What happens if a pump is not primed when drawing from a static source?

What happens if a pump is not primed when drawing from a static source?

• A. The pump will still be able to deliver water at high efficiency.
• B. The pump can develop suction without priming.
• C. The pump cannot develop suction and will not deliver water.
• D. Residual pressure will automatically compensate.

Answer: (C)

The main idea is that a pump needs to fill its suction path with liquid to create suction and draw water from a static source. If the suction side is air-filled, the pump cannot form a continuous liquid column to be lifted; it tries to lower pressure there, but air pockets break the flow and prevent any real draw of water. In practice, a non-primed pump will spin but deliver no water because it cannot develop suction. Cavitation can occur as the pressure drops below the liquid’s vapor pressure, further stopping any flow. Only after priming, which fills the suction line and impeller with liquid, can the pump start delivering water.

The main idea is that a pump needs to fill its suction path with liquid to create suction and draw water from a static source. If the suction side is air-filled, the pump cannot form a continuous liquid column to be lifted; it tries to lower pressure there, but air pockets break the flow and prevent any real draw of water. In practice, a non-primed pump will spin but deliver no water because it cannot develop suction. Cavitation can occur as the pressure drops below the liquid’s vapor pressure, further stopping any flow. Only after priming, which fills the suction line and impeller with liquid, can the pump start delivering water.