What Are Centrifugal Pumps?by Pauline Gill; Updated September 15, 2017
Centrifugal pumps are used for virtually all straight pumping applications of low viscosity fluids like water without complications, such as liquids containing hard solids. These pumps can be single stage, or they can be stages stacked in a series-flow arrangement to deliver high output pressures. Centrifugal pumps are simple in concept and construction and deliver the highest flow performance at moderate pressures. Centrifugal pumps are available in all machinable materials--including all metals, plastics, and ceramics.
Most centrifugal pumps are powered by electric motors operating in the range of 1,725 to 5,000 rpm with 3,450 rpm being common in industry. A simple bladed impeller is firmly attached to the pump shaft which is often an extension of the motor shaft. This impeller is located inside a round recess in the pump housing. An smooth outlet channel leaves the round recess tangentially (see diagram).
The inlet comes into the middle of the impeller. As the motor turns the impeller at high rpm, the liquid enters the impeller and is rapidly spun by the impeller blades until it develops a high component of centrifugal force. This centrifugal force is what forces the liquid outwards. It is contained by the round recess in the housing until it is able to exit the round recess through the exit channel to the pump outlet.
Stage centrifugal pumps take this outlet flow to yet another stage of the pump. There is another round recess and impeller mounted to the same shaft, but it's isolated by a shaft seal. Further pressure is added to the liquid flow. This is essentially having many pumps mounted to the same shaft. Many deep well pumps have many stages to overcome the considerable depth and pressure loss due to gravity.
Centrifugal pumps are used in a wide array of industrial, domestic and vehicular applications such as water pumps, multi-stage deep well pumps, swimming pool pumps, fountain pumps, drain pumps, sump pumps, mixing pumps, heating and cooling circulation pumps, automotive coolant pumps, industrial coolant pumps, hydrocarbon pumps, recirculating pumps, filter pumps, liquid chemical pumps, transfer pumps, jet outboard motor pumps, jet ski pumps, rocket motor fuel pumps, windshield washer pumps, cleaning pumps, and fire truck pumps.
Centrifugal pumps are generally not self-priming, meaning they must be full of liquid before they can start pumping if the height of the pump is above the liquid level being drawn to the pump. The tank receiving water from the pump can be higher than the pump. When in doubt, every thirty feet of water height is equivalent to about 15 psi. If a pump has an output pressure of 50 psi, about the very highest the receiving tank can be above the pump is about 90 feet.
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