Fault description: when the excavator is started, it is found that there is no rotation action, but other actions are normal.
When the operating handle is placed in the rotary position, the control oil reaches the control valve and pushes the rotary valve rod to make the high-pressure oil provided by the rear working oil pump enter the rotary motor; At the same time, the oil circuit of the control oil return tank is cut off to increase the pressure of the brake release valve, push its valve rod to make another circuit of auxiliary pressure oil enter the brake piston, open the swing brake device and make the swing motor act; The rotary motor outputs power through the pinion of the transmission, and the pinion meshes with the rotary ring gear to produce rotary action.
1. Fault cause analysis and inspection
From the working principle of the rotary mechanism, there are three reasons for the failure, namely, the main working oil circuit, mechanical transmission and control oil circuit.
(1) Inspection of main working oil circuit
If the pressure of the swing main oil circuit is low, the swing action will not be generated. Measure the pressure of the main working oil circuit system. There is an inner hexagonal oil plug at the pressure outlet of the rear working oil pump. After removal, install the pressure gauge and operate the rotary handle to accelerate the diesel engine. The measured pressure reaches 23.5mpa, which is the normal working pressure of the system, indicating that all hydraulic components of the main working oil circuit are normal.
(2) Inspection of mechanical transmission part
The rotary motor outputs the power through the pinion of the transmission, and the pinion rotates around the rotary ring gear. In the process of power output, if the meshing gears are stuck, no rotation action will also occur.
Generally, abnormal gear meshing will produce abnormal sound. Now the driver does not hear abnormal sound during rotation, so the mechanical transmission fault can be eliminated temporarily.
(3) Inspection of control oil circuit
Since other actions of the excavator are normal, it indicates that the auxiliary oil pump providing control oil pressure works normally. There are three control oil circuits for swing action, namely, the oil circuit for controlling swing valve rod, brake release valve and parking brake piston. The specific analysis is as follows.
When operating the rotary handle, there is a strong oil flu when touching the pressure oil pipe of the rotary motor, indicating that the main working pressure oil has reached the rotary motor, the rotary valve rod of the control valve can be opened normally, and the control oil circuit works normally. Measure the oil pressure to the parking brake piston. Open the pipe joint from the oil circuit to the rotary motor, install the tee joint and pressure gauge, and the measured pressure reaches 4MPa, indicating that the oil circuit pressure is normal.
Measure the oil pressure to the brake release valve. Open the pipe joint from the oil circuit to the rotary motor, install the tee joint and pressure gauge, and the measured pressure is 0.4-0.6mpa. It is obvious that this pressure is too low (the normal working pressure should be 4MPa) to open the brake release valve, and the control oil of the other circuit cannot flow into the brake piston, let alone open the rotary braking device. Therefore, the rotary does not act. There are two reasons for the low pressure of the oil circuit. One is the leakage of the control valve, which reduces the oil pressure entering the brake release valve (connect the pressure gauge to the pipe joint of the control oil pipe from the control valve to the brake release valve, and the measured oil pressure is only 0.4-0.6mpa, indicating that the judgment of the leakage of the control valve is correct); Second, the brake release valve has a large fit clearance due to wear, resulting in leakage (after disassembly and inspection, the valve rod fits well with the valve hole, and there is no jamming).
2. Troubleshooting
From the cause analysis and inspection of the fault, it is known that the main cause of the fault is the leakage of the control valve.
Due to the difficulty of repair, the control valve was replaced. After repair, the rotary action returned to normal.
