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Piston Valve questions

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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Piston Valve questions

Unread postAuthor: kraken » Mon Oct 23, 2006 6:59 pm

I'm gearing up to build my first pneumatic potato gun and I have some piston questions. I will be building an over-under with the piston in the tee. I understand how they work and plan to machine my piston from a 3" x 6" piece of some kind of plastic (to be determined). I've got the design in my head and plan to make and AutoCAD file so share assuming it works.

The Question:
Is it possible to put a spring opperated check valve (like the ones on
McMaster-Carr) where the small hole in the piston goes? The reason I ask is most of the valves have a craking pressure of 1 or 2 psi. Will that be enough to move the piston against the 2" pipe leading to the chamber? If it is I would think that it would be more efficient than the small hole because you wouldn't loose any air through it. Has anyone tried this? I couldn't find anything when I searched the forums.

I don't want to spend $20 on a slug of plastic and hours on the lathe only to find out it doesnt work. I'll probably try it anyway but thanks for the help.
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Unread postAuthor: SpudStuff » Mon Oct 23, 2006 7:03 pm

Yes you can use the check valve but it only does anything if the piston is airtight with o-rings. The plastic is good but make it as light as possible. This increaces performance and open time.
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Unread postAuthor: jrrdw » Mon Oct 23, 2006 7:11 pm

That mite make a good strong piston, but how heavy is it? Mines made of wood and is some what lite, and it's steady beating up my pilot chamber. To answer your question, yea with a spring loaded shutter valve on the piston will make it better. I was going to use a shutter out of a old auto lock.
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Unread postAuthor: Yonderknight » Tue Oct 24, 2006 12:21 am

Instead of a spring check valve, you could always just make a hole and cover it with a rubber flap. When air tries to escape through the hole, it pushes the flap against the piston and seals the hole.
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Unread postAuthor: kraken » Tue Oct 24, 2006 6:36 am

thanks for the input guys. I was going to try to make it as light as possiable and seal it with o-rings. I'll will try and get some pics up as soon as I get the plastic. I think I am going to get this "Ultra High Molecular Weight (UHMW) Polyethylene" from http://www.usplastic.com
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