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Noknroll

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Reply with quote  #1 
I have a center hung centrifugal fan/blower driven by a 2 pole motor. The outboard or NDE bearing is showing an increasing trend at 2X in the axial orientation.
The fan is blowing cooling air onto a boiler flame scanner. I've tried the search button here and the only thing I could find was a brief mention of a cracked shaft possibly causing 2X vibration, but didnt say if it was radial or axial.......any ideas?
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OLi

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Case of 2X with phase shift I have seen was radial and it was a nuke generator long time ago but still a crack, it was found to be true.
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Danny Harvey

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Reply with quote  #3 
I have found 2 x running speed in the axial on a center hung fan to almost always mean some sort of axial displacement like a bent shaft, distorted back plate...

The wall chart says that 2 x will dominate the spectrum if it is bent near the coupling. 

I would do cross channel phase analysis in all directions on both ends of the motor, across the coupling and across the fan rotor if access permits. You might want to do it both at running speed and 2 x. That sounds like a lot but you've got the 2140, right? It ought to be easy enough to allow you to do all that.

Edit:  You probably have already done this but you need to make sure that you are looking at 2 x running speed and not 2 x line frequency. 
Noknroll

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Reply with quote  #4 
Thanks Oli & Danny
I will mention to the client that there maybe the possibility of a bent shaft, and I can verify with phase if they want me to.
This forum and members never fail to provide answers
Thanks again

Danny Harvey

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Reply with quote  #5 
They can verify it themselves with a dial indicator, too.
Noknroll

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Reply with quote  #6 
Thats true, will see if they take any notice of the report 1st..........you know what some clients are like
Walt Strong

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Reply with quote  #7 
"The wall chart says that 2 x will dominate the spectrum if it is bent near the coupling. "

Wow, unless there is other evidence that a bent shaft could have occurred, this would be last on my check list!

What type of bearings on fan rotor?
Did you measure shaft alignment, check coupling condition, and check shaft end gap?
Any other indications of a loose or cocked thrust bearing?
Check bearing housing for loose bolts and relative motion across joints.

Walt
Danny Harvey

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Reply with quote  #8 
Walt,

Do you always put the easiest things last?
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