Oil samples can be taken and analyzed in a laboratory. The analysis can measure a large range of parameters and factors that influence oil quality. Typically these include tests that quantify:

• The number and size of particles.
• The types and quantity of contaminants present.
• The condition of the additives in the oil.
• Changes to oil chemistry caused by the working environment.
• The amount of water present.
• The oil’s viscosity (slipperiness).

It is not necessary to do all tests on all oils in all situations. The selection of the type of analysis depends on the oil and where it is used. The oil used in combustion engines, gearboxes, hydraulic systems and gas turbines is not the same and the conditions under which it operates are different in each situation. For example soot would be present in internal combustion engines but it would not be present in gearboxes. There is no value in paying money to measure the amount of soot in a gearbox. But the amount of soot in a diesel engine’s oil is of critical importance.

Testing laboratories are required to follow internationally recognized procedures when measuring oil contamination. Equipment used to measure contaminants is also to be calibrated to recognized international standards. However, just as there are clean and dirty maintenance shops, there are clean and dirty laboratories. Results from laboratories without good calibration procedures and sample hygiene practices or from people that don’t fully understand the equipment and procedures should not be trusted.

Not all solid particle counting laboratory equipment can count particles down to very fine sizes. Results from these laboratories would give false figures showing less contamination at low micron sizes than was actually present. Some laboratories use equipment and methods that do not count particles larger than 100 micron (0.004”). Results from these laboratories would show incorrect large particle counts. In future these large particles would be smashed-up and broken down and the resulting smaller particles would quickly contaminate the oil.

If the sample itself is too heavily contaminated then optical counting methods cannot be used because the light emitted by the analyzer will not pass through the sample in the same way the equipment was calibrated to receive. Optical counters can mistakenly count water droplets as solid particles. At times it can be necessary to confirm laboratory results by alternate means to prove the results are reliable.

SAMPLING CLEANLINESS

The method and cleanliness by which an oil sample is taken has a critical effect on the accuracy of the laboratory results. If the sample is falsely contaminated by mistakenly taking it from the wrong point or in the wrong way, or if the sample taking equipment or method introduce contaminants, then false contamination levels will be reported.

A good sample is one that is cleanly taken from the circulating oil flow. The proper sample taking method and procedure should be agreed with the laboratory and if necessary the laboratory should be asked to provide training for the sample takers.

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