What is the expected effect if an operator throttles back on the discharge valve of one of two parallel centrifugal condenser water pumps, while one is at maximum pumping rate?

When an operator throttles back on the discharge valve of one of two parallel centrifugal pumps while the other pump is operating at maximum capacity, the total flow rate to the condenser will decrease. This phenomenon can be understood by considering the principles of fluid dynamics and how parallel pumping systems interact.

In a parallel pumping arrangement, the flow rate from each pump can be combined to achieve the total flow rate. When one pump is fully open and actively pumping at its maximum capacity, it is contributing the maximum amount of fluid to the system. If the discharge valve of the other pump is throttled, it creates a restriction in the system. As a result, this throttling action directly limits the flow rate that the second pump can achieve.

Since the total flow rate to the condenser is dependent on the flow contributions from both pumps, reducing the flow capability of one pump consequently leads to an overall reduction in the total flow rate supplied to the condenser. Hence, the correct answer is that there will be a reduction in the total flow rate to the condenser.