How to filter hydraulic oil best?

Hydraulic oil filtration is a key step to ensure the stable operation of the hydraulic system. The best filtration method should be selected according to the type of oil contamination (water, particles, oxidation products, etc.) and working conditions. The following is a comprehensive solution for the efficient filtration of hydraulic oil:

Phased filtration process

(1) Pre-filtration (coarse filtration)

- Purpose: Remove large particles (>10μm) to protect subsequent precision equipment.

- Method:

- Use a centrifugal oil filter or a filter truck with a magnetic filter to quickly separate metal chips and dust.

- Filter element selection: stainless steel mesh (40-100μm).

(2) Fine filtration (core treatment)

- Purpose: Deeply remove micron-sized particles, water and gas.

- Method:

- Vacuum oil filter (best choice):

- Vacuum dehydration and degassing (water content can be reduced to below 50 ppm).

- Multi-layer precision filter element (1-5μm) filters particles to reach NAS 1638 level 6-8.

- Coagulation separation oil filter:

- Specializes in emulsified oil, removes water through coagulation, demulsification + stratification separation.

(3) Terminal protection filtration

- Purpose: Online maintenance of system cleanliness.

- Method:

- Install a high-pressure pipeline filter (β value ≥ 200, accuracy 3-5μm) on the hydraulic system return oil pipeline.

Key technologies and equipment selection

| Type of pollution | Recommended equipment | Treatment effect |

|--------------|-----------------------|----------------------------------|

| Particle impurities | Vacuum oil filter + glass fiber filter | Particle size ≤ NAS 7 |

| Moisture | Vacuum oil filter / coalescing oil filter | Moisture ≤ 50ppm (ISO 4406) |

| Gas | Vacuum oil filter | Gas content ≤ 0.1% |

| Oxidized colloid | Adsorption oil filter | Acid value reduction (TAN < 0.3mg KOH/g) |

Key points of operation

- Temperature control: Heat to 50-60℃ (when vacuum dehydration) to reduce oil viscosity and improve separation efficiency.

- Flow matching: Equipment processing capacity must be ≥ 2 times the system tank volume/hour (e.g. 500L tank, ｓｅｌｅｃｔ 1000L/h oil filter).

- Real-time monitoring:

- Use particle counters and moisture meters to verify cleanliness.

- Online monitoring of pressure difference (ｒｅｐｌａｃｅ filter element when ΔP＞0.3MPa).

Special case handling

- Emulsified hydraulic oil: first demulsify (add demulsifier or heat to 70℃ and let stand for stratification), then use a coalescing oil filter to process.

- High viscosity oil (such as VG68): Use a centrifugal oil filter with a preheating function to avoid filter element clogging.

Maintenance recommendations

- Regular filtration: Process every 500 working hours or when the oil sample exceeds the standard.

- System cleaning: Thoroughly clean the oil tank and pipeline before filtering to avoid secondary contamination.

- Filter element management: Use filter elements of different precisions in different grades (such as 20μm→5μm→1μm first).

The best filtration of hydraulic oil requires "graded treatment + symptomatic treatment":

- Particle pollution → Vacuum oil filter + precision filter element

- Water/gas → Vacuum dehydration and degassing

- Online maintenance → High-pressure pipeline filter

With strict monitoring and regular maintenance, the oil life can be extended by more than 3 times and the equipment failure rate can be reduced by 60%.