Basic Units of Measurement and Conversions - Basic Mathematics for Water and Wastewater Operators - page 46

Brake Horsepower
Brake horsepower (bhp) refers to the horsepower supplied to the pump from the
motor. As power moves through the pump, additional horsepower is lost from slip-
page and friction of the shaft and other factors; thus, pump efficiencies range from
about 50 to 85% and pump efficiency must be taken into account.

Water horsepower (wh p)

%Efficiency of pump

Brake horsepower (bhp) =

(2.21)

■ Example 2.104
Problem: Under the specified conditions, the pump efficiency is 73%. If the required
water horsepower is 40 hp, what is the required brake horsepower?

Solution:

40 whp
0.73

Required horsepower = = 55 bhp

Motor Horsepower
Motor horsepower (mhp) is the horsepower the motor must generate to produce the
desired brake and water horsepower.

Brake horsepower (bh p)

%Efficiency of motor

Motor horsepower (mhp) = (2.22)

■ Example 2.105
Problem: A motor is 93% efficient. What is the required motor horsepower when the
required brake horsepower is 49.0 bhp?

Solution:

49 bhp
0.93

Motor horsepower = = 53 mhp

e leCtriCal p oWer
Water/wastewater operators (especially senior operators) must occasionally make
electrical power calculations, especially with regard to electrical energy required
or consumed over a period of time. To accomplish this, horsepower is converted to
electrical energy (kilowatts) and then multiplied by the hours of operation to obtain
kilowatt-hours:

Kilowatt-hours = Horsepower (hp) × 0.746 kW/hp × Operating time (hr) (2.23)