ISO Classification of Hydraulic Oils
Here is information on the classification of hydraulic fluids according to ISO 6743-4 and ISO 11158.
ISO 6743-4 is the International Organization for Standardization’s H-family classification (hydraulic oils) which is included in ISO 6743 (Lubricants, industrial oils and class L related products).
| Designation | Description |
| General purpose hydraulic oils for hydrostatic systems | |
| HH | Mineral oils, without additives |
| HL | HL oils with anticorrosive and antioxidant properties |
| HM | HL oils with improved antiwear properties, also for heavily loaded components |
| HR | HM oils with improved viscosity-temperature properties |
| HV | HM oils with improved viscosity-temperature properties, mainly for construction and marine equipment |
| HG | HM oils with improved anti-seize and anti-vibration properties for slideways in hydraulic systems |
| HS | Synthetic fluids with special properties without special flame retardant properties |
| Flameproof hydraulic oils | |
| HFAE | Oil-in-water emulsions |
| HFAS | Chemical compounds in water |
| HFB | Emulsions, water-in-oil |
| HFC | Water/glycol |
| HFDR | Phosphorus esters anhydrous |
| HFDS | Chlorinated hydrocarbons anhydrous |
| HFDT | HFDR/HFDS blends |
| HFDU | Anhydrous fluids more stable than HFDR, HFDS or HFDT |
| Biodegradable hydraulic oils | |
| HETG | Triglycerides (vegetable oils) |
| HEES | Synthetic esters |
| HEPG | Polyglycols |
| Hydraulic oils for hydrodynamic systems | |
| HА | Oils for automatic transmissions |
| HN | Hydraulic fluids for switches and transducers |
ISO 11158 establishes minimum requirements for mineral hydraulic fluids, which are intended in particular for hydrostatic hydraulic systems. The classification of fluids used in hydraulic systems is defined in ISO 6743-4. Of the categories covered by ISO 6743-4, ISO 11158 covers only five types of mineral oil based fluids. These categories are HH, HL, HM, HV and HG.
| Designation | Description |
| HH | Mineral oils without additives |
| HL | HL oils with anticorrosive and antioxidant properties |
| HM | HL oils with improved antiwear properties |
| HV | HM oils with improved viscosity-temperature properties |
| HG | HM oils with improved anti-seize and anti-vibration properties |