Discussion on vibration in centrifugal compressors
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Moderator: At the shaft extension end of the centrifugal compressor, one set of probes shows high amplitude values, while the other set shows normal values. After inspection by the instrumentation staff, all probes, extension cables, and transmitters were replaced. It still shows a high alarm after turning on. The probe is installed at a 45-degree angle.
One of our company’s air compressors is experiencing the same issue as yours – there is a difference in the vibration levels on both ends. The instruments indicate that the readings are correct, and there is no mechanical explanation for this phenomenon.
1. The unit has not experienced surge； 2. There is no carbon buildup or dust on the impeller of the unit. 3. The coaxiality of the coupling meets the requirements. 4. The vibration at the non-shaft extension end of the unit is within normal limits.
How was it resolved in the end? What’s the reason? Is it due to mechanical or instrumentation issues?
It can’t be said that the problem has been solved; only that it has been alleviated—by increasing the oil supply (which lowers the oil temperature here and helps to make the oil film as thick as possible).
It’s a bearing bush, and it’s relatively difficult to replace.
Can the bearing clearance be checked?
This situation usually isn’t caused by the instruments or equipment themselves; rather, it results from an abnormal shutdown during operation, with something attaching to the blades or part of that attachment falling off.
Does the compressor have an online monitoring system? If it does, the spectrum diagram and the axis trajectory diagram can be used to determine whether the issue is related to misalignment or if there are external interference factors； If there is no monitoring system, it might be oil film turbulence; of course, it would be good to have actual data, so let’s discuss this together. There are several preliminary reasons: 1. Whether the probe is contaminated with impurities ； 2. Is there a magnetic field between the probe and the shaft (mainly, is there a possibility of the probe becoming magnetized)? ； 3. Check whether there are any adjustments to the process operations and unit load ； 4. The oil pressure can be manually adjusted within a controlled range for observation ； Therefore, there must be a reason for this phenomenon; we just need to explore it.