Pumps convert electrical energy into mechanical energy – imparting energy to give the fluid velocity, raise its elevation, and increase its pressure. The energy increase is expressed in terms of the height of a vertical column of the fluid, called the “total head” of the fluid. Some electrical energy is lost to heat in the electric motor and friction between parts of the pump, so the percentage that is successfully delivered to the fluid head is the overall efficiency. Many larger commercial centrifugal pumps have efficiency around 70%. Small retail pumps may have efficiency of less than 20%

The fluid flow energy produced by a pump is simply E = mgh, where m is the mass flow rate (kg/s), g is the acceleration due to gravity, 9.81 m/s2, and h is the total head (m). In these units, the product is Newton-m/s, or Watts. The density of water is about 1000 kg/m3 (1024 kg/m3 for seawater).

example: A pump with a flow of 20 m3/h (88 gpm), a total head of 10 m (33 ft, 14 psig), and an efficiency of 65% requires,

E = (20 m3/h)(1 h/3600 s)(1000 kg/m3)(9.81 m/s2)(10 m)/(65%) = 838 kg-m2/s3 = 838 watts (1.1 hp)

{limitation on suction head. less conventional approaches to pumping: ejection, air lifting, ?}