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My piston pilots but no air comes out of barrel

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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My piston pilots but no air comes out of barrel

Unread postAuthor: iisthemuffin » Mon Jul 21, 2008 10:29 pm

I know thats impossible but something weird is happening. I pump up the gun and i try to pilot it. the air poofs out the back and nothing happens. So i try to pilot again and nothing. I keep trying to pilot until all of the air is gone and nothing happens. Then when i go to pump it up again i hear the piston reseat and i repeat trying to pilot. Again nothing and i go to pump and piston reseats.

Whats going on? Any way to fix this?
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Unread postAuthor: frankrede » Mon Jul 21, 2008 10:46 pm

That happened to me.
tell us more about your piston and whats its made of.
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Unread postAuthor: iisthemuffin » Mon Jul 21, 2008 10:50 pm

Well i started wiht apiece of wood. Too thin. Then a marker. Didnt work at all. Now i have the nozzle off of a spray bottle. I use the flat side as the sealing side. This is a picture of a bottle with the nozzle i use. http://img.alibaba.com/photo/51260499/Spray_Bottle.jpg
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Unread postAuthor: blind909 » Mon Jul 21, 2008 10:54 pm

What is your sealing face? Can we see a picture of the gun? Is it 1/2 inch, 3/4 inch? Do You have an equilization hole? If so, how big is it? What is the pressure used? There is many more info needed than the fact that it is a cap of a spray bottle.
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Unread postAuthor: iisthemuffin » Mon Jul 21, 2008 10:58 pm

I provided the information he had requested. Also all of that information really is not needed. Obviously frank as encountered this problem also and may know how to fix it just by knowing my piston.

Even though i know you wont be able to offer any useful suggestion here is the information your requested.

Sealing face is a rubber washer of material i am unsure of.
No because my camera is being weird.
It is half inch pvc.
No i do not have an equalization hole.
60-80 for testing.

Also i would like to include that it is coaxial.
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Unread postAuthor: Insomniac » Mon Jul 21, 2008 11:24 pm

I assume your gun is pretty small, and I had a similar problem with mine. What valve are you using to pilot it? I have found that a schrader simply won't work for mine, but the massive ballvalve I have on it now works fine. Try attaching a ballvalve to it and see if that will pilot it.
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Unread postAuthor: frankrede » Mon Jul 21, 2008 11:28 pm

iisthemuffin wrote:I provided the information he had requested. Also all of that information really is not needed. Obviously frank as encountered this problem also and may know how to fix it just by knowing my piston.

Even though i know you wont be able to offer any useful suggestion here is the information your requested.

Sealing face is a rubber washer of material i am unsure of.
No because my camera is being weird.
It is half inch pvc.
No i do not have an equalization hole.
60-80 for testing.

Also i would like to include that it is coaxial.
How well of a fit is your piston?
If you cover one end of your pipe, does this piston fall slowly down the pipe? Does it get stuck? or does it go down fast?
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Unread postAuthor: iisthemuffin » Mon Jul 21, 2008 11:30 pm

I actually just looked at your gun in hopes of finding a solution to mine. I kind of feel like the shrader is the problem. But if the piston is going back why wont the air go out the barrel? Is the piston SLOWLY moving back?

I have a ballvavle i may be able to use.

What would you say about a blowgun? Would that pilot it well?


How well of a fit is your piston?
If you cover one end of your pipe, does this piston fall slowly down the pipe? Does it get stuck? or does it go down fast?


It does nothing.
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Unread postAuthor: noob of noobs » Mon Jul 21, 2008 11:33 pm

I think this happened to me. What happened was that I activated pilot, and all the air rushed out the pilot (then a blowgun.) Then just as the last of the pressure was escaping; then the piston moved back and opened, only to let out a small gust of air. A larger pilot and a better piston remedied this problem for me.
All my current pistons are now a very tight fit, and ussualy are piloted by a spring loaded 1/2" ball valve (One is piloted by a blowgun, but that's unoprational right now).
Hope this helped.

Edit: Since you seem to have tried a ballvalve, I'd recomend you try a sprinkler valve, just to see if your pilot's the problem.
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Last edited by noob of noobs on Mon Jul 21, 2008 11:37 pm, edited 1 time in total.
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Unread postAuthor: iisthemuffin » Mon Jul 21, 2008 11:35 pm

Very helpful actually. From your post i see that my problem is either pisotn size or my pilot. I would assume its the pilot as other have mentioned.
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 21, 2008 11:47 pm

could it be that the piston is too short - lengthwise - which allows it to skew and therefore jam, not allowing free movement?
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Unread postAuthor: iisthemuffin » Mon Jul 21, 2008 11:50 pm

Could be actually. Why would it being too short stop it from working? Im not sure what you mean.
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Poop.
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Unread postAuthor: MrCrowley » Mon Jul 21, 2008 11:57 pm

This is a VERY common problem.

Main causes: (can be a mix of several)

Piston is not a good enough fit
Piston is too tight of a fit
Piston housing is too rough and piston is getting jammed
Piston is too rough (tape can get caught sometimes) and is getting jammed
Pilot valve is too small (not enough flow)
Pilot volume is too large
Barrel isn't far enough into the tee (needs to be about halfway)
The seat (barrel) is similar size to that of the piston sealing face


I recommend you lube your piston, make sure it's smooth, make sure the piston housing is smooth, minimize pilot volume, make sure the barrel is in the centre of the tee, make sure your piston is a good enough fit (can you push it with your finger?) and try using a higher flow pilot valve, speed doesn't really matter, a 1/4" ball valve will be better then a blow gun for example.

Where is your pressure gauge? If it's in the pilot setup, it could just be measuring the pilot volume pressure and not the chamber pressure, if your piston is too tight it could be stopping air from going into the chamber. That's pretty rare though.

Usually, and I think in this case, your piston is sealing but when piloted the pilot valve cannot cope with one or several of the above issues and the air from the chamber is going around the outside of the piston and out the pilot valve, the piston is probably then sucked back a bit from what you could call a 'vacuum' making it seem that it did infact pilot normally but no air is coming out the barrel.

Have a think about those, and blind909 was right, you needed to give us more information so we can narrow it down.
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Unread postAuthor: iisthemuffin » Tue Jul 22, 2008 12:09 am

Well i suppose ill be purchasing a tee here soon so i can put a better pilot valve on. And just to let you know Crowley, its coaxial.

And im sorry for being rude blind. Im just a bit frustrated.

Thank you for your help MrCrowley.
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Unread postAuthor: MrCrowley » Tue Jul 22, 2008 12:15 am

Oh forgot about the co-axial part sorry.
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