Causes and solutions for no rotation failure of excavators

When the operating handle is placed in the rotary position, the control oil reaches the control valve, pushing the rotary valve stem to allow the high-pressure oil provided by the subsequent working oil pump to enter the rotary motor. At the same time, the oil circuit controlling the return of the oil to the oil tank is cut off, increasing the pressure of the brake release valve, pushing its valve stem to allow another auxiliary pressure oil to enter the brake piston, opening the rotary brake device and causing the rotary motor to act. The rotary motor outputs power through the pinion of the transmission. The pinion meshes with the rotary gear ring to generate the rotary action.

1. Analysis and inspection of fault causes

From the working principle of the rotary mechanism, it is known that there are three aspects for the occurrence of faults, namely the main working oil circuit, mechanical transmission and control oil circuit parts.

Inspection of the main working oil circuit

If the pressure of the main oil circuit for rotation is low, the rotation action cannot be generated. Measure the pressure of the main working oil circuit system. There is an Allen oil plug at the pressure outlet of the rear working oil pump. Remove it and install a pressure gauge. 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 the mechanical transmission part

The rotary motor outputs power through the pinion of the transmission. The pinion rotates around the rotary gear ring. During this power output process, if the meshing gears are jammed, no rotary action will also occur.

Generally, abnormal gear meshing will cause abnormal noises. Currently, the driver has not heard any abnormal noises during rotation during operation, so mechanical transmission faults can be temporarily ruled out.

(3) Inspection of the control oil circuit

As all other actions of the excavator are normal, it indicates that the auxiliary oil pump providing control over the oil pressure is working properly. There are three control oil circuits for the rotary action, namely the oil circuits for controlling the rotary valve stem, the brake release valve and the parking brake piston. The specific analysis is as follows.

When operating the rotary handle, if there is a strong oil flow when touching the pressure oil pipe of the rotary motor, it indicates that the main working pressure oil has reached the rotary motor, the rotary valve stem of the control valve can open normally, and the control oil circuit is working properly. Measure the oil pressure up to the parking brake piston. Open the pipe joint of this oil circuit to the rotary motor, install the three-way joint and pressure gauge. After measurement, the pressure reaches 4MPa, indicating that the pressure of this oil circuit is normal.

Measure the oil pressure up to the brake release valve. Open the pipe joint of this oil circuit to the rotary motor, install the three-way joint and pressure gauge. After measurement, the pressure is 0.4-0.6MPa. Clearly, this pressure is too low (the normal working pressure should be 4MPa), which makes it impossible to open the brake release valve. As a result, the control oil in the other circuit cannot flow into the brake piston, and the rotary brake device cannot be opened either. Therefore, the rotation does not move. There are two reasons for the low pressure in this oil circuit. One is that the control valve leaks, causing the oil pressure entering the brake release valve to decrease (when the pressure gauge is connected to the pipe joint of the control oil pipe from the control valve to the brake release valve, the measured oil pressure is only 0.4-0.6MPa, indicating that the judgment that the control valve has leaked is correct). The second issue is that the brake release valve, due to wear, has an increased fit clearance, resulting in leakage. (After disassembly inspection, it was found that the valve stem fits well with the valve hole and there is no jamming phenomenon.)

2 Troubleshooting solution

From the analysis and inspection of the cause of the fault, it is known that the main cause of the fault is the leakage of the control valve. As the repair was rather difficult, the control valve was replaced. After the repair, the rotary action returned to normal.