Pumps and fans
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This chapter discusses the working of pumps and fans. For flow in pipes, Bernoulli's equation can be applied between points in a pipe through which fluid is flowing, with the addition of a term to allow for energy lost from the fluid in overcoming friction. In centrifugal pumps, the action of pumps is most conveniently expressed in terms of head. The rotor gives the liquid a head. When the output of a pump is expressed as head of working liquid, it is independent of the density of the liquid. Actual head is less than ideal because of friction losses within pump. Overall efficiency is lower again because of mechanical losses in bearings and other factors. The specific speed of a centrifugal pump is the speed at which the pump would deliver 1 m 3 /s of water at a head of 1 m. A centrifugal pump takes the least power when the flow is zero.