Discussion on the reasons for reduced motor current and decreased outlet pressure in multi-stage centrifugal pump systems
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Personal analysis: A low current indicates that the pump’s power output is reduced. This reduction in power output can be caused by internal leakage (leaks at the inter-stage gaskets) or insufficient suction volume; please feel free to discuss this further
This pump is likely suffering from cavitation; if the motor is variable-frequency controlled, reducing the speed will also lead to a decrease in current and pressure
It’s difficult to determine this sentence; there are many possible causes, and more information about the phenomena could be provided
The original poster could provide more details about the situation; there are many factors at play, such as the type of pump design – is it BB3, BB4, or BB5? Is there also a decrease in current and pressure, gradually declining during operation at the rated point? When increasing the flow rate, does it decrease gradually or sharply, and is there any vibration or noise from the unit? If possible, it would also be helpful to have the values for Q, H, RPM, and NPSHa; this will help determine whether the issue is caused by hydraulic factors or, as you mentioned, by inter-stage leakage.
Low outlet flow, evacuation, and low medium density can all result in a low current