Self-priming water pumps use a water-air mixture to reach a state of a fully primed pump. When the impeller inside the casing rotates, it creates a low-pressure zone at its centre. Now there is a pressure differential between the outside air and the air inside the casing causing a suction effect that makes the water move up the suction pipe.

The self-priming pump mixes the air with the recirculating water in the casing, later all the air in the suction pipe is displaced, and water is delivered just like any other home water pump working on the centrifugal force.