Author: **btrettel** » Thu Jun 04, 2009 8:51 pm

What jimmy's suggesting might not be completely obvious unless you derive it from the ideal gas law.

The ideal gas law says P * V = m * R * T (here R is the specific gas constant, not R_bar like in the molar ideal gas law). Solve for m to do the procedure Technician and spot are thinking of. m = P * V / R * T

For simplicity we'll assume an isothermal process so T is constant for all equations. R is a constant too. Note that the mass is directly proportional to P * V. So you can subtract P * V instead of mass in the same procedure mentioned by Technician and spot.

Note that this is not strictly correct as the process will not be perfectly isothermal and not all regulators are consistent. It's close enough however.

Also, if you want a formula for the number of shots you can get from a regulated source, use this:

number of shots = V_r * (P_r - P) / P * V_c

V_r is the gas reservoir volume

P_r is the starting gas reservoir pressure

P is the regulated pressure

V_c is the volume of the pressure chamber

All pressures are absolute.

Round down. I derived this from P1 * V1 = P2 * V2 realizing that the two are proportional to mass.

Last edited by

btrettel on Wed Jul 08, 2009 6:45 am, edited 1 time in total.

All spud gun related projects are currently on hold.