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Posts: 1,810
Reply with quote  #1 
200 HP Baldor air compressor motor (Gardner-Denver twin screw) with C-face mount and two "hockey puck" ("marshmallow" ??) supports at the outboard end of motor.  Motor was recently rebuilt (don't know why just yet) and now has a dominant vibration that is a combination of 4X and 120 Hz.  Appears to have always been present but not sure since it was never intense enough that I had reason to do a zoom spectrum.  Bearings are 6319 (drive end) and 6314 (opposite end) but not seeing anything that would give 4.019X so pretty sure this is actually 120 Hz.

What would cause this?  Motor frame distortion?  Is it possible to mis-wire the motor leads and cause this?

200A Air Comp.png  200A Air Comp zoom.png 

"The trend is your friend"

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Posts: 384
Reply with quote  #2 
I monitor 4 screw compressors and can get very high 120hz spikes on all 4 of them at times. I have gone back and taken readings 15 minutes later and had them be normal. I always chocked it up to load changing in the compressor.
Danny Harvey

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Posts: 1,403
Reply with quote  #3 
Is a 6319 standard in that motor or has the end bell been bored and sleeved?
Ralph Stewart

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Posts: 235
Reply with quote  #4 
I sort of lean toward Danny's question.

My questions are, since we do not know yet, why the motor was rebuilt......

"Was the bearing end cap bores...... align bored and/or align checked, from DE to NDE?"

"And were the end caps re-installed correctly after the bore alignment was performed?"

Just some thoughts, since there was no problem before overhauling. Could have been a bearing failure that "destroyed" one of the bores. Surely an end cap from a different motor was not used and not aligned, if one of the motor's end caps was bad.

Thanks and Have a Great Day,

Ralph Stewart
Ron Brook

Posts: 35
Reply with quote  #5 
As I recall, screw compressors have four lobes so you also have to consider loading and blockages downstream etc. I have also seen this type of vibration on overhung motors. Possible air gap issues?
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