What could cause a centrifugal cargo pump to lose suction after working fine for a while?

A centrifugal cargo pump may lose suction even after functioning normally due to incomplete priming. This situation occurs when the pump has not been completely filled with liquid or if air remains trapped in the pump casing after initial setup. Priming is crucial because centrifugal pumps rely on being filled with liquid to create the necessary pressure to draw fluid into the impeller for effective pumping. If air pockets are present or if the pump is not sufficiently filled with the liquid being pumped, the ability to maintain suction can be compromised, leading to a loss of prime and an inability to effectively move the cargo.

The other choices highlight scenarios that can affect pump performance but do not specifically address the loss of suction due to initial conditions or setup. Running the pump backwards would result in ineffective flow but is less likely to lead to a suction issue post-operation. An excessively high discharge head can impede flow but would not cause a sudden loss of suction after the pump had been functioning properly. Head pressure on the suction side typically does not correlate directly with the pump losing suction after it had been working correctly, as proper design should account for pressure differentials to maintain operation.