Excavator construction for a long time, common motions such as walking and slewing often have failure problems, especially coupled with external factors such as long years and harsh construction environment, and such failure problems are unacceptable and must be repaired in time if encountered.
Failure phenomenon
A Kobelco SK250-8 Komatsu excavator, after 6500 hours of operation, caused the failure of the bucket cylinder and the left walking motor to work weakly, but the slewing motion and right walking were normal, and the remaining motions were slightly slow.
Failure analysis:
（L） Possible cause of failure of bucket cylinder work failure
① The pilot oil path of the control bucket is faulty.
② The control valve spool is stuck or badly worn.
③ The charge valve of the bucket circuit is stuck.
④The bucket cylinder, piston or oil seal is seriously damaged.
⑤ The main unloading valve is stuck.
⑥ The rear pump or its control system is faulty.
(2) Possible causes of the malfunction of the left walking motor
① The pilot oil circuit that controls left travel is faulty.
② The control valve spool is stuck or badly worn.
③The walking motor is faulty.
④The center slewing joint has serious oil leakage.
⑤ The main unloading valve is stuck.
⑥ The rear pump or its control system is faulty.
It is known from the principle of the hydraulic system of the machine that the bucket cylinder and the left travel motor are independently supplied by the rear pump. Therefore, the bucket cylinder and the left travel motor appear to be weak at the same time. The most likely reason is the main unloading valve Or after the pump and its control system. So the high-pressure fuel pipes of the front pump and the rear pump were exchanged with each other. When the machine was tested again, it was found that the bucket cylinder and the left travel motor had been working normally. On the contrary, the swing motor and the right travel motor were weak. This shows that the bucket cylinder and the left travel motor and their control systems are normal. The fault should be on the rear pump or its control system that supplies the bucket cylinder and the left travel motor separately.
3. Troubleshooting
In view of the fact that the end surface of the plunger cylinder is not damaged and the valve plate is seriously damaged, we adopt the maintenance program of grinding the plunger cylinder and updating the valve plate. That is, first use a surface grinder to finely grind the worn end surface of the plunger cylinder, then polish it with chromium oxide, and finally manually grind the plunger cylinder and the valve plate to ensure that the contact area is more than 95%.
Installed the repaired plunger cylinder and valve plate and tested the machine. The excavator returned to normal operation. It has been used for more than a year so far without any problems.
