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The fuel system entering the air is a common fault of the diesel engine. It causes the diesel engine to be unsmooth or interrupted, which makes the diesel engine difficult to start and the operation is not stable. In severe cases, the diesel engine will automatically shut down and fail to work. First, the way air into the fuel system (1) the aging of the oil pipeline, the joints are not sealed. For example, a plastic tube or a rubber low-pressure hose deteriorates or even breaks, and it is not tight with the coupling nipple, and air is sucked in from it. Another example is if the return pipe joint gasket is uneven, rough and tightly sealed. With the reciprocating movement of the fuel injector pressure regulating spring and the ejector pin, when the internal pressure of the injector housing has a negative pressure, the outside air is removed from the return pipe joint gasket. It is inhaled and then returned to the diesel filter via the return line. (2) The fuel pump fails. For example, the tappet of the oil pump is stuck at the top dead center position of the cam. At this time, the oil pump can not act as a pump oil, and the diesel fuel flows by gravity. When the diesel engine is working, the fuel injection pump continuously sends the diesel fuel pressure to the injector, but the diesel fuel is insufficiently supplied, so a negative pressure is formed in the fuel injection pump, a suction force is generated on the diesel filter, and the oil is sucked from the oil return pipe with less resistance. When the position of the return pipe to the tank is higher than the oil level, air enters the diesel filter through the return line. (3) The pump pump tappet is worn, and the plunger seal ring and the cylinder oil seal are worn or corroded. At this time, air is sucked into the fuel pump from the tappet and enters the fuel injection pump along with the diesel fuel, resulting in a weak engine operation. (4) The injection pump plunger set screw is damaged or missing. Because the positioning groove of the plunger sleeve communicates with the oil return hole, when the plunger descends, the space in the upper part of the plunger increases, generating suction, and the outside air is sucked into the plunger sleeve through the slot of the positioning screw copper pad; As the plug rises, the air is pressed into the tight seat of the oil valve. (5) The injection pump return valve fails. For example, the oil return valve and the valve seat are seriously worn, the oil return valve is thrown up by debris, the installation position of the parts is reversed, or the ordinary oil pipe joint bolts are installed at the oil return port of the fuel injection pump, etc., and the oil pressure of the upper body of the injection pump is reduced. When the plunger pump is in the suction stroke, the air is sucked from the bleeder screw, enters the diesel fine filter through the pressure limiting valve, and merges with the diesel from the fuel tank to enter the oil pump; when the oil pump pumps oil, these The air enters the upper body of the injection pump from the fuel pump with the diesel fuel. Therefore, there are always exhausted air in the oil circuit, which causes the diesel engine to automatically stop. (6) The fuel pump outlet valve gasket is damaged (eg, broken), and the injector needle valve seal is not tight. The high-pressure gas in the cylinder will enter the low-pressure oil circuit through the injector, the high pressure oil pipe, and cracks on the copper mat, causing the diesel engine to extinguish. (7) The fuel injector is in poor condition. Because the head of the fuel injector is facing the combustion chamber, when the pressure regulating spring is insufficient or loosely adjusted, the needle valve and the valve body are worn and strained, especially when the needle valve is bitten in the open position, the cylinder High-pressure gas enters the injection pump from the injector, high-pressure tubing, and discharge valve. At this time, if the outlet valve is tightly sealed, high-pressure gas flows from the injector through the return line to the filter, and then slowly enters the injection pump. (8) Other possible ways. For example, the deformation of the outer shell of the diesel filter causes airtight sealing of the filter seat gasket and inhalation of air; the plugging of the filter plug of the diesel filter and the plugging of the vent hole of the fuel tank cover cause the oil supply to be inadvertently or even interrupted to inhale air. Second, the basic method of excluding the air circuit In general, the appearance of air in the oil circuit should first look for from the negative pressure section. The so-called negative pressure section refers to the oil path from the fuel tank to the oil pump inlet. This is because when the diesel engine is in operation, the fuel injection pump and the oil pump generate suction on the oil passage, and the pressure of this section of the oil passage is lower than the atmospheric pressure. In the negative pressure section, there is less oil leakage and more leakage. In order to discriminate whether air enters from the low pressure oil line or the high pressure oil line, you can loosen the bleeder screws on the top of the fuel injection pump immediately after the diesel engine is automatically extinguished. If gas is ejected automatically and the oil valve is tightly seated, it can be discharged. Exhausting the air indicates that the air is coming from the high-pressure oil line. It is very likely that the high-pressure gas is flowing back in the cylinder. At this time, the fuel injector or fuel injection pump should be overhauled. If no gas is blown out, only the hand pump can pump the oil, indicating that the air comes from the low pressure oil line. At this time, we should follow the principles of easy-to-follow, from the table to the inside, first check whether the ventilation hole of the fuel tank is blocked, and if necessary, clear it. Second, check the fuel tank storage, if the tank is empty, or the amount of oil is less than 1/6 of the capacity (as the diesel in the tank oscillates back and forth, the air will be sucked into the circuit once the oil outlet exposes the oil level). Fuel should be replenished promptly. Author: Heilongjiang Province 555 Farms Heilongjiang Institute of Architecture and Technology