Fan Screeching Noise

[QualityTime]

Hi All,

I have a NYB vane axial fan with a 25 HP motor on a pulley and it draws about 18 HP running load. On startup the fan screeches very very loudly. A pulley alignment check was made by the fan contractor and supposedly everything is okay. The belt is tight. The belt supposedly shows powdery wear on all sides of the belt. The fan aligment contractor advises the motor has too much torque capability and the belt is slipping on startup. He advises to put on a vfd to get a softer start. Something that he is saying is not right. Any comments? Thanks

 

[MintJulep]

Or change to multiple belt pulleys.

 

[QualityTime]

From what i remember there are 4 or 5 belts already. Supposedly the belts match the pulley

 

[berkshire]

Quality Time.
Check that the belts themselves are a matched set, there will usually be code numbers on the belt.
If somebody has changed a worn belt with an odball, they may not be tensioning evenly, allowing one or two belts to slip.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[ScottyUK]

How big is the fan? Large diameter low speed fans accelerate slowly, and the motor wants to be at nominal speed almost immediately. During acceleration the motor can deliver 2x - 3x nominal torque, assuming it's a standard induction motor so it is possible that the belts are slipping during acceleration. Of course any competent designer would know this and make allowances in the belt drive for the acceleration torque... so what your contractor is saying may have a grain of truth, but a soft start or VFD sounds like it is patching a weak design.

 

[MintJulep]

Increase both pulley diameters - keeping the ratio the same. That will reduce belt tension for the same torque.

 

[msquared48]

Get rid of the rats.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[QualityTime]

I was on a scissor lift today to look at it first hand with a millwright. A spirit level was used and the belt was inspected and it is consistent with it not being aligned even though the contractor said it was aligned. Thanks everyone.

 

[Shophound]

Check sheave wear while you're at it. Sheave grooves should be v-shaped, not dished.

Also consider going with cogged belts unless you are already using them.