Old Elliott 3-stage Integrally Geared Air Compressor Vibration Issue 1

[Amer93]

I'm currently troubleshooting an old 50+ year old Elliott 3-stage integrally geared air compressor for high vibration. During normal switchover, the compressor tripped on LS shaft. The eddy current vibration sensor loop was replaced, the coupling was checked, and the shaft was rotated with no mechanical issues. A 10-second DCS bypass was applied on this point to allow the machine to run, where all parameters stabilized and is currently running within acceptable limit for more than 1 week. Nevertheless, this must have been triggered by something inside the compressor. I noticed an increase in vibration readings (from 0.4 mils to 0.7 mils) since after this issue with an increase in seal air pressure as well (0.7 kg/cm2 to 1.3 kg/cm2). H = 0.9 mil and HH = 1.2. What do you think need to be checked further to verify? Looking forward to your responses.

 

[JJPellin]

I have seen machines of this type experience elevated vibration as a result of increased radial bearing clearance, impeller rubs and cracked vanes. A detailed analysis of the vibration should help distinguish between these causes. The analyst may want to capture a coast down to compare the response passing through critical speeds to data from before this event. I suspect bearing clearance will be the issue.

Johnny Pellin

 

[nilesh cm]

Any follow up on this problem amer93...any findings...is the machine still running...do you have any online monitoring system for this old machine...do you have any trends for the trips...how has been the previous coastdown vs the last one...