The centrifugal pump doesn’t draw water – please provide guidance
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A single-stage, single-suction pipeline centrifugal pump that was operating normally was shut down for a week. The problem was that it failed to pump water; when it wasn’t started, the pump chamber filled with water and water flowed out from the exhaust valve (the exhaust valve is located about 50 centimeters above the pump chamber). After the pump was started, air continued to be discharged from the exhaust valve, and this air couldn’t be completely removed. The following work has been done so far: 1. It was checked that the bottom valve opens and closes properly, does not leak water, and can be filled with water completely. 2. The seal of the water inlet pipe was checked, and there was no air leakage. (8 kg compressed air test) 3. It was checked that the impeller had not fallen off. 4. Checked that there is no air leakage in the pump chamber. (8 kg compressed air test) 5. The mechanical seal does not leak; no air leaks from the mechanical seal area during the compressed air test of the pump chamber. 6. The water outlet valve can open and close properly. 7. Compressed air was used to test that the sealing surface where the inlet pipe flange meets the pump is leak-free. Thank you to all the teachers and senior engineers for their guidance. Thank you.
Is this a centrifugal pump being used as a self-priming pump, with a foot valve installed at the bottom of the inlet pipe?
This post was last edited by 3983596_FPPZ on 2021-10-19 15:43. Is the inlet pipeline under backflow or suction? Is there a lot of vibration and noise when operating the pump, especially at the inlet? What happens when the outlet valve is closed after the pump is started? What changes occur in the pump as the outlet valve is gradually opened? What is the change in motor current? What changes have occurred in the outlet pressure gauge? What is the change in pump flow rate?
This post was last edited by CHANGBAISHI on 2021-10-21 at 15:36. The problem with your question might lie in the way you are operating it. First, for the preparation to start the centrifugal pump, close the outlet valve completely, open the inlet valve fully, fill it with water and release air, rotate the pump shaft to check for any jamming, and then supply power. Start the water pump and monitor its pressure to ensure it reaches the pump’s rated value. While maintaining a pressure that is not lower than the rated value and ensuring that the current does not exceed the rated value, gradually open the outlet valve. During this operation, the system pressure behind the pump is often very low; usually, the system isn’t fully loaded, so waiting is required. Once the system is fully loaded, the pressure will reach the rated value. At this time, the opening degree of the outlet valve must correspond to the rated current, and overloading is not allowed. The pressure should not be lower than the rated pressure. At this point, the flow rate is essentially the maximum rated flow rate. Nor can the flow rate, pressure, and other process parameters be determined based on the valve opening degree. You might as well give this method a try; it’s for reference only.
Is there air in the liquid, and wasn’t it emptied during the liquid feeding process?
We have encountered this situation as well; it is recommended that you consider the possibility that the inlet pipe is not unobstructed
It is recommended to check whether the bottom valve can open completely. With this suction method, the bottom valve is the most prone to failure
Check the bottom valve, inspecting it level by level from bottom to top; check whether there is a filter screen in front of the bottom valve and whether that filter screen is clogged
This post was last edited by CHANGBAISHI on 2021-10-21 at 15:38. Sorry, I got it mixed up. The inlet valve should be fully open, and the outlet valve fully closed. Sorry! It has been changed.