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Monday, December 15, 2008

The Principle of a centrifugal pump

The centrifugal pump transfers fluid at a certain capacity from one point to another in a process. The pump builds up fluid pressure to overcome losses in the process. Capacity and pressure are created by the rotating impeller inside the pump casing.


General principle:

·         Fluid enters the pump casing and impeller center and is forced into a circular movement by the impeller vanes and the centrifugal force. The fluid thus leaves the casing with increased pressure and velocity.

·         Typically suitable for low viscous, non-particulate and non-aerated fluids such as beer, CIP, cream, juice, milk, soft drinks, water etc.


Single-stage principle:

The fluid inlet, the built-up of velocity and pressure and the fluid outlet all happens in one stage (one casing and one impeller).


Multi-stage principle:

·         Fluid enters the pump casing and impeller center, and fluid pressure and velocity are built up in the first stage (casing and impeller) similar to the single-stage pump.

·         Fluid with increased pressure and velocity is directed to the second stage (casing and impeller), where the fluid pressure and velocity is further increased.

·         The result is a pressure increase (boost) in each stage, where the total pressure increase depends on the number of stages in the pump.

·         Typically available with 2-4 stages.


Priming of a centrifugal pump:

·         The pump casing should always be filled with fluid before starting the pump to ensure correct operation.

·         The pump can operate with a positive inlet pressure (flooded inlet) or with a negative inlet pressure (suction lift).

·         For suction lift, fluid can remain in the pump casing by using a non-return valve in the suction line.