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Posts: 11
Reply with quote  #1 


the attached collected data are little bit tricky! I can see unbalance symptoms clearly but the resonance symptoms are also in place.

can you please review, edit and/or comment on the report.

PST: this is my second report in the VA journey. looking for your guidance and help as my line manager is assigning rotating equipment tasks form me.

your input will be highly appreciated,

Mohammed Abdullah

Attached Files
docx U-26003E-FM01B Boiler FD Fan Vibration Survey_21.07.2020.docx (8.51 MB, 35 views)


Danny Harvey

Sr. Member / Moderator / Supporter
Posts: 1,394
Reply with quote  #2 
That's a whole lot of reporting. I don't want to appear too critical but it seems that you are in the developmental stages of a program and while it is helpful to analysis to organize everything like you have, as a matter of practice, it is going to be difficult to perform this detailed an analysis and report on every piece of equipment you do. As you move on with this, I hope you will recognize that most reports do not require this sort of detailed method.

I would suggest that you submit your reports in a single sentence form in a report with all other equipment in the current survey. That is linked to a more thorough report where you have diagrams, comments, arrows pointing to things and a couple of graphs to support your conclusions.

This kind of report will get read on this site because we are all interested in the details that go into analysis, but if you are submitting that to management/clients, it's probably not going to get read.

I would add that in addition to a soft foot check, a coupling inspection and runout check (both radial and axial on both shafts) are well worth the time during any alignment. The resilient mounts should be checked for broken rubber elements and overtightening.

And remember this about resonance:  Without an exciting force, resonance doesn't really matter. It's nice to know if you have some natural frequency at running speed but if you fix the vibration at 1 x running speed, there is very little signal to amplify. 

Damper position will effect running speed amplitude. That needs to be fixed before you can really tell much. That might be the cause of that little subharmonic peak you pointed out. I don't recall what it was in orders, but turbulence and stall can create some substantial subharmonic amplitudes.

I had two similar dust collector fans that I covered, slightly larger but the same construction (New York Blower) with variable dampers and no resilient mounts. They are both effected by changing damper positions and one has a soft foot that causes increased 1 x running speed horizontally on the foot diagonally opposite. 


Posts: 62
Reply with quote  #3 
The soft foot check can be done while running depending on your safety rules. I often checked soft foot by loosening 1 bolt at a time while monitoring vibration. If you have soft foot you will see a drop in vibration when you get to the soft foot.
I would insert shims and tighten bolt. Would do this several times until vibration was acceptable. 
I worked in house and completed W.O.'s on down day.

Sr. Member
Posts: 659
Reply with quote  #4 

My opinion is that you have an unbalance phase at the motor, inspection for the motor fan and coupling are my first step.

For phase a bubble diagram is easier to understand, check this link

Why the check for soft foot wasn't done at the alignment?

I agree with Danny, long reports look nice but are not for everyday analysis you do, I do long reports and full graphs only when I know my report will be reviewed by another vibration analyst, usually a complaint to a third party or a second opinion for example this forum.

Check out my post for what I believe it's a resonant baseplate, try to do a similar cross phase at your baseplate and se where if you find some funny phase behavior.


Sr. Member
Posts: 634
Reply with quote  #5 
I will say the appropriate length / detail of a report depends on the purpose.  If I have one particular machine that I'm really studying and the answer isn't obvious, then I build a big report like you have because it helps me organize my own thoughts and make sure I'm being thorough.  And if the problem drags on (maybe you make a recommendation for a fix and then nothing gets done for six months, and then the problem didn't go away and you have to pick back it back up and figure out the next step), then the report will  help you get back up to speed where you were.  And if / when the problem finally does get resolved you can add that to the report for a nice case study you can refer back to. 

With all that said, I couldn't get through it. Too much detail for my time available at the moment.  But that's my problem, not yours.

Posts: 3
Reply with quote  #6 
The motor foundation structure installation is suspect (supported and mounted on 6 points?) and is susceptible to soft foot induced vibration. The soft foot vibration will mask 1X vibration related problem, like unbalance.
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