The typical failure mode of high-pressure fuel pipe is oil leakage. Its main manifestation is the lack of tight head seal, pipe crack, pipe wear, perforation and pipe rust.
The head is not tightly sealed
Fault analysis
The lack of tightness of the head seal refers to the oil leakage caused by the poor sealing effect of the high pressure oil pipe and the fuel injector or the fuel injection pump interface. The main reasons for this phenomenon are the following four aspects:
(1) The tightening torque of the lock nut on the high pressure oil pipe is too small. The tightening torque of the lock nut on the high pressure oil pipe is closely related to the diameter of the oil pipe, the material and the maximum pressure it bears. If the tightening torque is too small, the lock nut will loosen under the high frequency vibration of the diesel engine, and the joint may not be pressed to cause oil leakage.
(2) There is a defect on the sealing strip of the high pressure tubing head. If there is a defect on the sealing surface of the high pressure tubing head, it will directly lead to oil leakage.
(3) Repeated assembly of the high-pressure oil pipe? The sealing of the high-pressure oil pipe is caused by the deformation of the head of the oil pipe under the action of the pressing force to form a sealing band to achieve the sealing effect. If the number of repeated assembly is too many, the position of the sealing tape is not exactly the same as that of the first assembly, and since the front end of the head has no plasticity, the secondary micro-deformation cannot be formed, and a new sealing tape cannot be formed, which does not achieve the original sealing effect.
(4) High-pressure tubing assembly error? The high-pressure tubing assembly error causes the head seal band to form an ellipse, which cannot be effectively sealed. The manufacturing error of the high-pressure tubing tube shape, the assembly error of the high-pressure tubing head and the injector interface (see Figure 1), and the non-free alignment of the high-pressure tubing with the pipe clamp assembly are all causes high-pressure tubing assembly errors. The direct cause of existence.
Figure 1 Interface error between tubing head and injector
2. Inspection and elimination of poor head seal failure
The head seal is not strict. It is generally found in the engine test phase of the engine. When the engine is started, it is found that there is fuel seeping from the inside or the lower end of the high pressure tubing lock nut along the threaded portion, as shown in Fig. 2.
Figure 2 The tightening torque is too small, causing oil leakage
1) Check if the lock nut is kept in the factory state. If the lock nut is loose, use a torque wrench to tighten according to the required tightening torque.
2) Remove the high-pressure oil pipe (including loosening the lock nut and fixing the pipe clamp), check the head of the oil pipe for defects and irregular contact marks, and whether there is any debris or damage at the interface between the high-pressure fuel pipe and the injector or the fuel injection pump. If the above situation is found, the interface part needs to be cleaned, the new oil pipe is replaced, the fixed pipe clamp is installed, and the oil pipe is pre-tightened and tightened according to the required torque value.
3) If the fault occurs after the engine has been running for a period of time, it is generally not a problem of the high-pressure fuel pipe itself, mostly due to the loosening or disassembly of the high-pressure oil pipe during engine maintenance, resulting in repeated assembly of the high-pressure fuel pipe. This happens and a new tubing needs to be replaced.
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