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Q & A

"How do I check to see if my aged hydraulic and/or lubricating oils can still shed water effectively?"

This is an issue of demulsibility, which is the measure of an oil's ability to release water. Of course, if you have time, your lab can run a specific test (ASTM D1401) that can be performed to measure the remaining demulsibility potential.

For a quick Pass/Fail test, measure an equal amount (1 pint) new lubricant and water, and fill a blender. Heat to 100 degrees F (38 degrees Celsius), or whatever temperature closely resembles the operating temperature of the sump. Thoroughly mix the oil with the water. Measure the amount of time it takes to separate. Also measure how much of the mixture does not separate (the emulsion is called the 'cuff'). Now repeat the test with the aged lubricant.

If it takes more than 20 percent longer to separate then consider having a lab run the test according to the lab procedure. If the results indicate that the demulsibility capacity is diminished then consider how to best address the problem, particularly if the sump is prone to moisture contamination.

Today's Tip

• When converting a gearbox from a PolyAlkylene Glycol (PAG) synthetic that is water soluble, it is advisable to purchase the manufacturers' flushing medium and flushing the unit prior to putting the final charge in the unit and restoring it to service.

  Failure to do so may mean residual mixing of incompatible base fluids. This is likely to cause headaches and shortened lifecycle of the new fluid and possibly the gear drive. Consult the supplier of the PAG product for a good guideline and advice on the flushing fluid.

• The latest issue of Machinery Lubrication magazine is online at: www.machinerylubrication.com
  
  

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Book Bits

Evaporation. Lubricating oils are not generally volatile. Normally it is only with low-viscosity oils at higher temperatures or in vacuum applications that evaporation is likely to be significant. However, it has been shown that there is a significant loss of the lower fractions of engine oils in the region of the piston ring/cylinder interface. The effect of evaporation is generally to produce an increase in viscosity.

For more information about the "Lubrication and Lubricant Selection" go to:

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