## What is Pump Efficiency?

*Pump efficiency is a ratio that describes the relationship between rotational energy input into a pump and the hydraulic energy generated by the pump.*

The head and flow generated by a centrifugal pump can be converted into a horsepower equivalent by using the following equation:

Water Horsepower = (Flow in GPM x Head in Feet) / 3960

In this formula, 3960 is a constant which converts the result of the multiplication of head and flow into water horsepower- but only if head and flow are expressed in feet and gallons-per-minute. The resulting value can be compared to the amount of input horsepower required to operate the pump, and the resulting ratio is the efficiency of the pump.

For example, a pump that generates 1000 GPM at 100 Ft can also be said to be generating 25.25 water horsepower (WHP). If the input horsepower into the pump is measured while the pump is generating 1000 GPM at 100 Ft, and the input horsepower is found to be 33 brake horsepower (BHP), the efficiency of the pump would be approximately 76.5% (25.25 WHP / 33 BHP).

The peak efficiency of centrifugal pumps ranges from around 35% in small open-impeller solids-handling pumps to more than 90% in large split-case pumps, with the efficiency of most pumps falling between 70% and 85%. The efficiency of a centrifugal pump varies considerably depending on the point along the performance curve where operation is taking place. The point with the highest efficiency is known as the best efficiency point (BEP).