgun. If you don't have this, then you need it fast.

Schelkin Spiral - A method that causes turbulence in burning gasses. This increases the risk of [[DDT]].

[[Spark_gap|Spark Gap]] - A spark gap consists of two metal electrodes placed close to each other with a gap in between, where an electrical spark can jump. They are used for igniting the fuel in combustion and hybrid cannons. Electrodes that are more pointed can generate a longer spark at a given voltage than those that are more planar.

==T==
Tee - A name for pipe fittings that have sockets arranged so that the fitting looks like the letter "T".
==U==

==V==
[[Valve]] - Essential to pneumatic cannons. A valve retains pressure and then opens, or in the case of a burst disk, ruptures, to release the air. A valve will perform better if its flow rate is increased, or its opening speed is decreased.

==W==
Wye - A name for pipe fittings that have sockets arranged so that the fitting looks like the letter "Y".

==X==

==Y==

==Z==

Pneumatic air sources

2008-03-09T05:57:43Z

Pilgrimman: /* Gases */

This page lists some of the common sources of air pressure to power a pneumatic, and the advantages and disadvantages of each:

==Gases==

'''Acetylene'''

Advantages:
* Very powerful combustion pressure spikes

Disadvantages:
* Extremely unstable, will auto-ignite at pressues over 15 psi
* Pressure spikes are very rapid, and therefore can cause fatigue much more readily
* Safe to use in very few spudding applications

'''Air'''

Advantages:
* It's price (completely free of course)
* Global availability.
* Inert

Disadvantages:
* Limited performance approaching the sound barrier.

Performance of air is moderate. It is very uncommon for a air powered launcher to exceed the sound barrier, but not completely impossible. Most gases are compared against air as a benchmark
Sources: If you want to use air, you'll either need a [[compressor]], [[Hand pump|hand/foot pump]] or a [[gas bottle|High Pressure Air (HPA) tank]]

'''Helium'''

Advantages:
* Exceptional performance
* High speed of sound and particle speed
* Inert

Disadvantages:
* Costly
* Will leak faster than any other gas
* Helium regulators typically limited to 200 psi.

Performance is second only to Hydrogen.
Sources: Unless you have an on-site extraction plant, the only option is [[gas bottle]]s

'''MAPP'''

Advantages:
* More powerful than propane, but still safe for pressure rated PVC

Disadvantages:
* More expensive than propane

'''Nitrogen'''

Advantages:
* Performance slightly better than air.
* Option for high pressures.
* Inert

Disadvantages:
* Costly
* Particle speed is not significantly more than that of air

Nitrogen is slightly more powerful than air for a given pressure, but nitrogen regulators are capable of very high pressures.
Sources: Unless you have an on-site extraction plant, the only option is [[gas bottle]]s

'''Hydrogen'''

Advantages:
* Highest performance gas, in terms of perticle speed

Disadvantages:
* Costly.
* Potential explosive risk.
* Will leak fast.

Hydrogen is the most powerful gas that can be used in a pneumatic, but it has numerous risks associated with it.
Sources: Unless you have an on-site extraction plant, the only option is [[gas bottle]]s or electrolysis

'''Carbon Dioxide'''

Advantages:
* Reasonably cheap
* High pressure
* Highest gas volume to bottle volume ratio
* Inert

Disadvantages:
* Low power due to high molar mass and high density
* Very heavy cooling on decompression (can cause problems with PVC launchers)

CO2 is a very common bottled gas, but it's power is limited by it's high density.
Sources: [[Gas bottle]]s, [[CO2 cartridges|Gas bulbs]]

'''Propane'''

Advantages:
* Reasonably cheap
* High gas volume to bottle volume ratio
* Readily available

Disadvantages:
* Low power
* Low pressure
* Possible (if unlikely) fire risk

[[Propane]] is better known as a [[combustion cannon]] power source, but some pneumatics have used it as a gas. It's performance is low, because of it's high density and low pressures, but it is cheap and easily found.
Sources: [[Gas bottle]]s, either in large bulk tanks of several kilograms, or in small tanks of 0.5 - 1 lb.

==Supplies==

[[Compressor]]

[[Hand_pump|Hand/Foot Pump]]

[[Gas_bottle|Gas bottles]]

[[CO2 cartridge]]s

Pneumatic air sources

2008-03-09T05:55:39Z

Pilgrimman: /* Gases */

This page lists some of the common sources of air pressure to power a pneumatic, and the advantages and disadvantages of each:

==Gases==

'''Acetylene'''

Advantages:
* Very powerful combustion pressure spikes

Disadvantages:
* Extremely unstable, will auto-ignite at pressues over 15 psi
* Pressure spikes are very rapid, and therefore can cause fatigue much more readily

'''Air'''

Advantages:
* It's price (completely free of course)
* Global availability.
* Inert

Disadvantages:
* Limited performance approaching the sound barrier.

