Gas consumption question..

[TJButler]

If I have a 125 cu ft cylinder that starts out at 2000 psi and I have 500 psi remaining, how do I compute the remaining cu ft?

I know it couldn't be as easy as 4 /125?

Thanks in advance.

[BillC]

Assuming that 2000 psi gives you the full 125 cu ft, it should be as simple as 125 x (500/2000)... just like you said.

Regards,

[Zrexxer]

The ideal gas law says that PV=nRT where

P=Pressure
V=Volume
n=number of moles of the gas (essentially how many gas molecules)
R= Ideal Gas Constant
T = Temperature

So... if you reduce the pressure by half on the left side of that equation and the volume stays the same, then the right side has to decrease by half too. Assuming temperature stays the same and the gas constant is, well, constant... that means that the amount of gas (moles of gas) decreases by half.

That would suggest all else being equal that there's a linear relationship between pressure and the amount of gas in a cylinder of fixed volume.

****, that was reaching back WAY too far for college physics so I may have made some fundamental error here.

[TJButler]

Zrexxer I appreciate that VERY much...I just KNEW there was a genius lurking out there somewhere!

I also KNEW that is would not be linear but now I see the light.

Thanks again.

TJB

[Roger]

KISS, Lets assume 2000 PSI is maximum pressure of full cylinder and 500 PSI is present pressure.
500PSI divided by 2000PSI = .25 = 25% left.
Cylincer holds 125 cubic feet of gas when full.
125 X .25 = 31.25 left in cylinder

Get more complicated for a small improved accuracy.

[BillC]

And it IS linear...