Pump Bearing - Drive End 2

[neilsk]

Pump drive end bearing showed momentary vibration increasing abnormal sound after completion of test and commissioning of the new VFD for the 1000 Hp motor driving this 13,900 iGPM pump.
I'm new to this group, your opinions would help me a lot. My question is : Do frequent starts and stops during the test and commissioning of the new VFD has triggered this bearing abnormality?

many thanks..

neilsk

 

[Artisi]

Why do you suspect it is the motor bearing and why would frequent stop / start cause bearing problems for a correctly sized, installed and lubricated bearing?
If you do have a bearing problem, I would be looking for some mechanical abnormality, ie, lack of lubrication, poorly aligned pump / motor, poor assembly technique, faulty bearing etc.



It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[neilsk]

The reply is partially convered on the left with link. How can i removed this so i can read the whole sentences?

 

[EnergyMix]

neilsk,
It must be your browser as I can read all of Artisi's reply.
I've put in extra space on the right so hopefully you can read this.

He asked why you felt there was a problem with the bearings?
He also asked why you thought frequent starts or stops would cause bearing problems
if the bearings were correctly sized, installed and lubricated?

He then stated that if you took the pump apart and found that you had bearing problems, the
problems probably were due to some mechanical abnormality such as lack of lubrication, poorly
aligned pump or motor, poor assembly technique, or a faulty bearing.

Artisi has tremendous experience in this field, based on his posts in this forum.
I'd recommend paying attention to his advice.


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[LittleInch]

The only other point is whether running at a lower speed during the testing than the pump or motor was designed for has created some harmonic frequency? Is this a retrofit VFD? How old is the pump and motor? Did you change the motor or coupling during this work? If you supply all the background info you'll get a much better response.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[neilsk]

EnergyMix, thanks for the comments and this is the link that partially covered your 1st and 2nd paragraphs.

<a href="

http://www.eng-tips.com/threadminder.cfm?pid=407">Pump

engineering Forum at Eng-Tips</a>

The pump was not taken out. A new VFD drive was installed for the motor but before the new VFD was installed this pump was normally running with the old VFD in it an had no issues on pump drive-end bearing.

 

[neilsk]

LittleInch,
The pump and motor with VFD were in late 1990's. We replaced the VFD with a brand new one of the same rating.The coupling was not changed but there was alignment check as part of routine maintenance prior to the test and commissioning.

thanks..

 

[QualityTime]

When was the last time the bearings were checked and changed out. I would think that the bearings finally gave out coincidentally when the new vfd was installed.

 

[Artisi]

For once QT and I might be in agreement, certainly the suggestion is worth serious consideration.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[ApplicationENG]

First thing to look at would be changing out the bearings. If the problem persists (i lean with LittleInch), there may be electrical and mechanical harmonics (resonance) being generated by the use of a new VFD.

I know that motor manufacturers typically prefer one VFD mfg over another for this very reason. Im not an electrical expert (but i would ask one) - ive seen dV/dt filters used to filter the "harmful" electrical harmonics.

Another solution (if the pump can handle it), run the motor full speed and see if there is still a noise/vibration issue. That would isolate whether it is caused by the VFD or motor.

 

[neilsk]

All,
Thanks everyone who had shared their expertise, this is a good place of continuous learning!

We already had replaced the bearing including the NDE. Now, some expert said recheck the pump-motor alignment after it has run for a couple of hours or in hot condition, while others said if there were no noticeable abnormal noise and rise in bearings temperature there is no problem in the bearing and the alignment.

My new question is how many run-time should be good to recheck the alignment after recoupling with new bearings?

Many thanks.

 

[Artisi]

Run the unit until it comes up to normal operating conditions, the time depends on many factors - product, ambient temp., there are no rules other than sufficient time.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

Monitor the temperature of the coupling to see if your alignment needs checking. You'll see any impact there well before you see it on the bearings.

It could just be coincidence so monitor carefully for the next 100 hours run time and then monitor at increased intervals as time goes on. Assume you have vibration monitors so take records of readings to see if they stay stay or increase over time.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way