A sample of oil along with water and a copper catalyst is placed in a pressure vessel and pressurized with pure oxygen. Antioxidants present in the oil will act to resist oxidation, but once they have been consumed the oil will begin to react with the oxygen and the pressure in the vessel will drop. The time it takes to reach the specified drop in pressure is recorded and compared to new oil specifications. Results are considered to be in alarm when they drop below 25% of new oil value.
Oxidation is a critical mode of lubricant degradation. As oil oxidizes it forms acids and insoluble oxidation products, which can lead to formation of sludge or varnish. These degradation products can coat bearing and oil cooler surfaces, preventing adequate cooling of the bearings. Areas with tight tolerances such as hydraulic control valves can also become coated causing operational issues.
Mainly used for lubricants with antioxidant additive packages to help monitor fluid health and provide an estimate of remaining life.