ISO 4406 hydraulic oil cleanliness codes describe cumulative particle-count ranges at ≥4, ≥6, and ≥14 µm(c). First, check the units and find the range for each channel. Then compare all three numbers with the written requirement for the machine and its parts.
The report says 18/16/13. Does that meet the requirement on your drawing? A clear-looking sample cannot answer that question, and neither can a generic target copied from a pump chart.
Lab reports can make a simple comparison look obscure. This ISO 4406 hydraulic oil cleanliness guide links codes to raw counts. It shows a unit conversion and a worksheet for setting a target. You will also see when a result needs confirmation before it becomes a maintenance decision.
Key Takeaways
- The three channels overlap: do not add them together.
- Check particles per mL versus particles per 100 mL before using a range table.
- Use the applicable equipment requirement; 18/16/13 is an example, not a universal target.
- Keep raw counts, sample details, and the next action with every reported code.
- Particle cleanliness is one part of oil health.
For a component sourcing inquiry, send your pump model and operating duty, together with any available OEM cleanliness requirement. This gives the inquiry a specific machine context rather than an assumed target.
What ISO 4406 hydraulic oil cleanliness measures and leaves out
Three cumulative channels, not three separate size bins
In an ISO 4406 hydraulic oil cleanliness report, the first number represents the particle-count range at ≥4 µm(c). The second covers ≥6 µm(c), and the third covers ≥14 µm(c). Each describes a range of particle counts per unit of fluid, not a particle diameter. Code 18 does not mean an 18-micron particle.
In ISO 4406 hydraulic oil cleanliness data, a large particle also counts at the smaller thresholds. Think of nested groups. Particles at least 14 microns also belong in the group at least 6 microns. Both belong in the group at least 4 microns.
Adding the channels would count those larger particles repeatedly.
Fluid Life’s particle-count explanation describes this cumulative reporting convention and its limits. Keep this in mind if a report shows extra size channels. A lab may list more counts than the three used for the code.
Keep the measurement convention beside the code
For ISO 4406 hydraulic oil cleanliness, µm(c) identifies the calibrated size scale. ISO 4406 concerns contamination coding; ISO 11171 concerns automatic liquid particle-counter calibration. The calibration standard sets the measurement basis. The reporting code groups the counts.
They serve different roles. Keep both references with the report if the lab supplies them.
When comparing ISO 4406 hydraulic oil cleanliness reports, keep the lab’s method, size thresholds, and count units. Do not silently remove the suffix or relabel an older result. Ask the laboratory to explain a notation you cannot identify, especially when comparing historical records from another instrument or method.
Particle cleanliness is only one part of oil condition
ISO 4406 hydraulic oil cleanliness is not an ISO VG viscosity grade. The code does not tell you whether the oil has the correct viscosity for the pump, how much water it contains, or which metals appear in a wear analysis. Each needs its own test result and review.
A high code alone also does not identify the particles as pump wear debris. Keep the full report with the machine record, and read the particle data alongside the other test results. The short code helps you share a result. It cannot tell you the cause of a fault on its own.
Our hydraulic pump oil maintenance guide provides broader maintenance context. Use this article for decoding the report; use the equipment procedure and complete analysis for the wider oil-condition decision.
How to read ISO 4406 hydraulic oil cleanliness codes from a report
Check the count basis first
Start an ISO 4406 hydraulic oil cleanliness check at the heading above the counts. Does it say particles/mL or particles/100 mL? The table below uses particles per milliliter. A count reported per 100 mL must be divided by 100 before you use that table.
Illustrative scenario 1: A technician receives counts of 200,000, 50,000 and 6,000 particles per 100 mL at the three thresholds. Dividing each by 100 gives 2,000, 500, and 60 particles/mL. These are invented teaching values, not results from a customer’s machine.
The oil has not changed. You have only changed the units used to express the count. Keep both the original values and the converted values on the worksheet so another reader can check the arithmetic without guessing which units you used.
Map each threshold to its range
The following reference bands come from page 25 of Donaldson’s Hydraulic Filtration Overview. The lower boundary is exclusive; the upper boundary is inclusive.
| Code | More than, particles/mL | Up to and including, particles/mL |
|---|---|---|
| 11 | 10 | 20 |
| 12 | 20 | 40 |
| 13 | 40 | 80 |
| 14 | 80 | 160 |
| 15 | 160 | 320 |
| 16 | 320 | 640 |
| 17 | 640 | 1,300 |
| 18 | 1,300 | 2,500 |
| 19 | 2,500 | 5,000 |
| 20 | 5,000 | 10,000 |
The example gives an ISO 4406 hydraulic oil cleanliness code of 18/16/13: 2,000 falls in band 18, 500 in band 16, and 60 in band 13. Write the result in threshold order: 18/16/13. Do not rearrange the numbers or combine them into a single average.
At a boundary, 640 particles/mL belongs in code 16. A value just above 640 enters code 17. For a result near a boundary, keep the precision the lab reports. Do not round a count before you assign its band.
