Viscosity is a measure of a hydraulic fluid's resistance to flow. It is a hydraulic fluid's most important characteristic and has a significant impact on the operation of the system.
When a hydraulic oil is too thin (low viscosity), it does not seal sufficiently. This leads to leakage and wear of parts. When a hydraulic oil is too thick (high viscosity), the fluid will be more difficult to pump through the system and may reduce operating efficiency.
All hydraulic fluids must be able to retain optimum viscosity during operation in cold or hot temperatures, in order to consistently and effectively transmit power.
Compressibility is a measure of the amount of volume reduction due to pressure. Although hydraulic oils are basically incompressible, slight volume reductions can occur under certain pressure ranges.
Compressibility increases with pressure and temperature and has significant effects on high-pressure fluid systems. It causes servo failure, efficiency loss, and cavitation; therefore, it is important for a hydraulic oil to have low compressibility.
Wear resistance is a hydraulic fluid's ability to reduce the wear rate in frictional boundary contacts. Antiwear hydraulic fluids contain antiwear components that can form a protective film on metal surfaces to prevent abrasion, scuffing, and contact fatigue. Antiwear additives enhance lubricant performance and extend equipment life.
Oxidation stability is a hydraulic oil's resistance to heat-induced degradation caused by a chemical reaction with oxygen. Hydraulic oils must contain additives that counteract the process of oxidation, improve the stability and extend the life of the fluid. Without these additives, the quality of the hydraulic oil will deteriorate quickly.
Thermal stability is the ability to resist breakdown at elevated...