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Background & Properties
Industry Specifications
Hydraulic Fluids
July 2017
Performance standards for anti-wear hydraulic fluids are set primarily by original equipment manufacturers. Unlike
engine oils, anti-wear hydraulic oils do not have an industry licensing procedure. Therefore, anti-wear hydraulic fluid
users must seek out information on test results from the oil manufacturer itself. Without a standard industry licensing
program, it is worthwhile for users to research hydraulic fluid choices carefully.
Castrol's Liquid Engineers have developed a range of hydraulic flueds to meet performance standards required by
Original Equipment Manufacturers (OEMs). These include products that meet recent changes in hydraulic fluid
formulation, driven by industry trends and OEMs:
• Improved oxidation stability to accommodate higher operating temperatures.
• Improved air release, foam control and water separation to handle smaller reservoirs and reduced cycle times.
• Improved dry/wet filterability due to reduced filter pore size and tolerance to water contamination.
• Better hydrolytic stability to handle water contamination.
• Extended pump life to meet Denison T6HZOC pump performance.
• Increased drain intervals requiring the lubricants to retain original performance longer.
Importance of Oxidation Tests
When selecting a hydraulic fluid, resistance to oxidation is a key component of performance. The ability to protect
against oxidation in the oil prevents premature oil thickening, sludging and other critical lubrication failures. Good
oxidation protection comes from the combination of base oil selection and quality of the additives.
Types of oxidation tests include:
Turbine Oil Oxidation Test (ASTM D 943)
This test measures the oil's ability to prevent oxidation and the formation of destructive acids. To pass HF-O, the oil's
acidity level must not exceed 2.0 mgKOH/g after 1500 hours.
Test Criteria
Time to 2.0 TAN, hours 1,500 min
Rotary Pressure Vessel Oxidation (ASTM D 2272)
This test utilities an oxygen pressurized vessel to evaluate oxidation stability of lubricants in the presence of water and
copper @150°C.
Test Criteria
Time to 25-psi loss in minutes HF-O, HF-2 1500
C 2
