When one centrifugal pump in parallel is throttled back, what is the result?

When one centrifugal pump operating in parallel is throttled back, the total flow rate decreases. This is due to the fact that throttling a pump reduces its capacity to generate flow; as the resistance in the system increases, the pump must work harder to maintain the same flow rate, which is no longer possible if one of the pumps is operating at a reduced output.

In a parallel arrangement, each pump contributes to the total flow, and when one pump is throttled, it cannot effectively contribute as much flow to the system. As the throttled pump generates lower flow, the overall output of the parallel system is diminished. This results in a reduction in total flow rate since the throttled pump is now less capable of overcoming the system resistance compared to when all pumps are operating at their designed capacity.

Additionally, since the flow rate is impacted directly by the ability of each pump to push fluid through the system, modifying one pump’s performance inevitably leads to adjustments in the overall flow dynamics, confirming the reduction in total system flow rate.