Most pumps must be primed before startup in order to:

Priming a pump is essential because it fills the pump casing and suction line with liquid, which creates the necessary pressure to begin the flow of water. Without priming, air would occupy the space in the pump, leading to inadequate suction pressure. This situation could cause the pump to cavitate or run dry, which can severely damage the pump components. Therefore, ensuring that the pump is properly primed is crucial to initiating the flow of water effectively.

While priming may also have indirect positive effects on efficiency, energy consumption, and mechanical stability, the primary and immediate need for priming is to allow the pump to start moving water properly. Inadequate priming will prevent the flow altogether, which is why the focus is on starting the flow of water as the main reason for the need to prime pumps before startup.