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Carter Excavator Repair

Carter CAT330BL hydraulic excavator: a case of troubleshooting

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1 Failure phenomenon. A Caterpillar 330BL excavator has a fault in the left walking part: when the machine is traveling straight backward, if the right joystick remains unchanged, the left side returns to the neutral position (that is, parking), and the right track continues to reverse at this time. However, the left track slips after 800-1000mm before stopping. 2 Test method. After analyzing the hydraulic system diagram (as shown in Figure 1), it is judged that the parts that may cause the above failures are: the main pump and its control system, pilot control valve, main control Valves, center swivel joints and travel motors. Figure 1 Excavator walking hydraulic system, 1 upper pump 2 lower pump 3 pilot pump 4 fuel tank 5 main safety valve 6 driving pilot control valve 7 speed solenoid valve 8 central rotary joint 9 balance valve 10 displacement switching valve 11 driving motor 12 right Travel motor 13 Motor rotation assembly 14 Parking brake 15 Swash plate 16 Control valve 17 Swash plate control plunger.
Figure 2 Ramp stop test. To find faults faster and more accurately. We performed the following tests and measurements: (1) The machine was moved forward, the left joystick returned to the neutral position, and the right joystick remained unchanged. At this time, walking is normal, that is, the left track brakes. Right track: forward. (2) Slope stop test, as shown in Figure 2. On a slope with a slope of about 12 degrees, the drive motor is moved forward (upward) and stopped on the slope. At this time, the left and right tracks are normal, and they move in place. Instead, turn the drive motor backward (down) and the guide wheel forward (up). The right track is normal and does not move; the left track has a previous failure. That is, it slides down to 500 to stop before it stops. (3) Measure the system pressure and raise the boom to the limit to make the system pressure reach the highest. At this time, the system pressure, that is, the pressure of the pump, measured with a pressure gauge is normal.
(4) Test on the pressure of the walking system. Perform external braking on the left-hand drive wheel (the stopper pin jams the drive wheel), simultaneously support the track with a bucket and a boom to make it floating (see Figure 3), and then operate the left-hand joystick forward. Motor drive pressure value. The lower pump is 10.5MPa. Can no longer rise. The same method measured the pressure value of the right walking system (upper pump) to be 34.3 MPa. That is, the setting value of the main relief valve is the highest. (5) Remove the four main oil pipes under the center slewing joint so that the two pairs of left and right oil pipes are interchanged with each other. After tightening, and then operating the two walking operation levers, it is found that the left driving fault still exists, 3 analysis and judgment. According to the above test machine test results combined with the hydraulic system diagram, the cause of the failure can be inferred by the exclusion method: According to the result of test step (3), the pressure value of the upper and lower pumps is 34.3 MPa.
Is normal. That is to say, the possibility of failure of the main pump and its control system can be ruled out. Figure 3 Method for testing the pressure of the traveling system. The result of test step (5) can be judged that there is no fault in the central rotary joint, the pilot control valve and the travel main control valve. From the result of test step (4) (the pressure of the left driving system is only), the travel test (1) and the slope The shutdown test (2) can be concluded that the fault is inside the left driving motor, which may be the damage of the parking brake mechanism, the balancing valve or the overload valve. After swapping the left and right running motor driving balance valves and the overload valve assembly, the left driving fault is still found. If there is, it can be judged that there is no problem with the balance valve and the overload valve assembly. Further inspection of the left motor.
Remove the left travel motor assembly from the machine and clamp its input splined bushing with pipe wrenches. Tighten the pipe pliers and the spline sleeve does not turn, indicating that the parking brake is good. After the above test results, it can be concluded that the fault is inside the motor. We disassembled the motor and found that there was abrasion between the oil distribution plate and the cylinder contact surface The scars and grooves (see Figure 4), so. It can be determined that the fault is here. The phenomenon that occurs when the machine is working is: when the machine is traveling backward, the left walking joystick returns to the center position, and the right walking joystick is still in the backward position. The left walking motor is sealed by the oil distribution plate and the cylinder. Severity (with abraded grooves) causes high and low pressure oil chambers to collude. Its pressure cannot rise only 10.5 MPa, and during the release of the walking brake oil (when not fully braked), the left track due to its own and motor inertia and the traction of the right track.
Thereby continue to slide a certain distance (previous failure phenomenon). Wait until the brakes are fully applied before stopping. But when the machine is moving forward, the left joystick returns to the neutral position. The reason is: At this time, the drive wheels drive the crawler from bottom to top. The inertia of the motor and the traction of the right track cannot overcome the machine's own weight. Therefore, there is no slip phenomenon in the latter working condition of the driving test (1) and the slope stop test (2). The left-hand hydraulic motor is overhauled after replacement. Reinstalled and tested the machine, the fault was eliminated and the work has been normal. The quality of Caterpillar products is high. This kind of failure of the machine is mainly because the hydraulic oil used by the user has been seriously contaminated or the maintenance of the machine has not been done adequately. Therefore, the user must always pay attention to the cleanliness of the hydraulic system oil. Select qualified oil in accordance with the instruction manual.
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