ISO 6743-3:2003

Overview

ISO 6743-3:2003 - Lubricants, industrial oils and related products (class L) - Part 3: Family D (Compressors) defines a detailed, practical classification system for lubricants used in air compressors, gas compressors and refrigeration compressors. The standard provides a rationalized range of internationally available compressor lubricants (mineral, semi‑synthetic and fully synthetic) and coding conventions (e.g., ISO‑L‑DAB 68 or L‑DAB 68) to promote correct lubricant selection and reduce risks such as fire and explosion in stationary compressor applications.

Key topics and technical requirements

• Classification system: Family D is broken into category codes (e.g., DAA, DAB, DAG, DAH, DAJ, DVA–DVF, DGA–DGE, DRA–DRG) that identify lubricant types by application (reciprocating, rotary, oil‑flooded, vacuum, process gas, refrigeration).
• Viscosity grading: Lubricants are supplemented by ISO viscosity grades per ISO 3448 (e.g., “68” in ISO‑L‑DAB 68).
• Lubricant chemistries: Covers highly refined mineral oils, semi‑synthetic, and synthetic fluids (polyalkylene glycols, polyolesters, polyalphaolefins, polyvinylethers) and classifies miscible vs. immiscible behaviour with refrigerants.
• Duty definitions: Differentiates normal and severe duty (Annex A), with practical criteria - e.g., discharge temperatures (100 °C, 165 °C), differential pressures (2.5 MPa) and discharge pressures (7.0 MPa) - to guide lubricant selection and drain cycles.
• Process gas compatibility: Specific categories address gas chemistry and reactivity (inert, reducing, reactive gases) and warn against mixing incompatible formulations without supplier consultation.
• Vacuum and refrigeration guidance: Includes vacuum lubricant groupings (low to high vacuum) and refrigeration lubricant families matched to refrigerant types (NH3, HFC, CFC/HCFC, CO2, hydrocarbons).
• Safety focus: Primary aim is to reduce fire/explosion risk in stationary compressors; references safety rules in ISO 5388.

Applications and users

Who uses ISO 6743-3:2003:

• Compressor manufacturers and system designers specifying compatible lubricants
• Lubricant producers formatting product classifications and data sheets
• Maintenance engineers and plant operators responsible for oil selection, drain cycles and reliability
• Procurement and standards/specification writers ensuring proper lubricant coding and refrigerant compatibility
• Safety and reliability engineers managing risk in compressed‑gas systems

Practical uses:

• Selecting the correct lubricant code for reciprocating, rotary or oil‑flooded compressors
• Matching lubricants to refrigerants and process gases
• Defining drain intervals and duty classification (normal vs severe)

Related standards

• ISO 3448 - Viscosity classification of industrial lubricants
• ISO 5388 - Stationary air compressors - Safety rules
• ISO 8681 - Definition of lubricant classification classes
• ISO 6743-99 - General rules for class L (classification)

Keywords: ISO 6743-3:2003, compressor lubricants, lubricant classification, air compressors, refrigeration lubricants, process gas compressors, ISO 3448.