Created on:2021-09-16 10:26

Construction machinery_ Excavator hydraulic failure_ Control valve failure

Construction machinery_ Excavator hydraulic failure_ Control valve failure

Construction machinery is one of the main fields of hydraulic technology application. Most construction machinery are mobile field work devices, including many special hydraulic parts. The system is often complex, and it is more difficult to test, diagnose and monitor.

The control action of one group of control valves of a Kato HD excavator is abnormal, and the subsystems controlled by the other group of control valves are all normal. Therefore, there is no possibility of failure in the common part of the two groups of control valves. According to the analysis of the phenomenon that several actions are abnormal at the same time, the fault point should be in the common part of these actions. Combined with the specific structure of the hydraulic oil circuit of the hydraulic excavator, it can be seen that the fault causes are as follows.

(1) Subsystem main overflow valve failure

The main relief valves on excavators are. The reasons why the main relief valve can not work normally are often abnormal pressure regulation, wear of cone surface of cone valve, blockage of damping hole of pilot valve core, and of course, spring fracture. They will cause insufficient pressure of the whole subsystem, resulting in slow and weak system action, or even failure to act. How to judge whether the main relief valve fails? Transposition contrast method is a very practical method in field diagnosis. After the main overflow valve in the fault subsystem is exchanged with the main overflow valve in the normal subsystem for commissioning, if the fault is moved to another subsystem, it can be concluded that the main overflow valve of the original fault system is faulty. If the fault is still in the atomic system after the exchange, the main overflow valve works normally and the cause of the fault should be found separately.

(2) Subsystem hydraulic pump failure

Damage and improper assembly will cause the loss of several corresponding actions of the machine, and the wear of the hydraulic pump will make this group of actions slow and weak. No matter what the fault form is, as long as the approximate fault point is determined according to the above analysis method, further inspection and disassembly can finally find the problem. Similarly, for the suspected hydraulic pump, the transposition comparison method can also be used to replace the pump outlet pipeline, so as to change the working pump of the subsystem and observe whether the fault of the subsystem has changed. If it changes, it is the hydraulic pump fault, otherwise the fault is not in the hydraulic pump.

When a Kato HD800 - VII excavator rotates, the whole machine vibrates. When the boom and stick of the same group move, it also feels a little uncomfortable, but it is not very obvious. The track of the same group is slower than the track on the other side. After removing the main relief valve, changing the two hydraulic pump out of the tubing, the failure of the two subsystems also changes, and the fault is in the hydraulic pump. After disassembling the hydraulic pump, it was found that there were several metal spalling gaps on the arc surface of the hydraulic pump body in contact with the oil distribution plate. It was these gaps that caused the pressure pulsation phenomenon, resulting in the above faults, which disappeared after maintenance.

(3) Subsystem hydraulic pump regulating mechanism failure

When the machine is working, the working condition of the hydraulic pump cannot change with the working condition of the working device.

For a Kato hd770 II excavator, everything was normal when it was cold. After working for a period of time and the temperature increased, it was found that the actions of the same rotation, stick and one track (the same hydraulic pump as the rotation) slowed down at the same time, and everything was normal after shutdown and cooling. Later, the flow regulating plunger of the pump was checked and it was found that the plunger hole could not move freely. In this way, when the working device needed the hydraulic pump to increase the flow, the flow could not increase because the regulating plunger was stuck, and the action was slow. After disassembling the pump regulating mechanism, it was found that the regulating plunger was worn. After polishing and cleaning, it was installed back, and the fault disappeared.

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