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In This Issue:

• Readers Challenge: Hydraulic Fluid Darkening

• Book Bits: Inspection of Working Surfaces

• Today's Tip: Quick Filter Check

• Q & A: Motor Rebuilder Grease Compatibility

Readers Challenge

Hydraulic Fluid Darkening

After pulling a fluid sample from a hydraulic system you notice the hydraulic fluid has become darker. Concerned, you rush the sample to a lab for analysis.

The results of the fluid analysis appear normal: acid number, viscosity and FTIR-Ox (oxidation) have all remained stable.

A quick inspection of the hydraulic system reveals that the hydraulic valves have turned goldish in color. What would you do?

Submit your answer at http://www.noria.com/challenge.asp before Monday, January 28, 2003. Lube-Tips editors will choose the best answer and the $50 recipient will be announced next week

Book Bits

Inspection of Working Surfaces

From "The Lubrication Field Test and Inspection Guide".

Working surfaces include gears, bearings, cams, valve components, and pistons. These surfaces experience rolling and/ or sliding tribological contracts during operation. During routine PM's and repairs they should be examined for corrosion, abrasion, varnish, burnishing, denting, cavitation, galling, pitting, fretting, tempering, fatigue, etc. Many of these problems are related. For instance, a highly polished surface may be caused by an overly aggressive EP additive or high concentrations of abrasive fines in the oil.

More information about "The Lubrication Field Test and Inspection Guide".

Today's Tip

• When checking differential filter clogging indicators, also ensure that the pilot holes in the filter body (the ones that feed the indicator with oil pressure) are clear of debris. This helps ensure you are receiving the correct signal. (Submitted by Tim Monk, regional filtration specialist, Wyko Fluid Power Services. Thanks Tim!)
  

Each tip published will earn the sender $25. Submit your tip.

Q & A

Motor Rebuilder Grease Compatibility

"We recently switched electric motor rebuild shops. Since switching, a number of bearings have failed, typically just a few months after putting the motor back into service. For the most part, these failures have been attributable to inadequate lubrication. On closer inspection, the grease appeared to have thinned-out to almost a liquid consistency. We suspected that the rebuild shop was using a grease inferior to our electric motor grease, but they assure us they're using a premium-quality synthetic grease. What is your opinion?"

Without more details, it's hard to attribute an exact root cause. However with greases, one of the most commonly encountered problems is incompatibility between different types of grease made from different thickeners.

For electric motors, the most commonly used greases are made either from a lithium complex soap thickener or polyurea material. While both polyurea and Li complex-based greases can be used in this application, the two are usually considered to be incompatible with each other and should not be mixed unless proper compatibility testing has been performed.

To avoid these types of problems, it is advisable to request that the rebuild shop use the same grease that you plan to use to regrease the bearings, or at the very least, indicate the exact type and brand of grease being used, so that you can determine if there are any serious compatibility issues between the two greases.

It is often advisable to provide a tube of grease to the rebuild shop whenever a motor is sent to rebuild to avoid these issues.

Mark Barnes, senior technical consultant, Noria Corporation

Submit your question here.