Difference between heads at location (A) and (B) may be calculated as

where the terms in each parenthesis consist of pressure, kinetic energy and potential energy.

The increase or difference between the kinetic and potential heads is usually negligible. Therefore,

The efficiency of the pump  is defined as  where the term in the numerator represents power delivered by the pump because of the pressure-developed. BHP is the brake–horse power; required to drive the pump. BHP depends upon the speed of the pump, vane angle (design of the impeller) and the flow rate of the fluid.