Water Treatment Processes - Mathematics and Statistics for the Environment - page 607

23.2.2 v ertiCal t urbine p ump C alCulations
The calculations pertaining to well pumps include head, horsepower, and efficiency calculations.
Discharge head is measured by the pressure gauge located close to the pump discharge flange. The
pressure (psi) can be converted to feet of head using the equation:

Discharge head (ft) = Pressure (psi) × 2.31 ft/psi (23.5)

Total pumping head ( (field head ) is a measure of the lift below the discharge head pumping water
level ( discharge head ). Total pumping head is calculated as follows:

Pumping head (ft) = Pumping water level (ft) + Discharge head (ft) (23.6)

■ EXAMPLE 23.8
Problem: The pressure gauge reading at a pump discharge head is 4.1 psi. What is this discharge
head expressed in feet?

Solution:

4.1 psi × 2.31 ft/psi = 9.5 ft

■ EXAMPLE 23.9
Problem: The static water level of a pump is 100 ft. The well drawdown is 26 ft. If the gauge reading
at the pump discharge head is 3.7 psi, what is the total pumping head?

Solution:

Total pumping head (ft) = Pumping water level (ft) + Discharge head (ft) (23.7)

Total pumping head = (100 ft + 26 ft) + (3.7 psi × 2.31 ft/psi) = 126 ft + 8.5 ft = 134.5 ft

Five types of horsepower calculations are used for vertical turbine pumps; it is important to have
a general understanding of these five horsepower types:

• Motor horsepower refers to the horsepower supplied to the motor. The following equation
is used to calculate motor horsepower:

Fieldb rake horsepower

Motorefficiency 100

Motor horsepower (input horsepower) = (23.8)

• Total brake horsepower refers to the horsepower output of the motor. The following equa-
tion is used to calculate total brake horsepower:

Total bhp = Field bhp + Thrust bearing loss (hp) (23.9)

• Field horsepower refers to the horsepower required at the top of the pump shaft. The fol-
lowing equation is used to calculate field horsepower:

Field bhp = Bowl bhp + Shaft loss (hp) (23.10)