How does the gas law model work for a hydropneumatic tank?
Given the initial level/HGL and liquid volume, the gas law model keeps the “nrt” part of the equation constant (called K) and is thus able to compute HGL for a given volume, or vice versa, as the conditions in the model change over the course of an EPS simulation. One should still use controls to turn the pump on/off based on the minimum/maximum level/HGL in the hydropneumatic tank. The atmospheric pressure needs to be specified because the gas law equation needs to work with absolute pressure, NOT gauge pressure. So, in the pv=nrt equation, the atmospheric pressure head is added to the gauged pressure head in the tank, to acheive the absolute pressure.
