Force, Pressure, Head, and Velocity Calculations - Basic Mathematics for Water and Wastewater Operators - page 178

Solution: Find the difference in the pressures:

74 psi - 42 psi = 32 psi

Convert psi to feet of head:

32 psi × 2.31 = 73.9 ft of head

Subtract the difference in elevation to find the friction loss:

73.9 ft - 40 ft = 33.9 ft of head

The total 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 head = Static head + Friction head + Velocity head (12.4)

s tatiC h ead
Static head is the actual vertical distance the liquid must be lifted:

Static head = Discharge elevation - Supply elevation (12.5)

■ Example 12.5
Problem: A supply tank is located at elevation 108 ft. The discharge point is at eleva-
tion 205 ft. What is the static head in feet?

Solution:

Static head = 205 ft - 108 ft = 97 ft

f riCtion h ead
Friction head is the equivalent distance of the energy that must be supplied to over-
come 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 (12.6)

v eloCity h ead
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 due to maintaining velocity (12.7)