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Pneumatic Gun using Combustion as the compression source?

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Pneumatic Gun using Combustion as the compression source?

Unread postAuthor: HaiThar » Thu Sep 20, 2007 4:23 pm

Would it be possible to use combustion as a pressurization source for a pneumatic cannon? I.E.: Hairspray Axe, ect... is sprayed into a chamber, then ignited. You have a reuglator between your firing valve and the chamber. Open firing valve, regulator only allows however much pressure you want into your barrel.

I just hate pumping up my chamber, and I really dont have the $$$ atm to get a half-decent compressor...

Also, would it be possible to make a semi-automatic like this?

Ideas and thoughts are definatley welcome.

HAITHAR
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Unread postAuthor: MaxuS » Thu Sep 20, 2007 4:26 pm

Would have thought it would cost less to get a smallish compressor, the emergency tire compressors only cost £7 ($14) over here, and they'll happily pump up to 220psi+ in about 1 1/2 minutes. There must be a brand over there.
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Unread postAuthor: HaiThar » Thu Sep 20, 2007 4:31 pm

Do they make those with AC plugs? =\
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Unread postAuthor: jackssmirkingrevenge » Thu Sep 20, 2007 4:35 pm

This has been suggested many times before but fundamentally won't work - the pressures generated by combustion are a function of the heat, once the gasses cool they will return to atmospheric pressure. The only way to use combustion to obtain compressed air is to have the combusting gasses driving a piston that compresses air past a check valve into a reservoir, in the same way the Sims-Dudley Dynamite Gun used black powder.
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Unread postAuthor: DYI » Thu Sep 20, 2007 4:36 pm

This could be done, but not in the method you propose, since the only source of pressure from the combustion is the increased heat. Lose the heat, and you'll lose the pressure.

To make this work, you could have a long chamber with a piston. Combustion occurs behind the piston, pushing it forward. When the (airtight) piston moves toward the front of the chamber, it compresses the gas in front of it. The gas could be forced through a check valve at the front of the chamber by this method, and then stored in a chamber after the check valve. Altogether, this method would not be worth it, and it would be far more difficult and costly than buying a cheap 125 psi air compressor (unless you plan on combusting black powder or 10x hybrid mixes, in which case, go for it, and good luck stopping the piston).
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Unread postAuthor: MaxuS » Thu Sep 20, 2007 4:36 pm

Yeah, but an adapter is peanuts.
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Unread postAuthor: DYI » Thu Sep 20, 2007 4:37 pm

Damn you Jack, you answered while I was typing :D
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Unread postAuthor: jackssmirkingrevenge » Thu Sep 20, 2007 4:38 pm

*breathes on fingernails and polishes them against shirt*

:D
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Unread postAuthor: HaiThar » Thu Sep 20, 2007 4:38 pm

Alright thanks. I didnt realize that the pressure was just in the heat....

Back to the drawing board, eh?

But thanks for your help.
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Unread postAuthor: jimmy101 » Fri Sep 21, 2007 12:04 pm

HaiThar:

A couple possibilities;

1. Like others have said, the design you proposed won't work. But a hybrid is similar and works. Though you still need a compressor.

2. Alternative sources of compressed gas include PBall CO2 tanks, compressed air tanks and even Benzomatic propane cylinders.

A PBall setup probably works very well but I think when everything is done it'll cost close to what a small shop compressor would have cost.

If you don't mind the smell, and fire hazard, using propane as a compressed gas can probably be done for a lot less than CO2.
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Unread postAuthor: williamfeldmann » Fri Sep 21, 2007 1:26 pm

Paintball tanks work real good for medium or smallish guns. You get into a bigger chamber or somthing like that you get maybe 3 or 4 shots off a 68ci tank, that gets real expensive quick. And it sounds like you have a decent sized chamber on the gun, either that or a crappy bike pump.

I used propane once in a gun and found less than desirable results. You really need to vent your gun because otherwise you end up with propane leftover in your chamber and whatnot. Didn't think of it and put it in the garage. Almost threw up the next morning when I opened the door from the fumes, propane and potato are not a good combination smell.

However, propane is cheaper and available in much larger volumes than paintball tanks.

Personally, I would go to a bicycle specialty shop and spend the money for a good pump capable of 150ish PSI (maybe $40). It will work good with smaller guns and get you by till you can get an air compressor. Or if you know someone with an air compressor, buy an air tank (sometimes called air bombs, or maybe thats a local thing). You can get a 10 gallon tank from Lowes or any store that sells air compressors for under 40 bucks. Charge them using an air compressor and carry it with you to where you fire. They will hold pressure basically indefinetly if you want to charge it and wait a week or whatever.
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Unread postAuthor: iknowmy3tables » Fri Sep 21, 2007 2:23 pm

you don't get much air from propane not really worth it unless you plan on some green gas like setup

an air compressor is the best investment you can make if you build pneumatics
a palmer regulator is a really good investment if you you need to travel, but a compressor is a must have especially if you build a lot or want a gun with high ROF
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