Wastewater Treatment Operator Certification Practice Test

What problem could most likely cause a centrifugal pump to discharge at a reduced rate?

1. Damaged impeller

2. Slight water leak at the packings

3. Pumping against less resistance

4. Seal water is dripping slowly

The correct answer is: Damaged impeller

A damaged impeller is a significant factor that can lead to a centrifugal pump discharging at a reduced rate. Impellers are crucial components in centrifugal pumps, as they are responsible for converting rotational energy into hydraulic energy, thus moving water through the system. If the impeller is damaged—whether due to wear, corrosion, or physical breakage—it will not be able to impart the necessary kinetic energy to the fluid effectively. As a result, the flow rate decreases, leading to the pump discharging less water than it typically would. In contrast, a slight water leak at the packings, while potentially causing issues like reduced efficiency or increased maintenance needs, generally will not cause a significant drop in discharge rate. Pumping against less resistance would actually allow the pump to discharge at a higher rate, since the reduced resistance means the pump can perform more efficiently. Lastly, seal water dripping slowly might indicate a small leak but does not have a substantial impact on the pump's discharge rate as compared to an impeller that is severely compromised.