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Propane Pneumatic

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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Propane Pneumatic

Unread postAuthor: mako » Sun Jun 30, 2013 12:43 pm

Hey guys, Sorry if this has been discussed elsewhere, but I looked and couldn't find anything.

I want to build a cannon that uses compress propane as the propellant.

I don't want it to be combustion, but rather to use the expanding propane the same way CO2 is used.

Is this possible? And if so, what are the dangers of the propane combusting on accident?
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Unread postAuthor: hawktalk » Sun Jun 30, 2013 1:43 pm

it seams a waste to use expensive propane as a co2 replacement like all gases lighter than air, temperature and atmospheric pressures affect the guns performance id stick to co2 or use air if you want a pneumatic or even look into building a coaxial air gun( their really cool and much more simple to make than a decent ball valve or hammer valve gun) if you are going for a small build id go for a coaxial gun as the chamber is around barrel and you can move the trigger forward this allows longer barrel and bigger chamber.

hope this helps its what i have learned so far
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Unread postAuthor: mako » Sun Jun 30, 2013 2:34 pm

Lol. I'd agree with you on any other build, mate.

In this case, though, none of it is applicable. :(
The gun is for launching nerf balls for airsoft games.
It will be stationary, and therefore can use a big tank.
A single refill for a several gallon tank of propane at around 150 PSI is less than twenty bucks.
If I'm only firing a rubber foam ball 200+- feet, this tank should last for a very long time.
Also, where I live, CO2 is more expensive, because its a very long drive to get the CO2 refilled. This is why I don't play paintball very often.
In addition to this, CO2 comes out VERY cold, and I'd rather not deal with the problems that arise from this.

The question I had about propane is this; will using it create a cloud of gas that will catch fire at the drop of a hat?
I know that airsoft gas guns sometimes use propane. :D
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Unread postAuthor: cammyd32 » Sun Jun 30, 2013 4:52 pm

I know that airsoft gas guns sometimes use propane.


Your right in that respect, 'green gas' as it is marketed as, is just a mixture of propane and lubricants, pretty much every gas powered airsoft gun apart from those using co2 use green gas or derivatives of it. The risk of propane igniting as it leaves the barrel is pretty much zero, unless you're holding a lit flame to the muzzle, in which case you get a small fireball, pretty, but fairly safe. Also it's worth bearing in mind that the gas will disperse fairly rapidly, especially if your playing outside in a light breeze.
So as to your concerns about safety if it's deemed safe enough for the hundreds of manufacturers that produce gas guns, I'm pretty sure its safe for you to use in your project.

Your idea is possible, although for it to work to a 'decent' standard you really need to have an expansion chamber so the gas won't freeze (as much as it normally would) as you fire, the power drop associated with this is especially more noticeable with larger bores because of the greater volume of gas being used per shot.

I've toyed with the idea of using propane as a propellant gas in the past quite a few times, although I've always been put off by the multiple bulky fixtures that are required to connect to a propane tank, and trying to siphon gas off can be quite costly if you make a mistake,

Hope that answers your question(s)
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Unread postAuthor: Technician1002 » Sun Jun 30, 2013 5:16 pm

Safety first. Propane is flammable. It is heavier than air and like CO2, it can accumulate in low spots. A mixture in air of about 4% can be explosive. Be very sure there are no buildings nearby with a crawl space or basement.

In airsoft only small volumes are used. In airsoft it is called Green Gas.

Here is a story of a convience store that had a propane leak.

http://www.hazardexonthenet.net/article/19481/Little-General-store-propane-explosion.aspx

Image

Propane is a refrigerant. Under heavy use the temperature and pressure will drop.

Newer propane tanks have a high flow shutoff in the valve. Use on big bore cannons is likely to trip this protection valve.
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Re: Propane Pneumatic

Unread postAuthor: jackssmirkingrevenge » Mon Jul 01, 2013 2:27 am

mako wrote:I want to build a cannon that uses compress propane as the propellant.


Is it because you really want to use propane, or because it is the only compressed gas readily and cheaply available to you?
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Unread postAuthor: mako » Mon Jul 01, 2013 9:46 am

The latter. CO2 is more expensive, and controlling it would be more difficult(I think).
Compressed air would be OK, except I have no way of compressing the amount I would need. I'm limited to a bike pump for the air.
If there was another option, I'd go for it happily
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Unread postAuthor: jean » Mon Jul 01, 2013 9:48 am

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Unread postAuthor: jean » Mon Jul 01, 2013 9:49 am

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Unread postAuthor: cammyd32 » Mon Jul 01, 2013 1:52 pm

mako wrote:The latter. CO2 is more expensive, and controlling it would be more difficult(I think).
Compressed air would be OK, except I have no way of compressing the amount I would need. I'm limited to a bike pump for the air.
If there was another option, I'd go for it happily


If you are expecting to save money by using propane, wouldn't it probably be more economical in the long run if you bought a shop compressor? with propane you will find the costs can rack up quite considerably after a couple-of-hundred shots, and you don't have a lot of the flexibility as you would a compressor
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Unread postAuthor: mako » Mon Jul 01, 2013 2:33 pm

Long run? Possibly. However, this is going to be used for airsoft, which only happens maybe a few times a month, and you wouldn't be able to fire it very often during the game.

I'd be happy to buy an air-compressor, but the problem isn't having enough money over a period of time, its having enough money all at once.

I can afford maybe 20 bucks a month for a several gallon propane tank,
but it would be a long time before I can save up enough for a half-decent compressor.
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