The filter is used for fine filtration of the return oil of the hydraulic system to filter out metal particles produced by the wear of components in the hydraulic system and rubber impurities of seals and other pollutants,so as to keep the oil flowing back to the oil tank clean.The filter is installed on the top of the oil tank,the cylinder is immersed in the oil tank,and set up by-pass valve,diffuser,filter element pollution blocking transmitter and other devices.It has the characteristics of compact structure,convenient installation,large oil passing capacity,small pressure loss and convenient replacement of filter element and so on.