1 ips vertical turbine pump vibration

[morganwx]

I have an interesting dilemma in my utility plant. I currently have two vertical turbine cooling tower pumps, same model & vintage, that each have a vibration issue. The first pump is a 1.1 ips 1x vibration in one direction at the motor outboard. The second pump has a loud buzzing noise coming from the motor, .20 ips 53x vibration in all directions at the outboard.

We've been running the second pump out of fear that the first pump is too far above limits to safely run. However our pump maintenance contractor suggests that the second pump is much closer to failure, noting the loud buzzing noise and frequency of the vibration (he believes a bearing failure is imminent). The first pump is likely misaligned, and being a vertical turbine, it's understandable to see higher vibration on the unsupported end of the motor. Nonetheless, I'm resistant to running the first pump because of the high amplitude of vibration.

Thoughts?

 

[1gibson]

Thoughts? Put the good motor on the good pump, then repair the bad motor and the bad pump.

 

[morganwx]

1gibson, that's a novel solution, and one we should be able to implement when the misaligned pump is pulled. Thank you for the input.

 

[Tmoose]

Is there any detectable motion on the sole plate? How about the anchor bolts tha secure the sole plate to the concrete floor?
The first step would be a bunch of vibration measurements ( including 1X amplitude and phase) of several locations from bearing housings down to the concrete floor. Including every interface.

Vertical pumps are very vulnerable to having first bending mode "reed" frequency resonance. Due the variations in stiffness the resonance can be VERY directional. Simple "bump" tests can reliably reveal resonant frequencies.

Even if an installation is resonant, trim balancing the assembled pump attaching weights at the top of the motor/clutch in place can often really whittle down the 1X vibration.

 

[spciesla]

Are you sure that the 53X on the second motor/pump is a bearing? It might be the Rotor Bar Passing Frequency (RBPF) of the motor. Look for 2xLF (Line Frequency) sidebands around the 53X peak. A large vibration peak at RBPF may include a lot of noise, but it doesn't mean that the motor is failing. Suggest that you perform motor current signature analysis on the motor prior to pulling it.

 

[DubMac]

Agreed with all above. Get all the data you possibly can before pulling or making any decisions.

One extra note on verticals and probably the MOST violated rule during installation. The pumps MUST be absolutely vertical or you are going to have wear and vibration problems down the line. Make sure you check that soleplate/foundation is level and column pipe is perpendicular to discharge head mounting plate.

 

[morganwx]

Thank you all for the feedback. We're going to start by pulling the motor for the second pump, which had the high frequency vibration. Prior to pulling, a check will be performed to ensure everything is lined up & vertical. The sidebands are at 1x run speed (1800 rpm / 30 Hz); not sure if this suggests RBPF, but I let the motor group know to look for this. Also, when a VFD was put on this pump, we added some form of shaft grounding, though I can't find documentation anywhere on this. Is it possible the noise could be the result of excessive contact with a grounding ring or brush? I'm hoping my contractor can provide me that answer when we do a bearing check on the motor.

One thing I neglected to mention in the previous post is that all of our mechanic/millwright labor is contracted out. I have a core operations staff that can do very basic checks, but most of the detailed diagnostic work is done by an outside vendor (who would also perform any corrective work).

 

[Tmoose]

Who does the vibration measurements?
A full length vibration survey and a few "bump tests" on each unit right now would help answer questions both asked and unasked.

 

[morganwx]

Funny that you should ask. We have an operator who was shown how to take basic measurements at set positions (1H, 1V, etc). I have passed Emerson's level 1 ISO training, but have little experience taking the measurements myself. Unfortunately no one else at our plant has any expertise or experience performing or analyzing the data. Having never done a full bump check myself, are there any resources I could reference if I attempted the test myself?

 

[Tmoose]

The full vibration survey of the pump with high 1X should come first.
See attached "map" of locations to measure and record 1X amplitude and phase.
I'd want Those results first to steer and drive the rest of the test plan.
For both pumps.

For instance, if there is anything but ~ zero amplitude on the concrete floor/base AND the base anchors AND the sole plate AND the pump mounting feet or flange, I'd anticipate the details there need attention.

What analyzer and support accessories and equipment do you have?

Page 26 here and ff looks to pretty useful if you have a basic analyzer with no FRF options .

https://www.ctconline.com/pdf/pubTechPapers/13-Bump Testing.pdf

If your software supports it, It is often helpful to take some background measurements to "subtract" the background FFT from the FFT of the "bump."

For my money, whenever there is "excessive" vibration at 1, 2, 3 or 4X motor/pump/belt/etc on the bearing housings, A full survey up and down the machine should be made even before sprinting back to the office to download the route data and study the diagnostics chart.