An example is given to explain the causes of hydraulic oil blockage and its inspection and maintenance. A Komatsu 420 excavator can't be put into gear after it is stopped. It is preliminarily judged that there may be a problem with the power shift transmission. The reason is that this excavator failed to engage gear six months ago. Later, it was found that the fault was caused by a loose screw plug on the oil duct in the power shift transmission.
After analyzing the fault, it is considered that the transmission leakage is impossible; The transmission control valve group was disassembled and inspected, and everything was normal. Later, it was found in the data that "there is an exhaust hole on the hydraulic oil filter of the working device", and it was concluded that "gas" was causing trouble, that is, there was gas in the system, resulting in air resistance. The more the system was disassembled, the more air was mixed into the system. The next morning, after the machine started, unscrew the screw plug to exhaust. It was really "gas" that was fierce. After exhausting the gas, shift to gear again, all gears can be smoothly shifted to L, and then start after shutdown. Everything is normal. In order to prevent similar faults from occurring again, remember to exhaust after changing the oil, changing the filter element or replenishing the oil when the oil level is insufficient.
The diagnosis of mechanical failure caused by hydraulic oil blockage of Komatsu excavator. The blockage of hydraulic oil in the hydraulic system can be roughly divided into four categories: air resistance, solid material resistance, oil deterioration resistance, oil filter element resistance. Understanding its internal and external characteristics can prevent misdiagnosis.
The external characteristics of air resistance air resistance fault are: air resistance is generated before the power unit pump, there is no action, the action is slow, there may be abnormal sound in the pump or the pump is hot.
Air resistance occurs before the working device and after the pump, and the action is slow, unstable and jittery. The main reasons for the formation of air resistance are: insufficient oil in the system, no exhaust after maintenance or oil replenishment, and oil deterioration
Air lock fault is easy to be misdiagnosed as leakage fault and component card issuing fault. The air lock fault is easy to be eliminated, but it is often misdiagnosed and the parts that should not be removed and replaced are often removed, resulting in labor, material and delay in the construction period.
The external characteristics of filter element blockage are: slow action, unstable action, and unable to meet the operation requirements after exceeding a certain load. In fault diagnosis, it is easy to be misdiagnosed as internal leakage, insufficient pump output (pressure drop), and weak system.
From the examples and analysis of the above four cases, it can be seen that the fault formed by the obstruction of oil in the hydraulic system is not only hidden but also easy to be misdiagnosed, but it is relatively simple to deal with, which often does not take long.
But why did it take a lot of trouble and detours to diagnose each fault?
First, during fault diagnosis, instruments and meters are not used as much as possible to detect the basic parameters (pressure and flow) of the hydraulic system;
Second, the failure was not handled according to scientific procedures, that is, the diagnosis was not carried out according to the principles of "from simple to complex" and "from outside to inside", but from the beginning to think about the complex and start from inside, resulting in detours, which was both time-consuming and labor-consuming.
The procedure for diagnosing the fault of the hydraulic system is: check whether there is external leakage → check the oil level of the oil tank → check the oil quality → check whether there is air in the system → check the filter element → measure the pressure and flow of the system → fault analysis.