Performance of air is moderate. It is very uncommon for a air powered launcher to exceed the sound barrier, but not completely impossible. Most gases are compared against air as a benchmark
Sources: If you want to use air, you'll either need a [[compressor]], [[Hand pump|hand/foot pump]] or a [[gas bottle|High Pressure Air (HPA) tank]]

'''Helium'''

Advantages:
* Exceptional performance
* High speed of sound and particle speed
* Inert

Disadvantages:
* Costly
* Will leak faster than any other gas
* Helium regulators typically limited to 200 psi.

Performance is second only to Hydrogen.
Sources: Unless you have an on-site extraction plant, the only option is [[gas bottle]]s

'''Nitrogen'''

Advantages:
* Performance slightly better than air.
* Option for high pressures.
* Inert

Disadvantages:
* Costly
* Particle speed is not significantly more than that of air

Nitrogen is slightly more powerful than air for a given pressure, but nitrogen regulators are capable of very high pressures.
Sources: Unless you have an on-site extraction plant, the only option is [[gas bottle]]s

'''Hydrogen'''

Advantages:
* Highest performance gas, in terms of perticle speed

Disadvantages:
* Costly.
* Potential explosive risk.
* Will leak fast.

Hydrogen is the most powerful gas that can be used in a pneumatic, but it has numerous risks associated with it.
Sources: Unless you have an on-site extraction plant, the only option is [[gas bottle]]s or electrolysis

'''Carbon Dioxide'''

Advantages:
* Reasonably cheap
* High pressure
* Highest gas volume to bottle volume ratio
* Inert

Disadvantages:
* Low power due to high molar mass and high density
* Very heavy cooling on decompression (can cause problems with PVC launchers)

CO2 is a very common bottled gas, but it's power is limited by it's high density.
Sources: [[Gas bottle]]s, [[CO2 cartridges|Gas bulbs]]

'''Propane'''

Advantages:
* Reasonably cheap
* High gas volume to bottle volume ratio
* Readily available

Disadvantages:
* Low power
* Low pressure
* Possible (if unlikely) fire risk

[[Propane]] is better known as a [[combustion cannon]] power source, but some pneumatics have used it as a gas. It's performance is low, because of it's high density and low pressures, but it is cheap and easily found.
Sources: [[Gas bottle]]s, either in large bulk tanks of several kilograms, or in small tanks of 0.5 - 1 lb.

==Supplies==

[[Compressor]]

[[Hand_pump|Hand/Foot Pump]]

[[Gas_bottle|Gas bottles]]

[[CO2 cartridge]]s

Pneumatic air sources

2008-03-09T05:55:15Z

Pilgrimman: /* Gases */

This page lists some of the common sources of air pressure to power a pneumatic, and the advantages and disadvantages of each:

==Gases==

'''Acetylene'''
Advantages:
* Very powerful combustion pressure spikes

Disadvantages:
* Extremely unstable, will auto-ignite at pressues over 15 psi
* Pressure spikes are very rapid, and therefore can cause fatigue much more readily

'''Air'''

Advantages:
* It's price (completely free of course)
* Global availability.
* Inert

Disadvantages:
* Limited performance approaching the sound barrier.

Performance of air is moderate. It is very uncommon for a air powered launcher to exceed the sound barrier, but not completely impossible. Most gases are compared against air as a benchmark
Sources: If you want to use air, you'll either need a [[compressor]], [[Hand pump|hand/foot pump]] or a [[gas bottle|High Pressure Air (HPA) tank]]

'''Helium'''

Advantages:
* Exceptional performance
* High speed of sound and particle speed
* Inert

Disadvantages:
* Costly
* Will leak faster than any other gas
* Helium regulators typically limited to 200 psi.

Performance is second only to Hydrogen.
Sources: Unless you have an on-site extraction plant, the only option is [[gas bottle]]s

'''Nitrogen'''

Advantages:
* Performance slightly better than air.
* Option for high pressures.
* Inert

Disadvantages:
* Costly
* Particle speed is not significantly more than that of air

Nitrogen is slightly more powerful than air for a given pressure, but nitrogen regulators are capable of very high pressures.
Sources: Unless you have an on-site extraction plant, the only option is [[gas bottle]]s

'''Hydrogen'''

Advantages:
* Highest performance gas, in terms of perticle speed

Disadvantages:
* Costly.
* Potential explosive risk.
* Will leak fast.

