Hydraulic oil cleanliness: small particles, big consequences

Cleaner oil: potential for a sevenfold service-life difference

Contamination control can have a major effect on equipment life. WearCheck’s Technical Bulletin 65 presents an indicative hydraulic-system life-extension table: improving from ISO 24/22/19 to 17/15/12 gives a potential factor of 7. The comparison is seven code steps in each channel.

Three steps, from 20/18/15 to 17/15/12, correspond to a factor of 2 in that table. These are model estimates, not an ISO 4406 requirement or a guaranteed pump lifespan. Results depend on the equipment, operating conditions and sustained cleanliness.

• WearCheck — Keep It Clean, Technical Bulletin 65, Table 2 (PDF)

Same HLP-46 designation, different appearance

The HLP-46 designation does not assign an ISO 4406 cleanliness code. This comparison shows visible colour differences; it does not establish which sample contains fewer particles. No individual test reports for the six pictured samples are presented here, so no cleanliness ranking is assigned to them.

The HLP-68 batch example below is separate from these HLP-46 samples. Its numerical results come from the identified certificate, not from an assessment of this photograph.

Clean-looking oil is not a cleanliness test

Solid particles can enter during storage, filling or maintenance, and can also be generated by component wear. Circulating contamination may damage working surfaces and create further wear debris. Visual inspection alone cannot establish whether the oil meets the equipment’s particulate-cleanliness requirement.

Bosch Rexroth identifies fluid quality and cleanliness as important to system safety, efficiency and service life. The practical question is whether the fluid circulating through your equipment meets its specified target.

• Bosch Rexroth — hydraulic fluid selection and requirements
• Pall — contamination control and fluid service life

How to read ISO 4406

For automatic particle counting, ISO 4406 reports three cumulative particle-size thresholds per millilitre: ≥4, ≥6 and ≥14 µm(c). Each number is a concentration range. Lower codes indicate fewer particles; a one-code change corresponds to roughly a twofold shift in the range.

• ISO 4406:2021 — solid particle contamination code

A real batch result: ISO 13/10/7

The HLP-68 certificate supplied by FEOTECH provides a concrete example. COA No. 7338 records ISO 4406 cleanliness of 13/10/7 for Gazpromneft Hydraulic HLP-68, batch 2415161701. Each code is below the corresponding maximum of 20/17/14 shown in the certificate.

The oil was produced on 18 September 2024, sampled on 19 September and certified on 21 September 2024. The packaging is listed as 205-litre drums. These are reported batch-analysis results, not a universal cleanliness guarantee for every HLP delivery or for oil already circulating in a machine.

The target comes from the equipment

The example above is not a universal acceptance limit. Use the current OEM requirements for the machine and its most sensitive components. A cleanliness code alone also says nothing about water content, viscosity or oil oxidation: those need separate checks.

Oil selection and contamination control work together. An appropriate hydraulic oil supports the application, while storage, transfer, filtration and maintenance determine how its condition is preserved in service.

A filter needs a verified result

Installing a filter does not prove that the target has been achieved. Its efficiency, position, operating conditions and bypass behaviour all matter. Select filtration with the equipment or filtration specialist, then verify the circulating oil rather than relying on a micron label alone.

Use representative samples and a consistent sampling point to track changes over time. Clean sampling equipment, suitable bottles and a documented procedure help prevent a misleading result. High-pressure sampling must follow the equipment’s safety procedure and be carried out by trained personnel.

• Pall — contamination control and fluid service life
• Pall — Fluid Sampling Protocol (PDF)

From the drum to the machine in Indonesia

For Indonesian mining, construction, plantations and industrial plants, dust exposure and humid storage conditions are practical reasons to review how oil is handled. Keep containers closed, protect transfer connections and inspect reservoir breathers and cylinder-rod seals. Monitor water separately from particle cleanliness.

New oil should be checked against the required fill cleanliness, with suitable transfer filtration where needed. Ask three questions: what is the measured cleanliness in the drum, what is it after transfer, and what does the OEM require? A batch certificate or drum sample does not certify the machine after filling. Specify any special delivery-cleanliness requirement when ordering, alongside viscosity and product requirements.

Five actions for the maintenance team

1. Record the OEM cleanliness target for each critical hydraulic system.
2. Establish a baseline through representative particle counting and separate oil-condition checks.
3. Control filling and top-ups with clean, closed transfer equipment and application-matched filtration.
4. Inspect contamination entry points and monitor filter condition according to the service instructions.
5. Trend the results, investigate departures from the target and confirm the outcome after corrective work.

Turn a laboratory result into a maintenance decision

FEOTECH’s previous field-quality-control article explains how sampling and laboratory results can provide a documented starting point. The next step is to connect that evidence to a machine-specific cleanliness target and a repeatable maintenance routine.

Send FEOTECH the equipment model, OEM oil requirements and your latest analysis. These provide a useful basis for discussing Gazpromneft hydraulic oil selection and the next verification steps. The aim is dependable operation supported by evidence and measurable maintenance targets.

• Read the FEOTECH hydraulic oil field-quality-control article