belts came off - compressor runs OK - why?

by Elmer
(Cleveland, OH)

15hp two stage compressor. Electric motor was running, but both belts had come off. Put belts back on (a little loose) and compressor works normally. What could make belts come off by themselves?

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Bill says...

Elmer, things that come to mind are sheave misalignment, or either the motor sheave or pump sheave slowing forcing the belt to stretch and jump, maybe a mount has dislodged and the compressor is vibrating.

Might be intermittent, might happen often now that it has happened once.

If it happens again, and the sheaves are aligned, the belts are good and all mounts are secure then I would look to a motor issue or something amiss in the pump.
Cheers,

Bill