Hydrogen is the most powerful gas that can be used in a pneumatic, but it has numerous risks associated with it.
Sources: Unless you have an on-site extraction plant, the only option is [[gas bottle]]s or electrolysis

'''Carbon Dioxide'''

Advantages:
* Reasonably cheap
* High pressure
* Highest gas volume to bottle volume ratio
* Inert

Disadvantages:
* Low power due to high molar mass and high density
* Very heavy cooling on decompression (can cause problems with PVC launchers)

CO2 is a very common bottled gas, but it's power is limited by it's high density.
Sources: [[Gas bottle]]s, [[CO2 cartridges|Gas bulbs]]

'''Propane'''

Advantages:
* Reasonably cheap
* High gas volume to bottle volume ratio
* Readily available

Disadvantages:
* Low power
* Low pressure
* Possible (if unlikely) fire risk

[[Propane]] is better known as a [[combustion cannon]] power source, but some pneumatics have used it as a gas. It's performance is low, because of it's high density and low pressures, but it is cheap and easily found.
Sources: [[Gas bottle]]s, either in large bulk tanks of several kilograms, or in small tanks of 0.5 - 1 lb.

==Supplies==

[[Compressor]]

[[Hand_pump|Hand/Foot Pump]]

[[Gas_bottle|Gas bottles]]

[[CO2 cartridge]]s

Pneumatic cannon

2008-03-09T05:48:58Z

Pilgrimman: /* Operation & Theory */

Identifying Pressure Rated PVC

2008-03-09T05:44:50Z

Pilgrimman:

Pressure Rated PVC is a fairly common type of spudgun material that most spudguns are made from. It can be found at your local Lowes, Home Depot or Ace Hardware in America. If you are outside the US, you are more likely to find cheap PVC at a Plumbing Merchant, but it can also be found in Aus/NZ at a Bunnings or Mitre10.

Identifying the correct type of PVC to use in a [[Pneumatic]] or [[Hybrid]] cannon is vital because of the high pressures involved.
[[Combustion]] cannons don't need to be made from pressure rated pipe in most cases, but if you don't mind the weight and cost, the additional safety provided by the pipe can only benefit your cannon.

==PVC and Combustion Cannons==

Generally, most spudders who build combustion cannons will not use pressure rated PVC due to the relatively low pressure spike generated by most combustion cannons, and the cost and weight of pressure rated PVC. About 30-45 PSI is generated in hairspray fueled cannons and about 60-75 PSI in [[propane]] or [[MAPP]] powered cannons, which DWV (Non-Pressure Rated) PVC or ABS can typically withstand. However, wall thickness should be taken into account if the pipe is not rated.

There have been few reports of DWV PVC combustion cannons failing, but this is probably due to pipe fatigue, thin-wall PVC usage, or cracks formed from threaded fittings connected to the chamber.

Advanced Combustion cannons should be constructed with pressure rated pipes.

==PVC and Pneumatic Cannons==

Pressure rated components are essential in making a safe [[pneumatic cannon]]. Because of the higher pressures reached by pneumatic cannons compared to combustion cannons, pressure rated fittings are vital.

Pressure rated PVC is the most common pneumatic cannon material because of the reasonably low cost, availability, and relatively low weight. It also suits a pneumatic very well, having a wide range of different types of fittings and usually a high pressure rating, with a decent safety factor (3, in most cases).

DWV PVC has been exposed to around 80-120 PSI in a pneumatic, but this is definitely not recommended. DWV has no rating, meaning it could blow as low as 1 PSI.

==PVC and Hybrids==

Pressure rated PVC (Sch 80) was generally a common material in making hybrids until, by general concensus, it was deemed too dangerous after several cannon failures around 4-6x mixes.

If you plan on making a hybrid from PVC, NSF-PW Sch 80 PVC is the minimum requirement but it would be best to stay under 4x mixes.

Most hybrids are constructed from galvanized steel pipe, which is more expensive in larger sizes and weighs more, but the pressure rating is far higher.

==Identifying Pressure Rated PVC By Look==

If you are having problems separating Pressure Rated PVC components from DWV PVC, these few differences should make it crystal clear next time you go to a hardware store.

'''DWV Fittings:'''

DWV PVC fittings have a few obvious traits that you can use to identify them.
[[image:DWV Fittings.jpg|thumb|Non Pressure Rated PVC Fittings (DWV)]]
* Shallow sockets, DWV fittings have shorter socket depths in their fittings.
* Ring around fitting, DWV fittings usually have a 'ring' around the outside of the sockets, Pressure Rated fittings, don't.
* Thickness, DWV fittings and pipe are very thin compared to their Pressure Rated counterparts.
* Odd shape, some DWV fittings look very odd and drastically different to Pressure Rated fittings.

