Why is it necessary to prime a centrifugal pump before starting it up?

Priming a centrifugal pump is essential because it involves filling the pump with liquid, which removes any air that may be present in the pump casing and suction line. When air occupies the pump, it can prevent the pump from creating the necessary vacuum to draw fluid effectively. If the pump operates with air in the system, it could lose prime, leading to cavitation, reduced flow, and potential damage to the pump components.

By removing air through priming, the pump can achieve the correct operational conditions, ensuring that it can effectively transport sewage or water. This action is critical to maintaining the pump's performance and ensuring reliable operation during its lifecycle. Thus, priming directly influences the pump's ability to function as designed, making this a crucial step in preparation for operation.