What is "pressure head"

In fluid mechanics, pressure head is the internal energy of a fluid due to the pressure exerted on its container. It may also be called static pressure head or simply static head (but not static head pressure). It is mathematically expressed as:

$$\psi = \frac{p}{\gamma} = \frac{p}{\rho \, g}$$
where

ψ
is pressure head ( length, typically in units of m);

p
is fluid pressure ( force per unit area, often as Pa units); and

γ
is the specific weight (force per unit volume, typically N/m units)

ρ
is the density of the fluid ( mass per unit volume, typically kg/m)

g
is acceleration due to gravity (rate of change of velocity, given in m/s) Note that in this equation, the pressure term may be gauge pressure or absolute pressure, depending on the design of the container and whether it is open to the ambient air or sealed without air.