Can hydraulic oil still be used if there is water in it?

Water mixed into hydraulic oil will affect its performance and the safety of use. Whether it can continue to be used needs to be comprehensively judged based on the water content, oil type and system requirements. The following is a detailed analysis:

1. Hazards of water

- Decreased lubricity: Water will destroy the oil film and aggravate the wear of metal parts.

- Accelerated oxidation: Water promotes oil oxidation, generating acidic substances that corrode pipes and seals.

- Filter clogging: Water reacts with additives to form a colloid, which clogs the filter element.

- Low-temperature freezing: In cold environments, water freezing may cause valves to stick or pipes to rupture.

- Microbial growth: Long-term water content may breed bacteria and pollute the system.

2. Allowable water content standard

- General hydraulic system: Water content should be less than 0.1% (1000ppm) (ISO 4406 grade recommends keeping the oil cleanliness at ISO 18/16/13 or better).

- High-pressure/precision systems (such as servo systems): more stringent requirements (usually <0.05% or 500ppm).

3. Detection and treatment recommendations

Detection method

- Visual inspection: Turbid or emulsified (milky) oil indicates high water content.

- Crackle test: ｄｒｏｐ oil on a hot steel plate. If there is a "crackling" sound, it means there is water.

- Laboratory analysis: Accurately determine the water content (such as Karl Fischer method).

Treatment measures

- Small amount of water (<0.1%):

- Use a vacuum dehydrator or coalescing filter to remove water.

- Add oil-water separator (mineral oil only).

- Large amount of water (emulsified or >0.1%):

- ｒｅｐｌａｃｅ with new oil and thoroughly clean the system (including oil tank, pipeline, and filter element).

- Check the cause of water ingress (such as cooler leakage, breather valve failure, condensation, etc.).

4. Water resistance of different oils

- Mineral oil: Poor water resistance, water must be strictly controlled.

- Synthetic oil (such as phosphate ester, polyalphaolefin): Some models have good water resistance, but the manufacturer's recommendations must still be followed.

- High water-based hydraulic fluid (HFA/HFB): Designed for water-containing conditions, but the application scenarios are special.

5. System recovery steps

1. Drain: Drain water from the bottom of the oil tank (water is heavier than oil and usually settles to the bottom).

2. Circulation filtration: Use an oil filter with water absorption function (such as a molecular sieve or centrifugal).

3. Testing and verification: Ensure that the water content meets the standard before running the equipment.

4. Preventive measures: Install an air dryer and check the sealing regularly.

Conclusion

- Unusable: If the oil has been emulsified, the acid value exceeds the standard, or the system has abnormal noise/heat, the oil must be changed immediately.

- Use with caution: When there is a trace of water and it can be handled in time, it can be used for a short-term emergency, but it needs to be repaired as soon as possible.

It is recommended to monitor the oil status regularly (such as once every 3 months) and follow the technical specifications of the equipment manufacturer.