Which statement about priming a centrifugal pump when there is no head on suction side and no foot valve is provided is correct?

Which statement about priming a centrifugal pump when there is no head on suction side and no foot valve is provided is correct?

• A. It must be primed by a vacuum pump or ejector
• B. It can be started without priming
• C. It must be primed by manual cranking
• D. It cannot be primed

Answer: (A)

When a centrifugal pump has no head on the suction side and no foot valve, it cannot fill the suction line with water on its own. The pump will simply spin and move air rather than liquid, so it won’t develop flow. To establish the prime, you need to remove air from the suction line and draw water into the pump from the source. A vacuum pump or an ejector achieves this by creating a vacuum on the suction side, pulling water up from the source and expelling air until the suction line and pump casing are filled with liquid. Once primed, the pump can start and deliver water. Manual cranking isn’t a reliable priming method in this scenario, and saying it cannot be primed is incorrect because an external priming device can establish the prime.

When a centrifugal pump has no head on the suction side and no foot valve, it cannot fill the suction line with water on its own. The pump will simply spin and move air rather than liquid, so it won’t develop flow. To establish the prime, you need to remove air from the suction line and draw water into the pump from the source. A vacuum pump or an ejector achieves this by creating a vacuum on the suction side, pulling water up from the source and expelling air until the suction line and pump casing are filled with liquid. Once primed, the pump can start and deliver water.

Manual cranking isn’t a reliable priming method in this scenario, and saying it cannot be primed is incorrect because an external priming device can establish the prime.