ASTM D6158 Standard Specification for Mineral Hydraulic Oils
3. Classification
3.1 Type HH Hydraulic Oils - Non-inhibited refined mineral oils for hydraulic systems that do not have specific requirements of oxidation stability, rust protection, or anti-wear properties. Type HH oils are usually intended for total loss systems or very light-duty equipment.
3.2 Type HL Hydraulic Oils - Refined mineral oils with improved rust protection and oxidation stability for hydraulic systems where relatively high temperatures and long periods of operation time are expected, and where there is the possibility of water or humidity that could rust metal parts of the machinery. These oils are intended for use in systems where no metal to metal contact is expected between the moving parts. Usually systems working at low pressures specify HL oils. Some high-pressure piston pumps can operate satisfactorily on these oils.
3.3 Type HM Hydraulic Oils - Oils of HL type with improved anti-wear properties, for general hydraulic systems, especially for those working at high pressures and where the possibility of metal to metal contact between the moving parts exists. Type HM oils are usually specified for hydraulic systems with vane pumps, or when the system is intended to work at maximum pump capacity for long periods of time.
4. Classification Requirements
4.1 Type HH - The requirements for this type of oil are presented in Table 1 and include Viscosity Grades ISO VG from 10 to 150, according to Classification D2422.
4.2 Type HL - The requirements for this type of oil are presented in Table 2 and include Viscosity Grades ISO VG from 10 to 150, according to Classification D2422.
4.3 Type HM - The requirements for this type of oil are presented in Table 3 and include Viscosity Grades ISO VG from 10 to 150, according to Classification D2422.
