Force, Pressure, Head, and Velocity Calculations - Basic Mathematics for Water and Wastewater Operators - page 177

HEAD
Head is the vertical distance the water must be lifted from the supply tank or unit
process to the discharge. If the pressure (psi) is known, the height of the water col-
umn can be determined by multiplying the psi by 2.31:

psi × 2.31 = Feet of head (12.3)

■ Example 12.1
Problem: A pressure gauge at the bottom of a storage tank reads 35 psi. What is the
water level in the tank?

Solution: Convert psi to feet of head.

35 psi × 2.31 = 80.9 ft of water above the gauge

Note that if the height of a column of water is known, the pressure it exerts can be
determined by dividing the feet of head by 2.31:

Feet of head ÷ 2.31 = psi

■ Example 12.2
Problem: The reservoir level is 120 ft about the pump discharge. What is the dis-
charge pressure on the pump?

Solution: Convert feet of head to psi.

120 ft ÷ 2.31 = 51.9 psi

■ Example 12.3
Problem: A pump is installed at 5410 feet above sea level. The overflow of the reser-
voir is at 5530 feet above sea level. What is the discharge pressure on the pump in psi?

Solution: Find the difference in elevation:

5530 ft - 5410 = 120 ft of head

Convert feet of head to psi:

120 ft ÷ 2.31 = 51.9 psi

■ Example 12.4
Problem: A discharge pressure gauge on a pump reads 74 psi when the pump is run-
ning. The pressure gauge at the top of a hill 40 ft above the pump reads 42 psi. What
is the friction loss in the pipe in feet of head?