What will happen if the discharge valve on a centrifugal pump is partially closed?

What will happen if the discharge valve on a centrifugal pump is partially closed?

• A. amperage will increase, discharge head will increase
• B. amperage will decrease, discharge head will increase
• C. amperage will decrease, discharge head will remain constant
• D. amperage will decrease, discharge head will decrease

Answer: (D)

When you partially close the discharge valve on a centrifugal pump, you’re adding backpressure in the discharge line. The pump’s head–flow relationship means that as backpressure increases, the pump must develop more head, but the flow it can deliver decreases. To push water against that higher head at the same rotation speed, the hydraulic load on the motor increases, which typically makes the motor draw more current (amperage). So the expected outcome is higher discharge head and higher amperage. In other words, throttling the discharge valve tends to push the pump to operate at a higher head with reduced flow, requiring more motor torque and often resulting in increased current draw.

When you partially close the discharge valve on a centrifugal pump, you’re adding backpressure in the discharge line. The pump’s head–flow relationship means that as backpressure increases, the pump must develop more head, but the flow it can deliver decreases. To push water against that higher head at the same rotation speed, the hydraulic load on the motor increases, which typically makes the motor draw more current (amperage). So the expected outcome is higher discharge head and higher amperage.

In other words, throttling the discharge valve tends to push the pump to operate at a higher head with reduced flow, requiring more motor torque and often resulting in increased current draw.