Dear Sir,
Normally subharmonic between 0.42 to 0.48X indicates oil
whirl, but I come across 0.32X, which fluctuating between 40 to 135
microns. What will be the probable cause of above subharmonic, which
severely fluctuates.

Regards
Ramudu P

.32X is awful close to 1/3X which I have found at times to be an indication of excessive looseness on an anti-friction bearing between the shaft and the inner race, but undoubtly you are dealing with a sleeve type bearing in your example or the mention of oil whirl would not have been mentiomed, huh?

Is this a belt driven system?

On what kind of machine? I assume that since the amplitude is expressed in microns you are looking at proximity probes on a turbo machine, a compressor or turbine. In the case of a compressor it could well be an instability due to gas circulation in either a balance piston seal, or a center bushing. Might also be rotating stall. Are you near the surge point? Can you change the pressure ratio on the machine? If so does it go away?

In a steam turbine it may be steam whirl due to the way steam is being admitted. If so, then loading up the turbine should make it go away.

Please in the future, let us know what the machine is. Just randomly throwing out a vibration frequency is not much to go on....

Nameste, Ramudu (did I spell that right?)--

Steve's right, we need some machine configuration information to start with. With that said, other sources of 1/3Xrunning speed vibe are air turbulance/swirl in a fan or loss of a sleeve bearing in a vertical pump.

Regards, Tony

I've also seen ~ 1/3x in a starved fan. If it's a fan, check filters and dampers for proper position.

Jon
http://www.spintelligentlabs.com

Sorry for half of information. It was a Industrial steam turbine of 15 MW. Turbine was fitted with Two lobe sleeve bearings. Vibrations were severely fluctuating at rear end of turbine from 40 to 135 microns at 1/3X.After increasing the pressure of lubrication from 1.5 kg/cm2 to 1.7 kg/cm2 at rear bearing the vibration fell in the range of 40 to 85 microns.That perticular sub harmonic totally was not gone.

Could very well be oil whirl. With the lobes in that bearing the oil circulation rate would be slower, and the frequency might be closer to 1/3 than 0.43.

But as I mentioned before it may also be steam whirl. Is the admission rack fully open when you see this vibration?