Centrifugal pump doesn’t deliver flow – request help for analysis
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This post was last edited by yspme014 on 2016-1-21 at 23:40. Two centrifugal pumps are used, one in operation and one as a backup; under normal operation, the inlet is at negative pressure while the outlet pressure is 0.2 MPa. Conventional pump shutdown before the festival: the standby pump is fully filled with fluid and thoroughly degassed. After the pump started, the pressure fluctuated around 0.2 MPa; gradually opening the outlet valve until it was fully open reduced the pressure to around 0.18 MPa. During the process of closing the outlet valve of the main pump, the pressure of the standby pump gradually decreased, from 0.18 MPa to 0.1 MPa and eventually almost reached zero; the flow rate was also almost zero. I would appreciate it if some experienced users on this forum could help analyze what might be the cause of this. Cavitation has never occurred in the pump; the inlet filter is clean, and the medium is a non-volatile liquid at around 170 degrees. All joints and connections on the pump body have been tightened properly, and the gaskets are new as well. The pump is a reboiler feed pump; its inlet is connected to the reboiler bottom, and its outlet is connected to the column reboiler. The column top is evacuated by a vacuum pump, creating a negative pressure.
1. Based on your analysis, you can ensure normal exhaust flow, no cavitation, and good inlet sealing. 2. The main pump has stopped operating; both pressure and flow rate have decreased. The pressure is 0.1 MPa and the flow rate is zero. What is the pressure in the reboiler? What is the difference between the current drawn by the backup pump and that drawn by the main pump? Is the motor running in reverse?
Based on past experience, the reasons are: 1. The pump was not filled properly. The exhaust from the negative pressure pump should be directed into the return tank; discharging it on-site is incorrect. 2. The mechanical seal was not properly installed, resulting in air leakage.
Does the pump have a return line? It is recommended to open it when filling the pump. When starting the pump, first activate the return flow (if the return line is thick, open it slightly), then gradually open the outlet (while slowly closing the return valve)~~
It might be that the mechanical seal is leaking; relieve the vacuum to a slight positive pressure and check whether fluid is leaking from the mechanical seal
The exhaust pipeline is also known as the return pipeline, which leads back to the bottom of the tower; there is negative pressure in that area. If the mechanical seal leaks, will material leak out during pump operation? Pump outlet pressure: 0.2 MPa
That’s how I tried it; I tested all the methods of operation
Could you provide the layout diagrams for the pumps, pipelines, and valves? Import is in a negative pressure state as a backup; are you using a vacuum pump for exhaust?
Does the process allow stopping the pump first and then starting it again? For a short period of time~~if permitted, it is possible to start the backup pump first; after shutting down the main pump, start the backup pump immediately~~If it’s not possible to shut down the pump, one can first reduce the flow at the outlet of the main pump (by slightly opening the return valve), and then gradually increase the flow at the outlet of the backup pump (by slowly closing the return valve)~~Additionally, each pump has its own separate piping system, right?~~