Some centrifugal pump works on the principle that when a certain mass of fluid is rotated by an external source, it is thrown away from the central axis of rotation also a centrifugal head is impressed which enables it to rise to a higher level.
The working of a centrifugal pump remains
Here delivery valve is closed and the pump is primed that is, the suction pipe, casing and portion of the delivery pipe up to the delivery valve are filled with some liquid (to be pumped) so that no air pocket remains left.
Fulfilling the delivery valve still closed the electric motor is started to rotate the impeller. Some rotation of the impeller causes strong suction either Vaccum just at the eye of the casing.
Each speed of the impeller is gradually increased until each impeller rotates at its normal speed and also develops the normal energy required for pumping the liquid.
Following the impeller attains the normal speed the delivery valve is opened while the liquid is continuously sucked (from the sump well) up the suction pipe, which passes through the eye of the casing also enters the impeller at its centre or enters the impeller vanes at their inlet tips. Here liquid is impelled out by the rotating vanes and it comes out at the outlet tips of the vanes into the casing. Due to impeller action the pressure head, as well as velocity heads of the liquid, are increased (some of these velocity heads is converted into pressure head in the casing and also in the diffuser blades/vanes if they are also provided).
Of casing, the liquid passes into a pipe and is lifted to the required height (and discharged from the outlet at either upper end of the delivery pipe).
Such long as motion is given to the impeller including there is a supply of liquid to be lifted the process from listing the liquid to the required height rests continuously.
While a pump is to be stopped the delivery valve should be first closed otherwise there may be some backflow of the reservoir.