'''Pressure Rated Fittings:'''

Pressure Rated PVC fittings generally have the opposite traits as DWV fittings.
* Deeper socket lengths
* 'Full' fitting, no rings around the fittings.
* Thickness, thicker then DWV fittings.
* Symmetrical look to the fitting, no odd shapes.
[[Image:PR PVC.jpg|thumb|Pressure Rated PVC Fittings]]

''Common Misconception:'' Even though [http://www.championlighting.com/pics/pumppics/dolphin/bell_red.jpg Bell Reducers] look Pressure rated, in most cases they are not. It is best to stick to [http://www.milmar.com/images/Sch%2040%20Reducing%20Bushing%20(SxS).JPG Reducing Bushings] because they usually are always pressure rated, make sure to check first though.

==Identifying Pressure Rated PVC By Text==

''Common Misconception:'' Sch 40 written on the fitting/pipe does not mean the fitting/pipe is pressure rated, the 'Sch' system is a thickness rating, not a pressure rating. You need to look for NSF-PW.

''Tip:'' On a Pressure Rated fitting, the writing is usually raised and can be read once painted over. In the case of pipe, if enough layers of paint are on the pipe, you probably can't read the print, so make sure to write down what the pipe has written on it before you paint over it.

''Note:'' The above is intended for identifying American fittings and pipe. To identify Australia/New Zealand fittings, see below.

'''Fittings:'''

To find out if a fitting is pressure rated, it should have 'NSF-PW' written in raised text, it may also have Sch 40 (or 80,120 etc) on it. Most American fittings don't have a pressure rating on them, but if they have NSF-PW ("PW" stands for Potable Water, which, by nature is under pressure), you're okay, it will be pressure rated.

'''Pipe:'''

For pressure rated pipe, it should have written on the side: 'NSF-PW Sch 40 (or 80,120, etc) XXXPSI @73F'

XXXPSI, is the pressure rating, it changes depending on the 'schedule' rating and the diameter of the pipe. The pipe may also have a different temperature rating, but the most common say '@73F'.

The pipe may also have 'DWV" written on it, as long as the pipe has a pressure rating, e.g '300PSI @73F' you're okay.

If it doesn't have 'NSF-PW' or pressure rating, chances are it's DWV.

You can also identify Pressure Rated or DWV fittings and pipe by their 'AS' number written on them, but it's not essential to learn. More details about 'AS' numbers coming soon.

'''Identifying Australian/NZ Pressure Rated PVC fittings:'''

Since Aus/NZ use a different measuring system, PVC fittings and pipe have a different way of identifying if they are Pressure Rated or not.

'''Fittings:'''

To find out if a PVC fitting is Pressure Rated or not, it should have written on it in either raised or plain text, either:

* Class X (The class ranges from A-F, with F being the most pressure rated, usually Class 'C' is a minimum in a pneumatic.)
* PN XX (The PN (Pressure Number) system has ratings ranging from 0-22+. PN 10, 12 or 18 are the most common and PN 10 should be the lowest rated fitting you should use in a pneumatic.)

It's that simple. To find the pressure rating in PSI, multiply the PN number by 14.5. E.g PN18 x 14.5PSI = 261PSI.
The PN number is in BAR, to find it in Kpa, multiply the PN number by 100. E.g PN18 x 100 = 1800Kpa.

'''Pipe:'''

To find the pressure rating of PVC pipe, use the same system as you did with the fittings. Find the PN or Class number.
Try not to get confused with the 'DN' number, which is the nominal diameter in millimetres. E.g DN50 = Diameter 50mm.

As with the American system, there is another way to determine the pressure rating, and that is by AS/NZS number. More information to come soon.

Index

2008-03-09T05:32:11Z

Pilgrimman: Added some terms, clarified some definitions.

This page is under construction, but should provide an '''alphabetical''' list of common spudding terms, as well as a note/definition about the term.

If you feel like it, start adding things.

==A==
ABS (Acrylonitrile Butadiene Styrene) - A plastic used in plumbing applications. More resistant to shock, low temperature, and chemicals, but difficult to find rated for pressure. Pressure rated ABS is legal for compressed gas applications.

==B==
[[Barrel]] - Present on all cannons. A barrel is a tube designed to allow the projectile to reach maximum velocity before the pressurized gas propelling it escapes to the atmosphere. Barrels also improve accuracy, and can be rifled to improve accuracy further.

BBMG - See [[BB machine gun]].

[[BB Machine Gun]] - Pneumatic gun designed to fire airsoft pellets or metal BBs at high rates of fire.

Bottled Gas - See [[Gas Bottle]]

[[Butane]] - A common fuel for combustion spud guns.

==C==
[[Chamber]] - An element shared by all pressure based cannons, where either the pre-compressed air or flammable gas mixture is stored before firing.

[[Chronometer]] - 1. A device for measuring time. 2. A device for measuring the muzzle velocity of a gun. See also Chrony, muzzle velocity.

Chrony - A commercial device for measuring the muzzle velocity of a gun. Used for "real" guns, paintball guns, bows, and spud guns.

[[Combustion Cannon]] - A cannon that generates pressure by burning flammable gases.

