How to filter hydraulic oil?

In order to make the hydraulic oil clean and thorough, it is necessary to scientifically handle it in steps according to the type of pollution (particles, moisture, oxidation products, etc.). The following is a full-process solution for professional hydraulic oil purification:

Pretreatment stage (basic purification)

1. Sedimentation separation

- Let the oil stand for more than 48 hours, and use gravity sedimentation to separate large particles of impurities and free water

- It is recommended to maintain an ambient temperature of 20-40℃ to accelerate the sedimentation of impurities

2. Coarse filtration

- Use a 20-50μm stainless steel filter for preliminary filtration

- Use a filter with a magnetic bar to adsorb ferromagnetic particles

- The recommended processing flow rate is 1.5 times the system tank volume

Deep purification stage (core treatment)

1. Vacuum dehydration and degassing

- Use a three-stage vacuum oil filter:

- First-stage vacuum: -0.08～-0.095MPa, remove free water

- Second-stage vacuum: -0.096～-0.099MPa, remove dissolved water

- Third-stage vacuum: -0.1MPa, remove trace moisture and gas

- The oil temperature is best controlled at 60±5℃

- After treatment, the moisture content can be reduced to below 50 ppm

2. Precision filtration

- Use multi-layer gradient filtration:

- Pre-10μm glass fiber filter element

- Main filte:r 5μm polymer filter material

- Terminal 1-3μm glass fiber composite filter element

- Cleanliness after filtration can reach NAS 1638 level 6 or higher

3. Adsorption treatment (optional)

- For oil products with severe oxidation:

- Use diatomaceous earth or activated white clay adsorbent

- Addition amount 0.5-1.5% (depending on the condition of the oil product)

- Treatment time 4-6 hours

Post-treatment stage

1. Online circulation filtration

- Install a high-pressure filter with β≥200 on the return oil pipeline of the hydraulic system

- It is recommended to use a duplex filter with a pollution alarm function

2. Performance recovery

- Add an appropriate amount of antioxidant (such as T501)

- Supplement anti-wear additives (such as ZDDP)

- Adjust the oil viscosity index improver

Quality inspection standards

1. Physical and chemical indicators

- Moisture: ≤50ppm (ASTM D6304)

- Cleanliness: NAS 1638 Level 6 or ISO 4406 15/13/10

- Acid value: ≤0.3mg KOH/g (ASTM D664)

2. Performance test

- Demulsification: ≤30min (ASTM D1401)

- Air release value: ≤5min (ISO 9120)

- Anti-foaming: ≤300/0mL (ASTM D892)

Equipment selection recommendations

1. Mobile oil filter truck

- Processing capacity: 200-1000L/min

- Recommended brands: Pall, Hy-Pro, Pall

2. Fixed purification system

- Integrated vacuum dehydration + precision filtration + adsorption regeneration

- With PLC automatic control function

Maintenance recommendations

1. Daily maintenance

- Take samples every 250 working hours

- Check the filter pressure difference regularly (change if ΔP＞0.2MPa)

2. In-depth maintenance

- ｒｅｐｌａｃｅ the entire system oil once a year

- Clean the oil tank and pipeline every 2 years

Through the above systematic treatment, the hydraulic oil can achieve:

- Reduce particle contamination by more than 98%

- Reduce water content by 95%

- Extend the service life of the oil by 3-5 times

- Reduce the equipment failure rate by 70%

Key tips: For hydraulic oil with heavy pollution (water content＞1000ppm or particle NAS level 10 or above), it is recommended to directly ｒｅｐｌａｃｅ the new oil for more economical. Pay special attention to fire and explosion prevention during the treatment process, and the vacuum oil filter needs to be reliably grounded.