The structure of the diesel filter is roughly the same as that of the oil filter, and there are two types: replaceable and spin-on. However, its working pressure and oil temperature resistance requirements are much lower than those of oil filters, while its filtration efficiency requirements are much higher than those of oil filters. The filter element of diesel filter mostly uses filter paper, and some also use felt or polymer material. In addition to filtering the mechanical impurities in diesel oil, the diesel filter also has an important function of filtering water. The existence of water is extremely harmful to the diesel engine oil supply system. Rust, wear, damage to the cylinder piston ring and even cylinder pull phenomenon can worsen the combustion process of diesel. The diesel filtration system separates the water to achieve the effect of filtering the water through the fluid flow direction control technology according to the difference of the liquid density.