Under what condition is a centrifugal water pump called a lift pump?

• A. When the discharge pressure is higher than the suction pressure
• B. When the water supply to the pump suction inlet is below the pump level
• C. When the pumped fluid temperature is above 100°C
• D. When the pump is running dry

Answer: (B)

Lift pumps are defined by whether the pump must raise water up to its suction inlet. When the water supply at the suction inlet sits below the pump, the pump has to lift the water to reach the inlet. That lifting action is what characterizes a lift pump. So the condition where the suction inlet is fed from a source below the pump level means the pump is performing suction lift, making it a lift pump.

If the water source were at the same level as or above the pump, gravity helps the water reach the suction, and it isn’t performing lift in the same sense.

The other options don’t define lift behavior: discharge pressure vs suction pressure reflects pressure head, not the lifting condition; temperature and running dry are unrelated to whether the pump is lifting water.