Electric Motor Horsepower Calculation for Pump Drive

How to calculate the horsepower needed for an electric motor to drive a pump?

You need to select an electric motor that runs at 1160 RPM to drive a pump with a displacement of 25 cubic inch per revolution. You want to generate 1000 PSI of pressure, and 3 GPM of flow. How many horsepower will the electric motor need to be (assume 100% efficient)?

a) 0 - 9.5 HP
b) 0 - 75 HP
c) 0 - 3.0 HP

Answer:

The horsepower of the electric motor required to drive the pump is 3.0 HP.

Here's the solution to the given problem: The displacement per revolution of the pump is 25 cubic inch. The flow rate is 3 gallons per minute, which implies that the pump must deliver 25 x 1160 = 29000 cubic inch per minute. In addition, we need to produce 1000 PSI of pressure at this flow rate.

The following formula can be used to calculate the horsepower of an electric motor:
HP = (Pressure x Flow rate) / 1714

We can use this formula to calculate the power required to drive the pump using the above data. The calculated power required is:
HP = (1000 x 3) / 1714 = 1.75

We must also convert the flow rate to cubic inches per minute before plugging it into the formula. Hence,
3 GPM = 3 x 231 = 693 cubic inch per minute

Therefore, the electric motor needs to be 3.0 HP (rounding off the calculated value). To drive the given pump, the electric motor needs to be 3.0 HP.