Vibration problems in high-speed pumps
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Today, we cut off a high-speed pump. When it was disconnected, the pump vibrated extremely violently once all the return lines were closed; the pipelines also vibrated heavily. The vibration stopped as soon as the return lines were slightly opened. The medium used by the pump is water; I would like to ask what the reason for this is
What you’re describing could be resonance – resonance that occurs when both pumps are running; stopping one of them might solve the problem. Also, check whether the foundation bolts are loose, as this issue can sometimes arise even when the bolts are tightened
When the return line is turned off, what percentage of the flow rate (relative to the rated flow rate) does the pump still vibrate at? Is the traffic too low?
Does the return line refer to the minimum flow line? Are you conducting tests using water? If that’s the case, consider finding the stable operating condition of the pump and checking whether the inlet filter is too restrictive
With one pump in operation, we carry out normal daily pump switching; it won’t work even if the pump is stopped, and only by allowing a slight excess flow through this return line can it work
Well, the smallest return path. It’s not water transport; when it’s operating normally, the medium used is water
It can’t be due to low flow rate; at that time I was switching pumps outside, and it was indicated that the flow rate inside was sufficient, with the outlet valve also fully open
(1) When a centrifugal pump operates at low flow rates, fluid separation can occur within the pump, which can easily lead to vibration and noise. By setting a minimum flow rate for the pipeline, it is ensured that a certain amount of fluid flows through the pump at all times after it starts up, thereby preventing cavitation ； (2) When a centrifugal pump with high power is operated with the outlet valve closed, the fluid inside the pump becomes increasingly hot; in severe cases, this can damage the bearings. By installing a minimum flow line, it is possible to ensure that a certain amount of fluid flows through the pump at all times while it is operating, thereby preventing such issues from occurring ； (3) When operating at low flow rates, the pump shaft is subject to additional radial forces. By installing a minimum flow line, it is possible to ensure that a certain amount of fluid flows through the pump at all times during operation, thereby preventing the pump shaft from being subjected to excessive radial forces ；
The summary upstairs is very comprehensive; when starting a centrifugal pump, it is required that the outlet valve be fully closed or slightly open in order to minimize the workload on the motor during startup and thus protect the motor. However, ordinary high-pressure pumps or multi-stage centrifugal pumps are equipped with return lines to ensure a minimum flow rate during startup; it is also possible to use a slightly open outlet valve in the absence of such return lines. If the outlet valve is not opened for a long time after the centrifugal pump starts, it can easily lead to pressure buildup within the pump, which in turn damages the mechanical seal. If this situation persists for too long, leakage from the mechanical seal may occur. Additionally, the centrifugal pump converts the mechanical energy of the motor into internal energy of the working medium, which can easily result in an excessively high temperature of the working medium, even its vaporization, leading to vibrations and other problems.
Seeing your reply, is the pump outlet fully open? This is not normal. Is there any blockage at the outlet?
Could it be that the flow rate is too low while the pump’s capacity is too high, resulting in too high an outlet pressure for the pump? ? Check what pressure the pressure gauge at the pump outlet shows. It is recommended to consider using an inverter to reduce the pump’s speed.