What is the purpose of a priming mechanism on a centrifugal fire pump?

• A. To regulate discharge pressure
• B. To rapidly fill the pump casing with water and remove air to enable starting
• C. To lubricate bearings
• D. To measure pump RPM

Answer: (B)

The main concept is that a priming mechanism ensures the pump is filled with water and free of air so it can start and develop flow. A centrifugal fire pump relies on creating suction at the eye of the impeller to pull water into the pump. If air remains in the casing or suction line, the pump can’t create that suction and will not start or will air-lock. The priming device rapidly fills the pump casing with water and exhausts the trapped air, establishing prime so the impeller can begin moving water. Once prime is established and the pump reaches operating speed, the system can continue pumping with water in the casing, and the pump may become self-priming as needed. This function does not regulate discharge pressure, lubricate bearings, or measure RPM.