Dear All,

I'm facing High vibration issue in my FD fan. The attached excel sheel have all the details.

Maintenance History- Before PM the vibration of Fan DE was normal, But after PM high axial vibration observed at fan Driving End. I don't have spectrum of that as i was on leave , so my maintenance department decided to change the bearing. But after Bearing change the vibration problem was not resolved. SO they waited for me to come. So when i came i saw that Horizontal vibration levels was increased so i did balancing. AFter balancing H and V direction vibration reduced but not Axial. It was still coming above 6 mm/sec but  it increased to 7.2mm/sec while loading the fan.

I observed the spectrum and felt that Fan DE spectrum is showing high BPFO in axial direction, while the acceleration is only 7m/s^2. As it is a new bearing and after analyzing i felt that the bearing is under heavy preload and is not properly mounted on shaft and housing  thus yielding high BPFO in axial direction. So i increased the bearing clearance to 0.08mm and interference to 0.03. checked skewness of bearing and found nothing. Levelling check of Fan DE to NDE done with master Leveller. After doing all these i started the but no success. The High axial vibration is still there.

fan DE-22224 E K C3

Fan NDE- C 2222 E.

Kindly share your feed back.


Original Post

One point to observe carefully is the Motor axial also increased after bearing change and before balancing. Even horizontal and vertical increased in the motor.

Something got disturbed in PM and increased fan axial. But something else also got disturbed during bearing change and increased motor vibration. Strange. But it doesn't look like a balancing issue. Looks more like a rigidity issue

What is the type of bearing in both fan and motor? Fan to motor arrangement? Coupling type? Also what was done in PM?

Hello All. Thanks for your reply.

Update on this case.

This same fan went through maintenance activity on Saturday and removed the housing and performed blue match. the results were satisfactory so we reinstalled the same plummer block. We checked bearing clearance(0.08mm), interference, bearing alignment and Shaft alignment. After performing all these jobs we started the fan and found high vibration of approximately 14mm/sec at fan DE and you can see the spectrum that i have attached. we decided to remove the previously attached balancing weight. and after removing the balancing weigh the vibration decreased to 9.0mm/sec. But the spectrum changed completely. now the dominant is 3X with harmonics. so i inspected the bearing for skewness but found nothing. now what are the the solutions i'm left with? 

kindly help your valuable comments.


Files (1)
FD fan before and after weight removal.

Hi Becar.

Actually i didn't had any photos yesterday.

I'm Posting some videos of this equipment that i have taken.

And During PM the maintenance dept. only checked lubricant condition , they found the condition okay and then reinstalled the housing. This is a grease lubricated


Photos (3)
Videos (1)

Dear Vibration guy,

Referring to the first excel attachment the dominant peak seems to be like blade pass frequency. Kindly confirm the no of blades in fan.

Coming to the second attachment. The spectrum are entirely different from the previous spectrum. Kindly verify the plots and if correct i would doubt on the alignment and coupling condition/grid condition.


When I see your spectrum, it have afew problem.

1. Before remove weight, spectrum have kxrpm - fault basement. You will check it and fill beton or sika

2. After remove weight, spectrum appears kx BPFO. In case of fault basement will appear kxBPFO and other fault bearing (with new bearing).

The first you will check the basement. The mark is not strong.


Photos (1)

You need to be Sherlock Holmes at this point. Yes you see two fans that appear to be the same, but in fact they are not....

Yes there is a bearing fault, normal pk-pk g values for double row bearing would be 4-8 g's, yours is 40, no matter 2 days of run time or 20 years.

The ratio of vibration from H to V is over 10:1, this indicates the H direction is soft, I also would assume the A direction is also soft. You are measuring vibration which is "movement", you have to find what is moving or what is driving the movement, typically a mechanical or structural problem.

The support structure needs to be cleaned and inspected. I can see a large crack in the supporting foundation.

Do the hold down bolts for the support structure go all the way into the large foundation block?

Are ALL hold down bolts tight/any broken?

What does the other side look like?

Are there any broken welds on the fan support structure?

What is the shaft runout with a dial indicator?

Have you taken any phase data?

Are you doing a 2 plane balance on the fan wheel or is the fan wheel close to the coupling side fan bearing?

Nothing is "moving" when the machine is sitting still, as long as the mechanical fits are within tolerance, then the source is somewhere else, this is where phase comes into play. IF the support structure is moving while in operation then phase will tell you where.


Photos (1)

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