Overview - ISO 4975:2022 compressed air quality for railway braking systems
ISO 4975:2022 specifies the quality classes of compressed air used by pneumatic apparatus and systems on rail vehicles, with a focus on braking systems. It defines how to determine and designate compressed air purity produced by air generation and treatment units (AGTUs) and applied across all pneumatic equipment on rolling stock. The standard is railway‑specific and derives its contaminant measurement approach from ISO 8573 series.
Key topics and technical requirements
- Scope and applicability: Applies to compressed air produced by AGTUs and used in all pneumatic systems of rail vehicles, including brake and auxiliary devices.
- System breakdown: Describes functional units of a rail vehicle compressed air system (intake, compressor, treatment, storage, distribution, brake and auxiliary usage).
- Contaminants covered: Particle, liquid water (condensate), water vapour (humidity/dewpoint) and oil (liquid and vapour) - see Annex A for details.
- Air quality classes and designation: Defines classes and characteristics (see Tables 2–4 in the standard) and how to designate compressed air purity for a rail application.
- Test and measurement requirements:
- Sampling for classification is taken at the AGTU outlet.
- Reference intake/test temperatures: compressor intake 20 °C ± 5 °C (specific humidity tests may use other intake temperatures).
- AGTU outlet pressure for tests: 9 bar ± 0.5 bar (can be adapted to vehicle system pressure).
- Measurement methods reference ISO 8573 parts: ISO 8573-1, -2, -3, -4, -5 as applicable.
- Life‑cycle assurance: Air quality shall be demonstrated over the AGTU life cycle or monitored in service; demonstrations must consider operational duty cycle, environmental conditions (vibration, ambient temperature range) and maintenance plans.
- Reference conditions: Normalization of test results uses 20 °C, 1 bar absolute pressure, and zero relative water vapour pressure.
Practical applications and who uses ISO 4975:2022
- Rolling stock designers and systems engineers specifying pneumatic and braking subsystems.
- AGTU and air treatment manufacturers designing compressors, dryers and filters for rail applications.
- Maintenance planners, depot engineers and safety assessors implementing monitoring and life‑cycle validation.
- Procurement teams and compliance officers ensuring contractual and regulatory conformity of compressed air quality for rail vehicles.
Related standards
- ISO 8573 (all parts) - Compressed air contaminant measurement and class definitions (primary reference for test methods).
- ISO 7183 - referenced for pressure measuring tube details and related test setup elements.
Keywords: ISO 4975:2022, compressed air quality, railway braking system, AGTU, pneumatic systems, air quality classes, ISO 8573.
Open preview (PDF)Railway applications — Braking system — Quality of compressed air for pneumatic apparatus and systems
