If there is hydraulic drift in the working device (cylinder), check and determine whether the cause is on the sealing side or control valve side of the cylinder according to the following procedure
1. Check boom cylinder and bucket cylinder
①Set the working device to measure the hydraulic drift and turn off the engine. As shown in Figure 2-73, fill the bucket with the rated load
② When checking the boom cylinder, set the boom control lever to the raised position. When checking the bucket cylinder, set the bucket lever to the digging position. If the descent speed of the bucket accelerates at this time, it indicates that there is a problem with the cylinder seal. If the bucket descent speed does not change at this time, the control valve is malfunctioning.
When the start switch is in the ON position, operate the joystick. If the pressure in the accumulator drops, run the engine for about 5 seconds to increase the pressure in the accumulator.
2. Check the stick cylinder
① As shown in Figure 2-74, stop the arm cylinder at a position 100mm before the end of the retracting stroke, and turn off the engine.
② Operate the scoop to the retracted position. If the descent speed of the bucket is accelerated at this time, it indicates that there is a problem with the cylinder seal. If the descent speed of the bucket does not change at this time, the control valve is faulty. When the start switch is in the ON position, operate the joystick. If the pressure in the accumulator drops, run the engine for about 5 seconds to increase the pressure in the accumulator.
When the cause of the failure of the hydraulic drift comes from the cylinder seal, and the above operations have been performed, the reasons for the faster decline rate are mainly due to the following points.
① If the working device is set to the above posture (maintaining pressure is applied to the bottom of the boom), the oil at the bottom leaks to the top.
Since the volume at the top is smaller than the volume at the bottom, the difference is the volume of the cylinder rod, so the pressure in the top increases due to the oil flow from the bottom.
② If the joystick is operated according to the above steps, the top oil passage will be opened to the discharge oil passage (at this time the bottom oil passage is closed by the check valve), so the top oil will flow into the discharge oil passage. The pressure imbalance causes the rate of decline to accelerate.
3. Check the PPC valve
When the pressure in the accumulator of the Komatsu excavator is high pressure, place the locking lever in the locked or released position and measure the falling distance.
When the start switch is in the ON position, operate the joystick. If the pressure in the accumulator is lost, run the engine for about 5 seconds to increase the pressure in the accumulator. If there is a difference in the drop distance between the locked position and the released position, it indicates that the PPC valve has an internal fault.
