Aerzen USA insights and guidance for blower, compressor and vacuum pump applications

PD Blower "Free" Oil Analysis - There Is Usually A Good Reason For It

Posted by Ralf Weiser on Thu, Mar 17, 2011 @ 11:11 AM

Oil analysis and vibration analysis make a great tag team when it comes to assessing rotating equipment condition.  Even if oil analysis trending is carried out by itself it still can be a powerful tools assessing whether or not there may be trouble coming down the pike – rolling element bearings, gears and other key components leave key evidence of them failing behind in the lubricant.  Depending on your plant size and usage of lubricant, quite a few lubricant suppliers also offer free oil analysis.  While that seems great at the first glance, there are quite a few wrinkles that can lead straight to catastrophes that the analysis was supposed to help prevent.  I will review a few issues and elaborate on what an analysis report should cover in the course of this blog. 

For one, the report is only as good as the one who reads it can understand and interpret it.  Most reports that I have come across in my career have a line with CYA-ish terminology in them, e.g. “Action: Resample next service interval to further monitor”.  How are you supposed to make any heads or tails of it on your own?  The advice tends to be too broad to be useful.  Two more big issues can arise if you do not know what all the different tests that are out there and which one you should apply for which machine.  The greatest print out will not do you any good if it is the wrong test or you really do not know what the readings mean. One of the most often overlooked issue id the task of sampling the oil.  Location, time and sampling cleanliness have a huge impact on analysis accuracy.   Is the sample taken from a sump or a centralized pressurized lube oil system?  Is the sample bottle and sampling port clean?  Are you taking the sample with the machine down and not having operated in quite some time allowing for sediment to settle in the sump?  Are you taking it from a running machine up or down stream of the filter (if any), oil pump, sump?

Aerzen Oil Change

Then there is the lubricant.  Only when you know what you put into the machine in the first place (and you let the analysis crew know what it is) will the report be meaningful.  Finally, there is the issue with knowing what kinds of parts reside on the inside of the machine you got the report for.  Your analysis accuracy goes way down, if you do not know what kind of bearings, cage materials, how many bearings there are, what kind of gears may be contained in the machine, etc.  What other parts are in the machine?  Are there lip seals, labyrinth seals, or other parts that may come in contact with one another?  All of these components leave traces of themselves behind that can be invaluable in the condition monitoring process. 

I bet that most people who offered the free oil analysis to you did not tell you about all these potential issues.  There is a method to this madness.  First identify how critical the machine is for the operation of your plant.  For those machines do yourself and management a favor and get either the manufacturer or an oil analysis lab, e.g. Stavely involved.  Most reputable OEM’s offer a good condition monitoring program.  For machines that you feel like you can make use of the free oil analysis, make sure that the following criteria and information is included in the report:

  • Oil make, quality and quantity
  • Viscosity @40C is Cst and @100C in Cst
  • Viscosity index or VI change
  • Spectrochemical analysis in ppm
  • Wear element concentration (particle couont) as per ISO 4406
  • Water concentration in %
  • Additives listing
  • TAN index (for some applications the TBN index)
  • Oxidation index

Next best thing is to contact the equipment manufacturer and obtain their expert opinion where, when and how the sampling should take place.  While you are at it please ask them too what their best lubricant and test recommendation is.  Ask them for a list of bearings, gears and any other wear and tear items within the machine.  Please call our product support group, if you need any Aerzen blower, compressor, hybrid or vacuum booster information. 

In the Internet age nothing beats free advice – I love it myself and make use of it as much as possible.  Think twice before starting to rely on free oil analysis for critical machines though.  

Please drop me a note in case you have comments, suggestions or questions.    

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Ralf Weiser
Technical Manager

Tags: Aerzen, positive displacement, rotating equipment, screw compressor, pd blower, rotary lobe blower, turbo blowers, WWTP, pneumatic conveying

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