Keep raw counts for trend review
Each higher band spans roughly twice the count of the one below it. A one-code rise does not prove that the measured count has doubled. Near a band edge, a small change can move a result into the next band.
Two ISO 4406 hydraulic oil cleanliness reports can share a code but have different raw counts. Retain both forms: the code supports a quick comparison, while the underlying counts show what changed within the band. Neither tells you how long a part will last or when it will fail.
Schroeder Industries provides an accompanying explanation of code reading and target selection:
The worked calculation above remains available in text if you prefer to check each threshold without using the video. To check an ISO 4406 hydraulic oil cleanliness calculation, use this sequence:
- Copy the three threshold labels and original count units.
- Convert each count to the table’s per-mL basis.
- Assign each band using its stated endpoints.
- Write the code in threshold order and retain the raw values.
This leaves a calculation another person can follow. If the laboratory’s printed code differs, ask it to check the original values and method before you overwrite either record.
Set an ISO 4406 hydraulic oil cleanliness target for the actual machine
Start with the applicable equipment documents
A pump-family table cannot set the ISO 4406 hydraulic oil cleanliness target for every machine. Begin with the applicable machine specification, then check the relevant component requirements and operating duty. Include sensitive valves and other components sharing the oil circuit.
HYDAC’s target-selection guidance, updated June 16, 2026, points readers to machine and component manufacturers. It also highlights component sensitivity and operating conditions. Use those sources to establish the requirement, rather than treating a generic internet number as approval for your system.
For ISO 4406 hydraulic oil cleanliness control, separate three entries in your records: the documented operating limit, any approved site control target, and the measured sample result. A site may approve a tighter target to flag a change before it reaches the limit. Name who approved it and what action it triggers.
Record where the target came from
Use this ISO 4406 hydraulic oil cleanliness worksheet to record the target before checking a result. Blank fields are questions to resolve, not permission to substitute a familiar code.
| Record field | What to enter |
|---|---|
| Equipment identity | Machine model, serial number and circuit |
| Relevant components | Pump, valves and other applicable component models |
| Operating duty | Conditions covered by the cited requirement |
| Source document | Manual or specification number, revision and section |
| Operating limit | Required code and any accompanying conditions |
| Control target | Approved target, owner and escalation rule |
| Sampling basis | Sample point, operating state and test method |
| Acceptance record | Person responsible, result and next action |
Keep component maintenance advice in its proper role. Our guides to axial piston pump maintenance and hydraulic gear pump maintenance offer related maintenance context. They do not replace the current requirement for a particular machine.
Resolve missing or conflicting requirements
Illustrative scenario 2: A machine manual and a replacement servo component document specify different cleanliness requirements. The team notes both document revisions. It asks the machine maker which rule applies to this circuit. This example gives no test result or repair outcome.
Do not relax an ISO 4406 hydraulic oil cleanliness target just because the pump can tolerate it. Equally, a stricter number from an unrelated application is not automatically the correct system requirement. Check which requirement applies, where to sample, and what duty it covers before you record the target.
If the requirement is missing, request it from the equipment or component manufacturer. Record that it is pending rather than marking the machine compliant. A published table can help you ask the right questions. It cannot settle which rule applies to the machine.
For example, JLG’s January 17, 2018 guidance gives 19/17/14 or below for the equipment it discusses. That is a dated manufacturer example, not a target to transfer to every pump. The current applicable model manual and conditions take precedence.
For procurement, carry the approved ISO 4406 hydraulic oil cleanliness requirement into the component inquiry with the pump model. Ask the person who owns the specification to resolve open questions before treating the number as settled. Identifying a replacement and authorizing the machine’s operating condition are separate decisions.
Check whether the cleanliness report is comparable and credible
Sample location and operating state matter
For an ISO 4406 hydraulic oil cleanliness trend, compare tests made on the same basis. A reservoir sample and a sample taken elsewhere in the circuit may describe different conditions. Check the sample point, machine state and timing of recent work.
Use the approved sampling procedure for that machine. Do not open a pressurized connection or improvise a sample port to follow an educational example. This guide helps you check reports, not take live samples.
In the first scenario, the sums can be right while the machine ID or sample point is missing. The code is valid, but the record is incomplete. Ask the lab or sampling team to fill those gaps before you use it in a trend.
Ask the laboratory about a surprising count
Air, water and fluid additives can affect optical particle counts. HYDAC notes these limits in its guide. Check both the method and the machine if a count looks wrong. The code alone does not identify wear debris.
Ask the lab whether the test suits this fluid. Could the way the sample was prepared, or air or water in it, affect the reading? The lab may consider dilution or a patch test under a microscope. Ask trained lab staff; do not alter the sample yourself.
For an ISO 4406 hydraulic oil cleanliness review, ask: Did the lab retain the raw counts? What volume basis and size convention were used? Was sample preparation consistent with earlier tests? Is the result suitable for comparison with the previous report?
