Overview of pump efficiency
Whether operating under harsh or mild external conditions, environmental surroundings can put a great deal of stress on the pumping equipment that is required to run 365 days a year. To achieve optimum performance and reliability in a centrifugal pump, it must operate close to its best efficiency point, or BEP – the point at which the hydrodynamic unbalanced load of the centrifugal pump is at its minimum.
When a pump operates at a point some distance from the actual BEP, the result is an overall increase in hydrodynamic unbalanced load. This, in turn, affects the performance, reliability, and efficiency of the centrifugal pump. (Based on experience and experiments, the unbalanced load is at its peak at the shutoff point.)
In any operational atmosphere, a routine maintenance program will extend the life of a pump since well-maintained equipment lasts longer and requires fewer and less-expensive repairs.
A machine’s efficiency indicates its ability to convert one form of energy to another. If one unit of energy is input to a machine and its output is one-half unit, the machine’s efficiency is 50%.
For a centrifugal pump, much of the work involves two very efficient machines: the pump itself and the AC induction motor that drives it. The centrifugal pump converts mechanical energy into hydraulic energy (flow, velocity, and pressure), and the AC motor converts electrical energy into mechanical energy.
While mechanical and volumetric losses are important contributors to total efficiency, hydraulic efficiency is the largest factor. There are various conditions that decrease the efficiency of a centrifugal pump:
Heat generated due to packing
Rubbing between wear rings and maintaining impeller clearances
Recirculation using a bypass line from the discharge of the pump to the suction
Double volute design
Throttled discharge valve
Corroded internal pump passages that cause fluid turbulence
Obstacles, hindrances, or any sort of restrictions inside the piping passages that might include foreign particles or dirt
Overlubricated bearings