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Piloting via shreader?

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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Piloting via shreader?

Unread postAuthor: iisthemuffin » Mon Sep 01, 2008 8:13 pm

Im trying to pilot a mini coaxial with a shreader valve. The problem im having is that when i unglug my pump from the gun, i loose too much air. My chamber is 8 inches of 1/2 SCH 40 pipe. I take it to 100 psi, but when i unhook the pump it drops to like 10-30. And then when i try to pilot all of the air in the chamber comes out.

I was wondering how the rest of you avoided this problem in smaller piston guns?
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Unread postAuthor: elitesniper » Mon Sep 01, 2008 8:33 pm

a smoother sliding piston and more air tight?
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Unread postAuthor: iisthemuffin » Mon Sep 01, 2008 8:49 pm

Well ive greased up the piston and its smooth as can be.

It pilots now, but i still loose alot of pressure when disconnecting the pump.
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Unread postAuthor: brogdenlaxmiddie » Mon Sep 01, 2008 9:00 pm

I think that the pressure that you think your losing it actually the air left in the tubing from the pump. Are you using a pressure gauge on the gun itself to determine your air loss? Or are you just thinking it?
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Unread postAuthor: jackssmirkingrevenge » Mon Sep 01, 2008 10:53 pm

Most bicycle pumps have a cam which physically depresses the shrader valve stem when disconnecting, it depends on what type of valve you have. I fitted an extra o-ring to my shock pump so that air passes only through pressure difference, so when I start to disconnect the pump the schrader remains closed. Have a look towards the end of the pneumatic pengun thread where this problem is discussed in detail.
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Unread postAuthor: jimmy101 » Tue Sep 02, 2008 1:09 pm

You might consider installing a second schrader into either the pilot volume or the chamber. That way you can leave the compressor / pump hose in place on the new schrader and fire the gun with the one you already have.
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Unread postAuthor: Sticky_Tape » Tue Sep 02, 2008 1:20 pm

Make a adapter. Get a lenth of 1/4'' i/d flexible pipe that is braided, a tubless tire valve striped of rubber, and two hose clamps. hose clamp the hose onto the the air out side of the shrader not the fill side of it and you are done hook the pump onto the fill of the shrader on the adapter and hose clamp the hose onto the shrader that is on the gun wan't a diagram?
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Unread postAuthor: psycix » Wed Sep 03, 2008 10:03 am

I had that problem too.
What you should do is either a "safety" ballvalve between the fill valve and the chamber OR a checkvalve.
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