When is a centrifugal water pump considered fully primed?

A centrifugal water pump is considered fully primed when it is full of liquid, which is the correct answer. Priming is the process of removing air from the pump and ensuring that the pump casing is filled with the liquid it is intended to move. If the pump is not completely filled with liquid, air pockets can prevent proper functioning, leading to reduced efficiency or even damage to the pump.

For example, if air is present in the pump, it can cause cavitation, which adversely affects the pump's performance. Additionally, if the pressure is equalized but the pump is not filled with liquid, it can still lead to air being present in the system, preventing smooth operation. Starting the motor does not guarantee that the pump is primed; the pump must already be full of liquid for it to function effectively. Thus, focusing on ensuring that the pump is full of liquid allows for optimal operation and longevity of the equipment.