Head Pump is the energy per unit weight that should be provided to flow liquid which is planned in accordance with the conditions of the pump installation, or the pressure to flow some amount of fluid, which is usually expressed in length units. According to Bernoulli equation, which states that “when incompressible fluid flowing along the pipe and its cross section has a different height, the pressure difference depends not only on the difference in height but also on the difference between velocity at each point ".

In the Bernoulli equation, there are three kinds of head pump (energy) flow of fluid from the installation system, namely, pressure energy, energy potensial and kinetic. This condition can be expressed as the following formula: (Bruce Munson, 2006)

H = (P/γ) + Z + (V2/2g)

Where:
H         = Total head pump (m)
P/γ       = pressure head pump (m)
Z          = Total static head pump (m)
V2/2g   = Velocity head pump (m)

Because of energy is conserved, so the head (high press) may vary in different sections. But in fact there are always losses of energy.
 Figure 1: Scheme of Head Pump

Caption:
1                    = suction reservoir
2                    = suction pipe
3                    = pump
4                    = press pipe
5                    = press reservoir

In different conditions as in the figure above, the Bernoulli equation is as follow:

(PAA) + (VA2/2g) + ZA + H = (PBB) + (VB2/2g) + ZB + HL (Loss A to B)

H = ((PBB) - (PAA)) + ((VB2/2g) - (VA2/2g)) + (ZB - ZA) + HL

Because of γA = γB so:

H = ((PB - PA)//γ) + ((VB2 - VA2)/2g) + (ZB - ZA) + HL

H = (ΔP//γ) + (ΔV2/2g) + HST + HL

Where:
H         = total head pump (m)
ΔP/γ     = head pump because of different pressure on suction side with press side (m)
ΔV2/2g = head pump which is caused by different velocity (m)