When diesel oil is produced every effort is made to make it clean and to save it from getting mixed with any impurities. Yet in the process of loading-unloading, transportation and storage of diesel oil some impurities do come in. As we know, diesel oil is already quite thick and when it gets mixed with other elements, it is not fit for use in the fuel system. Because it would damage parts, like fuel injection and fuel injector. The passage in these parts are very narrow. If impure oil mixed with dust or other things is used, it would block their narrow passages. Therefore, necessary arrangements are made to clean the oil before it is used in these parts. For this purpose diesel filter is used.