The horsepower of a pump can be determined once basic information is known about the pumping station.

Horsepower is the unit of power to define hydraulic or water horsepower. In System International System (SI) it is in kilowatts (kw).

The hydraulic power is the next energy transferred to the water per unit time. The input power delivered by the motor to the pump is called brake horsepower (bHp).

The difference between the brake horsepower and hydraulic power is the pump efficiency.

(9.81) x Head (meters) x Flow Rate ( L / S ) x (Specific Gravity)

1000

Multiply kilowatts by 1.341 to obtain horsepower

Brake Horsepower and Motor Efficiency

Brake Horsepower

=

Hydraulic Power

Pump Efficiency

Once the hydraulic horsepower is known, the brake horsepower can be determined based on the pump efficiency. A pump efficiency of 60% can be used as a conservative estimate for a basic calculation to provide a general approximation.

Many technical references are available that can provide guidance on the use of these equations and the user should refer to these references.

Sample Horsepower Calculations

Question: Determine the estimated pump horsepower based on the 200 gpm flow rate and 100 ft discharge pressure at the pump.

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