Fan reliability issues

[rdco]

Hello,

I have a single-inlet centrifugal, backward inclined, belt driven fan rated at 15000cfm and 3.6kPa differential pressure that has been consistently having higher bearing temperatures compared to the other two identical fans. During start-up the fan also makes abnormal noises and belt failure has been frequent. The bearings and sheaves were replaced two years ago. I am thinking of trying to increasing the sheave size and changing the belt arrangement from 3 to 4 belts. I am looking to take some of the load off the bearing and increase belt reliability without changing the performance requirements of the fan. Is this a good approach? If not what can also be considered?

Thank you.

 

[MechEngNCPE]

You are talking about increasing both the fan and motor sheave, in order to maintain the same ratio, correct? Otherwise you will get a different fan rpm. Many times, during startup, the fan will pass through a "surge mode" operating to the left of the fan curve, which would produce vibrations and noise. I'd suggest changing to a 4V belt arrangement, making sure the line-up is precise. Is the fan seeing higher total static pressure requirements than it was designed for? This would also lead to surging. Just some thoughts from an industrial HVAC PE.

 

[MintJulep]

You can't solve a problem before you understand what the problem is.

You need to identify what is different between this fan and the other two "identical" fans. Then assess if that difference would lead to the failures that you are seeing.

Adding a belt might make belts last longer, but it will probably make things worse on the bearings.

 

[ChrisConley]

Dynamic balancing could lead to a solution as well. A fan that is even slightly out of alignment will have more frequent bearing failures.

 

[willard3]

+1 on dynamic fan balancing. If anything is out of balance, even a little, you will have bearing failures and noise.