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Pneumatic Gun?

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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Pneumatic Gun?

Unread postAuthor: BrodMan » Mon Nov 19, 2007 6:38 pm

i was a member before, but i lost my information, so i thought id rejoin, and ask some more questions. i havent been to a hardware store for a while so i'll check next time i go, but im in the business for building a pneumatic airgun, and was wondering whether i should use pvc, or copper pipe. i dont know the price difference, but i know pvc is pretty cheap, and copper is fairly expensive, but i would rather use copper, for saftey reasons, but i dont know about the price. also i was wondering, what is the best valve for releasing all the air as fast as possible. i will try and draw up plans, and post them asap, but i want to do a little more research first. i think i want to go 1/4" or smaller.
thanks.
BrodMan
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Unread postAuthor: potatoflinger » Mon Nov 19, 2007 6:45 pm

If you want something that is (fairly) reasonable in price, you could go with black iron, or galvanized steel pipe, plus it's all threaded, so if you ever get tired of the same gun, you could take it apart and reconfigure it. Also for the valve, wince you want 1/4" or smaller, you could go with a QEV, they are great, but kind of pricey and hard to find. Another alternative for the valve would be a piston valve, but if you're new I would recommend a QEV. (If you have trouble finding a QEV, you could check fastenal, it's not too bad for a QEV under 1") http://www.fastenal.com/web/products.ex ... &N=0&Nty=1
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Unread postAuthor: BigJon » Mon Nov 19, 2007 6:45 pm

For a Valve try using a modded sprinkler valve. They are not very hard to mod, all you do is drill a hole and tap some threads basicaly.

Also I would use PVC just because its cheaper and is perfectly safe as long as you don't want to use high pressures. Just make sure its pressure rated.

EDIT: Sorry didn't see that you wanted it 1/4" but go with what potatoflinger said. also, why so small?
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Unread postAuthor: Zen/// » Mon Nov 19, 2007 6:54 pm

I think he want's more of a rifle like design, instead of a cannon like gun.
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Unread postAuthor: DYI » Mon Nov 19, 2007 6:57 pm

If you really want to release all the air as fast as possible, use a burst disk valve. If you want to enjoy shooting it, build a piston valve. Copper is safer than PVC, but I would suggest steel pipe for the chamber. Easy to work with, dirt cheap, and capable of surviving over 1000 psi in most cases. And 1/4" is pretty small, unless you plan on using a LOT of pressure.
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Unread postAuthor: BrodMan » Mon Nov 19, 2007 7:26 pm

the reason its so small, is because i want it for reasons that are not to be discussed here. i just came here to figure out how to build it.
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Unread postAuthor: Zen/// » Mon Nov 19, 2007 8:00 pm

:O :o

Your a secret agent aren't you!!! 8) :shock: :D
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Unread postAuthor: BrodMan » Tue Nov 20, 2007 7:03 am

no its just against the rules to talk about it.
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Unread postAuthor: Hotwired » Tue Nov 20, 2007 9:05 am

Well as long as you know its highly discouraged and you were told not to do it, whatever it is that is not to be discussed.

You really need to sketch up some plans before anything much can happen.

Theres homemade piston or diaphragm valves, commercial piston or diaphragm valves (generally quick exhaust valves) and the wonderfully simple but annoyingly fiddly to use, burst disk valve.

For 1/4" and relatively new to making spudguns a QEV would be fine, a 3/8" or 1/4" QEV should be enough.

Pipe is just a matter of preference and pocket, if theres rated plastic to the pressure you're going to use then thats fine.
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 20, 2007 9:22 am

If you're going small calibre, you need a small chamber and high pressure for decent power - meaning get yourself a bicycle shock pump and make sure your piping can take 300 psi+
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Unread postAuthor: jimmy101 » Tue Nov 20, 2007 10:53 am

The choice of metal versus PVC really should be made based on your source of compressed air.

If you'll be using a typical shop compressor (~120 PSIG maximum pressure) then PVC is probably best since it'll handle the pressure and is cheap. Metal will handle much higher pressures but the extra $$$ gets you a capability that you can't use with a generic shop compressor.

If you've got a high pressure pump, or will be using high pressure compressed gas (like a CO<sub>2</sub> bottle), then you'll need a metal gun to take advantage of the higher pressure capability.

For a PVC/shop compressor setup a sprinkler valve is a pretty good way to go. Much simpler than buiding your own valve, though not quite as powerful. One nice thing about the sprinkler valve is that it can be used unmodified (and electrically activated) when you first build the gun. You can mod the sprinkler at any time without needing to make any other changes to the gun.
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