I know very little about bearings.

[PUMPDESIGNER]

I know very little about bearings.
We have had problems however that must be analyzed.
My company manufactures skid mounted pumping plants.
Our expertise is in controls and pumps, not motors.
I will make multiple postings.

The problems we have with bearings are spotty and inconsistent. Here is a sample, please comment as best you can which will then allow me to supply more information and ask the right questions.

1. Two of our stations had twin 30 hp pumps. Motors were US Motor Unimount series, 3500 rpm nominal, 460 volt supply (although motors are dual voltage capable). Motors were supplied by the pump manufacturer, so the motors were obviously sold to the pump manufacturer as OEM. In both cases just one of the 30 hp motors on each station had a bearing failure within 2-3 months, one on each station. After two years the other two motors that had not failed and are still running well. The bearings in both cases became noisy, and in one case the bearing spun inside the motor end cap, which then increased clearances and the rotor rubbed against the motor stack and ruined the motor.

We believe this is a case of poor quality control as the other 30 hp identical motors are still running fine under identical circumstances. We are not sure if the problem is with the bearing, grease, motor end cap clearances or concentricity. We would go to US Motor except that past experience with them shows them disinterested.

I know this is not much, but we do not know where to look.
Any ideas?
Richard Neff
Irrigation Craft

 

[ischgl99]

There could be many reasons for the failure, were the pump motors that failed located in the same position on your skid? Have you done any vibrational analysis of the system to see if the pumps in question are exciting a natural frequency at the motor speed? The couplings may not have been alaigned properly, the bearing housings may not be machined within tolerances, etc. Are the connecting pipes rigid or have you used flexible connectors?
Sometimes a manufacturer gets bad bearings and they fail early, but since you had 2 fail, that is probably not the reason. Looks like you need to have someone do a thourough analysis of your skids, could be the way the pumps are mounted is causing the problem. Mike Bensema

http://www.dutchmenservices.com

 

[PUMPDESIGNER]

Thank you mbensema for your reply.
Here is the information.

The motors are close coupled to the pumps, JP frame motors.
On both stations the motors are side by side and alternated to produce even starts and wear.
Pipes are rigidly connected as on all our stations. We asked one vibration "expert" on this and he said that rigid is best unless it causes problems.

It has been 1 year since the two motors were corrected (one motor replaced, 1 bearing replaced).
Both are working fine.
I will study your issues but the results indicate that it was a bearing inconsistency, although I would not stake my life on that.

Thank you,
Richard Neff Richard Neff
Irrigation Craft

 

[ischgl99]

Richard,
since it has been a year since the failure without any more problems, it probably was something with the bearing itself. I missed that part of the original post. The bearings may not have been packed properly with grease, could have been dropped before installation, maybe not installed properly, many possibilities and not easy to say without seeing the bearing.
I'm curious about your vibration experts recommendation not to isolate the machine with flexible pipe connections, this is standard practice on rotating machinery where vibration could be transmitted. The danger is vibration can be transmitted from one machine to the other through the piping and increase the vibration, flex couplings help avoid this. If things are working well now, then maybe you don't need them.
Do you have a website showing the pumps that I could look at?

Mike Bensema

http://www.dutchmenservices.com

 

[PUMPDESIGNER]

The whole story of the vibration "experts" advice was this.
We were interested in using isolators underneath the motors and pumps, as well as flexible pipe couplings.
We consulted with this guy (many years ago) and he studies our situation and how our equipment was installed and used.

His opinion was that the only way to be sure was to do a vibration analyses. Since that would be prohibitive on every job he then asked us if we were having problems. We said no because we have never had a problem that we know of. Then he said that until we had a problem it would be best to keep going as we were. Then he added that rigid mounting is not necessarily bad and in fact sometimes the best solution.

Now I am not absolutely sure we have never had a problem, but not that I know of.

Also, our equipment is almost always remote from buildings and other machines, we are litterally in the boondocks. We set next to lakes, rivers, canals, etc. We pump water to remote places.

We do not have a website, but with your permission I could email you a few reduced size photos of our equipment. If you let me I will email them to that address on your website.

Thank you.
Richard Neff Richard Neff
Irrigation Craft

 

[ischgl99]

Richard,
feel free to send me any pictures, I am interested in seeing your application. Your vibration guy was correct in that rigid is usually good, more rigidity means a higher natural frequency, hopefully out of the operating range, but it is also important to isolate the equipment from vibration from other sources that could cause problems with the machine running. After I have a look at your pumps, we'll see if we can find a solution to your problem, or at least some suggestions on things to check.

Mike Bensema

http://www.dutchmenservices.com

 

[8ptbuck]

Richard
Whenever a bearing fails prematurly the first response is usually a bad batch of bearings or poor machining on the OEM's part. Those two should be the last to consider.
As Mike mentioned you may be hitting a natural frequency or pipe strain etc. In most applications I've seen with multiple units on one pad whether they are pumps, blowers compressors, etc are isolated from one another.
Just because the units are close coupled does not mean you may not have a coupling problem. Make sure the coupling halves are properly spaced. Find out what brand coupling you have and get the specs. If they have the rubber inserts as I suspect then in most cases the field mechanics will squeeze the halfs together not allowing for thermal growth if any or the minor misalignnment that is there. Since your units appear to be running good now I would also suspect you may have had poor lubrication or false brunelling due to poor shipping. This can be determined if you send the bearings out for failure analysis. As a vib guy I recommend to every customer to collect baseline readings on all newly installed equipment upon initial startup. There are several reasons for this. Speak with your vibration guy or anyone in the field and ask them how many problems they detect and correct during startups.
1, the baseline readings will identify any problems such as bearings, coupling , pipe strain, bad end caps etc.
2, If any of these signs are there then the OEM can be contacted with your concerns. OEM's will find any way possible to pass the blame if the unit has been running a while.
3, If the baseline readings look good and a problem shows up down the road then the customer and the vib guy can compare a new set with the baseline.
I also tell customers to have the equipment shipped as late as possible because most company's purchase new equipment well in advance of installation and have the units sitting around for a while using up the warranty. When a failure does occur the unit is most likely out of warranty and now leaves the customer with the problem.
Here are a few other tips.
1, Stay away from motors with aluminum end caps. (that's a personal preference I've come up with over the years)
2,Always check lubrication and (alignments if applied) before startup even if the unit was labled pre-greased and pre-aligned. I've never seen a pre-aligned unit stay aligned after being installed. One pump outfit I used to work for was great at labeling pre-aligned. What that means is a good straight edge was used.
A good vibration guy should be able to help with any problems or concerns you have.
3, make sure that any equipment overhauled in your repair shops use top brand bearings. there are a lot junk bearings out there with no specs.

Randy.
nevibes@aol.com