Selecting the appropriate hydraulic filter is crucial for ensuring the stable operation of hydraulic systems and extending equipment lifespan. Below are several key factors to consider when choosing a hydraulic filter, with detailed explanations based on relevant standards and industry experience.

I、 Determine filtering accuracy
The filtration accuracy is the primary factor in choosing a hydraulic filter. The filtration accuracy is usually measured in micrometers (μ m), which represents the minimum particle size that the filter can filter out. When selecting, it is necessary to match according to the cleanliness requirements of the hydraulic system:

1. Determine the cleanliness level based on system requirements:
According to the international standard ISO 4406, select the corresponding filtration accuracy based on the hydraulic oil cleanliness level required by the system.
For example, hydraulic servo valve systems require high cleanliness and typically require a filtration accuracy of 1-3 μ m; For general hydraulic systems, a filtration accuracy of 10-20 μ m can be selected.
2. Nominal accuracy and actual performance:
The nominal accuracy of a filter cannot fully represent its actual filtration capacity. The true reflection of filtration capacity is the beta value (filtration efficiency measured multiple times through experiments), which is the ratio of the number of particles at the inlet and outlet of the filter element. The higher the beta value, the better the filtering effect.
3. Avoid high precision:
Excessive filtration accuracy may lead to a decrease in the oil flow capacity of the filter element, making it easy to clog and shorten its service life. At the same time, high-precision filter cartridges have higher costs, so it is necessary to choose the "appropriate" precision instead of blindly pursuing high precision


II、 Flow characteristics and pressure drop
The flow characteristics of hydraulic filters directly affect the operating efficiency and stability of the system. When selecting, the following parameters should be considered:

1. Flow rate and pressure drop:
Conduct flow characteristic testing according to ISO 3968-91 standard and draw a flow pressure drop characteristic curve. Normally, under the rated fuel supply pressure, the total pressure drop (the sum of the pressure drop of the filter housing and the filter element) should be less than 0.2 MPa.
If the pressure drop is too large, it may lead to insufficient system flow and affect the efficiency of equipment operation.
2. Filter element area:
The larger the filter area, the lower the resistance and pressure drop when the oil passes through, and it can also extend the maintenance cycle of the filter. Therefore, when choosing a filter, priority should be given to models with larger filter element areas

III、 Filter strength and durability
Hydraulic filters require significant pressure and vibration during operation, therefore the strength and durability of the filter element are key factors:

1. Fracture impact resistance test:
Conduct a rupture impact test according to ISO 2941-83 standard to test the strength of the filter element during a sudden drop in pressure. The pressure difference when the filter element is damaged should be greater than the specified value to ensure that it is not easily broken under high-pressure conditions.
2. Flow fatigue characteristics:
Conduct 100000 cycles of fatigue testing according to ISO 3724-90 standard to ensure that the filter element will not fail due to fatigue during long-term use.
3. Adaptability to hydraulic oil:
Conduct pressure flow resistance experiments according to ISO 2943-83 standard to test the adaptability of the filter element to different hydraulic oils. Especially when using highly corrosive oil, a filter element with strong corrosion resistance should be selected

IV、 Installation location and function matching
The installation position of hydraulic filters varies, and their functions and precision requirements also differ. Therefore, when choosing a filter, the installation location should be considered:

1. Oil suction filter:
Installed at the suction port of the hydraulic pump to prevent impurities from the oil tank from entering the pump. The filter element is required to have high oil flow capacity and be not easily clogged, usually with a filtration accuracy of 10-20 μ m.
2. Pressure filter:
Installed on the outlet of the hydraulic pump or the system return oil pipeline, it is used to filter impurities in high-pressure oil. The filter element is required to have high strength and compressive strength, usually with a filtration accuracy of 5-10 μ m.
3. Return oil filter:
Installed on the system return oil pipeline, it is used to filter impurities in the return oil and prevent impurities from re entering the system. Usually, a filtration accuracy of 10-20 μ m is chosen

V、 Materials and sealing properties
The material selection of hydraulic filters directly affects their service life and filtration effect:

1. Filter material:
Common filter materials include fiberglass filter paper (BN), stainless steel woven mesh (W), wood pulp filter paper (P), etc. Different materials are suitable for different working environments and oil types. For example, stainless steel filter cartridges are suitable for high temperature and high pressure environments, while fiberglass filter papers are suitable for general hydraulic oil filtration.
2. Sealing material:
The sealing material is usually fluorine rubber ring or nitrile rubber to ensure that the filter does not leak under high pressure. When selecting, it is necessary to match according to the type of hydraulic oil and working temperature


VI、 Maintenance and replacement cycle
The maintenance and replacement cycle of hydraulic filters directly affects the operating efficiency and cost of the system:

1. Regular inspection:
Regularly check the differential pressure indicator of the filter. When the differential pressure reaches the set value, replace the filter element in a timely manner to avoid clogging the filter element and causing excessive system pressure.
2. Replacement cycle:
Develop a reasonable replacement cycle based on the operating environment and oil quality of the hydraulic system. It is generally recommended to replace the filter element every 6-12 months, which can be adjusted according to the system's usage.
3. Precautions for replacement:
When replacing the filter element, it is necessary to ensure the use of original or high-quality substitute products to avoid early wear or failure of the hydraulic system caused by inferior filter elements