Pumping Calculations - Basic Mathematics for Water and Wastewater Operators - page 200

The pumping test was conducted over a period of 80 minutes. Using Equation 14.4,
calculate the pumping rate in gallons per minute:

Pumping rate = Gallons ÷ Minutes = 22,021 gal ÷ 80 min = 275.3 gpm

C alCulating h ead l oss
Note: Pump head measurements are used to determine the amount of energy a
pump can or must impart to the water; they are measured in feet.

One of the principle calculations in pumping problems is used to determine head
loss. The following formula is used to calculate head loss:

H f = K × ( V 2 /2 g ) (14.6)

where
H f = Friction head.
K = Friction coefficient.
V = Velocity in pipe.
g = Gravity (32.17 ft/sec ⋅ sec)

C alCulating h ead
For centrifugal pumps and positive-displacement pumps, several other important
formulas are used to determine head. In centrifugal pump calculations, conver-
sion of the discharge pressure to discharge head is the norm. Positive-displacement
pump calculations often leave given pressures in psi. In the following formulas, W
expresses the specific weight of liquid in pounds per cubic foot. For water at 68°F, W
is 62.4 lb/ft 3 . A water column 2.31 feet high exerts a pressure of 1 psi on 64°F water.
Use the following formulas to convert discharge pressure in psig to head in feet:

• Centrifugal pump

Pressure (psig)
Specificgravi

× 231 .

ty

Head (ft) = (14.7)

• Positive-displacement pump

Pressure (psig) ×144

Head (ft) = (14.8)

W

Use the following formulas to convert head in feet to psig:

• Centrifugal pumps

Head (ft)Specificgravity ×

(14.9)

Pressure (psig) =

2.31