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. They are used to convey fluid from one place to another by mechanical means. They can be classified into two main groups, namely, centrifugal and positive displacement pumps.

Centrifugal Pump

Centrifugal pumps make use of centrifugal force to work. The liquid to be pumped is usually water. The construction of the housing is such that water is piped in at the centre of the impeller. The impeller is then rotated at a high speed so that the water is thrown outwards with high velocity. The housing of the impeller is usually constructed in the shape of a volute such that the volume is gradually expanded until the placed the water is led out as the discharge. The gradual expansion of the volume has the effect of converting the velocity of the water into pressure. Some centrifugal pumps make use of diffuser fins at the housing to achieve the same change of state.

Positive Displacement Pump

Positive displacement pumps make use of a mechanical object to displace the liquid. The liquid to be pumped can be water, oil, or other thick liquid. The mechanical object can move in a reciprocating manner or a rotary manner. Examples of the mechanical object are: pistons, gears, screws, lobe, vanes. The liquid is literally pushed aside by the object. Some pumps need to have inlet and outlet non-return valves fitted to work. Examples of this are piston pumps. Others like gears, screws, lobe, and vanes rotating at high speed need not employ valves to work. One characteristic of these pumps is the fact that the pressure can build up in time if it is not released. Usually a pressure relief valve is fitted at the discharge side of the pump to prevent over pressure.



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