What happens to the power requirement of a radial-flow centrifugal pump when throttling the discharge?

When throttling the discharge of a radial-flow centrifugal pump, the power requirement is reduced due to the relationship between flow rate, head, and power consumption.

Centrifugal pumps operate based on the principles of converting mechanical energy from the motor into hydraulic energy. When the discharge valve is throttled, the flow rate of the fluid leaving the pump decreases. This throttling creates an increase in the hydraulic resistance within the system, causing the pump to operate against a greater head. However, because the flow rate is also reduced, the overall power requirement decreases.

The power that a pump consumes can be described by the equation: Power (P) = Flow (Q) x Head (H) x Efficiency (η). With throttling, although the head may increase slightly due to the resistance, the flow is significantly reduced, leading to a net decrease in power consumption.

This makes the reduction in power requirement a characteristic behavior of centrifugal pumps under throttling conditions, indicating how they are efficiently designed to adjust to varying loads and maintain performance across a range of operational scenarios.