spraying a belt with water for troubleshooting noise

I saw the following tidbit in Gate's belt PM manual:

"When a belt drive is excessively noisy, the belt is often incorrectly blamed. It is easy to eliminate the belt as the problem by spraying it with soapy water while it is running. If the noise goes away, or decreases, then the belt is part of the problem. If you still hear the same noise, the problem is likely due to other drive components."

I'm at a loss to understand what that's all about.  What is the physical effect of spraying water... does it improve the traction between the belt and the groove?

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

The water makes the belt slip, which removes the source of acoustic energy... if the belt was generating the noise.

If the noise was coming from something else, e.g. a bearing, it will still be present when the belt slips.

Mike Halloran
Pembroke Pines, FL, USA

I believe that the soap acts as a lubricant that stops some kind of "Stick Slip" that is happening between the belt and the pully.  I use Isopropyle alsohol as a test since it evaporates (and sometimes cleans the belt and stops the nosise).  There are commercial belt dressing that will stop belt noises at least for a while.

Ok, makes sense.

My initial reaction would have been that making the belt slip more would produce more noise.

But I guess it is a smoother slip instead of the stick/slip metioned and that's the difference.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

I think it would be more correct to say that the purpose of the spray is to make quite whatever belt slippage that may be occuring. It will also increase slippage but that is not the important point.

Water mist Works  great on v-belts under the hood cars as old as I drive.  My dad had 5 or 10 year old Plymouth whose power steering pump made a horrific metallic crackling kind of noise. Suggestively Reminiscent of ball bearing whose cage had worn and broken, allowing the balls to crowd together and jam. Swapped in a good used pump, and the noise remained.  Sanding the well worn sheet steel pulley/sheaves and cleaning the belt with carb or maybe brake cleaner quieted it right down for quite a while.  Probably could have gotten away with a spritz of brake clean. I bet water mist would have saved us the pump excercise.