ISO 23369:2022

Overview

ISO 23369:2022 - Hydraulic fluid power: Multi-pass method of evaluating filtration performance of a filter element under cyclic flow conditions specifies a reproducible laboratory procedure to evaluate hydraulic filter elements when subjected to cyclic (varying) flow. The standard defines a multi-pass filtration test with continuous contaminant injection to determine contaminant capacity, particulate removal performance, and differential pressure behaviour of filter elements used in hydraulic fluid power systems. It complements steady‑state multi-pass tests (e.g., ISO 16889) by addressing real-world cyclic flow effects.

Key topics and requirements

• Test method: Multi-pass filtration under cyclic flow with continuous contaminant injection and periodic fluid sampling to measure particulate removal.
• Target elements: Applicable to filter elements with an average filtration ratio ≥ 75 for particle sizes ≤ 25 µm(c).
• Contaminant and fluid: Uses ISO 12103-1 A3 (Arizona) medium test dust and a specified test fluid (see Annex A of the standard).
• Gravimetric baseline levels: Three base upstream gravimetric test conditions - 3 mg/L, 10 mg/L, and 15 mg/L.
• System limits: Final test system reservoir gravimetric level must be < 200 mg/L; injection systems and flow ranges must be validated for each test facility.
• Cyclic flow parameters: Recommended cycle rate is 0.1 Hz (industry default); testing at other frequencies is allowed if agreed, but only 0.1 Hz results may be claimed as “in accordance with ISO 23369.”
• Measured outputs: Contaminant mass injected, retained capacity, filtration ratios (particle‑size resolved), and differential pressure (clean, terminal, and assembly pressures).
• Repeatability controls: Procedures to avoid electrostatic effects on particle counts, accuracy/validation of injection and test circuits, and sampling methods are included.

Applications and users

ISO 23369:2022 is practical for:

• Filter manufacturers - product development, validation and performance claims for applications where flow is cyclic.
• Test laboratories - standardized test protocols for comparative evaluation and quality control.
• OEMs and system designers - selecting filters matched to hydraulic system duty cycles and contamination tolerance.
• Maintenance and reliability engineers - understanding filter lifetime under realistic cyclic conditions and planning element replacement strategies.
• Procurement/specifiers - specifying test-proven filtration performance for contracts and tenders.

Use cases include R&D comparisons, acceptance testing, supplier verification, and risk assessment for hydraulic systems in mobile equipment, industrial machinery, and transmission hydraulics.

Related standards

• ISO 16889 - steady-state multi-pass filtration test (complementary)
• ISO 12103‑1 - Arizona test dust (A3)
• ISO 11171 - particle counter calibration
• ISO 4405 - gravimetric contamination determination
• ISO 3968, ISO 4021, ISO 2942 - supporting methods for differential pressure, sampling, and integrity checks

Keywords: ISO 23369:2022, hydraulic fluid power, cyclic flow, filtration performance, multi-pass method, filter element testing, ISO 12103-1 A3, gravimetric level, filtration ratio.