[[Compressor]] - Motorized air pump.

[[Copper]] - Metal. Construction material.

==D==
[[DDT]] - Deflagration to Detonation Transistion. This very dangerous effect occurs when the flame front in a combustible gas mix exceeds the speed of sound in the gas - creating a super sonic shockwave and a very large pressure spike which may damage or destroy the [[chamber]].
It is very rare, and is only likely to occur in high mix [[Hybrid cannon]]s, or in combustion cannons with very long chambers.

[[Diaphragm valve]] - Related to [[Piston valve]]. Generally rarer, but often considered to open faster but have lower flow. Typically used in coaxial designs, and commercially manufactured as inline sprinkler valves.

Drain Waste Vent (DWV) - A designation by the NSF (National Sanitation Foundation) that means the item is approved for drain, waste, or venting applications. By nature, DWV does not require a pressure rating, but some DWV pipes are rated for pressure.

==E==
[[Epoxy]] - A combination of chemicals that form a bond much stronger than any glue. Often used for sealing leaks or during sprinkler valve modification. Some people have created very large parts of cannons from epoxy, as well as pistons.

==F==
Flame Front - The edge of a flame whose speed, in part, affects the power of the cannon it is powering. If the flame front exceeds the speed of sound, [[DDT]] occurs.

==G==
[[Gas Bottle]] - A metal cylinder filled with pressurized gases.

==H==
[[Hybrid Cannon]] - A cannon that uses a pre-compressed flammable gas mixture. The particle speed of the gas is increased by the energy of combustion, which makes supersonic velocities much more attainable. Ignition is somewhat difficult, as spark length is roughly inversely proportional to pressure. Very powerful, but requires experience to successfully and safely implement.

==I==

[[Ignition source]] - Used to start the combustion reaction in a [[combustion cannon]] or [[Hybrid Cannon]]. Sources range from lantern sparkers, to piezoelectric grill ignitors, to ignition coils and camera flash circuits.

==J==

==K==

==L==
Lathe -

==M==

Mach - The speed of sound for a given set of environmental conditions. The speed of sound changes somewhat with temperature and the nature of the fluid involved. For dry air at 15C, one Mach is equivalent to 340.3 m/s (1,225 km/h, 761.2 mph)

MAPP - A bottled gas used in combustion or hybrid applications. MAPP has been experimentally determined to produce muzzle velocities 11% greater than those of propane.

Muzzle Knife - (Aka [[spud cutter]].) The sharpening of the muzzle of a barrel so that it will automatically cut a spud to the proper size for the barrel. Internal beveling of the muzzle can produce a better seal. See also [[spud cutter]].

==N==
Nitrogen - An inert gas with a lower molar mass than the average of air. This allows slightly higher particle speeds, and therefore, higher muzzle velocities.

NSF - National Sanitation Foundation. "NSF" is often printed on pipe, along with letters that designate what applications the pipe is NSF-approved for.

==O==
O-Ring - Often made of Neoprene or similar, these rings can seal thousands of pounds of pressure, but must be mounted very precisely for most applications, which often requires use of a lathe.

==P==
Piezoelectricity - A property of certain materials where the material can be mechanically stressed, and produce high voltage electric current. When electricity is applied to the crystal, it vibrates. This property is implemented in grill ignitors, which are commonly used as ignition sources in spud guns.

Pilot Valve - A valve whose purpose is to exhaust pilot air, thus triggering a larger main valve, or, in cases, another pilot valve.

[[Piston valve]] - A high power home-made valve which is generally considered to be second only to [[Burst disk]] valves in performance, but more practical to use. Releases air by rapidly exhausting the area behind the piston (pilot), thus causing the piston to be pushed backwards, and stop sealing the chamber from the barrel. See also: [[Diaphragm valve]]

[[Pneumatic Cannon]] - A cannon that uses pre-compressed air for power.

Potable Water (PW) - An NSF designation found on some plumbing pipe and fittings. Potable Water systems are pressurized, so, by nature, NSF-PW pipes are pressure rated.

[[Propane]] - A common fuel for combustion spud guns, as well as hybrid cannons.

[[PVC]] - Most common spudgun construction material. Gets brittle in cold weather, and may shatter if dropped or abused. Pressure rated PVC is easy to find in the U.S., although large diameter pipe is difficult to find. PVC is illegal for compressed gas applications.

==Q==
[[QEV]] - Quick Exhaust Valve. Essentially a pre-made [[piston valve|piston]] or [[diaphragm valve]]. These are quite hard to find, and are moderately expensive.

==R==

==S==

[[Safety]] - More important than even the spudgun. If you don't have this, then you need it fast.

Schelkin Spiral - A method that causes turbulence in burning gasses. This increases the risk of [[DDT]].

