There are several types of hydraulic oil filters?

The hydraulic oil filter is mainly divided into the following types according to the purification principle and application scenario. Each type is designed for different pollution problems (particles, moisture, gas, oxidation products, etc.):

Classification by filtering technology

1. Mechanical oil filter

- Principle: intercept solid particles through a filter element (filter paper, filter cloth, metal mesh).

- Applicable scenarios: remove mechanical impurities such as metal chips and dust.

- Features:

- Filtration accuracy: 1~50μm (high accuracy can reach 0.5μm).

- Typical equipment: plate and frame oil filter, bag filter, self-cleaning filter.

2. Vacuum oil filter

- Principle: vacuum dehydration + precision filtration, using negative pressure to evaporate moisture and gas.

- Applicable scenarios: remove moisture, gas and particles at the same time (such as hydraulic oil emulsification).

- Features:

- Moisture can be reduced to ≤ 50 ppm.

- Often equipped with a heating system (60~65℃).

3. Centrifugal oil filter

- Principle: High-speed rotation (3000~8000rpm) uses centrifugal force to separate water/solids.

- Applicable scenarios: hydraulic oil with high water content or high impurities (such as ship hydraulic systems).

- Features:

- No filter element is required, and the processing capacity is large.

- Limited effect on tiny particles (<5μm).

4. Coalescing and dehydrating the oil filter

- Principle: Coalescing filter element combines tiny water droplets → separation layer, sedimentation and drainage.

- Applicable scenarios: demulsification (such as turbine oil, water-containing hydraulic oil).

- Features:

- Can handle oil with a water content of ≤10%.

- Water outlet accuracy ≤ 100 ppm.

5. Electrostatic oil filter

- Principle: High-voltage electrostatic field adsorbs colloidal particles and oxidation products.

- Applicable scenarios: Precision hydraulic systems (such as aviation hydraulic oil).

- Features:

- Can remove 0.1μm ultrafine particles.

- Ineffective for water, needs to be used with other equipment.

6. Adsorption oil filter

- Principle: activated clay, silica gel and other adsorbents remove acid and colloid.

- Applicable scenarios: regeneration of old oil with severe oxidation.

- Features:

- Acid value can be reduced by more than 50%.

- The adsorption medium needs to be replaced regularly.

Classification by usage

| Type | Features | Applicable scenarios |

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

| Mobile oil filter | With wheels or carts, flexible and maneuverable | On-site maintenance, temporary purification |

| Fixed oil filter | Integrated in the hydraulic system, long-term operation | Continuous filtration of the production line |

| Online oil filter | Real-time monitoring and automatic purification | High-precision hydraulic system (such as injection molding machine) |

3. Classification by purification target

| Pollution type | Recommended equipment type | Treatment effect |

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

| Solid particles | Mechanical/electrostatic oil filter | Cleanliness up to NAS 1638 level 6 or below |

| Moisture | Vacuum/coalescing oil filter | Moisture ≤50ppm |

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

| Oxidation products | Adsorption oil filter | Acid value ≤0.1mgKOH/g |

Key factors for selection

1. Oil state:

- High water content → ｓｅｌｅｃｔ centrifugal or coalescing type.

- Many particles → ｓｅｌｅｃｔ mechanical or electrostatic type.

2. Accuracy requirements:

- Ordinary hydraulic system: 5~10μm.

- Servo hydraulic system: ≤1μm (β₅≥200 filter element required).

3. Processing capacity:

- Small equipment: 100~500L/h.

- Industrial grade: 1000~5000L/h.

Typical Application Comparison

| Equipment Type | Advantages | Limitations |

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

| Vacuum Oil Filter | Multifunctional (water/gas/particles) | High energy consumption, large volume |

| Centrifugal Oil Filter | No consumables, large processing capacity | Ineffective for tiny particles |

| Electrostatic Oil Filter | Ultra-precision purification | Not applicable to oil with high water content |

Maintenance Points

- Filter element replacement: ｒｅｐｌａｃｅ immediately when the pressure difference is > 0.3MPa.

- Vacuum pump oil: ｒｅｐｌａｃｅ every 200 hours.

- Adsorbent regeneration: After saturation of white clay/silica gel, high temperature activation or replacement is required.

Selecting a suitable filter according to the pollution type of hydraulic oil and system requirements can extend the oil life by 3~5 times and reduce the equipment failure rate. For key equipment (such as CNC machine tools), it is recommended to use the "vacuum + electrostatic" combination process to achieve all-around purification.