LOSES IN ROTODYNAMIC PUMPS

In all rotodynamic pumps, the rotating element usually called the impeller, converts the continuous supply of shaft work into kinetic energy of the fluid being pumped. The kinetic energy achieved in the rotating element is dissipated in the pump casing. This energy conversion is from Kinetic to pressure (head).

1.   Fluid Friction or Disk - friction loss - This is due to friction of the fluid on the pump internals and also due to friction in the fluid itself. This loss varies with the pump throughput (the higher thethroughput, greater is the friction loss) and also increases
with the viscosity of the pumped liquid.

2.                    Shock loss -This losses are caused by shocks, eddy currents and friction at entry to the impeller, at exit from the impeller (with diffuser pumps) and in the volute (for general purpose pumps). In addition to the effect on pump efficiency, shock losses can be physically damaging to the pump.

3.                    Parasitic or leakage or short circuit loss - Losses caused by leakage from the dis­charge to the suction side of a pump through the clearances between the casing and impeller wear rings. The fluid in this parasitic circuit has had its energy in­ creased in the impeller and this is dissipated as friction when it leaks back to the suction side. This leakage reduces the effective capacity of the pump because the leakage has to be repumped from suction to discharge.

4.         Mechanical losses-This losses resulting from friction in the stuffing box, bearings and bushes, i.e. the power to spin the impeller at the rated speed without any work being done on the fluid.                                                                                

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