Step 1 : The delivery valve is closed and the suction pipe, casing and portion of the delivery pipe up to the delivery valve are completely filled with the liquid so that no air pocket is left. This process is called priming a Centrifugal Pump.
Step 2 : The electric motor is started to rotate the impeller by keeping the delivery valve still closed. The rotation of the impeller causes strong suction or vacuum just at the eye of the casing.
Step 3 : The speed of the impeller is gradually increased till the impeller rotates at its normal speed and develops normal hydraulic energy required for pumping the liquid.
Step 4 : The delivery valve is opened after the impeller attains the normal speed. Now, the liquid is continuously sucked by the suction pipe and passes through the eye of casing. Then, it enters the impeller at its centre, at their inlet tips. This liquid is impelled out by the rotating vanes and it comes out at the outlet tips of the vanes into the casing. During the process, the pressure head as well as velocity head of the liquid are increased.
Step 5 : The liquid is now entered into vortex/volute chamber of the casing where some of the velocity head is converted into pressure head in the casing.
Step 6 : From casing, the liquid passes into the delivery pipe and is lifted to the required height.
Step 7 : When pump is stopped, the delivery valve should be closed. Otherwise, there may be some back flow from the reservoir. If there is a foot valve, no need to close the delivery valve because it is a one-way non-return valve. It arrests the back flow.