An excavator has been operating for more than 15,000 hours. It is currently malfunctioning and cannot turn left or right at all. Except for rotation, other actions are normal, which means that the working pump should be normal. We troubleshoot problems in order from easiest to hardest. First, use a pressure gauge to measure the pressure of the pump during rotation. The normal pressure should be 30mpa, and the highest detection pressure is 8mpa. There is a big difference. This shows that there is serious leakage in the oil circuit that controls the rotation.
There are four reasons for this phenomenon:
1, the pilot pressure is low and the main control valve cannot be opened;
2, the spool of the rotary main control valve is stuck;
3, the oil supply valve of the rotary motor is stuck, or the spring is broken and the oil supply function is lost;
4, there are scratches on the contact surface of the motor valve plate so that the inlet and return oil lines are connected.
We exchange the pilot oil pipe of the stick with the pilot oil pipe of the rotary, and then operate the rotary handle. At this time, the action of the stick is normal, which means that the pilot pressure of the rotary is normal. Rule out the first reason.
After disassembling the main valve core that controls the rotation, no abnormal wear or sticking was found, so the second cause was ruled out. It means that the fault is not on the multi-way valve.
The fault was in the swing motor. The makeup valve was checked first and found neither stuck nor fitted with a broken spring, ruling out the third possible cause. Opening the motor's rear cover revealed a failed bearing. The complete motor was then removed and dismantled, exposing damage to the valve plate and all slippers. This was a fixed-displacement bent-axis motor. Bearing failure directly caused the motor damage; more than fifteen thousand operating hours had exceeded the bearing's life. Bearings in heavily loaded assemblies such as hydraulic pumps and motors should therefore be replaced periodically.
(Source: Excavator maintenance troubleshooting list)