If a fluid is stored in a (pressure) vessel, the fluid has a certain pressure. If more fluid is in the container, the pressure is larger. The concrete pressure – volume relation is called the pV-characteristic.

The pressure of the fluid is called the capacitive pressure difference (pressure difference with respect to an arbitrary reference pressure).

The relation can be expressed graphically, formally with an equation interpolating the measured function delta_pC(V), or with the help of the elastance alpha_V (first equation), or in terms of the hydraulic capacitance C_V (second equation).

If C_V = const:

    ∆V = C_V·∆p_C

capacitive characteristic (general),

hydraulische kapazitive Charakteristik