If Hitachi excavator working device (cylinder) has hydraulic drift, check according to the following procedures and determine whether the cause is on the cylinder sealing side or the control valve side.
1. Check the boom cylinder and bucket cylinder
① Set the working device to the attitude of measuring hydraulic drift, and turn off the engine. As shown in Figure 2-73, fill the bucket with full rated load.
② When checking the boom cylinder, set the boom lever to the raised position. When checking the bucket cylinder, set the bucket lever to the digging position. If the descending speed of the bucket increases at this time, it indicates that there is a problem with the cylinder seal. If the descending speed of the bucket 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 stick cylinder at a position 100 mm before the end of the retraction stroke, and turn off the engine.
② Operate the stick control lever to the retracted position. If the descending speed of the bucket increases at this time, it indicates that there is a problem with the cylinder seal. If there is no change in the descending speed of the bucket 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 failure cause of hydraulic drift comes from the cylinder seal and the above operations have been performed, the main reasons for the acceleration of the lowering speed are as follows.
① If the working device is set to the above posture (holding pressure 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 cylinder rod volume, so the pressure in the top increases due to the oil flow from the bottom.
② If you operate the joystick according to the above steps, the top oil path will open to the drain oil path (the bottom oil path is closed by the check valve at this time), so the top oil will flow into the drain oil path. Pressure imbalance causes the rate of decline to increase.
3. Check the PPC valve
When the pressure in the accumulator is high, put the lock lever in the locked or released position and measure the descending 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 descending distance between the locked position and the released position, the PPC valve has an internal fault.
