Screw compressor readings. 1

[referdude]

MYCOM 300 h.p. (R 717) screw compressor vibration analysis report: "The compressor is showing indications of some internal looseness and possibly some internal misalignment. The readings are showing a 4th order harmonic throughout the spectrums with the time waveform showing 4 distinct peaks through each rotation. The waveform peaks are at high amplitude and showing impacts. This could be due to the fits on the compressor have developed some wear."
This machine has very few hours on it. After replacing coupling center (which was a little loose) and re-aligning motor (which was found to be a few thousandths off) the next vibration analysis shows more vibration and increased noise to the fourth and eighth harmonics. Both analysis were performed with compressor under full load.
There is no discernable shaft end thrust. The vertical thrust on the main shaft is only .008". Any suggestions on this machine?

 

[MachineryWatch]

Is the analyst familiar with screw compressor vibration analysis? Screw compressors' vibration spectra are typically dominated by pressure pulsation peaks and their harmonics. The overall vibration amplitudes are also typically higher than analysts are comfortable with on other types of rotating machines.
Is there another similar machine nearby for comparative readings? What are the measured amplitudes?

Skip Hartman

http://www.machinerywatch.com

 

[referdude]

The analyst is not overly familiar with screw compressors. However, this ones sister machine (which has many more hours on than this one) can be used for comparison purposes. If you would like to see the complete analysis on both machines I would be happy to e-mail both to you.

 

[MachineryWatch]

Please send the analyses to skip@machinerywatch.com. Include any details about the machines you might have including speeds, gear tooth counts, # of rotor lobes, etc.

Skip Hartman

http://www.machinerywatch.com

 

[sms]

High 4X and 8X running speed is pretty common on screw compressors, depending on the screw arrangement. Is this a first time analysis, or has there been an increasing trend in vibration level?

 

[referdude]

Three different analysis using two different analists show an increasing amount of noise. However, yesterday we found the softfoot on the screw to be out of spec. Maybe rectifying this will help. Also, we now have two expert opinions that the noise found in this machine is very much within normal limits for a screw compressor.

 

[Modula2]

A question from an EE. Do these harmonics result in torque harmonics on the motor shaft?