==T==
Tee - A name for pipe fittings that have sockets arranged so that the fitting looks like the letter "T".
==U==

==V==
[[Valve]] - Essential to pneumatic cannons. A valve retains pressure and then opens, or in the case of a burst disk, ruptures, to release the air. A valve will perform better if its flow rate is increased, or its opening speed is decreased.

==W==
Wye - A name for pipe fittings that have sockets arranged so that the fitting looks like the letter "Y".

==X==

==Y==

==Z==

Chronometer

2008-03-09T04:45:10Z

Pilgrimman:

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

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 a couple percent 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 chronometers 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 Chronometers ==

It is fairly easy to construct a useable shooting chronometer from readily available parts. If you have access to a PC or laptop then a chronometer 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 chronometer.

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 Chronometer ==

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 chronometer. [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 chronometer.

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

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 [[BBMG]];
[[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.

Construction materials

2008-02-16T17:46:26Z

Pilgrimman: Started this page, fix/add what you want.

==Introduction==

Many materials are readily available for use in construction of a spudgun. The most common, perhaps, are PVC and ABS. Both are so common, that a page has been dedicated to them ([[PVC vs. ABS]]). For information on other materials, see below.

==Common Materials==

* Copper Pipe
* Galvanized Steel Pipe
* Aluminum Pipe

'''Copper Pipe'''

Identifying Pressure Rated PVC

2008-02-16T17:31:04Z

Pilgrimman: Added a small thing, will add more later.

Pressure Rated PVC is a fairly common type of spudgun material that most spudguns are made from. It can be found at your local Lowes, Home Depot or Ace Hardware in America. If you are outside the US, your best bet for cheap PVC is a Plumbing Merchant, but it can also be found in Aus/NZ at a Bunnings or Mitre10.

Identifying the correct type of PVC to use in a [[Pneumatic]] or [[Hybrid]] cannon is vital because of the high pressures involved.
[[Combustion]] cannons don't need to be made from pressure rated pipe, but if you don't mind the weight and cost, go right ahead.

==PVC and Combustion Cannons==

Generally most spudders who build combustion cannons will not use pressure rated PVC due to the combustions low pressure spike and the cost and weight of Pressure Rated PVC. About 30-45PSI is generated in hairspray cannons and about 60-75PSI in [[propane]] or [[MAPP]] powered cannons, which DWV (Non-Pressure Rated) PVC or ABS should be able to take.

There have been few reports of people having combustions made from DWV PVC blowing up on them, but this is probably because of pipe fatigue, thin-wall PVC used or cracks formed from threaded fittings in the chamber.

If you are thinking of making a basic or advanced combustion, DWV ABS is probably the best choice aside from the rarely found, Pressure Rated ABS.

==PVC and Pneumatics==

Pressure rated components are essential in making a safe [[pneumatic cannon]]. Because of the higher pressures reached by Pneumatics compared to Combustions, pressure rated fittings are vital.

Pressure Rated PVC is the most common pneumatic cannon material because of the reasonably low cost, availability and low weight compared to metal fittings. It also suits a pneumatic very well, having a wide range of different types of fittings and usually a high pressure rating.

People have taken DWV up to around 80-120PSI in a pneumatic, but this is definitely not recommended. DWV has no rating, meaning it could blow as low as 20PSI. Just spend the extra few dollars and get the pressure rated stuff.

==PVC and Hybrids==

Pressure rated PVC (Sch 80) was generally a common material in making hybrids until a few people deemed it too dangerous after several cannon failures around 4-6x mixes.

If you plan on making a hybrid from PVC, NSF-PW Sch 80 PVC is the minimum requirement but it would be best to stay under 4x mixes.

Now most hybrids are constructed from galvanised pipe, which is more expensive in larger sizes and weighs more, but the pressure rating is far higher.

==Identifying Pressure Rated PVC By Look==

If you are having problems separating Pressure Rated PVC components from DWV PVC, these few differences should make it crystal clear next time you go to a hardware store.

'''DWV Fittings:'''

DWV PVC fittings have a few obvious traits that you can use to identify them.
[[image:DWV Fittings.jpg|thumb|Non Pressure Rated PVC Fittings (DWV)]]
* Shallow sockets, DWV fittings have shorter socket depths in their fittings.
* Ring around fitting, DWV fittings usually have a 'ring' around the outside of the sockets, Pressure Rated fittings, don't.
* Thickness, DWV fittings and pipe are very thin compared to their Pressure Rated counterparts.
* Odd shape, some DWV fittings look very odd and drastically different to Pressure Rated fittings.

