Because the total energy of water remains constant over time, according to Bernoulli's principle, when the flow of water in a system increases, the pressure must decrease. The pressure in a hydraulic system reduces when water starts to flow, and it rises when the water flow stops.

As a result, in a hydraulic system, the total energy head equals the sum of three distinct energy heads.

As an example, consider the following:

Total Head = ElevationHead+PressureHead+VelocityHead

Where,

The elevation head is the pressure caused by the water's elevation.

The pressure head is the maximum height of a water column that a given hydrostatic pressure in a system can support.

The velocity head is the energy present as a result of the water's velocity.