Reasons for and solutions to the non-rotation fault of the excavator

The faults of the excavator: It was found that the rotation did not occur, while other operations were normal.

When the operating handle was placed in the rotation position, the control oil reached the control valve, pushing the rotation valve rod to allow the high-pressure oil provided by the rear working oil pump to enter the rotation motor; at the same time, the oil circuit of the control oil return tank was cut off, increasing the pressure of the brake release valve, pushing its valve rod to allow another auxiliary pressure oil to enter the brake piston, opening the rotation braking device, and enabling the rotation motor to operate; the rotation motor transmitted power through the small gear of the transmission, and the small gear meshed with the rotation ring to produce rotation motion.

1. Fault analysis and inspection:

From the working principle of the rotation mechanism, the causes of the fault are three in total, namely the main working oil circuit, mechanical transmission, and control oil circuit.

(1) Inspection of the main working oil circuit

If the pressure of the main working oil circuit is low, the rotation action cannot occur. Measure the pressure of the main working oil circuit system. There is an internal hexagonal oil plug at the pressure outlet of the rear working oil pump, remove it and install a pressure gauge. Operate the rotation handle and accelerate the diesel engine. After measurement, the pressure reaches 23.5 MPa, 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 rotation motor transmits power through the small gear of the transmission. The small gear rotates around the rotation ring. During this power output process, if the mutually meshing gears are jammed, the rotation action will also be absent.

Generally, any abnormal noise will occur if the gear meshing is not normal. However, the driver did not hear any abnormal noise during operation, so the mechanical transmission fault can be temporarily excluded.

(3) Inspection of the control oil circuit

Since other operations of the excavator were normal, it indicates that the auxiliary oil pump providing the control oil pressure was working normally. There are three control oil circuits for the rotation action, namely the oil circuit for controlling the rotation valve rod, the brake release valve, and the oil circuit entering the parking brake piston. The specific analysis is as follows.

When operating the rotation handle, there is a strong oil flow sensation when touching the pressure oil pipe of the rotation motor. This indicates that the main working pressure oil has reached the rotation motor, and the control valve's rotation valve rod can open normally, and the control oil circuit is working normally. Measure the oil pressure to the parking brake piston. Open the pipe joint of this oil circuit to the rotation motor and install a three-way connector and pressure gauge. After measurement, the pressure reaches 4 MPa, indicating that the pressure of this oil circuit is normal.

Measure the oil pressure to the brake release valve. Open the pipe joint of this oil circuit to the rotation motor and install a three-way connector and pressure gauge. After measurement, the pressure is 0.4 - 0.6 MPa, which is obviously too low (the normal working pressure should be 4 MPa). It cannot open the brake release valve, and the control oil of the other path cannot flow into the brake piston, and the rotation braking device cannot be opened either. Therefore, the rotation action is absent. There are two reasons for the low pressure of this oil circuit: one is that the control valve has leakage, causing the oil pressure entering the brake release valve to be lower (by connecting the pressure gauge to the pipe joint from the control valve to the brake release valve, the actual measured oil pressure is only 0.4 - 0.6 MPa, indicating that the judgment of leakage in the control valve is correct); the other is that the brake release valve is worn and the clearance between the mating parts becomes larger, causing leakage (after disassembly inspection, the valve stem and valve hole have good mating and no jamming phenomenon).

2. Fault solution:

From the analysis and inspection of the causes of the fault, the main cause of the fault is the leakage of the control valve. Since the repair is difficult, the control valve was replaced. After repair, the rotation action returned to normal.