'''Pressure Rated Fittings:'''

Pressure Rated PVC fittings generally have the opposite traits as DWV fittings.
* Deeper socket lengths
* 'Full' fitting, no rings around the fittings.
* Thickness, thicker then DWV fittings.
* Symmetrical look to the fitting, no odd shapes.
[[Image:PR PVC.jpg|thumb|Pressure Rated PVC Fittings]]

''Spud Myth:'' Even though [http://www.championlighting.com/pics/pumppics/dolphin/bell_red.jpg Bell Reducers] look Pressure rated, in most cases they are not. It is best to stick to [http://www.milmar.com/images/Sch%2040%20Reducing%20Bushing%20(SxS).JPG Reducing Bushings] because they usually are always pressure rated, make sure to check first though.

==Identifying Pressure Rated PVC By Text==

''Spud Myth:'' Sch 40 written on the fitting/pipe does not mean the fitting/pipe is pressure rated, the 'Sch' system is a thickness rating, not a pressure rating. You need to look for NSF-PW.

''Tip:'' On a Pressure Rated fitting, the writing is usually raised and can be read once painted over, with pipe, if you have enough layers of paint you probably can't read it, so make sure to write down what the pipe has written on it before you paint over it.

''Note:'' This is identifying American fittings and pipe. To identify Australia/New Zealand fittings, see below.

'''Fittings:'''

To find out if a fitting is pressure rated, it should have 'NSF-PW' written in raised text, it may also have Sch 40 (or 80,120 etc) on it. Most American fittings don't have a pressure rating on them, but if they have NSF-PW ("PW" stands for Potable Water, which, by nature is under pressure), you're okay, it will be pressure rated.

'''Pipe:'''

For pressure rated pipe, it should have written on the side: 'NSF-PW Sch 40 (or 80,120, etc) XXXPSI @73F'

XXXPSI, is the pressure rating, it changes depending on the 'schedule' rating and the diameter of the pipe. The pipe may also have a different temperature rating, but the most common say '@73F'.

The pipe may also have 'DWV" written on it, as long as the pipe has a pressure rating, e.g '300PSI @73F' you're okay.

If it doesn't have 'NSF-PW' or pressure rating, chances are it's DWV.

You can also identify Pressure Rated or DWV fittings and pipe by their 'AS' number written on them, but it's not essential to learn. More details about 'AS' numbers coming soon.

'''Identifying Australian/NZ Pressure Rated PVC fittings:'''

Since Aus/NZ use a different measuring system, PVC fittings and pipe have a different way of identifying if they are Pressure Rated or not.

'''Fittings:'''

To find out if a PVC fitting is Pressure Rated or not, it should have written on it in either raised or plain text, either:

* Class X (The class ranges from A-F, with F being the most pressure rated, usually Class 'C' is a minimum in a pneumatic.)
* PN XX (The PN (Pressure Number) system has ratings ranging from 0-22+. PN 10, 12 or 18 are the most common and PN 10 should be the lowest rated fitting you should use in a pneumatic.)

It's that simple. To find the pressure rating in PSI, multiply the PN number by 14.5. E.g PN18 x 14.5PSI = 261PSI.
The PN number is in BAR, to find it in Kpa, multiply the PN number by 100. E.g PN18 x 100 = 1800Kpa.

'''Pipe:'''

To find the pressure rating of PVC pipe, use the same system as you did with the fittings. Find the PN or Class number.
Try not to get confused with the 'DN' number, which is the nominal diameter in millimetres. E.g DN50 = Diameter 50mm.

As with the American system, there is another way to determine the pressure rating, and that is by AS/NZS number. More information to come soon.

PVC vs. ABS

2008-02-16T00:13:28Z

Pilgrimman: Basic information about ABS and PVC, edits are needed, please add a section about advantages/disadvantages with regard to the launcher being built.

==Introduction==

Although many materials are available for launcher construction, arguably the materials most used are PVC (Polyvinyl Chloride), and ABS (Acrylonitrile Butadiene Styrene). Both materials have many advantages and disadvantages, as outlined below.

==Physical Characteristics==

'''PVC'''

* Density: 1380 kg/m^3
* Melting Point: 212 Degrees Celsius
* Becomes brittle when cold
* Natural Color: White
* Other characteristics: [http://en.wikipedia.org/wiki/Polyvinyl_chloride Wikipedia]

'''ABS'''

* Density: 1024 kg/m^3
* Melting Point: 105 Degrees Celsius
* Resistant to changes due to temperature
* Natural Color: Black
* Other Characteristics: [http://en.wikipedia.org/wiki/Acrylonitrile_butadiene_styrene Wikipedia]

==Chemical Characteristics==

'''PVC'''

* Less resistant to shock than ABS

'''ABS'''

* Resistant to loads and shock
* Resists aqueous acids, alkalis, alcohols, and oils
* Swells when mixed with glacial acetic acid, carbon tetrachloride and aromatic hydrocarbons
* Soluble in esters and ketones

==Failure Characteristics==

'''PVC'''

* Shatters upon failure. For this reason, it is illegal in most areas to use PVC in compressed air applications.

