Environmental Engineering Reference
In-Depth Information
Total Dynamic Head (Total System Head)
The total dynamic head includes the vertical distance the liquid must be lifted ( static
head ), the loss to friction ( friction head ), and the energy required to maintain the
desired velocity ( velocity head ):
Total dynamic head = Static head + Friction head + Velocity head
(4.5)
Static Head
Static head is the actual vertical distance the liquid must be lifted:
Static head = Discharge elevation - Supply elevation
(4.6)
Example 4.7
Problem: A supply tank is located at elevation 118 ft. The discharge point is at eleva-
tion 215 ft. What is the static head in feet?
Solution:
Static head = 215 ft - 118 ft = 97 ft
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 distances for various sizes and types of pipes, fittings, and valves. The
total friction head is the sum of the equivalent vertical distances for each compo-
nent. For friction head,
Friction head (ft) = Energy losses due to friction
(4.7)
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
(4.8)
Pressure and Head
The pressure exerted by water is directly proportional to its depth or head in the
pipe, tank, or channel. If the pressure is known, the equivalent head can be calcu-
lated as follows:
Head (ft) = Pressure (psi) × 2.31 (ft/psi)
(4.9)
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