Sign up Calendar Latest Topics Donate
 
 
 


Reply
  Author   Comment   Page 2 of 2      Prev   1   2
RustyCas

Avatar / Picture

Admin
Registered:
Posts: 1,810
Reply with quote  #16 
Oh, I've seen "cocked" coupling hubs cause high 1X, or oversized covers (using hubs/covers from different manufacturers).


__________________
"The trend is your friend"
fburgos

Sr. Member
Registered:
Posts: 670
Reply with quote  #17 
Here's an small extraction of the spreadsheet.

Attached Images
png Screenshot_20180426-172632~01.png (438.07 KB, 18 views)

billy7590

Member
Registered:
Posts: 21
Reply with quote  #18 
Coupling pads have also been replaced with new ones. But the problem is still there.
Curran919

Avatar / Picture

Sr. Member / Supporter
Registered:
Posts: 599
Reply with quote  #19 
Quote:
Originally Posted by billy7590
Coupling pads have also been replaced with new ones. But the problem is still there.


I've seen something similar recently, but it was the same problem on 20 identical, new motors. It was accompanied by heavy 1x axial shaft displacement as the motor hunted, but couldn't stabilize at its magnetic center. I believe the conclusion was a poor design/build of the field windings.

To exclude this possibility, did you use a strobe to look at shaft displacement?

This would also be an 'always' problem. Has this vibration developed over time?
billy7590

Member
Registered:
Posts: 21
Reply with quote  #20 
I must mention that in the annual plant shutdown, mechanical maintenance team added an additional resting support on the suction spool on the request of operations division. Is there a possibility that this additional support made the pump side more fixed, thus resulting in all the vibrations being transferred to the motor side??
billy7590

Member
Registered:
Posts: 21
Reply with quote  #21 
Quote:
Originally Posted by Curran919

This would also be an 'always' problem. Has this vibration developed over time?

This pump was not in use due to relatively high axial vibration of 8 mm/s on motor side. The motor was replaced with a maintained motor on the request of mechanical group as they thought the fault was in the motor.
Now with the maintained motor, the vibrations are even higher in axial direction and now vertical vibration is also higher than horizontal.
Curran919

Avatar / Picture

Sr. Member / Supporter
Registered:
Posts: 599
Reply with quote  #22 
Quote:
Originally Posted by billy7590
This pump was not in use due to relatively high axial vibration of 8 mm/s on motor side. The motor was replaced with a maintained motor on the request of mechanical group as they thought the fault was in the motor. Now with the maintained motor, the vibrations are even higher in axial direction and now vertical vibration is also higher than horizontal.


Yeah, that is a critical piece of information. Are the motors the same model? And this 'maintained' (refurbished?) motor was running normally on a different baseplate? If Yes and Yes, I would feel better about the 'pitching' structural resonance theory. However, because the vibes do drop to 1.5 mm/s decoupled, this wouldn't necessarily rule out other parallel problems as well.

Quote:
Originally Posted by billy7590
I must mention that in the annual plant shutdown, mechanical maintenance team added an additional resting support on the suction spool on the request of operations division. Is there a possibility that this additional support made the pump side more fixed, thus resulting in all the vibrations being transferred to the motor side??


I highly doubt this. A v-stop support on the pipe is not going to have a tremendous effect on the modal properties of your pump, certainly not enough to completely change your system and increase motor vibrations 100%. Unless of course, this somehow has introduced flange loads on the pump, which can really screw up your pump, but still, if the pump vibe has gone down or stayed flat, then it is probably not the case.
John from PA

Sr. Member
Registered:
Posts: 963
Reply with quote  #23 
Has the alignment been checked?  This is an essential thing to do, especially when you have the presence of excessive axial vibration.  The alignment should be checked using reverse dial techniques (as opposed to rim and face).  
billy7590

Member
Registered:
Posts: 21
Reply with quote  #24 
Quote:
Originally Posted by John from PA
Has the alignment been checked?  This is an essential thing to do, especially when you have the presence of excessive axial vibration.  The alignment should be checked using reverse dial techniques (as opposed to rim and face).  

The alignment was checked using reverse dial method and found satisfactory. Yesterday, I took another set of data on the same equipment, motor axial vibration remained up to 3 mm/s for about 30 minutes with 1X, 2X and 3X peaks.
Afterwards, vibration quickly started increasing and went up to 14 mm/s with 1X now the only peak in the spectrum.

Then we loosened the foundation bolts of motor one by one, and the vibration reduced to about 4 mm/s by loosing each bolt individually. I was not expecting this soft foot behavior because in my previous experience, soft foot caused horizontal vibration to increase. Moreover, why does this soft foot not create twice line frequency in the spectrum?

fburgos

Sr. Member
Registered:
Posts: 670
Reply with quote  #25 
I think a resonance was excited or modified because of the tension, but the air gap had very little change
billy7590

Member
Registered:
Posts: 21
Reply with quote  #26 
Quote:
Originally Posted by fburgos
I think a resonance was excited or modified because of the tension, but the air gap had very little change


Why would it take about 30 minutes to excite resonance?
fburgos

Sr. Member
Registered:
Posts: 670
Reply with quote  #27 
dont know, tension and thermal growth, if its posible try a bump test
RustyCas

Avatar / Picture

Admin
Registered:
Posts: 1,810
Reply with quote  #28 
2-pole motors are just evil.
__________________
"The trend is your friend"
Previous Topic | Next Topic
Print
Reply

Quick Navigation:

Easily create a Forum Website with Website Toolbox.