The function of three filters 
1. The air filter is located in the intake system of the engine. It is an assembly composed of one or several filter components for clean air. Its main function is to filter out harmful impurities in the air that will enter the cylinder to reduce the early wear of the cylinder, piston, piston ring, valve and valve seat. There are two types of air filters, namely dry and wet. At present, most engines use a dry air filter with a paper filter element that is small in quality, low in cost, easy to replace, and high in filtration efficiency.
2. The oil filter is located in the engine lubrication system. Its function is to filter out harmful impurities in the oil from the oil pan, and supply the crankshaft, connecting rod, camshaft, supercharger, piston ring and other motion pairs with clean oil for lubrication, cooling and cleaning. In order to extend the life of these parts, oil filters are divided into replaceable, spin-on, and centrifugal types according to their structure. At present, most engines use spin-on oil filters. This type of filter is a disposable filter that cannot be removed and washed. The oil filter must be replaced when the lubricating oil is changed.
3. Fuel filters include diesel filters and gasoline filters. Its function is to filter out harmful particles and water in the engine fuel gas system to protect the oil pump nozzle, cylinder liner, piston ring, etc., reduce wear and avoid clogging. At present, most engines are equipped with disposable non-removable and washable paper filter elements.
4. The filter accuracy of the filter: indicates the size value that can filter out the smallest particles of dust. There are 2mm, 5mm, 25mm, etc., and the standard filtration accuracy is 5mm. Imported diesel engines require air filtration accuracy of 5μm, and domestic diesel engines also require less than 20μm. The filtration accuracy of high-efficiency filter paper is 2μm, and that of ordinary imported filter paper is 30μm. The domestic filter paper is only 80μm. The level of filtration accuracy is directly related to the size of the vent of the filter element. The larger the pore size, the lower the filtration accuracy, but the resistance loss is also lower.