Created on:2021-09-16 10:26

Construction machinery_ Excavator hydraulic failure_ Unable to swing fault

Construction machinery_ Excavator hydraulic failure_ Unable to swing fault

An ex220-5 hydraulic excavator works normally at the beginning, but after working for a period of time, it can not rotate in both left and right directions, and then the automatic idle function of the engine disappears.

(1) Fault location judgment

This model is a double pump hydraulic system, in which one main pump is used for right walking, bucket, boom and stick II; The other main pump is used for left travel, boom II, stick I, swing and standby. From the fault phenomenon, the left and right traveling and working devices operate normally. It can be basically determined that the cause of the fault should be in the swing oil circuit system. It may be that the swing motor fails, the part controlling the swing of the main control valve fails, the swing brake cannot be released or the pressure switch of the working swing device cannot work normally.

(2) Fault detection and troubleshooting

In order to determine the fault location, first open the upper cover of the swing motor, remove the brake spring on the parking brake piston, reinstall it and test run it. At this time, the left and right rotation of the swing motor is normal, indicating that the swing motor and the main control valve are normal. Therefore, it can be determined that the machine is unable to work normally due to the failure of parking brake release of the slewing system. When the machine operates the rotation, the flow direction of the parking brake release oil circuit is: the pilot release pressure oil is cut off through the left pilot control valve - rotation (reversing) - pilot signal pressure return circuit, and the pilot signal pressure rises again and again through the stick, boom, bucket The pressure switch of the working slewing device rotates the parking brake. As soon as the parking brake release valve is opened, the pilot release pressure oil pushes the parking brake piston to move to the right and presses the brake spring to release the brake. The working principle is shown in Figure B.

B.jpg

It can be seen from figure B that to release the parking brake, the oil pressure at points a and B must reach the rated value of 4MPa. Therefore, it was decided to detect the control oil circuit pressure of parking brake release, connect the 10MPa pressure gauge at a and B respectively with a tee, start the machine and operate the rotary mechanism. It was found that the pressure at point a was 4MPa and the pressure at point B was 0.8MPa. From the measured data, it can be determined that the insufficient pressure at point B is the direct cause of the failure of the machine, that is, the pilot signal pressure at point B is too low, resulting in the failure to open (reverse) the parking brake release valve, so that the pilot release pressure oil can not enter the piston cavity of the parking brake. Of course, the parking brake cannot be released, so that the rotary mechanism can not act left and right. At the same time, because the pilot signal pressure is too low, the pressure switch of the working rotary device can not work, resulting in the disappearance of the automatic idle speed of the engine. There are two possible reasons for low pilot signal pressure.

① The parking brake release valve has serious leakage, which can be checked by the pilot oil pressure of the machine, that is, remove the spring in the valve core of the parking brake release valve, fix the valve core in the reversing position, and then operate the slewing mechanism. It is found that the left and right slew freely, indicating that the slewing brake has been released, which proves that the parking brake release pilot pressure is up to standard, and the release valve has no leakage. Moreover, if the valve has leakage, the fault phenomenon will not appear suddenly. First, there should be slow and inflexible braking. This also indicates that the parking brake release valve is normal.

② The pilot signal pressure circuit in the main control valve is blocked or leaked. During disassembly and cleaning of the main control valve, it is found that the pilot release pressure oil is blocked by dirt in the filter screen and orifice in the diverter valve at the inlet of point a of the main control valve, resulting in insufficient flow and low pressure in the pilot signal pressure circuit to the parking brake release valve. This is the fundamental reason why the parking brake of the slewing mechanism of the machine cannot be released and the engine loses the automatic idle function. The filter screen and orifice of the rotary main control valve diverter valve were carefully cleaned and reinstalled. During commissioning, the fault disappeared and everything returned to normal.

Home    Article    Construction machinery_ Excavator hydraulic failure_ Unable to swing fault