Why is priming necessary for a centrifugal bilge pump?

Priming is necessary for a centrifugal bilge pump primarily because of its inability to generate suction sufficient to lift water from a level lower than the impeller. Centrifugal pumps rely on the centrifugal force generated by the impeller to move liquid, but if the pump is not filled with water prior to operation (primed), there is insufficient fluid in the pump casing to create the necessary vacuum for drawing in more fluid.

When the pump is primed, it is filled with fluid, allowing it to start with a full volume of liquid, which facilitates the creation of a pressure differential. If the pump has air instead of water in it, it cannot effectively move the fluid, leading to a state known as airlock. This condition can prevent the pump from functioning correctly, highlighting the importance of ensuring that the pump is adequately primed before usage.

By ensuring the pump is primed, you take advantage of its design and efficiency, allowing it to operate effectively without the risk of airlock or insufficient lifting capability, which would hinder its overall performance.