'''ABS'''

* Rips upon failure, although it can shatter in the form of cellular core ABS. ABS is legal for compressed air applications, as long as it is pressure-rated.

==Availability, Price, and Other Information==

'''PVC'''

* Typically cheaper than ABS
* Pressure-rated, usually well beyond what a launcher would require, except in the case of Hybrid launchers.
* More common than ABS
* Fused by solvent welding, which requires two parts: Primer (a mixture of solvents), and Cement (Solvents with PVC resin).
* Easier to acquire in different diameters

'''ABS'''

* More expensive than PVC
* Not pressure-rated (Pressure-rated ABS does exist, but it is much less available, and much more expensive).
* Less common than PVC, especially pressure-rated
* Fused by only one chemical, ABS cement

It should be noted that ABS cement will NOT work on PVC, or vise-versa.

FAQ

2008-02-15T23:33:32Z

Pilgrimman: Stipulated certain situations and facts in the cannon pros/cons.

==Introduction==
This page aims to answer some of the common '''"Which is better?"''' questions seen on the forums in a simple manner.

Normally, there is no simple resolution to the question, because if there were, you wouldn't need to ask it. For example, if we '''knew''' pneumatics were best, then you wouldn't see any combustions.

It's not as simple and clear cut as people asking the question might think. However, this page will hopefully give you the information you need to make the decision for ''yourself'', depending on what is most important to you in your launcher.

==Combustion vs. Pneumatic==

''"Which is better? Combustion or Pneumatic?"''

This is probably the most common question that gets asked on the forums, and the big problem with it is that it is unanswerable.
Without knowing what a person wants from a spudgun, nobody can put one type ahead of another.

However, most experienced spudgunners will agree on this short list:

* [[Combustion Cannon|Combustion]]
* [[Pneumatic cannon|Pneumatic]]
* [[Hybrid Cannon|Hybrid]]

Where down is ascending order of "power" but also difficulty to use and build.

But, here are the main advantages and disadvantages in easy lists for you to decide on your own:

'''Combustion cannons'''

Advantages:
* Usually cheaper and easier to build
* Usually quicker to refuel and reload.
* More portable. Just needs a can of some flammable vapour, not a pump or compressor.
* Can be made bigger, but still kept practical.
* Easier to later upgrade.

Disadvantages:
* Less power, with a upper limit to what is practically possible (with all safe fuels).
* Less controlled (Maintaining consistency and altering power)
* Often inconsistent and unreliable (Advanced Combustion launchers can overcome this, but often cost more to construct).
* Potentially noisier. This can be remedied to some extent by having a good [[Chamber to barrel ratio|Chamber to Barrel Ratio]].
* Very large chambers are more prone to [[DDT|DDT]], although this is only likely to occur in chambers that are very long, on the order of a meter or more, and depends on many variables.

'''Pneumatic cannons'''

Advantages:
* Normally more powerful, with less of a "ceiling" to power (The particle speed of the gas does limit power to some extent).
* More controllable and consistent, as power can be varied with pressure.
* Easier to simulate in a program, although programs have been written for Combustion cannons.

Disadvantages:
* Takes longer to fill, unless you have a decent compressor or bottled gas (Especially true with large chambers).
* Less portable.
* More complicated to construct.
* Leaks are a greater problem, as they can cause a valve to open prematurely.
----

As a final note, a large majority of the launchers that Spudfiles (and other similar spudgun forum) users build are pneumatic cannons, but amongst people who don't take it up as a hobby, combustion cannons are more common.

==Working on==

* [[PVC vs. ABS]]

==To come soon==
* Metal vs. Plastic
* Boys vs. Girls (I'm kidding about this one)

Triggered burst disk

2008-01-22T01:51:07Z

Pilgrimman: Example of triggered burst disk.

[[Image:Triggered_burstdisk.PNG|frame|The firing cycle of a triggered burst disk]]
A triggered [[burst disk]] system consists of two burst disks mounted between the chamber and barrel of a [[pneumatic cannon]], with a trigger chamber in between and a trigger valve that either dumps said chamber to the atmosphere, or connects it to the main chamber.

The burst disks must be dimensioned to break somewhere between half and full chamber pressure. The trigger chamber is filled to half the chamber pressure, and then the chamber is filled to full pressure. When the trigger valve is opened, one of the disks is subjected to the full chamber pressure and ruptures, in turn overloading and rupturing the second burst disk.

The design has the advantages of quick opening and full flow of a burst disk, and with the reliability and repeatability of normal [[pilot valve]]s. It has the other disadvantages of a burst disk system, as well as higher consumption of burst disks.

An implementation of this idea may be found here: [http://www.spudfiles.com/forums/triggered-burst-disk-by-pilgrimman-t12809.html]

[[category:valves]]