ISO 23309:2020

Overview

ISO 23309:2020 - "Hydraulic fluid power systems - Assembled systems - Methods of cleaning lines by flushing" - defines procedures for removing particulate contamination from hydraulic lines and assembled systems by flushing. The standard focuses on achieving a specified required cleanliness level (RCL) after manufacture, assembly, maintenance or repair so that particles do not circulate and damage hydraulic components. It clarifies flushing principles, planning, monitoring, and verification of cleanliness for hydraulic fluid power systems.

Key topics and technical requirements

• Scope and purpose: Specifies flushing to remove residual and introduced particulate contamination from lines and components (not chemical pickling or major component cleaning).
• Flushing principle: Use of high fluid velocity, elevated temperature and turbulence (greater than normal service) to dislodge particles and transport them to filters.
• Required Cleanliness Level (RCL): Target cleanliness to be achieved; recommended to flush to a level at least one ISO code cleaner than the RCL.
• Hydraulic system design for flushing: Avoid dead-ends, provide series or monitored parallel circuits, and ensure connectors have uniform internal diameters to prevent particle trapping.
• Filters and separation: Flushing filters must be equal to or finer than built-in filters; refill/reinstate original filters after flushing.
• Monitoring and verification: Sampling procedures (ISO 4021), monitoring options, minimum flushing time before sampling, and verification of final cleanliness.
• Flushing parameters: Importance of fluid velocity, Reynolds number (Re), temperature and viscosity - ISO 23309 highlights that relying on Re alone can be misleading and that other factors affect flushing effectiveness.
• Procedures and stages: Preparatory actions, low-pressure and higher-pressure flushing stages, and final cleanliness verification.
• Storage, preparation and installation: Guidance on preparation during fabrication, surface treatments, and storage to reduce contamination before flushing.

Applications and users

ISO 23309:2020 is used by:

• Hydraulic system designers and OEMs planning systems for effective cleaning
• Maintenance and service engineers responsible for repair, refurbishment and system clean-up
• Contamination control specialists and quality managers setting acceptance criteria and verifying RCLs
• Suppliers of hydraulic components and filters documenting component cleanliness and selecting appropriate filtration for flushing

Typical applications include new system commissioning, post-repair clean-up, maintenance flushing, and verification of cleanliness before system handover.

Related standards

Normative references and complementary documents include:

• ISO 4021, ISO 4406, ISO 4407, ISO 5598
• ISO/TR 10949, ISO 12669, ISO 16431
• ISO 16889, ISO 18413, ISO 21018-1

Keywords: ISO 23309, hydraulic fluid power, flushing, cleanliness level, RCL, contamination control, Reynolds number, hydraulic lines.