characteristics that will extend performance and the life of the equipment.
Hydraulic oil formulations characteristically are >98% base oil, compared to 75–85% for automotive lubricants. Because of the low additive treat rates, hydraulic oil performance is reliant on the properties of the base oil.
Hydraulic equipment design changes have created greater demands on lubricant performance including:
Smaller Fluid tanks Fresh oil purity
Fine Filters Easy filterable
Operate with small pressure difference for long period
Connectors & seals Material compatibility
Pumps Protect from wear and corrosion Reduce friction
Reduce deposit accumulation Avoid cavitation (air release)
Actuators Transfer energy (air release) Seal
Lubricate piston & guide, reduce wear Avoid stick-slip Protect against corrosion
Valves
Dissipate heat Reduce wear Minimize friction Avoid corrosion Avoid deposit formation Allow proper functioning (air release)
oil life. When oxidative and thermal stability are poor, high operating temperatures lead to undesirable compounds that react with other compounds in the oil to form both soluble and insoluble products. Soluble acidic products may increase the viscosity of the oil and corrode the system, while insoluble products (e.g. gum, sludge, varnish) may increase wear and will eventually plug lines and valves and reduce clearances, which could lead to system failure. Group II base oils have much better oxidative and thermal stability than Group I.
For modern hydraulic equipment, the properties inherent in Group II base oils provide better equipment protection and extend oil life over Group I formulations. These are the same properties that formulators have found beneficial in meeting evolving automotive specifications in Europe. They include:
• Wide viscosity range • Excellent oxidative and thermal stability • Water separability • Low temperature properties • Air release • Seal compatibility
Oxidative and thermal stability Oxidative and thermal stability are key to extending
Water separability
In many hydraulic fluid applications, the possibility of incursion of water into the system is very high. The ability of an oil to “shed” or separate from water is particularly important. In these situations, the oil must be able to separate water rapidly and cleanly. By draining separated water from the system, operators can extend the life of the lubricant and possibly prevent rust and corrosion from forming. Due to their very high levels of saturated hydrocarbons and very low levels of polar compounds, Group II base oils separate from water more rapidly than Group I base oils.
Continued on page 28 LUBE MAGAZINE NO.145 JUNE 2018 27
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