How to filter hydraulic oil more clearly?

Here are clear steps and methods for hydraulic oil filtration to help you efficiently purify the oil and extend the life of the equipment:

Identify the type of contamination (targeted filtration)

1. Solid particles → cause valve core jamming and pump wear

- Target: Cleanliness reaches ISO 4406 15/13/10 or NAS 1638 Class 6.

2. Water → Causes rust and oil emulsification

- Target: Water ≤100 ppm (≤50 ppm for precision systems).

3. Gas/Oxide → Produce cavitation and accelerate aging

- Target: Gas content ≤0.1%, acid value ≤0.1 mg KOH/g.

Hydraulic oil filtration steps (from coarse to fine)

1. Pretreatment: coarse filtration (large particle removal)

- Equipment: centrifuge or 100μm metal mesh filter.

- Operation:

- Drain the oil from the bottom of the oil tank and circulate it through the coarse filter equipment.

- Note: If the oil contains a lot of metal chips, it is recommended to filter it magnetically first.

2. Deep filtration (micron particles)

- Equipment: precision oil filter (filter element with β₅≥200).

- Parameters:

- Filtration accuracy: 1~10μm (servo system requires 1~3μm).

- Flow matching: usually 1~2 times the system tank capacity (such as 200L oil tank, ｓｅｌｅｃｔ 200~400L/h flow).

- Operation:

- Connect the inlet and outlet pipes to form a closed loop.

- Monitor the filter element pressure difference and ｒｅｐｌａｃｅ the filter element when it is >0.15 MPa.

3. Dehydration treatment (optional)

- Coagulation dehydration:

- Equipment: Coagulation separation oil filter.

- Effect: The water content is reduced to 50~100 ppm.

- Vacuum dehydration (when emulsified):

- Equipment: vacuum oil filter (vacuum degree ≤-0.095 MPa).

- Heat the oil to 50~60℃ to improve efficiency.

4. Degassing and anti-oxidation (high-end demand)

- Vacuum degassing: dissolved gas content ≤0.1%.

- Add antioxidant: such as T501 (addition amount 0.3%~0.5%).

Operation precautions

1. Safety regulations:

- System pressure relief before filtration to avoid oil splashing.

- ATEX-certified equipment is used in explosion-proof environments (such as the chemical industry).

2. Oil temperature control:

- Heating should not exceed 70℃ to prevent oil oxidation.

3. Filter element selection:

- Mineral oil: cellulose or glass fiber filter element.

- Phosphate ester oil: special fluororubber filter element (corrosion resistant).

Post-filtration verification

1. Particle detection:

- Use a particle counter to confirm that the ISO grade meets the standard.

2. Moisture test:

- Karl Fischer method (≤100 ppm is qualified).

3. Appearance inspection:

- The oil is transparent and free of suspended matter, and has no sour odor.

Maintenance cycle recommendations

- Daily filtration: Filter online every 500 working hours.

- Thorough purification: Offline deep filtration every year or before oil change.

- Filter element replacement: Pressure difference > 0.15 MPa or every 6 months (whichever comes first).

Solutions to Common Problems

- Problem 1: Particles still exceed the standard after filtration

Cause: Insufficient filter element precision or residual contaminants in the oil tank.

Solution: ｒｅｐｌａｃｅ with a higher precision filter element (such as 1μm) + flush the oil tank.

- Problem 2: Excessive oil foam

Cause: High gas content or failure of the anti-foaming agent.

Solution: Vacuum degassing or adding a new anti-foaming agent (such as T901).

Efficient filtration of hydraulic oil needs to be processed in stages: first coarse filtration to remove large particles, then fine filtration to remove micron-level impurities, and finally dehydration and degassing (depending on demand). The key is to ｓｅｌｅｃｔ equipment according to the type of pollution (such as fine filtration for particles, coalescence/vacuum for water), and strictly verify the oil quality after filtration. Regular maintenance can reduce equipment wear by more than 60% and significantly extend the life of the oil.