Water separability, demulsifying capacity

OELCHECK test instrument: Measuring cylinder in warming bath
Sample quantity: 40 ml
Unit: The result is usually given as a numeric value. Furthermore, the appearance of the three layers and their boundary layers is indicated in a letter code.
Test result: determining the water separation of mineral oils and synthetic fluids
Analysis for: mineral oils, synthetic fluids
Brief description: 40 ml of distilled water and 40 ml of the oil are heated at 54 °C or 82 °C (depending on the viscosity of the lubricant) for the test. Once filled, the measuring cylinder is immersed in a warming bath with a constant temperature.

A large stirring blade which is powered by an engine with 1,500 rotations in the 1:1 mixture of oil and water is used to intensively mix the two fluids for five minutes. An unstable emulsion with an equally murky and opaque appearance is produced. After mixing, the stirring blade is removed from the milky emulsion. Decomposition occurs in the resting sample as a result of gravity. Water settles on the base. Oil floats in the top part. At five-minute intervals, the volume of the water, the oil and the emulsion stage in between are measured.

The appearance of the three individual stages is described. The volumes continue to be measured until the volumes of the emulsion layer between the oil and water is equal to or less than 3 ml. The test is stopped after an hour if the emulsion content is still over 3 ml.
Statement: Usually water quickly separates from oil due to its strong polarization. However, separation may be negatively affected by additives and impurities.

In most uses, a quick separation of the oil from the water is desirable. The oils should have a demulsifying effect. However, the opposite effect can also be useful. Some lubricating oils, such as hydraulic oils from the category HLP-D, should not have a demulsifying effect, but a dispersing and detergent effect. They must ensure any fluid penetrated is microdispersed and suspended.
Underlying test standard: DIN ISO 6614, ASTM D1401