The ability of an R&O oil to separate from water is an important characteristic in most turbine, compressor, pump, and blower applications. This is called the Demulsibility of the oil. You want the water to come out of suspension and fall to the bottom of the reservoir or sump where it can be drained, and not carried with the lubricant to the bearings where it will cause corrosion and other problems.
AW and EP additives, contaminants, and the base stock are all factors that determine the Demulsibility of the oil.
Demulsibility should not be part of your routine analysis program. It is a quality check of the lubricant and should be performed for evaluation of new oils or when a demulsibility problem is apparent in the reservoir or sump.
Test summary: A mixture of 40 mL water and 40 mL oil in a graduated cylinder are heated to 130° F and thoroughly mixed for 5 minutes. As the water separates from the resulting emulsion, three layers are formed: oil, free water, and emulsion. The time it takes for the emulsion layer to reach 3 mL or less is recorded. The results are reported as “40/38/2” or 40 mL oil, 38 mL water, and 2 mL emulsion. If the emulsion layer reaches 3 mL in 30 minutes or less it has ‘passed’. Most quality R&O oils will pass within 10 minutes.