Propane as a propellant (not combustion)

Zippster · Tue Jan 22, 2008 2:12 pm

I was pondering portable gas options the other day, and it struck me that theres a propane tank sitting right there in the back yard. I know gas airsoft guns use the stuff as a propellant - notably NOT for its combustive properties, rather its compression - and thought that it might work for a 'pneumatic' cannon.
My questions are:
- What is the unregulated pressure of propane?
- Is it stored as a gas, or a liquid?
- Do air regulators, gauges, etc. work for propane without modification?
- Is it corrosive/etc. to not allow use of PVC?
and most importantly...
- How dangerous would it be?

I'd feel quite comfortable about using this stuff considering how hard it was to intentionally fire my old combustion cannon with a spark igniter. But if the risks outweigh the benefits...
Could I just use empty propane tanks for air storage?
I'd think so, but I remember hearing something about the contrary...

Thanks for the input, I know thats a lot to ask - and I'll be looking it up to - but I'd trust the opinion of someone with a little more experience to my own.

Hubb · Tue Jan 22, 2008 3:00 pm

Propane generally runs around 90 to 100 psi, unregulated, and is stored as a liquid (LP gas = liquid propane gas). I'm not too sure about normal air regulators working with propane, but why not just get a propane regulator? It works fine in PVC as a pneumatic and a combustion fuel and is no more dangerous (as far as pneumatics go) than any other gas that is put into the chamber.

This topic has been discussed before and may have been looked up but it's okay. At least your topic is neat and orderly and has good grammar.

seudo411 · Tue Jan 22, 2008 3:28 pm

hubb017 wrote: At least your topic is neat and orderly and has good grammar.

I agree,

If you want to go for an even more portable design, try to acquire a small camping stove and unscrew the burner part, you'll be left with a valve and the stem that the jet screws into, I think the standard thread size is 1/4" and you can carry it your back pack or what ever you please. For a larger portable air tank you might want to consider an empty refrigerant can, ask your local air con supplier for one.

note: there is a topic dealing with this in the how to section explaining how to convert the tank as well.

psycix · Tue Jan 22, 2008 5:14 pm

My questions are:
- What is the unregulated pressure of propane?
- Is it stored as a gas, or a liquid?
- Do air regulators, gauges, etc. work for propane without modification?
- Is it corrosive/etc. to not allow use of PVC?
and most importantly...
- How dangerous would it be?

-answered above, 90-100 PSI (also depends on temperature)
-liquid
-a gas is a gas, so yes
-AFAIK its not corrosive, hairspray is more
-it would not be very dangerous unless you aim it at a fire hazard. It will not likely ignite inside the chamber, it cant explode if theres more than about 10% of propane in the air, and if it would, you would get a combustion or maybe some hybrid wich is way out of its stoichiometrics.

Thing I got to add:
-Its a bit wasting of fuel... you can get more pressure out of it when buring it.
-Propane is a heavy gas (compared to air) it will perform bad, even worse like CO2. Its like the opposite of helium or hydrogen(far more dangerous btw but okay) that is lighter and flows better instead of worse.
So propane gives BAD flow and also the sound barrier will be too low in propane, giving you this "sound barrier blockade" at lower velocities than if you would use normal air.

clide · Tue Jan 22, 2008 5:30 pm

Another big problem with propane (in my opinion) is the smell. Propane itself doesn't smell, but any of the stuff you can buy at the store will have an additive that makes it smell bad so people know if there is propane leaking around them.

I've heard somebody say that if you use it for an unburned power source in a gun then that smell will stick around for a long time inside the gun.

maxfreke88 · Tue Jan 22, 2008 6:28 pm

i wouldn't recommend a propane tank as an air source, because it is use to letting go of propane at a slow rate, this causes less stress than at a faster rate as with pressurizing a gun. propane tanks are not made for that amount of stress. Also propane is dry, air is moisture laden, thus creating condensation, and ultimately, RUST.

Tom Hogan · Tue Jan 22, 2008 7:44 pm

I use propane in my gas blow-back airsoft gun, and the smell is only a problem inside. Outside it dissipates almost instantly.

experament-u2 · Tue Jan 22, 2008 8:22 pm

iv being using a portable propane bottle(the long blue ones used for blow torches) to charge some of my smaller guns every now and again, it works fine but it dose fill a little slow and only to around 95 psi. i have had no problems using it and the smell inst even that noticeable.

DR · Wed Jan 23, 2008 12:38 am

jimmy101 · Wed Jan 23, 2008 3:53 pm

In other words, propane works fine for a pneumatic.

There is a fire hazard.

If you chop the tip off a standard Bernzomatic torch head it'll put out gas at a pretty fair clip. The standard tip has an extremely small hole in it, nearly too small to see without magnification. (DR made up his own valve assembly.)

You won't get all that many shots out of a standard Bernzomatic tank. Of course the number of shots you do get is dependent on the size of the gun's chamber. The standard Bernzomatic tank contains 400g of propane. At 44g/mol that is 9.1 moles of gas. At STP that gas occupies a volume of 204 liters, 7.2ft<sup>3</sup>. That is a cube with edges of just 1.93 feet.

The pressure in the tank is very dependent on the temperature of the tank. See the SpudWiki on propane for a chart of pressure versus temperature.

DR · Wed Jan 23, 2008 9:06 pm

Propane as a propellant (not combustion)

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