The function of the hydraulic filter is to filter various impurities in the hydraulic system. Its sources are mainly mechanical impurities remaining in the hydraulic system after cleaning, such as rust, casting sand, welding slag, iron filings, paint, paint and cotton yarn scraps, etc., and impurities that enter the hydraulic system from outside, such as through the fuel filler and anti-corrosion Dust entering the dust ring; impurities generated during the working process, such as the fragments formed by the hydraulic pressure of the seal, the metal powder generated by the relative wear of the movement, the gum, asphaltene, and carbon residue generated by the oil due to oxidative deterioration.

There are many ways to collect contaminants in fluids. An appliance made of filter materials to capture contaminants is called a filter. Magnetic materials are called magnetic filters. In addition, there are electrostatic filters, separate filters, etc. In the hydraulic system, all the pollutant particles in the collected fluid are called hydraulic filters. At present, the most widely used hydraulic filters are in addition to the use of porous materials or winding crevices to intercept pollutants, as well as magnetic filters and electrostatic filters used in hydraulic systems.

After the above-mentioned impurities are mixed into the hydraulic oil, with the circulation of the hydraulic oil, it will cause damage everywhere, seriously affecting the normal operation of the hydraulic system, such as making the small gap (in μm) between the relatively moving parts in the hydraulic component and the joint Flow small holes and gaps are stuck or blocked; damage the oil film between relative moving parts, scratch the surface of the gap, increase internal leakage, reduce efficiency, increase heat generation, aggravate the chemical action of the oil, and make the oil deteriorate. According to production statistics, more than 75% of the failures in the hydraulic system are caused by impurities mixed in the hydraulic oil. Therefore, maintaining the cleanliness of the oil and preventing the contamination of the oil are very important for the hydraulic system.

Generally, hydraulic filters are mainly composed of filter element (or filter screen) and shell (or skeleton). Numerous tiny gaps or pores on the filter element constitute the flow area of ​​the oil. Therefore, when the size of the impurities mixed in the oil is larger than these tiny gaps or pores, they are blocked and filtered out of the oil. Because different hydraulic systems have different requirements, it is impossible to completely filter the impurities mixed into the oil, and sometimes it is not necessary to be exacting.