Working of a Centrifugal Pump

When pumping liquids, it is sometimes possible that the local pressure inside the pump falls below the vapor pressure of the liquid. If the suction pressure is only slightly above the vapor pressure, some of the liquid may flash to form vapors inside the pump. These vapors may then collapse, causing damage to the pump. This condition is known as cavitation and it should be completely avoided in order for the pump to function efficiently. In order to prevent this, water should be always filled in the impeller and suction side. This is known as priming.

Working Principle of Centrifugal Pump

The general requirement of a pump is to transport liquids from low pressure regions to high pressure regions. The induction motor provides electrical energy and rotates the shaft, which causes the rotation of the impeller. When the impeller rotates, a region of low pressure is generated and water is then sucked into the pump inlet from the reservoir (any fluid naturally moves from a region of high pressure to low pressure). The water then enters the impeller axially. The rotating impeller pushes the water outward to the boundary and towards the volute section.

The volute area keeps increasing from its starting point, right up to the discharge line. As per mass conservation principle, mass flow rate through any section of a stream tube is constant. Therefore, velocity and area become inversely proportional to each other. Thus, as the area keeps increasing, the velocity of the flow decreases and hence its kinetic energy decreases. As per Bernoulli’s equation, decrease in kinetic energy results in increase in its pressure energy. This increase in pressure head causes the liquid to rise to the desired height.