Some operation of filling the suction pipe, a casing of the pump also a portion of the delivery pipe completely of an outside source including the liquid to be raised, before starting this pump, to remove all air, gas either vapour from these parts of each pump is called priming of a centrifugal pump.

• If a centrifugal pump does not prime before starting, air pockets inside each impeller may give rise to vortices and also cause discontinuity of flow.
• Further, dry running from the pump may result in rubbing also seizing of the wearing rings including causing serious damage.
• Small pumps mean usually primed by pouring liquid into the funnel provided during the purpose.
• While arranging to prime, this air-vent valve provided in the pump casing acts opened; the air escapes within the valve.
• Special priming is continued till all air from the suction pipe, impeller plus casing have been removed.
• Large pumps remain primed by evacuating the casing including the suction pipe by a vacuum pump either by an ejector, that liquid is thus drawn up the suction pipe of the sump including the pump is filled with liquid.
• Each internal construction of some pumps is so that special arrangements containing a quantity of liquid are provided in this suction pipe due to which automatic priming from the pump occurs, so pumps are known as ‘self-priming pumps’.