The basis is Bernoulli's equation for ideal, incompressible fluids:
= static pressure + dynamic pressure + geodetic pressure.
This equation yields the related energy element as
The last term ρ · g · h can generally be ignored in hydraulics, as it is mostly only a few tenths of a bar. The kinetic energy also only makes itself apparent where the mass forces of the flowing column of fluid have an effect.
As hydraulic fluids are in reality not incompressible, but are compressible, in addition to the energy elements above there is the compression energy. To generate the pressure p in a space V o a specific portion of the volume ΔV K must be added:
(in a pump this process takes place continuously or at very short intervals in the individual displacement chambers). If this ΔV is allowed to flow away (e.g. on switching over a directional valve), then the pressure in the still full chamber will be zero.
The compression energy released during this process can be significant. Example: ΔV k = 1.0 L; p = 300 bar; compression energy: 15 · 103 Nm. If this 1 L flows away in 0.5 s, a power of approx. 30 kW is released.