What to do if the hydraulic oil is not clear after filtration?

If the hydraulic oil remains unclear after filtration, it may be due to incomplete filtration, severe oil contamination, or other system issues. The following are step-by-step solutions:

1. Check the filtration equipment and process

- Is the filtration accuracy sufficient? Confirm the filter accuracy (usually the hydraulic system requires less than 10μm, and the high-precision system requires 5μm or less). If the original filter does not meet the requirements, ｒｅｐｌａｃｅ the filter element with a higher precision.

- Is the filtration time sufficient? Extend the filtration time or cycle filtration to ensure that particulate matter is fully removed.

- Is the filtration system matched? Check whether the filter element type (such as glass fiber, sintered metal) is suitable for the current oil contamination type (particles, gel, etc.).

2. Analyze the oil contamination type

- Particle contamination: Use a particle counter to detect. If it exceeds the standard, mechanical filtration needs to be strengthened or the filter element needs to be replaced.

- Water contamination:

- Observe whether the oil is turbid or milky (water mark).

- Use a vacuum dehydrator, centrifugal separation or adsorption filter element (such as a coalescing filter element) to remove moisture.

- Oxidation or chemical contamination:

- Yellow, black or odorous oil indicates oxidation or additive failure.

- New oil needs to be replaced and the system cleaned.

3. Clean the hydraulic system

- Drain the old oil thoroughly: Check whether there is sediment in the oil tank, pipeline, valve block and other parts when draining the oil.

- Sectional flushing:

- Use low-viscosity flushing oil or a special cleaning agent to circulate and flush the system.

- Focus on cleaning the dead corners of the oil tank, filter screen, radiator and other parts that are prone to dirt accumulation.

- ｒｅｐｌａｃｅ all filters: including return oil, suction oil and pressure line filter elements.

4. Check external pollution sources

- Oil tank sealing: Check whether the breather and oil tank cap are sealed to prevent dust/water from entering.

- Wear of hydraulic components: Metal wear particles of pumps, valves or cylinders will continue to contaminate the oil, and wear parts need to be repaired or replaced.

- Is the new oil clean? Even new oil may be contaminated, and filtering is recommended before filling.

5. Verify oil quality

- Laboratory testing: Take samples to test ISO cleanliness level, moisture content, acid value and other indicators to confirm whether they meet the standards.

- On-site simple test:

- Oil ｄｒｏｐ test: ｄｒｏｐ oil on filter paper to observe whether the diffusion ring is uniform (impurities or moisture will show obvious boundaries).

- Transparency comparison: Compare with the new oil. If it is still turbid, the pollution has not been completely removed.

6. Consider oil change

If multiple filtrations are ineffective or the oil has been severely oxidized (viscosity changes, high acid value), it is recommended to ｒｅｐｌａｃｅ new oil and thoroughly clean the system.

Preventive measures

- Regular maintenance: ｒｅｐｌａｃｅ the filter element and oil according to the requirements of the equipment manual.

- Online monitoring: Install a particle sensor or humidity sensor to monitor the oil status in real time.

- Control oil temperature: Avoid high temperature (over 60°C) to accelerate oil oxidation.

Through the above steps, the problem of unclear hydraulic oil filtration can be systematically solved. If the problem persists, it is recommended to contact the oil supplier or a professional hydraulic service provider for diagnosis.