Basic Math Operations - Mathematics and Statistics for the Environment - page 69

2.12.2.1 Static Head
Static head is the actual vertical distance the liquid must be lifted.

Static head = Discharge elevation - Supply elevation (2.15)

■ EXAMPLE 2.54
Problem: The supply tank is located at elevation 108 ft. The discharge point is at elevation 205 ft.
What is the static head in feet?

Solution:

Static head (ft) = 205 ft - 108 ft = 97 ft

2.12.2.2 Friction Head
Friction head is the equivalent distance of the energy that must be supplied to overcome friction.
Engineering references include tables showing the equivalent vertical distance for various sizes
and types of pipes, fittings, and valves. The total friction head is the sum of the equivalent vertical
distances for each component:

Friction head (ft) = Energy losses due to friction (2.16)

2.12.2.3 Velocity Head
Velocity head is the equivalent distance of the energy consumed in achieving and maintaining the
desired velocity in the system:

Velocity head (ft) = Energy losses to maintain velocity (2.17)

2.12.2.4 Total Dynamic Head (Total System Head)

Total head = Static head + Friction head + Velocity head (2.18)

2.12.2.5 Pressure and Head
The pressure exerted by water/wastewater is directly proportional to its depth or head in the pipe,
tank, or channel. If the pressure is known, the equivalent head can be calculated:

Head (ft) = Pressure (psi) × 2.31 ft/psi (2.19)

■ EXAMPLE 2.55
Problem: The pressure gauge on the discharge line from the influent pump reads 75.3 psi. What is
the equivalent head in feet?

Solution:

Head (ft) = 75.3 × 2.31 ft/psi = 173.9 ft