Pump stages and their effect on the efficiency of the pumps

It is advisable to always select pumps that are achieving the best possible peak efficiency. The best attainable efficiency of a pump depends essentially of 2 parameters: the capacity flow rate at BEP and the specific speed ns. Usually, for centrifugal pumps with pure radial impellers , the best attainable efficiency will increase if the specific speed increases. For the same (duty) manometric head, working with more stages will reduce the head per stage, hence will increase the specific speed which should result in an improved peak efficiency. This assumes of course that the pump is selected with the duty point matching with the BEP. There are also other factors to take into account, such as the dimensions of the pump, its mechanical behaviour etc..