Which type of fire pump must be primed using an external priming device?

• A. A Rotary vane
• B. B Piston
• C. C Centrifugal
• D. D Rotary-gear pump

Answer: (C)

Centrifugal pumps must be primed with an external priming device because their operation relies on creating suction to lift water into the pump. If air is present in the suction line or inside the pump, a vacuum cannot be formed and the pump cannot develop flow. An external priming device removes that air and fills the suction line and pump with water, establishing the initial suction needed for the pump to start delivering water. Once primed, a centrifugal pump can continue to draw water from the source as long as the intake remains filled.

The other pump types listed are positive-displacement designs that don’t depend on pulling water up from a source in the same way, so they are not described as requiring external priming in the same sense.