When is a centrifugal water pump considered a lift pump?

A centrifugal water pump is considered a lift pump when the water supply to the pump suction inlet is below the pump level. This designation is critical because a lift pump is specifically designed to move water from a lower elevation to a higher elevation. In this scenario, the pump must exert sufficient suction to draw water up from below its level, overcoming the force of gravity in the process. This characteristic is vital for applications such as drawing water from wells or basements.

While other factors such as the pump's speed can affect its performance, they do not define whether it is classified as a lift pump. Similarly, drainage and situations where the supply is above the pump level do not involve lift action and thus fall outside this specific category. Understanding the definition and function of a lift pump is crucial for its appropriate application in various water movement scenarios.