How does suction lift influence pump performance?

• A. Increased suction lift increases risk of losing prime and decreases the pump’s output.
• B. Suction lift has no effect on performance.
• C. Increasing suction lift can improve pump efficiency.
• D. Suction lift only affects discharge pressure, not prime.

Answer: (A)

Suction lift changes the pressure at the pump inlet. As you lift the water higher, the suction pressure at the pump drops. If that pressure falls toward or below the liquid’s vapor pressure, cavitation occurs and air pockets form; this disrupts the flow and can cause the pump to lose prime. When prime is lost and cavitation occurs, the pump cannot develop its intended flow and head, so the overall output and efficiency drop.

That’s why increasing suction lift raises the risk of losing prime and reduces the pump’s output. The other statements aren’t accurate because suction lift does affect performance, and higher lift typically hurts efficiency rather than improves it; it also influences prime, not only discharge pressure.