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Cheap semi-auto

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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Cheap semi-auto

Unread postAuthor: The Engineer » Tue Nov 25, 2008 12:23 am

I posted it here rather than the BB section because it would be easier to use as a standard pneumatic cannon without change barrel size.

Please take a look at the diagram and tell me if you think it will work. Also, does anyone know where to obtain a check valve such as the one depicted in the digram? (Spring keeps it closed, opens at certain psi)

How it works: Once connected, the chamber will instantly pressurize (or at least very quickly pressurize). When fired, the pressure will open the check valve, enter the barrel, and fire the projectile However, the difference is that the chamber will begin to repressurize as soon as it loses any pressure. This would usually result in some air escaping into the barrel if the pilot pressure has been completely exhausted. With the check valve, however, the air will not enter the barrel, preventing any misfire from it. Using this, I hope to achieve a true semi-automatic cannon which is also fairly easy to build, as well as cheap, for people such as myself with limited resources.
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Unread postAuthor: Gippeto » Tue Nov 25, 2008 12:58 am

I'm not sure if you can get swing checks that are spring loaded. Try local plumbing and hydraulic shops.

Circle Seal may have something useable as well;

http://www.circle-seal.com/products/check/index.html


And by the way, you have the blowgun mounted backwards. :)
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Unread postAuthor: Hydra » Tue Nov 25, 2008 3:05 am

Yeah haha! that blowgun is backwards... But who cares! as long as you havent done it on the real thing.

That idea seems okay. But there are two things i wanna point out
1. Air source. Is the air source coming from a compressor or another big tank? If it is from a compressor the compressor might not compress "instantly or quickly" If it is from a big tank the tank will have to be massive or the chamber will have to be pretty small.
2. Check Valve thing. I dont know if check valves have a good flow. I mean the sprinkler valve has OK flow but that doesnt matter if the check valve has bad flow. I guess you could make your own check valve (People make them when they create hand/foot pumps. Try searching around this site, ive seen some homemade stirrup pumps.)
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Unread postAuthor: The Engineer » Tue Nov 25, 2008 1:00 pm

OOPS, backwards blowgun, that was a stupid mistake. I forgot to flip it in paint, lol.

My chamber will indeed be quite small, and the source will be from a 20oz CO2 tank. (It doesn't have to be an extremely fast semi-auto, only about 1 round per second-ish)

What I was really concerned about is if the sprinkler valve will still reset if the excess air going through is stopped by the check valve on the other side.
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