A primed pump will have what inside the pump?

A primed pump is one that contains liquid, typically water, and is free of air. When a pump is described as "primed," it means that the pump has been filled with liquid up to a point where all air has been removed from the pump casing and the suction line. This is critical because the presence of air in the pump can lead to cavitation, which is harmful to the pump and disrupts its ability to maintain proper pressure and flow.

Ensuring that there is no air inside the pump allows for efficient operation and maximizes the pump's efficacy in moving the desired liquid. The pump's ability to generate a vacuum and pull liquid into the system relies on having a complete liquid fill without air pockets. In this context, the focus on having no air is essential to the operational integrity of the pump, making it vital for effective functioning during firefighting, water supply, or similar applications.