If a centrifugal pump is not delivering the expected sewage flow, which of the following is NOT a potential cause?

When considering the factors that can affect the performance of a centrifugal pump, it is important to evaluate the role of proper priming. A centrifugal pump requires adequate fluid in the casing to generate suction and create flow. If the pump is not properly primed, it cannot establish the pressure needed to draw in sewage effectively, leading to decreased or nonexistent flow.

Therefore, the assertion that a pump not being properly primed is not a potential cause of insufficient flow is incorrect. In reality, failure to prime the pump would indeed result in poor performance, including an inability to deliver the expected sewage flow.

In contrast, the other options—speed of the pump being too slow, defective stuffing box packing, and a partially clogged suction line—are all legitimate reasons that can interfere with a centrifugal pump's ability to function correctly. A slow speed may not generate enough flow rate, defective packing may cause leaks leading to a loss of pressure, and clogs in the suction line can significantly restrict the volume of sewage reaching the pump.