Sudden decrease in flow and pressure and increased vibration during the operation of a multi-stage centrifugal pump
Thread Content
This post was last edited by jacobxu87 on 2021-3-22 01:05. On the morning of March 19, one of our injection pumps (a centrifugal pump with 5 stages in each chamber) suddenly experienced a gradual decrease in outlet flow and pressure during operation; simultaneously, several vibration levels started to rise. Subsequently, the flow rate became unstable and the vibrations intensified, leading to the manual shutdown of the pump. Under normal operation, at the same rotational speed, the outlet flow rate is lower, accompanied by an increase in outlet pressure. Therefore, we wonder whether it is possible that abnormal vibration in a certain area has led to a decrease in pump efficiency, resulting in reduced flow rate and pressure. On the morning of March 20, an endoscopy was performed. Some substance similar to sludge attached to the impeller was seen at the low-pressure chamber end, while the high-pressure chamber end was quite clean with no abnormalities found. On the afternoon of March 20, following the manufacturer’s advice, we performed a backflow test on the pump to conduct a low-speed test. At the initial stage, the parameters were normal; then the speed was increased gradually, with the hydraulic coupler being adjusted to 10% over time. During loading, the X and Y vibrations on the non-driving side jumped suddenly before returning to normal. After reaching 11%, without an increase in speed, all 4 vibrations began to rise, and these vibrations became on par with those of other normal pumps (under a 49% load). When the load reached 12%, the vibration began to increase significantly; a tapping noise could be heard on site, which later turned into a harsh metallic sound, prompting the immediate shutdown of the pump. Test curve: Pink: Unpowered side X direction; Grass green: Powered side X direction; Light purple: Powered side Y direction; Light yellow: Unpowered side Y direction; Gray-green: Return flow rate; Dark purple: Outlet pressure
The most direct reason: insufficient flow in front, and the filter is clogged； Or the pump mechanical seal is leaking!
But the inlet pressure remained stable. This afternoon we conducted another test with the recirculation pump; when the load reached 12%, the vibration levels rose again to those seen under normal load conditions, and unusual noises were also heard on site – it’s clear that there is a problem inside the pump. Contact the manufacturer now to send over both the curves and the sound, so that they can be analyzed and diagnosed. At the same time, preparations are being made to remove the pump for inspection.
Disassembling the pump for inspection is a necessary step; only by taking it apart can the cause be determined.
If it is a process-related issue, it will cause the outlet flow to gradually drop to 0; such a curve suggests a problem with the equipment, and it is very likely that debris has entered.
It seems there might be some surge; let’s check the inlet filter first
However, the inlet pressure remained very stable, with no fluctuations. The other three pumps also use the same water source and are working properly as well.
That’s also what we plan to do now. If the manufacturer sends someone, it’s likely they won’t know when it will be possible; probably we’ll have to organize our own people to carry out the demolition. Only after opening it do you know what spare parts are needed.
We currently only have 2 years’ worth of spare parts on hand, including sealing rings, but no impellers. For the newly signed contracts, with the goods domestically, we plan to select some essentials and airship them over.
It’s such a complicated affair just for one water pump – it can be taken apart easily; it’s a simple task, right?:)