Overview
EN ISO 6743-4:2015 defines the detailed classification scheme for Family H (Hydraulic systems) fluids within class L (Lubricants, industrial oils and related products). Designed to be read alongside ISO 6743-99, this part standardizes category codes, composition groupings and typical applications for hydraulic fluids. It excludes automotive brake fluids and aircraft hydraulic fluids and incorporates categories for fire-resistant and environmentally acceptable fluids.
Key Topics
- Classification structure: Categories are designated by letter codes beginning with H, for example HH, HL, HM, HV and HG for mineral- and performance-based hydraulic oils.
- Composition-based categories: Synthetic and bio-based families appear as HETG (triglycerides), HEPG (polyglycols), HEES (synthetic esters), HEPR (polyalphaolefins and other synthetics), and HF* codes for water-containing or phosphate-ester fluids.
- Viscosity grades: The designation may be supplemented with viscosity grades per ISO 3448 (example: ISO-L-HV 32 or L-HV 32).
- Normative references: Important referenced documents include ISO 3448, ISO 11158, ISO 12922 and ISO 15380, which provide viscosity classification and detailed specifications for categories listed in this part.
Applications
This classification provides practical value for procurement, specification and compliance activities across industries that use hydraulic systems:
- Selection of the correct hydraulic fluid category for industrial and mobile equipment
- Identification of fire-resistant fluid groups and water-based systems where safety is critical
- Choosing environmentally acceptable fluids for ecologically sensitive sites or regulatory compliance
- Specifying fluids for combined systems (hydraulic plus plain bearing lubrication) and for systems requiring anti-stick/slideway properties
Benefits include consistent product identification, simplified supplier communication and clearer mapping between fluid composition and intended application.
Related Standards
- ISO 6743-99: General information for class L classifications
- ISO 3448: ISO viscosity classification (viscosity grades used with H codes)
- ISO 11158: Specifications for HH, HL, HM, HV, HG categories
- ISO 12922: Specifications for HFAE, HFAS, HFB, HFC, HFDR, HFDU (water-containing and water-based)
- ISO 15380: Specifications for HETG, HEPG, HEES, HEPR (synthetic and environmentally acceptable fluids)
Consulting EN ISO 6743-4:2015 alongside these referenced standards ensures robust, standards-aligned specification and selection of hydraulic fluids for industrial applications.
