piston valve inlet

[c11man]

i want to make a new piston vavle soon and was wondering about the inlet size. it it is built into a 1 1/4 tee with 1inch porting. the inlet will be threaded just like the mauler. will having the threaded inlet the same size (instead of bigger) than the porting reduce flow enough to get a decrease in preformace?

[Carlman]

No noticeable performance loss mate

[c11man]

ok this will simplify the design ALOT. if i make this i will do some tests comparing triggered burstdisks with a piston valve. this valve will have all the goodies like orings and a check valve. also with the 1 1/4 tee with 1inch porting i should be able to get a more QEV like effect where the piston snaps back

[Technician1002]

No noticeable performance loss mate

Actually having two significant restrictions in a row do make a difference. In high flow situations, the pressure drop on the first restriction will causes a pressure drop and in a gas a pressure drop is a volume increase. The volume increase is before the second valve.

In a nutshell if air flows near supersonic through the first and then hits the second and you want all the air through the second at the same speed, the second will need to be bigger.

If the first restriction is eliminated (made insignificant) then the second will receive air at the higher pressure the first restriction had, and speed.

In piston valves the inlet port is considered good if the porting into the outlet is of the same area as the outlet. To prevent pressure loss going into the valve, I make the inlet ports about 150% to 200% the size of the valve orifice. For example my 2 inch piston valve has an orifice size of 2 inches which is just a little over 3 square inches in size. The inlet to the valve from the chamber is 3 ports 2 inches by 1 inch for an area of 6 square inches.

I'm not sure how much this affects the flow, it may be no noticeable performance loss, but I think it may be noticeable. GGDT is showing my valve efficiency as "Optimistic". I like that.

[c11man]

but if the air can only flow around the bend inside of the tee so fast the inlet might not have to be as big right?

also this will be to test a typical piston valve against a triggerd burst disk valve. this will be a example of a "normal" piston valve where many of them do have a imput the same as the porting.

so this will not be the highest preforming 1inch porting valve out there but that is not what the test will be about

[Technician1002]

but if the air can only flow around the bend inside of the tee so fast the inlet might not have to be as big right?

also this will be to test a typical piston valve against a triggerd burst disk valve. this will be a example of a "normal" piston valve where many of them do have a imput the same as the porting.

It is true the bend in the piston will have a higher resistance to flow (lower COF) than the inlet.

I will eagerly await your test results. I was getting results in modeling my valve where it was comparing quite favorably with a burst disk.

The thread is here; I was getting chronograph numbers on the high side of what was expected with lightweight projectiles.
http://www.spudfiles.com/forums/ggdt-an ... 18090.html

I still need more testing to see if the results are real.

[c11man]

for this test i still need to figure out a good barrel and standard ammo to test the speeds of it. i dont have a crony so i will have to use audoclady to find the fps. ammo ideas and tips on how to set up the target to get easyer reading would be greatyly appreciated

[Technician1002]

for this test i still need to figure out a good barrel and standard ammo to test the speeds of it. i dont have a crony so i will have to use audoclady to find the fps. ammo ideas and tips on how to set up the target to get easyer reading would be greatyly appreciated

Since you are using Audacity, a pair of coils at the muzzle can pick up a passing magnet in your projectile. My linked thread above has an example using a scope and printer, but a sound card can substitute for this portion. More info on using a sound card and magnetic pickup is on this page.

Edit.. Oops forgot the link. http://inteltrailblazerschallenge.wikis ... rim+method

We used the magnet method to trim the length of a barrel to match the performance of a valve, pressure, and projectile for the most efficient launch in a competition.

Changes in pressure, or projectile changes the length the barrel needs to be for the most efficient launch. This trim is partly responsible for the insane performance we were getting with it.

Attached is a photo of the Arlington team with the winning cannon putting a T shirt on the roof of the PGE Park at a Portland Beavers home game. It is 5 stories up.

[Carlman]

cant help yaself can ya tech

[c11man]

i was accualy thinking about using it to measure the time between the noise from the launch and hitting the target

[Gippeto]

cant help yaself can ya tech

Gratuitous self promotion score... 3 for 3 posts in this thread alone. 100%


Back on topic;

c11, I try to keep the passages feeding the valve larger than the porting. This minimizes the velocity of the air in the passages, and since drag increases as the square of velocity, keeping the velocity in the passages lower even by a little, pays back in reduced losses.

At least, that's how I see it.

I'm sure I'll be corrected if I'm even remotely mistaken.

[c11man]

i have desided that the 1inch inlet is fine because this test is going to be for a "normal" piston valve and not some the best valve possible.

since it will have orings and a check valve i will be better than some but still not be over the average persons valve

right now i realy need some standard ammo and barrel size to test these 1inch porting valves

[Technician1002]

i was accualy thinking about using it to measure the time between the noise from the launch and hitting the target

A microphone completely sealed and attached to the targets works well as a contact mic so you get target vibration from impact instead of just the sound of the cannon. My 2 cents worth. A magnet on the targets and a nearby pickup coil can be a target motion sensor to measure the actual target impact times.