In order to ensure the uninterrupted operation of the diesel engine, the fuel from the fuel tank must be carefully cleaned of impurities. If the fuel filter is poor, the precision couplings in the fuel injection pump and the fuel injector will quickly wear out or seize. The wear of precision couplers will cause uneven oil supply to each cylinder, increase fuel consumption, and decrease power. Two filters are generally installed in diesel engines. The is a coarse filter, which is installed before the transfer pump to filter out larger impurities. The second is a fine filter, which can filter out tiny impurities, which are installed before the fuel injection pump. The coarse filter generally uses a mesh filter. Fine filters are usually paper and felt filters and high-pressure slot filters.

1. Paper filter element
It is mainly composed of three parts: filter element, shell, and filter seat. The fuel is sent to the fuel filter by the fuel transfer pump, and the impurities in the fuel are removed through the paper filter element, and then enter the inner cavity of the oil filter cartridge, and then pass through the oil collecting cavity on the filter seat to the fuel injection pump. There is an oil return joint on the filter seat and a built-in overflow valve. When the fuel pressure in the fuel filter exceeds 0.08MPa, the excess fuel is returned to the fuel tank from the oil return joint. The connection of the low-pressure fuel pipeline should be in the direction of the arrow on the seat, and the connection should not be wrong. The sealing washer at the bottom of the filter element is installed in the spring seat, and the spring makes the sealing washer close to the bottom surface of the nut for sealing. The filter seat and the shell are connected by a tie rod and sealed with a rubber ring. The upper end of the filter seat is provided with a bleed screw, which can be loosened to remove the air in the fuel filter during use.

2. Felt filter
The felt filter is mainly composed of a filter, a filter element and a filter cover. The filter element is installed in the filter body, which is composed of metal mesh, silk cloth cover and felt filter. A pressure plate is welded on the upper end of the filter screen, a base is welded at the lower end, a nut is screwed on the base, and the felt filter sheet is tightly pressed on the upper-pressure plate through the lower tray. The filter cover is screwed with inlet and outlet pipe joints, as well as the cock of the bleed pipe, and a bleed nozzle is installed on the cock. The filter body and the filter cover are connected by a central rod, one end of which is screwed into the screw plug at the bottom of the filter body, and the other end is screwed with a nut to connect the two. The filter element is pressed against the filter cover by a spring mounted on the plug.

3. High-pressure slit filter
Before the fuel enters the fuel injector, many diesel engines are also equipped with a high-pressure slit filter for the latter filter. This kind of filter is made of a ground steel filter element rod, which is inserted into the sleeve with a small gap. There are 8-40 oil grooves milled on the filter element rod, half of which is for oil inlet and the other half is for oil out. Interlaced with each other, the fuel enters from one end, passes through the gap, and flows out from the other end, so that some tiny impurities remain in the tank to achieve the purpose of filtration. And can prolong the use time of the fuel injector, but when the fuel quality is good, this filter can work for 400-500 hours before cleaning.