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Air Compressor Vibration

Air Compressor Vibration

Air Compressor Vibration

(OP)
We have installed a Ingersoll-Rand Type 30 Model 3000X30 air compressor. This is a two stage three cylinder 100 psi 100 ACFM electric motor driven machine.
Per the direction of the vendor who supplied the machines, we shimmed under each of the holddown bolts of the base plate to correct vibration problems. The procedure was to loosen one bolt and lift the corner of the base plate, if vibration decreased we shimmed under this point and retightened the bolt. This worked just fine on one of our machines. On the other machine this did not solve the vibration problem. To get an acceptable vibration level the mechanics had to leave one of the bolts loose. They found that putting shims under the holddown point or even running the nut down finger tight would cause the machine to vibrate. Either of the holddowns across from each other will do this. The machine presently has three bolts tight and one loose and the vibration is acceptable. Any suggestions to the cause?

RE: Air Compressor Vibration

I couldn't find your compressor in the ingersoll rand web site(http://www.air.ingersoll-rand.com/). How large is this unit? Where are the base plate hold-down bolts in proximity to the motor base? Do you have any spectral information on frequency of vibration, etc.?

RE: Air Compressor Vibration

(OP)
Go to: http://air.ingersoll-rand.com/CMP/sap/scdlubbaselevel3.htm

our compressor is the 30X3000 at the bottom.
The compressor is belt driven by a 30 HP 1460 RPM electric motor. The motor hold down bolts are about five inches back from the baseplate bolts. They are about four inches in from each base plate bolt. The baseplate bolts are 39" center to center on one side and 19" center to center on the ends.
I do not have information regarding frequency of vibration.

Thanks,
Jim

RE: Air Compressor Vibration

It would appear you are checking for "soft-foot". (eg: check out http://www.reliability-magazine.com/wwwboard/wwwboard_rel//messages/1089.html). It's hard to diagnose a problem like this without spectral information, but on the second machine you may have a resonant condition which is affected by releasing one of the hold-down bolts. Motor frame distortion, alignment, or poor foundation may also be issues. More detailled vibration measurements are required.

If these are new installations, then consider getting an independent vibration analysis and get the vendor to fix the problem. Leaving one base bolt loose is not a solution. Pls let us know how this turns out.

RE: Air Compressor Vibration

(OP)
For now we have installed pieces of conveyor belting under the four feet of the compressor base plate and left one of the feet loose. The compressor is running with only slight vibration. I have contacted the vibration engineer from one of our other plants and he is going to take vibration readings on the compressor.

RE: Air Compressor Vibration

What vibration level we are talking about?
As stated by brin, you're checking for soft foot propblem.  You need to check both alignemnt and resonance within the operating speed of the machine.
When holding the forth bolt, you are making the system more stiff and this could cause the system natural frequency to be excited.  Usually the separation margin should be 15-20 % away from the excitng running frequency.

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