Keep the answers with the ISO 4406 hydraulic oil cleanliness report. Keep any lab caveat when you copy the code to a dashboard. A short status label must not hide a test limit.
Treat legacy reports carefully
A historical two-number code may use a different reporting or calibration basis. Do not turn it into a modern three-number code by inserting an assumed first value. You cannot recover a missing threshold count from two reported bands alone.
Ask the lab if the raw data and method allow a sound comparison. If they do not, keep the old and new records in separate groups. Note what changed. A gap you can explain is better than a smooth chart based on guessed values.
For the same reason, note a laboratory or method change next to the first affected result. That prompts the next reviewer to check whether the tests match before blaming the machine for the whole change.
Turn an above-target code into a documented response
Compare every channel
For ISO 4406 hydraulic oil cleanliness acceptance, a lower first number cannot offset a high second number. Compare each channel with its corresponding acceptance limit. Do not average the three code numbers. Two channels within their limits do not make the full result acceptable.
Illustrative scenario 3: The documented example ceiling is 17/15/12, while the measured example is 17/16/12. The ≥6 µm(c) channel exceeds its limit. The other channels do not erase that excursion; the specified site response still needs to be considered.
These values show how to compare the codes. They do not set a machine target or decide if it should keep running. Use the equipment instructions and authorized site procedure for that decision, with the sample’s reliability clearly recorded.
Confirm, investigate and verify
Use an ISO 4406 hydraulic oil cleanliness response record that separates the finding from the next action. The following framework organizes the review; it does not impose a universal resampling schedule or shutdown threshold.
| Finding | Documented response |
|---|---|
| All channels meet the target and the trend is stable | Record the result and continue the approved monitoring plan |
| A comparable, credible result exceeds a limit | Apply the defined escalation process and investigate the excursion |
| Sample context or counting method is uncertain | Mark the limitation and arrange confirmation through the approved procedure |
| Corrective work is complete | Verify cleanliness under the specified conditions and retain the evidence |
Investigate the context before naming a failed component. Review recorded fluid additions, maintenance work and filtration condition as relevant to the machine. Record what you found and what you suspect in separate fields. That helps the next reviewer see what is known.
A new filter or fresh oil does not prove that the ISO 4406 hydraulic oil cleanliness target has been met. Neither does a nominal micron label establish the achieved code. The hydraulic pump filter guide covers related filter considerations; acceptance still depends on suitable verification in the system.
To close the record, name the person in charge. Add the approved action, check result and source of the requirement. For ISO 4406 hydraulic oil cleanliness acceptance, keep the verification sample location and test basis beside that result. A work order marked complete is not a measurement of the oil.
If a result remains uncertain, carry that uncertainty forward. Do not replace it with an unqualified green status simply because work has been completed.
Frequently asked questions and your report checklist
What does 18/16/13 mean in a hydraulic oil report?
It gives three overlapping count ranges: more than 1,300 up to 2,500 particles/mL at ≥4 µm(c), more than 320 up to 640 at ≥6 µm(c), and more than 40 up to 80 at ≥14 µm(c). The upper boundaries are inclusive; these are overlapping thresholds, not separate particle bins.
Is 18/16/13 clean enough for every hydraulic system?
No. The machine, its parts and their duty set the requirement. Check each channel against that requirement. A code used in an example or generic component table cannot establish a universal target, and meeting it does not independently authorize a machine to operate.
Can brand-new oil fail the required cleanliness target?
Yes. Newness alone does not demonstrate that oil meets the machine’s particle-cleanliness requirement. Use suitable cleanliness evidence rather than assuming a fresh container guarantees the target. Follow the approved fluid handling and verification procedure; do not infer a specific oil delivery’s condition without a representative test or other applicable evidence.
Does a lower ISO 4406 hydraulic oil cleanliness code prove oil health?
No. A lower code means lower particle-count bands, if you can compare the tests on the same basis. It does not establish correct viscosity, acceptable water content or suitable wear-metal findings. Review those properties separately in the full oil report, and preserve any laboratory qualification that limits the particle-count result.
Can I compare a two-number report with a three-number code?
First check the test method, how the counter was calibrated and whether the raw data are available. Do not invent the missing channel or assume the old and new thresholds are interchangeable. Ask the laboratory whether a valid comparison is possible; otherwise, keep the records distinct and document when the reporting basis changed.
Keep the ISO 4406 hydraulic oil cleanliness report and decision together
Before filing a result, check for the raw counts, units, size thresholds and test method. Add the machine identifier, sample point and operating state. Attach the source document and its revision, the result for each channel and the name of the person taking the next action.
The three ISO 4406 hydraulic oil cleanliness scenarios show why each part matters: units control the calculation, equipment documents control the target, and every channel controls the comparison. Keep that chain intact when you move a result from a lab PDF into a maintenance worksheet or purchase inquiry.
For a replacement pump inquiry, contact us with the model, operating conditions and documented cleanliness requirement. Use ISO 4406 hydraulic oil cleanliness as a traceable specification supported by a report, rather than an isolated number with no agreed meaning.
