Overview
ISO 21018-4:2019 - "Hydraulic fluid power - Monitoring the level of particulate contamination in the fluid - Part 4: Use of the light extinction technique" defines a standardized method for measuring particulate contamination in hydraulic liquids using the light extinction (aka light blockage or light obscuration) technique. The standard covers both online and offline measurements (containers and sample bottles), procedures for instrument calibration and verification, and guidance for safe, repeatable sampling. It applies to single‑phase liquid systems and is intended to help control contamination that impacts hydraulic performance and reliability.
Key topics
- Measurement technique: Use of the light extinction/light obscuration principle to quantify particle concentrations and size distribution.
- Modes of operation: Sampling from a pressurized line, system reservoir, bulk container, or sample bottle - with recommended procedures for each.
- Instrument commissioning: Calibration and verification procedures (Clause 7) and requirements for equipment used in calibration/validation.
- Operating procedures: Steps to avoid extraneous contamination, flushing requirements, verification by replicate analyses (acceptance criteria such as ≤1 cleanliness code difference or ≤20% particle-count difference at the smallest monitored size).
- Health & safety: Operate instruments per manufacturer instructions and assess hazards before use.
- Data reporting: Test report and identification requirements to ensure traceability and consistency.
Applications
ISO 21018-4 is practical for:
- Monitoring general cleanliness in hydraulic systems to prevent wear and maintain performance.
- Tracking the progress of flushing operations during system assembly or maintenance.
- Verifying cleanliness of support equipment and test rigs used in hydraulic testing and production.
- Implementing online condition monitoring with Particle Contamination Monitors (PCM) for trend analysis and predictive maintenance.
Keywords: ISO 21018-4:2019, hydraulic fluid power, light extinction, light obscuration, particulate contamination monitoring, PCM, online monitoring, calibration, verification, flushing operations.
Who should use this standard
- Hydraulic engineers and system designers
- Maintenance and reliability teams
- Test-rig operators and lab personnel
- OEMs and suppliers of particle counters and PCMs
- Contamination control specialists and quality managers
Related standards
Normative references cited in ISO 21018-4 include:
Using ISO 21018-4 helps standardize light‑extinction monitoring practices, improve measurement consistency, and support effective contamination control in hydraulic systems.