Brief Analysis of the Seizure Failure of the Plunger Pair of a Diesel Engine High-Pressure Oil Pump (II)

1. Analysis of the Causes of the "Seizure" of the Plunger Pair

Improper use of the plunger pair will cause the plunger pair to "seize". The matching clearance between the plunger pairs is very small. During use, if the appropriate lubricating oil is not used according to the use requirements, some impurities will enter the gap between the sleeve and the plunger, causing the plunger pair to be blocked and seizure.

During the repair and assembly process of the high-pressure oil pump, the plunger pair is also prone to damage. The surface cleaning of the plunger pair should be carried out in clean diesel. Do not use sharp or sharp tools to scrape the surface of the plunger and sleeve. Once the matching surface is scratched, it will cause the plunger pair to be stuck and blocked. When pre-tightening the oil outlet valve nut, the pre-tightening force should not be too large. If the pre-tightening force is too large, the top of the plunger sleeve will be subjected to a large external load and deformed, which will also cause the plunger pair to be stuck. The plunger pair is a precision component and has strict requirements for production and processing.

Some plunger pair products with poor quality may not be produced strictly in accordance with the requirements of processing accuracy during production and processing, resulting in a relatively small gap between the plunger and the plunger sleeve, which causes the plunger pair to bite during the debugging stage of the high-pressure oil pump.

The normal operation of the plunger pair is inseparable from good lubrication conditions. The diesel leaked from the small gap between the plunger and the sleeve can lubricate the plunger pair. The plunger and the sleeve move relative to each other, and a certain oil pressure is generated by the fluid dynamics characteristics of diesel to balance the external load. A layer of lubricating oil film is established between the plunger and the sleeve. The existence of the lubricating oil film ensures that the plunger and the sleeve will not bite due to dry friction. Any factors that may damage the lubricating oil film will cause a bite failure.

Other faults in the diesel engine fuel system can also cause the plunger pair to bite.

During the operation of the diesel engine, improper adjustment of the fuel supply advance angle will cause the working temperature of the needle valve pair to be too high, and the needle valve pair will be stuck in the state of stopping fuel injection. The diesel in the high-pressure oil pump will not be able to enter the cylinder, and the pressure and temperature in the high-pressure oil rail will increase. Similarly, the pressure and temperature on the top of the reciprocating plunger will also increase, and the plunger will be deformed, resulting in the occurrence of plunger sticking failure.

Fourth, preventive measures for the "sticking" of the plunger pair

The sticking failure of the plunger pair is mostly caused by improper operation and use during use. As long as you can pay attention to it in daily work and carefully observe and record the working conditions of the high-pressure oil pump, you can greatly reduce the occurrence of the sticking phenomenon of the plunger pair of the diesel engine high-pressure oil pump.

Based on the above analysis of the causes of the sticking failure of the plunger pair, the following measures can be taken to avoid the occurrence of this failure.

① When disassembling and cleaning the high-pressure oil pump, clean the plunger pair in clean diesel, especially the protection of the plunger surface, and do not damage it. When tightening the nut of the oil outlet valve, do not use too much force to avoid deformation of the lower part of the plunger sleeve, which can effectively reduce the incidence of plunger pair seizure failure.

② When replacing the stock plunger pair, carefully clean the plunger pair and test whether it can reciprocate normally up and down to prevent the parts from deforming due to long storage time. Parts that do not meet product requirements are prohibited from use.

③ Before starting the diesel engine, check the high-pressure oil pump to ensure that the oil circuits of the high-pressure oil pump are connected normally and check whether the rack on the high-pressure oil pump moves normally. If the rack is found to be stuck, open the oil outlet valve and use a small pry bar to move the rack back and forth until the rack can be pushed by hand. After such adjustments, general jamming and seizure problems can be solved. When adjusting the rack, be careful not to use too much force, otherwise the rack will be damaged, and the rack cannot be knocked with a pry bar. ④After the diesel engine is started, let it run at no load for a period of time, and test various parameters of the system, such as pressure, temperature and other parameters. After the data shows normal, gradually load and run.

⑤The diesel engine high-pressure pump should be checked regularly, especially the lubricating oil. When the quality of the lubricating oil does not meet the requirements, the lubricating oil should be replaced in time. The deterioration of the lubricating oil is most likely to cause the high-pressure oil pump to bite.

In addition, other components of the fuel system should be cleaned in time, and the fuel filter should be cleaned and replaced frequently. The fuel filter plays an important role in preventing impurities from entering the high-pressure oil pump.

During normal use, the diesel engine may add fuel from different origins. Different fuels have slightly different viscosities, and their recommended inlet temperatures are also different. Improper oil viscosity entering the high-pressure oil pump will cause damage to the plunger, and metal particles produced by wear will also cause the plunger to bite.

Therefore, before the fuel enters the high-pressure oil pump, the fuel filter should be carefully filtered.

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