Science of Water : Concepts and Applications

330 The Science of Water: Concepts and Applications
There are fi ve types of horsepower calculations for vertical turbine pumps. It is important to
have a general understanding of these fi ve horsepower types:
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Motor horsepower refers to the horsepower supplied to the motor. The following equation
is used to calculate motor horsepower:
field bhp
Motor hp (input hp)
motor efficiency100 (10.8)
Total bhp refers to horsepower output of the motor. The following equation is used to
calculate total brake horsepower:
Total bhp field bhpthrust-bearing loss (hp)
(10.9)
Field horsepower refers to the horsepower required at the top of the pump shaft. The following
equation is used to calculate fi eld horsepower:
Field bhp bowl bhpshaft loss (hp)
(10.10)
Bowl or laboratory horsepower refers the horsepower at the entry to the pump bowls. The
following equation is used to calculate bowl horsepower:
(bowl head, ft)(capacity, gpm)
Bowl bhp (lab bhp)
3960 (bowl
efficiency/100)
(10.11)
Water horsepower refers to the horsepower at the pump discharge. The following equation
is used to calculate water hp:
Or use the equivalent equation:
Example 10.10
Water hp
Water hp
(field head, ft)(capacity, gpm)
3960
(field head, ft)(capacity, gpm)
33,000 ft-lb/min
(10.12)
Problem:
The pumping water level for a well pump is 150 ft and the discharge pressure measured at the pump
discharge centerline is 3.5 psi. If the fl ow rate from the pump is 700 gpm, what is the water horsepower?
(Use Equation 10.12.)
Solution:
First calculate the fi eld head. The discharge head must be converted from psi to ft:
The water horsepower is, therefore:
(3.5 psi)(2.31 ft/psi) 8.1
ft
150 ft 8.1 ft 158.1
ft