TEST METHOD

ISO 16889 Multipass vs. Single-Pass Filter Testing

Two protocols for measuring filter element performance — how test method affects the efficiency values reported

ENGINEERING OBJECTIVE

Understand what each test method measures and why ISO 16889 multipass data cannot be directly compared with historical single-pass data, ensuring correct interpretation of filter element performance specifications.

COMPARISON SCOPE

Covers ISO 16889:2022 (multipass) and single-pass test methods (ISO 4572, withdrawn 2000). Does not cover air filter testing (ISO 5011/SAE J726) or cabin filter testing (ISO 29463).

GOVERNING STANDARDS

ISO 16889:2022ISO 11171:2010ISO 4406:2021

OPTION DEFINITIONS

AISO 16889 Multipass Test

The current international standard test method for hydraulic fluid filter element performance. Fluid circulates continuously through the test circuit, with upstream particle counts measured before the filter and downstream counts measured after. Contamination is continuously injected upstream. The Beta ratio is computed from cumulative upstream vs. downstream particle counts measured by an ISO 11171-calibrated optical particle counter. The test continues until the filter reaches terminal differential pressure. Both filtration efficiency and dirt holding capacity are outputs. The (c) suffix on Beta values (β_x(c)) indicates calibrated ISO 11171 particle counter data.

ADVANTAGES

+Real-world simulation: continuously circulating contaminated fluid reflects actual operating conditions better than single-pass

+Both efficiency AND dirt holding capacity measured in one test — complete performance characterisation

+Particle counter calibration (ISO 11171:2010) ensures inter-laboratory reproducibility — different test houses produce comparable results

+Current mandatory standard for all ISO 16889 compliance claims — required for international procurement

+Terminal ΔP data enables service interval and bypass valve setting engineering calculations

+Produces β_x(c) values that map directly to ISO 4406 cleanliness code system design calculations

LIMITATIONS

−More complex test rig — particle injection, continuous circulation, ISO 11171 APC — requires higher capital investment than single-pass

−Test duration is longer than single-pass — element must be loaded to terminal ΔP

−Beta values from multipass and single-pass methods are numerically different for the same element — legacy comparison is impossible without knowing which method was used

TYPICAL APPLICATIONS

·All current hydraulic and lube oil filter element performance testing

·OEM procurement specifications for new equipment

·Research and development of new filter media formulations

·ISO 16889 compliance validation for certification claims

·Forensic performance verification of elements from field failures

BSingle-Pass Test Method (ISO 4572, withdrawn)

Contaminated test fluid is passed once through the filter element; upstream and downstream particle counts are measured. Efficiency is calculated from this single-pass count ratio. ISO 4572 used ACFTD (Air Cleaner Fine Test Dust) and early-generation optical particle counters without the ISO 11171 calibration. ISO 4572 was withdrawn in 2000 and replaced by ISO 16889. Single-pass efficiency values reported before 2000 are numerically different from ISO 16889 multipass values for the same filter media — direct comparison is not valid. Note: some non-filtration single-pass methods exist for specific applications (e.g. membrane testing) but these are not referenced by ISO 16889.

ADVANTAGES

+Simpler test rig — single pass does not require continuous contamination injection or a full circulation loop

+Faster test execution — no need to load element to terminal ΔP

+Useful for rapid development screening where relative (not absolute) efficiency is the objective

+Large historical dataset exists from pre-2000 products — useful for legacy system maintenance reference

LIMITATIONS

−Withdrawn ISO standard — not valid for current procurement specifications or compliance claims

−ACFTD test dust is discontinued — ISO 12103-1 A4 (the ACFTD successor) produces different particle counts at the same nominal size

−No ISO 11171 calibration requirement — inter-laboratory variability was poor; results from different labs for the same element could vary significantly

−Single pass does not capture how efficiency changes as the element loads — multipass shows efficiency variation with loading state

−Beta values from ISO 4572 single-pass are NOT interchangeable with β_x(c) from ISO 16889 multipass

−Dirt holding capacity is not a primary output of single-pass testing

TYPICAL APPLICATIONS

·Historical reference for legacy product data sheets (pre-2000)

·Internal development screening where relative efficiency comparison is more important than absolute calibrated values

·Interpreting legacy OEM filter element specifications that pre-date ISO 16889 adoption

ENGINEERING COMPARISON MATRIX

DIMENSION	A — ISO 16889 Multipass Test	B — Single-Pass Test Method (ISO 4572, withdrawn)
Fluid circulation	Continuous — fluid recirculates throughout test	Once through — fluid passes filter once only
Contamination injection	Continuous upstream injection throughout test	Pre-mixed or upstream add once
Test dust	ISO 12103-1 A3 Medium (or A2/A4)	ACFTD (discontinued, no longer available)
Particle counter	ISO 11171:2010-calibrated APC — mandatory	Uncalibrated APC — pre-ISO 11171 era
Current standard status	Active — ISO 16889:2022	Withdrawn — ISO 4572 (2000)
Outputs	Beta ratio β_x(c) + DHC [g] + terminal ΔP	Single-pass efficiency % (no DHC)
Reproducibility	High — ISO 11171 calibration ensures lab agreement	Poor — particle counter not calibrated; lab variation large
Data comparability	Comparable globally (same calibration basis)	Not comparable with ISO 16889 data; internal only

WHEN TO USE A

ISO 16889 Multipass Test

✓All current filter element performance specifications and procurement

✓Any application requiring ISO 4406 cleanliness code design calculations

✓New product development, certification, and compliance validation

✓Forensic analysis of filter elements from field performance investigations

WHEN NOT TO USE

✗There are no valid reasons to avoid ISO 16889 for fluid filter element performance characterisation

WHEN TO USE B

Single-Pass Test Method (ISO 4572, withdrawn)

✓Interpreting historical (pre-2000) product data for legacy equipment maintenance decisions

✓Rapid internal development screening where relative comparisons (not certified values) are sufficient

WHEN NOT TO USE

✗Any current procurement specification — ISO 4572 is withdrawn

✗Any certification or compliance claim — ISO 4572 values are not internationally recognised

✗Cross-comparison with modern ISO 16889 data

ENGINEERING IMPLICATIONS

01A filter rated "99% efficient at 10 µm" from a 1995 data sheet using ISO 4572 is NOT equivalent to β₁₀(c) ≥ 200 from a current ISO 16889 test — never compare these values directly.

02Any procurement specification written today must reference ISO 16889 and require β_x(c) values with calibrated (c) suffix — specifications citing "single-pass efficiency" are technically incomplete.

03ISO 16889 multipass data tells the engineer how the element performs throughout its service life (efficiency changes as loading increases) — single-pass data reflects only initial clean element performance.

04When evaluating filter element substitutions for legacy equipment, ensure the replacement element has ISO 16889 multipass data, then establish which performance metric (β rating, DHC) matches the original design intent.

RELATED KNOWLEDGE

STANDARDS

ISO 16889 →ISO 11171 →ISO 4406 →

TECHNOLOGIES

NANOFORCE →SYNTRAX →

ARTICLES

testing and validation →filter media science →fluid cleanliness →

ISO 16889 Multipass vs. Single-Pass Filter Testing

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