Water Source and Storage Calculations - Basic Mathematics for Water and Wastewater Operators - page 223

Vertical Turbine Pump Calculations
The calculations pertaining to well pumps include head, horsepower, and efficiency
calculations. Discharge head is measured to the pressure gauge located close to the
pump discharge flange. The pressure (psi) can be converted to feet of head using the
following equation:

Discharge head (ft) = Pressure (psi) × 2.31 ft/psi (15.5)

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:

Total pumping head (ft) = Pumping water level (ft) + Discharge head (ft) (15.6)

■ Example 15.8
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 15.9
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)

= (100 ft + 26 ft) + (3.7 psi × 2.31 ft/psi)

= 126 ft + 8.5 ft = 134.5 ft

There are five types of horsepower calculations for vertical turbine pumps. It is
important to have a clear and retained understanding of these five types of horse-
power (refer to Figure 15.2):

• Motor horsepower refers to the horsepower supplied to the motor. The fol-

lowing equation is used to calculate motor horsepower:

Fieldbrake hor sepower (bhp)

Motorefficiency 100

Motor horsepower (input hp) = (15.7)

• Total brake horsepower ( bhp ) refers to the horsepower output of the motor.

The following equation is used to calculate total brake horsepower:

Total bhp = Field bhp + Thrust bearing loss (hp) (15.8)