Priming of the pump:
- If air pockets remain either in suction pipe or in the pump casing, the pump will not be able to lift water.
- Before starting the pumping operation, the suction pipe and the pump casing are filled with water. This process is known as priming.
Types of centrifugal pump
a. Volute type:
- The volute type casing starts with a small cross-sectional area near the impeller periphery and increases gradually to the pump discharge.
- The casing reduces the velocity of water gradually as it flows from the impeller to the discharge thus changing velocity head into pressure head.
b. Diffuser type:
- The impeller is surrounded by diffuser vanes.
- The diffuser vanes have small openings near the impeller and enlarge gradually to their outer diameter.
- The liquid flows into the chamber and around to the pump discharge.
- A major part of the conversion of velocity into pressure takes place between the diffuser vanes.
