During the long-term construction of excavator, common actions such as walking and slewing often have faults. In particular, external factors such as long years and poor construction environment are more likely to cause excavator failure. Moreover, this kind of fault can not be delayed, and it must be repaired in time after discovery. Taking the medium crawler excavator with a working time of nearly 10000 hours as an example, the bucket cylinder and left travel motor failed to work, but the slewing action and right travel were normal, and the rest were slightly slow. This article will explain how to deal with this fault for reference only.
1. Fault analysis
Firstly, the possible causes of bucket cylinder weakness are analyzed as follows:
① The pilot oil circuit for controlling the bucket is blocked. ② The control valve spool is stuck or severely worn so that it cannot work normally. ③ The makeup valve for the bucket circuit is stuck. ④ The bucket cylinder, piston or oil seal are severely damaged. ⑤ The main unloading valve is stuck. ⑥ The rear pump or its control system is faulty.
Then, through comprehensive analysis, the possible causes of the failure of the left travel motor are as follows:
① The pilot oil circuit that controls the left travel is faulty. ② The control valve spool is stuck or severely worn. ③ The travel motor is faulty. ④ The oil leakage of the center swivel joint is serious. ⑤ The main unloading valve is stuck. ⑥ The rear pump or its control system is faulty.
2. Maintenance steps
Compare and analyze the fault causes, combined with the specific situation of the excavator. The bucket cylinder and left travel motor of the excavator are separately supplied by the rear pump. The bucket cylinder and left travel motor of the excavator are unable to work at the same time. It can be judged that the cause is most likely to be the main unloading valve or rear pump and its control system.
Therefore, the high-pressure oil pipes of the front pump and the rear pump were exchanged with each other. During the test, it was found that the bucket cylinder and the left travel motor had worked normally. On the contrary, the swing motor and the right travel motor are unable to work.
This shows that the bucket cylinder, left travel motor and their control system are normal. The fault should be on the rear pump or its control system that supplies oil to the bucket cylinder and the left travel motor separately. A thorough measurement check is required at this time.
① Since the front pump works normally, it is proved that the control pilot pump and TVC valve common to the front pump and rear pump work normally.
② Since there is no measuring point for the outlet pressure of CO valve, an oil pressure gauge with a measuring range of 6Mpa is installed at the outlet of NC valve. The measured oil pressure is pi. When the co valve adjusting bolt was tightened for 2-4 turns, it was found that the pI value increased. When the adjusting bolt is adjusted back to the original position, PI decreases to the original value. The test results conform to the working characteristics of CO valve, indicating that CO valve works normally.
③ When the adjusting bolt of NC valve was tightened for 2-4 turns, it was found that the pI value increased. When the adjusting bolt is adjusted back to the original position, PI decreases to the original value. The test results conform to the working characteristics of NC valve, indicating that NC valve works normally.
④ After disassembling and inspecting the servo mechanism, it is found that the return spring is not broken and has good elasticity, the connecting rod mechanism does not fall off, and the valve core is not stuck and worn, which indicates that the servo mechanism works normally.
According to the above inspection results, the control system of the rear pump works normally, and the weak operation of the bucket and left travel motor can only be caused by the failure of the rear pump.
After removing the hydraulic pump assembly, it is found that the hydraulic components of the front pump are intact and the rear pump is seriously damaged. There are several deep grooves at the oil sealing belt of the port plate, the end face of the plunger cylinder is slightly strained, and the other hydraulic components are not obviously worn.
Obviously, the reason why the rear pump can not work normally is that the contact surface between the plunger cylinder and the port plate is seriously worn, resulting in serious leakage of hydraulic oil, so that the oil pressure can not be established, resulting in weak operation of the bucket cylinder and the left travel motor.
3. Troubleshooting
Because the piston cylinder end face of the fault excavator is not damaged much, and the valve plate is seriously damaged, considering the maintenance time and cost, the engineer adopts grinding the piston cylinder and updating the valve plate to deal with the fault.
First, the worn end face of the plunger cylinder is finely ground with a plane grinder, then polished with chromium oxide, and finally the plunger cylinder and port plate are manually ground to ensure that the contact area is more than 95%.
After reinstallation, the test machine is normal and the fault does not appear again.
