The ability of an oil to reject water, measured in ASTM D1401 by stirring 40 mL of oil with 40 mL of water at 54 C and timing how long the oil, water and emulsion layers take to settle. Results read as oil-water-emulsion volumes plus minutes, such as 40-40-0 (10). Turbine, paper machine and circulating oils need strong demulsibility so free water drops out in the reservoir; detergent engine oils are built to do the opposite.
Demulsibility went to 38-37-5 at 30 minutes, the turbine oil is starting to hang onto water.
One top-up with detergent engine oil can wreck a turbine oil's water shedding, so keep engine oil out of turbine lube rooms entirely.
Also heard as
- water separability
- D1401
Related terms
Milkshake
Oil turned milky or creamy by emulsified water, seen in gearboxes, hydraulics and engines.
Turbine oil
Highly refined, lightly additized circulating oil built to last for years in steam, gas and hydro turbines.
R&O
Rust and oxidation inhibited: a lightly additized oil with no antiwear or EP chemistry.
Karl Fischer titration
Chemical titration that measures water in oil down to about 10 parts per million.