Analysis of low inlet pressure at the moment of starting a centrifugal pump
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The inlet pressure is low at the moment the centrifugal pump in the power plant starts up (as indicated by the pressure gauge on the inlet pipe). Has anyone experienced a similar phenomenon? Where are the detailed analyses or experiments? Is it related to the opening degree of the outlet valve during startup?
If you consider the working principle of a centrifugal pump separately, first, when the pump is stopped, the pressure at the center of the impeller is equal to the pressure at the pump inlet as well as the pressure in the pipeline leading to the pump inlet. When the pump starts rotating, the liquid at the center of the impeller is thrown toward the edges of the impeller; it can be considered that there is no liquid at the center of the impeller anymore. At this point, the pressure at the center of the impeller is lower than the pressure at the pump inlet, and as a result, the liquid at the pump inlet is drawn into the center of the impeller, causing the pressure at the pump inlet to drop. The pressure in the pump inlet pipe is higher than the pump’s inlet pressure, causing the liquid in the inlet pipe to be drawn into the pump inlet. The impeller keeps rotating, continuously drawing in liquid and throwing it out. So the inlet pressure will be low when the pump starts. I’m not sure if I’ve made myself clear. It is related to the export traffic.
Start the centrifugal pump with the inlet fully open and the outlet slightly open; after startup, gradually open the outlet valve to achieve the appropriate outlet pressure or flow rate
Great, then why doesn’t this phenomenon occur after reaching steady state?
Is Bernoulli’s equation applicable?
Are you saying that once the outlet flow is stable, the inlet pressure won’t be low?
Yes, because the process you described is the same in a steady state as well?
Normally, as the impeller rotates, the liquid inside it is carried away, creating a suction effect at the inlet. It takes some time for the liquid at the pump inlet to go from a stationary state to a flowing state, and this is what causes the temporary low pressure at the inlet
Starting the pump is a special state; the reason has already been explained in the XiXi version! When the outlet flow is stable, the subsequent process can be considered as a steady-state operation.