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    What causes the exhausting air in the diesel oil circuit

    2021-02-22 | Pageviews: CHANGZHOU FOAN M AND E CORPORATION
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    If the air in the oil circuit is not exhausted, the exhaust pipe will change sound after the diesel engine has been running for a period of time, and white smoke will be emitted intermittently, the speed will drop, the work will be weak, and the engine will shut down when it is serious. The air in the oil circuit mainly comes from two aspects.

    1. Low pressure oil circuit sucks in air

    The reasons for the low pressure oil circuit to inhale air are as follows: first, the diesel oil is used up safely, the air hole of the fuel tank cover is blocked, the vacuum is formed in the tank, and the air is inhaled. Second, the sealing gasket of the hand pump and the pump body on the oil pump is broken or uneven, and the air rushes in. Third, the piston or cup of the hand pump is seriously worn, and the air enters the low-pressure oil circuit from the upper part of the hand pump through the gap between the piston or cup and the pump barrel. Fourth, the sealing gasket of the oil pipe joint in the low-pressure pipeline is uneven, damaged or the hollow screw is not tightened, and the air escapes. Fifthly, the low-pressure oil pipe of the fuel supply system was broken, leading to air channeling. The inspection method is to remove the low-pressure oil pipe, clean the joint, plug one end of the oil pipe with fingers, and pump air with a nozzle at the other end. If the tubing is not broken, a vacuum has basically formed in the tubing and the tip of the tongue is sucked; if the tip of the tongue is always not sucked, the tubing is broken. Sixth, the mechanical impurities make the return valve not closed tightly, and the diesel oil is discharged through the return valve, resulting in the over generation of pressure in the oil passage of the injection pump, the reduction of injection volume, and the inexhaustible air in the oil passage.

    2. The high pressure gas flows back from the fuel injection nozzle into the fuel supply circuit

    At this time, if the needle valve of the injector is stuck in the open position, the sealing of the outlet valve of the same cylinder is not tight, the guide part of the needle valve and the needle valve body is seriously worn, the high-pressure spring in the injector is broken, and the matching hole of the injector tappet and the needle valve is worn, the high-pressure air will flow back into the fuel supply circuit after each working cycle of the cylinder.

    The reason of high pressure air flowing into the fuel supply system is that the injector injects diesel into the cylinder at a certain angle before the top dead center of the piston after the compression stroke of the diesel engine. At the moment when the nozzle is opened, the gas in the cylinder and the oil circuit form a channel (the gas in the channel has a pressure difference varying with time). When the quality of the injector is poor, the high-pressure gas in the cylinder will flow from the nozzle hole through the sealing cone, through the clearance at the needle valve of the nozzle couple, the tappet hole in the injector body, and the return pipe of the injector back into the diesel filter until it is in the oil circuit, Over time, the diesel supply will be blocked.

    For the diesel engine whose fuel return pipe is not directly connected with the diesel filter (take 4115 diesel top as an example), the high pressure air may enter into the fuel injection pump cover from the injection hole through the sealing cone, through the oil inlet hole of the injector body, the high pressure oil pipe, the clearance between the oil outlet valve and the seat, and return to the fuel delivery pump through the oil return valve hole on the pump cover.

    The method to check whether the injector leaks is as follows:

    Remove the fuel injector main return pipe from the diesel filter to connect it with the atmosphere, then plug the return pipe hole of the diesel filter to exhaust the air in the oil circuit, and then start the diesel engine again. If there is no more gas in the injection pump, it can be concluded that the injector is leaking. At this time, all the return pipe joints of each injector should be removed to further determine which injector is leaking; if there is air at the return hole of an injector, it can be determined that the injector is leaking.
    For the diesel engine whose fuel injector return pipe is not connected with the diesel filter, the air can be removed first, and then the high-pressure fuel pipe joints on the fuel injection pump can be loosened one by one when the diesel engine is running. If a certain joint is loosened and then the gas rises continuously, it means that the cylinder fuel injector is leaking.

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