Hydropneumatic tanks can be modeled using a regular tank element and converting the tank pressures into equivalent water surface elevations. Based on the elevation differences, the tank’s cross-sectional area can then be determined.

For example, consider a hydropneumatic tank that operates between 50 psig and 60 psig. The tank’s storage volume is approximately 50 cubic feet.

The tank base elevation is chosen to be equal to the ground elevation, and the pressures are converted into feet of water (1 psi = 2.31 feet). It is apparent that the tank operates between levels of 115.5 feet and 138.6 feet. The difference between the levels is 23.1 feet, which brings us to a needed cross-section of 2.16 square feet.