This kind of filter is used in the hydraulic system for fine filtration. The filter can filter metal impurity, rubber impurity or other contamination, and keep the tank clean. This filter can be installed on the top of the cover directly or installed with pipe. It has indicator and by-pass valve. When the dirt accumulate in the filter element or the temperature of the system is too low, and the oil inlet pressure reaches 0.35Mpa, the indicator will give signals showing that the filter element should be cleaned, changed or rise the temperature. If no service is done and as the pressure reaches to 0.4mpa,the by-pass valve will open. The filter element is made of glass fiber;so it has high filtration accuracy, low initial pressure loss, high dirt-holding capacity and so on. Filter radio 0 3, 5, 10, 20>200, filterefficiency n>99.5%, and fit the ISO standard.