Propane fills

[Carlman]

If i had a 2kg bottle of bbq propane, how many times could i fill a 831 cubic cm chamber (50 CI) without it dropping below 40psi?

[Carlman]

anyone?

[jrrdw]

I'd say fill it up and start counting, or do the math for a good estimate.

[Fnord]

1 pound of liquid propane =~7 cubic feet gaseous propane.

Go from there.

[SpudFarm]

my father once droved a car with a 11kg propane tank at the back and he saw that white smoke behind the car but did not think more of it.
he drove for about two hours and stoppes to fill diesel when he saw the propane tank fully open. that means that out of a 3mm hole you can get atleast 2 hours of continous blowing.

so 2Kg of liquid propane is MANY shots.

[Jared Haehnel]

That tank must have been COLD!

[SpudFarm]

he said that the ice was on the whole car and tank.

[Carlman]

so anyone got the maths skillz to do this for me?

[Fnord]

If you really need to be spoonfed, I got 400 times at 45 psi. Not sure how accurate it is, but I believe it should be in the ballpark.

[Carlman]

bloody hell thats awsome, thanks alot _Fnord i really dont trust my maths for this kind of stuff

[Lentamentalisk]

PV=nRT

3.7atm*8.3E^(-4)L*[fills]=45.45mol*.08206*300K
strange, I got you having 362 fills... you have a tiny chamber though...

Anyone see an error in my math?

correction, you won't be filling the chamber from a vacuum so it will actually be: 2.7atm*.831L*[fills]=45.45mol*.08206*300K
which will give you 495 fills

Now those numbers should be right, I had a cm2 to L conversion error

That is not accounting for when it will drop below 40 psi, that is just how many fills you will have of 40psi, assuming you regulate it to exactly that every time. What pressure does your tank give you now?

[jon_89]

I thought about doing this also. Except I will have twice the chamber volume. I think a propane setup definitely make a cannon more portable and less expensive than a co2 setup.

[Lentamentalisk]

But highly flammable and stinky as hell... You would be giving your cannon a high IGB factor, and liquid propane is horrid volume and weight wise compared to CO₂ for turning it back into a gas.

[Carlman]

maybe you guys did not quite get me, i want to fill my gun to max 100psi and min 40psi. Propane is at 150ish psi at aussie temps at the moment when full.

so how many fills can i have within that margin, aiming for the highest pressure given the parameters?

[Lentamentalisk]

well that depends entirely on how much you use every shot. If you use 100 psi, then: 6.8atm*.831L*[fills]=45.45mol*.08206*300K
fills=198 assuming you use a compressor to get it out of the tank as the pressure lowers, which you wont want to do, so we will just divide that by 3, to get the amount of gas that will be emptied

66 fills at 100psi before it goes below 100psi. Then you should have another 130 fills at 50psi before it goes below 50psi.

NOTE: I am not entirely sure this is how you calculate the pressure when some of the gas is actually a liquid. Could someone back me up on this?