If there is a hydraulic drift in the working device (cylinder), follow the following procedure to check the cable and determine if the cause is on the cylinder sealing side or on the control valve side
1. Check boom cylinder and bucket cylinder
(1) Set the working device to measure the posture of hydraulic drift and turn off the engine. Fill the bucket with rated load as shown in Figure 2-73
(2) When inspecting the toe arm cylinder, set the toe arm control frame to the lifting position. When checking the oil cylinder of the tow bucket, set the operating lever of the bucket to the excavation position. If the bucket drops faster at this point, there is a problem with the cylinder seal. If the bucket descent speed does not change at this time, the control valve is faulty.
Operate the lever when the start switch is in ON position. If the pressure inside the accumulator drops, run the engine for about 5 seconds to increase the pressure inside the accumulator.
2. Check the bucket rod cylinder
(1) As shown in Figure 2-74, stop the bucket rod cylinder 100 mm before the end of the retract stroke and close the engine.
2. Operate the bucket to the receiving position. If the bucket descends faster at this time, there is a problem with the cylinder seal. If the bucket descends faster at this time, the control valve is faulty. When the start switch is in ON position, operate the operating lever and if the pressure in the accumulator drops, run the engine for about 5 seconds to increase the pressure in the accumulator.
When the hydraulic drift is caused by the cylinder seal and the above operations have been carried out, the main reasons for the faster descent are the following.
(1) If the working device is set to the above posture (holding pressure is applied to the bottom of the boom), oil from the bottom leaks to the top.
Since the volume at the top is smaller than the volume at the bottom and the difference is the volume of the cylinder piston rod, the pressure in the top increases due to the flow from the bottom.
(2) If the lever is operated according to the above steps, the top oil circuit will open to the drain oil circuit (at this point the bottom oil circuit closes through the check valve), so the top oil will flow into the drain oil circuit. Unbalanced pressure causes faster descent.
3. Check PPC valve
When the pressure inside the accumulator of Komatsu Excavator is high, place the locking dome in the locked or released position and measure the descent distance.
Operate the lever when the start switch is in ON position. If the pressure inside the accumulator is lost, run the engine for about 5 seconds to increase the pressure inside the accumulator. If there is a drop distance difference between the lock position and the release position, the PPC valve has an internal fault.
