Should a centrifugal pump be primed with it running or off?

Priming a centrifugal pump is best done with the pump turned off to ensure that there is no risk of damaging the pump or creating operational inefficiencies. When a centrifugal pump is running, the impeller spins at high speeds, which can cause cavitation or air binding if you attempt to introduce liquid into an already active system. This could lead to damaging impulses or vibrations, which can affect both the pump’s performance and its longevity.

Additionally, priming with the pump off allows the fluid to fill the casing and the impeller without interference, ensuring that all air pockets are removed and that the system is fully operational once restarted. This method also prevents the risk of overheating the pump due to insufficient fluid flow, which could happen if there is no liquid to absorb the heat generated by friction in a running pump.

Thus, turning off the pump before priming creates a safer and more effective environment for fluid introduction, making it the correct approach.