When the discharge of a centrifugal pump is throttled, the suction lift of the pump increases. This is because throttling the discharge of the pump restricts the flow of fluid from the pump, which in turn creates a higher pressure differential across the pump.

Explanation:
- Throttling the discharge of a centrifugal pump means reducing the flow rate of fluid being discharged from the pump. This can be done by partially closing a valve on the discharge line.
- When the discharge is throttled, the flow rate of fluid leaving the pump decreases. However, the impeller of the pump continues to rotate at the same speed, causing the impeller to generate a higher pressure head.
- The increased pressure head at the discharge of the pump creates a higher pressure differential between the suction and discharge sides of the pump.
- According to Bernoulli's principle, the pressure differential between the suction and discharge sides of the pump affects the suction lift. A higher pressure differential corresponds to a higher suction lift.
- Therefore, when the discharge of a centrifugal pump is throttled, the suction lift of the pump increases.
- It is important to note that while the suction lift increases, the actual suction pressure at the pump inlet may decrease due to the higher pressure differential. This means that the pump may experience a reduction in performance, as it is operating at a lower suction pressure.

In summary, when the discharge of a centrifugal pump is throttled, the suction lift of the pump increases due to the higher pressure differential across the pump. This can result in a decrease in pump performance, as the pump is operating at a lower suction pressure.