An ISO 4406 cleanliness code needs a sample, method and requirement beside it. A hydraulic-fluid report may show three numbers, but the purchasing team still needs to know what was assessed and which equipment requirement applies.
Begin by preserving the report exactly as issued. Keep its code, sample identity, method reference and notes together. Then connect the result to the requested review.
This guide explains those document fields. It does not set a cleanliness target, select a filter or supply a hydraulic sampling procedure.
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1. Read the ISO 4406 cleanliness code by position
ISO’s public description of ISO 4406:2021 identifies a code for the quantity of solid particles in a hydraulic-system fluid. It is a classification of that reported subject.
HYDAC’s explanation of cleanliness classes describes cumulative size categories of 4 µm(c), 6 µm(c) and 14 µm(c). In its example 18/16/13, the three code positions correspond to those categories in that order.
| Code position | Referenced size category |
|---|---|
| First: 18 | 4 µm(c) |
| Second: 16 | 6 µm(c) |
| Third: 13 | 14 µm(c) |
The 18 is a code entry associated with the first category, not an 18 µm particle-size label. Keep the three positions in their original order.
Read the report’s full counting basis and method before interpreting any accompanying count data. Do not infer counts from this position table; it supplies no count-range conversion.
The example is not a target for a JiurunCut machine or a measured result from one. Use the actual system requirement and issued report.
2. Identify which fluid was sampled
Request the fluid product, system or asset identity and collection-point reference. Retain the sample date and applicable operating-condition notes.
A sample from delivered oil and a sample from an operating system should retain their own subjects. A matching fluid brand does not make the two records interchangeable.
Where a report covers several points, keep the result attached to the relevant point. Do not move a favorable code from one location into the summary for another.
Ask the issuer to resolve missing sample information. The word oil alone leaves the reviewer unable to establish what the document covers.
Keep the sample record connected to the actual equipment documentation. A machine photograph can provide context, but it does not identify the fluid path or collection procedure.
Use the applicable equipment, workplace and test-provider instructions for actual sampling. This article supplies no instruction to open a hydraulic line or collect from running equipment.
3. Retain the method and its applicability
Keep the reported method, applicable edition, instrument or laboratory reference and any qualifications. Have the issuer explain an unclear heading or an omitted method field.
HYDAC’s 2026 fluid-cleanliness guidance notes limitations of online laser particle counting for some fluids. It also explains that such a counter does not distinguish water, air, additives and solid particles.
Ask the test provider whether the method is appropriate for the identified fluid and reported condition. Preserve its answer with the record instead of treating every displayed code as equivalent evidence.
If two reports use different references, have the responsible reviewer establish how the comparison should proceed. Do not relabel another standard as ISO 4406 solely because it also reports a cleanliness class.
A laboratory attachment and a monitoring display may provide different record detail. Request the evidence required by the actual acceptance or maintenance plan.
Keep any uncertainty or qualification supplied by the issuer. Removing a note to shorten the purchase file can change how the result should be used.
4. Identify the applicable equipment requirement
Ask the machine and component suppliers for the cleanliness requirement relevant to the identified configuration. HYDAC’s guidance directs the user to those manufacturers when determining the target.
Keep the requirement separate from the measured result. A favorable-looking sample code cannot fill a blank requirement field.
If different components have different requirements, ask the responsible system supplier to resolve the complete arrangement. Retain its reviewed target and stated conditions.
Keep filter selection with that technical review. A cleanliness-code example does not identify the correct filter element, its performance or the components included in the offered system.
Also preserve the complete approved fluid specification. Our ISO VG purchasing guide addresses a viscosity classification; that field describes a different property.
When the fluid or component arrangement changes, identify the change and request review of the applicable requirement. A previous report should remain tied to its original configuration.
5. Keep the result and decision traceable
Consider a fictional maintenance file labeled H-27. It contains an identified sample report but leaves the system’s target-reference field blank.
The immediate task is to recover the target and its applicable conditions. The report should retain its identity while the requirement question is resolved.
Now suppose the sample collection point is also missing. Keep that issue separate. Adding the target reference does not recover the sample identity.
This fictional file illustrates document gaps. It establishes no acceptable code, fault diagnosis or hydraulic-system condition.
A completed review should name the requirement, sample report and decision owner. Retain the actual disposition and any stated follow-up.
If a subsequent report follows a corrective action, connect it to the action and collection conditions. Keep the earlier record available so the reason for the follow-up remains understandable.
For another laboratory property, our oil air-release report guide organizes method and condition fields. Do not substitute that result for particle-cleanliness evidence.
A short report-review sequence
Confirm the reported code and method, identify the sample, recover the applicable requirement, then retain the reviewer’s decision. Leave missing fields visibly unresolved until the responsible party supplies them.
Keep the final documentation with the equipment record. The next maintenance purchaser should be able to understand which system and requirement the decision covered.
Make the maintenance question specific
Contact JiurunCut with the equipment identity and relevant documents. Include the actual report and component reference when an ISO 4406 cleanliness code appears in the supplier-review question.