<Dd> Δ P = (v 2 2 − v 1 2) 2 + Δ z g + Δ p s t a t i c ρ (\ displaystyle \ Delta P = ((v_ (2) ^ (2) - v_ (1) ^ (2)) \ over 2) + \ Delta zg+ (\ Delta p_ (\ mathrm (static)) \ over \ rho)) </Dd> <P> For a typical "pumping" configuration, the work is imparted on the fluid, and is thus positive . For the fluid imparting the work on the pump (i.e. a turbine), the work is negative . Power required to drive the pump is determined by dividing the output power by the pump efficiency . Furthermore, this definition encompasses pumps with no moving parts, such as a siphon . </P> <P> Pump efficiency is defined as the ratio of the power imparted on the fluid by the pump in relation to the power supplied to drive the pump . Its value is not fixed for a given pump, efficiency is a function of the discharge and therefore also operating head . For centrifugal pumps, the efficiency tends to increase with flow rate up to a point midway through the operating range (peak efficiency or Best Efficiency Point (BEP)) and then declines as flow rates rise further . Pump performance data such as this is usually supplied by the manufacturer before pump selection . Pump efficiencies tend to decline over time due to wear (e.g. increasing clearances as impellers reduce in size). </P> <P> When a system includes a centrifugal pump, an important design issue is matching the head loss - flow characteristic with the pump so that it operates at or close to the point of its maximum efficiency . </P>

Various methods of flow control in centrifugal pump