The diesel engine fuel supply system consists of fuel tank, diesel filter, fuel delivery pump, fuel injection pump, governor, fuel injector and fuel pipe. When the fuel system is working, under the suction of the fuel transfer pump, the diesel oil in the fuel tank is sucked into the fuel transfer pump through the sediment cup and fuel pipe, and is pressed to the filter. The filtered clean diesel oil enters the fuel injection pump to boost pressure, and then is sent to the fuel injector through the high-pressure fuel pipe. The fuel injector sprays the diesel oil into the combustion chamber after atomization. The diesel leaked from the fuel injector flows back to the fuel tank through the fuel return pipe. The failure of any component of the fuel system will affect the normal operation of the diesel engine. This paper focuses on how to maintain these components to ensure the normal operation of the diesel engine.

1 Fuel tank and sediment bowl
The fuel tank is a place to store diesel oil. If it is used for a long time, impurities will settle at the bottom. It is better to clean it once a year. When cleaning, remove the oil tank and clean the bottom carefully. The fuel tank is fixed on the bracket by the fuel tank strap (or bolt). When disassembling, first remove the instrument panel and hood, and then loosen the fuel tank strap nut (or bolt fixing the fuel tank) to remove the fuel tank. The fuel tank is closed by the fuel tank cover, which has a small hole with a diameter of 2 mm to communicate with the atmosphere, so as to supplement air to the fuel tank after fuel consumption, and prevent the air pressure in the fuel tank from being lower than the atmospheric pressure, and the fuel cannot flow out. Therefore, the fuel tank cap must not be replaced by other fully sealed items.
The settling cup is used to deposit water and impurities in the fuel during the flow process. Therefore, when the water and impurities are deposited to a certain extent, the oil cup should be removed to clean the oil cup and filter screen. When disassembling, just loosen the nut fixing the oil cup. When cleaning, pay attention to the integrity of the rubber gasket and filter screen of the oil inlet pipe.

2 Diesel filter
The diesel filter is a component for further filtering the diesel oil. It can remove impurities in the diesel oil, ensure the normal operation of the diesel engine, and reduce the wear of precision parts in the fuel injection pump and injector. The diesel filter is mainly composed of filter base, cover, filter element, sealing ring, etc. The inner part of the filter element is a perforated thin steel sheet central tube, the outer part is covered with a folding filter paper, and the two ends are closed with a thin steel sheet end cover with a hole in the center, which is sleeved on the central bolt of the housing. The bolt passes through the hole on the filter seat and is compressed with the compression nut to make the filter element tightly pressed between the bowl ring and the spring seat under the action of the spring force. The upper and lower ends of the filter element and the rod at the lower end of the bolt are sealed with sealing rings.
In order to prevent the filter element from being blocked by too many impurities and affecting the oil supply, it is generally necessary to replace the filter element when 500 L diesel fuel is consumed (it is better that the filter element is not reused to prevent impurities from entering the inner cavity of the filter element during cleaning). When replacing the filter element, pay attention to whether the sealing washer and sealing ring are sealed. Before installation, oil must be coated on the gasket, and then screw on the filter element. After the gasket contacts the filter base, tighten it for 3/4 turns. After that, diesel can be supplied. When supplying diesel, loosen the vent plug to discharge the internal gas. Restart the engine and check the filter for oil leakage.
The diesel filter is not only small in size, but also easy to install and troubleshoot. When the engine is difficult to start, first check whether there is gas in the filter and pipeline. If there is gas, use the hand pump to pump oil to drain the gas. Secondly, the filter may intercept too many impurities, which has blocked the filter screen, and the filter element needs to be replaced. The maintenance of the filter should not be sloppy.

3 Fuel transfer pump
The function of the fuel transfer pump is to suck out the diesel oil in the fuel tank and generate a certain pressure to overcome the resistance of the low-pressure fuel circuit and diesel filter and ensure continuous delivery of sufficient diesel oil to the fuel injection pump. There are many types of oil transfer pumps, such as gear type, diaphragm type and plunger type. Plunger type fuel transfer pump is commonly used in agricultural diesel engines. The eccentric wheel of the fuel transfer pump is integrated with the camshaft of the fuel injection pump. When the engine is working, under the action of eccentric wheel and plunger spring, the plunger will reciprocate in its sleeve and separate the inner cavity of the pump body into front and rear cavities. When the protruding part of the eccentric wheel pushes the push rod, the plunger moves forward against the tension of the plunger spring, so that the volume of the rear chamber increases while the volume of the front chamber decreases, and the pressure increases, forcing the oil inlet valve to close and the oil outlet valve to open. Then the diesel oil in the front chamber is sent to the rear chamber to prepare for the next oil pressure. When the eccentric cam rotates, the plunger moves back rapidly under the action of the spring, which increases the oil pressure in the rear chamber, closes the outlet valve, and then the diesel oil in the rear chamber is pressed to the injection pump. At the same time, the volume of the front chamber increases to generate suction, open the oil inlet valve and inhale diesel. As the eccentric wheel continues to rotate, the plunger continuously reciprocates, so the fuel delivery pump continuously delivers oil to the fuel injection pump. The pump oil volume of the fuel transfer pump has an automatic adjustment function. When the diesel engine works with light load and consumes less fuel, there will be more diesel oil in the rear chamber and the oil pressure will rise. At this time, the plunger spring cannot push the plunger to the maximum position, and the plunger stroke decreases, thus automatically reducing the oil output. On the contrary, if the load increases, the oil consumption increases, the rear chamber oil pressure decreases relatively, and the plunger stroke increases, so the oil delivery also increases.
When using, pay attention to the small filter screen for filtering diesel oil installed in the oil inlet pipe joint of the oil transfer pump, and clean it frequently to prevent it from being blocked. Check whether the fastening bolts of the oil pipe connector and the pump body are loose. Regularly clean the inlet and outlet valves and valve seats of the oil transfer pump to make the contact between the valve and the seat smooth and well sealed. If necessary, grind them or replace them with new ones.

4Fuel injection pump and injector
The function of the fuel injection pump is to inject high-pressure diesel into the combustion chamber regularly and quantitatively according to the load of the diesel engine. Regularly check and adjust the oil supply advance angle and the oil supply interval angle of each cylinder; Regularly check the sealing condition of the oil outlet valve coupling to roughly judge the wear of the plunger and the working condition of the oil pump; There is a skeleton oil seal between the fuel injection pump and the governor, and oil shall be added separately. If the oil level rises due to oil dilution, it indicates that the fuel injection pump and fuel transfer pump have serious oil leakage, which should be eliminated in time; The fuel injection pump shall not be disassembled and adjusted at will, especially the parts with sealing marks. When it is determined that the fuel injection pump needs to be disassembled and repaired, it shall be cleaned before proceeding.
The function of the fuel injector is to spray the high-pressure diesel delivered by the fuel injection pump into the diesel engine combustion chamber through the nozzle at a certain pressure to form a uniform mixture with compressed air for combustion. When the engine has been operating for 500~1000 h accumulatively, check the injection pressure and spray quality of the injector, remove and clean the needle valve coupling if necessary, and readjust the injection pressure. If it is unqualified, it shall be repaired or replaced.