Dear all

In centrifugal compressor ( IR centac) we are facing axial vibration high. The oil pr. 2bar trend maintained..Delta P also Ok.
We are getting axial vinb high, what will be the root cause???
Thanks in advance...

How high is high? What is the acceptable value by OEM?

What is the service? Is it compressing gas?

Is the balancing line and thrust bearing working properly?

Axial vib - 6.8 mm/sec RMS in stage 3.
Details as follows:
Motor (3000 rpm)coupled with Bull gear having 258 tooth and stage 1 having 26 and stage 2 & 3 having 18 tooth. FFT and trend Attached
But my online vibs are in with in limit as per OEM
Thanks in Advance.
Regards

Gurusamy

Axial_3_Stage.doc (82 Kb, 48 downloads) Comp. FFT Tend

Air compressor Make Ingersoll Rand

Regards

Gurusamy

Seeing the Signature it look as if your system is subjected to resonance problem. Can you share the details of the static structure/ foundation over which it is mounted.

Is your system placed on fixed foundation or over Dampers?

What is the first critical speed of your rotor system. Ckeck this and ensure it is 30% away from your operating frequency?

Also let me know the details about the flow entry. Like is it radial or axial?

I would just like to know the type of gears used in gearbox. Is it helical or Straight Spur?
Second thing is whether compressor suffered surge recently?
The vibration spectrum of axial direction is completely dominated by 1X of Bull gear.In case if your gears are helical,there is a possibility of increased axial clearance in thrust bearing.Request you to give vibration spectrum in Horizontal direction also,Also take vibration readings in the axial direction with Fmax of 300000cpm & LOR 800/1600 and see whether hi-freq gearmesh is surrounded by sidebands of 1x of Bull gear.
Bye

Gearmesh frequency is 754650 cpm so you need to set your fmax to at least that high and I would set it to the maximum capability of your analyzer with as many lor as possible. Make sure your mounting and accelerometer selection are appropriate for the high speed.

Identify the other peaks in the spectrum also. It looks like there are other sets of harmonics and sidebands.

I have been told also that these compressors are sensitive to changes in the humidity of the air they compress. An increase in humidity will result in an increase in amplitude at impeller vane passing frequency which is usually somewhere around 20 times impeller speed.

Actually the vibration is fluctuating from 4.5 mm/sec to 6.8 mm/sec, and we took High frequency of 8.5 Lacs CPM with 1600 lines. (Sensor Max- 12 Lacs)
Recently this compressor Lube oil pump shaft (Main shaft coupled with bull gear shaft)got sheared.