Lubricants, industrial oils and related products (class L) - Classification - Part 4: Family H (Hydraulic systems) (ISO 6743-4:1999); German version EN ISO 6743-4:2001
2Expert Interpretation
This article provides an in-depth analysis of the EN ISO 6743-4:2002 international classification standard for hydraulic fluids, covering a complete classification system for mineral oils, synthetic oils, and environmentally friendly hydraulic fluids. It offers a guide to selecting lubricants for hydraulic systems and provides technical specifications applicable to the maintenance of industrial hydraulic equipment and oil procurement decisions.
Technical Interpretation of EN ISO 6743-4 Hydraulic Oil Classification Standard
EN ISO 6743-4:2002, as an international classification standard for lubricants in hydraulic systems, provides a systematic framework for the scientific selection and application of hydraulic oils. This standard was developed by ISO/TC 28, the Technical Committee on Mineral Oil Products and Lubricants, adopted by the European Committee for Standardization (CEN) in October 2001, and published in German by the German Association for Standardization (DIN) in April 2002.
Background and Technological Evolution of the Standard
As a core component of industrial transmission, the performance of lubricants in hydraulic systems directly affects equipment reliability, energy efficiency, and lifespan. The development of the ISO 6743-4 standard stemmed from the urgent need for standardized specifications of hydraulic oil performance. During the standard's evolution, particular attention was paid to the development of environmentally friendly hydraulic fluids, and for the first time, environmentally friendly categories such as HETG, HEPG, HEES, and HEPR were systematically introduced, reflecting the industry's emphasis on sustainable development.
This standard aligns with the general classification principles of ISO 6743-0, establishing a complete classification system for hydraulic fluids. Notably, the standard explicitly excludes automotive brake fluid and aviation hydraulic fluid, focusing solely on the application needs of industrial hydraulic systems. The standard employs a four-level classification coding system. The first letter, **H**, represents the hydraulic system family, with subsequent letter combinations identifying specific product characteristics. A complete classification designation can be combined with ISO 3448 viscosity grades to form standard codes such as **ISO-L-HM 46** or the abbreviation **L-HM 46**.>Environmentally Friendly Hydraulic Fluid Technical Specification
The standard systematically defines four types of environmentally friendly hydraulic fluids for the first time, marking an important milestone in the green transformation of hydraulic technology:
HETG (Triglycerides): Biodegradable hydraulic fluid based on vegetable oils, with good lubrication performance and environmental protection characteristics, suitable for agricultural machinery and forestry equipment.
HEPG (Polyethylene Glycol): Synthetic base oil with excellent hydrolytic stability and low-temperature performance, exhibiting stability in harsh environments.
HEES (Synthetic Esters): High-performance synthetic ester hydraulic fluids, combining excellent thermal stability and biodegradability, suitable for demanding industrial applications. HEPR (Polyalpha Olefins and Related Hydrocarbons): A synthetic hydraulic fluid based on PAO, possessing excellent viscosity characteristics and oxidation stability, primarily used in mobile hydraulic equipment. The standard clearly stipulates that the base fluid content of environmentally friendly hydraulic fluids must not be less than 70% (mass fraction) to ensure the product's environmental attributes. Fire-Resistant Hydraulic Fluid Classification System For hydraulic applications in high-temperature and flammable environments, the standard defines a complete classification of fire-resistant hydraulic fluids: [table]>Classification Code Composition Characteristics Water Content Flame Resistance Rating Application Restrictions
Special Function Hydraulic Fluid Technical Specifications
The standard also covers hydraulic fluid categories with special functions:
HG Category: Designed specifically for hydraulic guideway systems, with anti-stick-slip properties, suitable for combined hydraulic and guideway lubrication systems that require reduced vibration or intermittent slippage.
These fluids are designed for versatility, but the standard explicitly states that they are **not suitable for all hydraulic applications**. HA and HN categories: used in hydraulic power transmission systems for automatic transmissions and clutch torque converters, respectively. The standard states that the specific classifications for these applications have not yet been reviewed in detail and may be supplemented in the future. Standard Implementation Recommendations and Selection Guidelines Based on EN ISO 6743-4, hydraulic fluid selection should follow a systematic approach: Basic Selection Principles: First, determine the basic category based on the equipment manufacturer's recommendations, then refine the selection based on specific operating conditions. The viscosity grade must match the operating temperature range according to ISO 3448. Environmental Application Selection: In environmentally sensitive areas, prioritize HETG, HEPG, HEES, or HEPR categories, while verifying that the product's biodegradability and ecotoxicity meet local regulatory requirements. High-Temperature Environment Selection: In environments with fire risks, fire-resistant hydraulic fluids of the HFA, HFB, HFC, HFDR, or HFDU class must be selected, and the appropriate fire resistance level should be determined based on the specific risk level. Performance Verification Requirements: After selection, product performance should be verified through laboratory testing and field trials, paying particular attention to key indicators such as viscosity stability, oxidation resistance, wear resistance, and filtration performance. Technology Development Trends and Standard Outlook: As hydraulic technology develops towards higher pressure, intelligence, and environmental friendliness, hydraulic oil standards also face new challenges and opportunities: High-Performance Trend: The continuously increasing working pressure of modern hydraulic systems places higher demands on the extreme pressure anti-wear performance and thermal stability of hydraulic oils. Environmental Regulations Driven: Increasingly stringent global environmental regulations are driving the rapid development of biodegradable hydraulic fluid technology; future standards may further refine environmental performance indicators. Intelligent Monitoring: The widespread adoption of IoT-based hydraulic oil condition monitoring technology has prompted standards to consider the correlation between online monitoring parameters and oil lifespan. EN ISO 6743-4, as the foundational standard for hydraulic oil classification, provides the industry with a unified technical language and selection criteria; its systematic classification system will continue to guide the development of hydraulic technology.