This is probably a simple question but I am really struggling as to where to start. We have a tank of compressed air, Volume of tank (V1) = 0.2litres Pressure of tank (P1) = 206.8 bar Regulator Pressure (P2) = 58.6 bar I would like to find the volume of air that can pass through the regulator before the pressure drops below the 58.6 bar value (i.e. when the output pressure is no longer constant). I assume I couldn't use boyles law for this due to the fact that the air is compressed/compressible or would the flow between the tank and regulator be in-compressible. Overall we are trying to obtain values for thrust provided by the air (over a range of tanks and regulators) and assumed that this was a reasonable place to start. Any help would be greatly appreciated.