Why does a single-stage centrifugal pump have normal pressure but insufficient flow rate?

Insufficient flow. Possible causes: 1) The impeller or the inlet/outlet pipes are blocked; the impeller or pipes should be cleaned； 2) The sealing ring and impeller are severely worn; the damaged sealing ring or impeller should be replaced ； 3) If the pump shaft speed is below the specified value, the pump speed should be adjusted to the specified value ； 4) If the bottom valve is not open enough or the check valve is blocked, the bottom valve should be opened or the machine should be stopped to clean the check valve ； 5) The submersion depth of the suction pipe is insufficient, allowing air to be drawn into the pump ； 6) Air leakage in the suction pipe ； 7) Packing air leakage ； 8) If the sealing ring is worn, it should be replaced with a new one, or the impeller should be rounded off and equipped with a thicker sealing ring ； 9) Severe wear of the impeller ； 10) If the sand content in the water is too high, filtering facilities should be added or operation should be avoided.

I think if the pressure gauge for export is working properly, there should be no problem with the pump itself. If the outlet flow is insufficient, the outlet piping system should be checked for any blockages or increased resistance.

Agree with the opinion on floor 3; we should take a look at the pipelines

It is also a common cause for insufficient flow: blockages by debris at the impeller that lead to inadequate liquid supply

A specific head-flow curve of the pump corresponds to an impeller of a certain diameter. You can compare the pump’s data sheet with its performance curve. The pressure value is the same as the rated flow and pressure points on the performance curve; the flow rate is simply lower, which may be due to a reduction in the diameter of the pipes, valves that are closed partially, or internal leakage in the pump. If both the pressure value and flow rate are lower than the rated flow rate and pressure on the performance curve, and the pipeline is in good condition with no change in the pipeline resistance curve, then it is an internal leakage within the pump.

Reply to 2# cxkstc: Thank you!

Reply to 6# Michaelhu: This pump has been in use for a long time; the problem appeared suddenly. We also replaced the impeller mouth ring, and after checking all aspects of the pump’s rotation, everything seemed fine; however, the flow rate remains low. I’m too stuck on this

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It’s either a medium issue or there’s a blockage

Is it because the condensate contains air, or is the temperature of the condensate too high, causing some of it to vaporize as the pump operates?