air tank supply

[jon_89]

I was thinking of using one of those big propane tanks for an air supply. I would charge the propane tank to about 110 psi. Then I would regulate it to about 90 psi. If my chamber was 1 inch x 30 inches. How would I figure out how many shots per tank? Thanks in advance

[POLAND_SPUD]

obviously it won't be able to provide air at 90psi when the air inside the tank is below 90 psi
thus the volume of air that you can use equals --> (volume of the tank) * (the difference between the tank pressure and desired pressure)

110psi - 90 psi = 20 psi

then convert psi to atm
20 psi = ~1.37atm

and finally
(1.4atm * the volume of the tank ) / ( 6atm * chamber volume) = number of shots per tank






I don't have much time to explain in more details - sorry I got to go

ohh one final advice... pump the tank to higher pressure (in theory they can handle up to 20atm) to get more shots per fill... even 130 psi will increase teh numer of shots you can get from it by factor of 2

EDIT
sorry 20 psi is more like ~1.4 atm not ~1.7... wel it seems I am not that good at rough esstimates

[jon_89]

So if my math is correct I should get 13 shots. Now are these 13 shots at 90psi though?

[POLAND_SPUD]

they should be at 90 psi assuming that your regulator works fine

I don't know if your math is ok because I don't know which tank you were talking about when you said 'those big propane tanks'.... what is its volume?

[jon_89]

Whoops sorry about that. I think they are 5 gallons. 1 gallon eqauls 231 cubic inches. So a 1155 cubic inch tank.

[potatoflinger]

While we are on the topic (sorry to hijack your thread jon_89) would this work to find the number of shots per tank?

(volume of tank*tank pressure)/(volume of chamber*chamber pressure)

[POLAND_SPUD]

yeah you'll get about 11 shots (i know you said 13 but I assumed that's becasue of the error in my first post (20 psi is ~1.4atm not 1.7atm - sorry about that I didn't have time to calculate then)

@potatoflinger - I assume you don't want to regulate it down to a set pressure so it's a bit different now.... each time you are going to fill the gun the pressure inside the gun and the tank is going to fall and equalize... so after each shot the pressure will fall...

but at the moment I am too drunk and to be honest I've never been good at maths.... maybe I'll pm DYI to help us.... he seems to be good at stuff like this

[potatoflinger]

@potatoflinger - I assume you don't want to regulate it down to a set pressure so it's a bit different now.... each time you are going to fill the gun the pressure inside the gun and the tank is going to fall and equalize... so after each shot the pressure will fall...

No, it will be regulated, but I just wanted to know if the method would work.

For example, a 100 cubic inch air tank at 100 PSI, and a gun with a 20 cubic inch chamber regulated to 50 PSI.
(100*100)/(20*50)=10
So if that method is correct, I would get 10 shots per tank, the only problem is that I don't know whether that method is correct or not.

[DYI]

[(TP-CP)*TV]/(CP*CV) = # of shots before tank drops below intended chamber fill pressure, where:
TP = tank fill pressure
TV = tank volume
CP = intended chamber fill pressure
CV = chamber volume

[marpat]

isnt the propane in those tanks liquified because if it was then u would get a lot more shots off at 90 psi because the liquid propane would expand to take the place of the leaving propane represusurizing the tank in a way

[POLAND_SPUD]

@DYI so this is basically what I've written here.... At least once my math is ok

@marpat We are talking about using used propane tanks as air reservoirs... not about using propane

[jon_89]

According to DYI eqaution I would get 5 shots. I think though I will get one of those 5 gallon air tanks for like $20 and it has a pressure gauge and air hose.

[POLAND_SPUD]

Ok at least once I am right....


of course you have to put pressure in atm not PSI.... 1atm = 14.7 PSI

otherwise it won't make any sense