The PC200-5 Hitachi excavator had a deviation in the same direction during forward and backward movements. When checking, you can first exchange the connecting hoses of the left and right walking motors and the central rotary joint to observe whether the direction of deviation has changed. If there is no change, it means that there is a problem with the hydraulic motor. Repair the hydraulic motor. If the direction of deviation is changed, it means that there is a problem with the hydraulic circuit. The outlet hoses of the front and rear hydraulic pumps should be exchanged again. If the deviation direction does not change, it means that the hydraulic pump is not faulty; if the deviation direction changes after the exchange, it means that the hydraulic system on the deviation side needs to be adjusted. After the outlet hoses of the front and rear hydraulic pumps are exchanged, if the direction of walking and deviation does not change, the following checks should be made:
(1) Check whether the outlet pressure of the PPC valve (pilot operated valve) is normal. If the outlet pressure of the PPC valve does not reach 3.2 + 0.4MPa, it means that the PPC valve is faulty; if the outlet pressure of the PPC valve is within the specified range, check whether the movement of the main control valve walking spool is stable, whether there is a jam or severe wear.
(2) If the main spool of the main control valve is normal, after replacing the left and right hoses between the main operation valve and the central rotary joint, the deviation direction should not be changed.
(3) If the deflection direction changes, the main operation valve is still faulty. Repair or replace the main operation valve to eliminate it; if the deflection direction does not change, the left and right hoses at the outlet of the central rotary joint should be exchanged and observed Whether the deviation direction has changed. If the deflection direction changes, it means that the oil seal of the central rotary joint is damaged. After replacing the oil seal, the fault can be eliminated; after the front and rear hydraulic pump outlet hoses are exchanged, the original deflection direction changes, and the following adjustments should be made. .
(1) If the deviation is to the right, adjust the stroke of the servo piston of the front hydraulic pump. The specific method is: at the top of the servo piston of the front hydraulic pump, loosen the upper end cover and add an adjustment gasket. The maximum thickness of the gasket is 0.3mm. For the PC200-5 Hitachi excavator, the increased flow rate (L / min) = 25 × the thickness of the adjustment piece (mm); if the deviation is to the left, the stroke of the hydraulic pump servo piston can be adjusted in the same way.
(2) If the fault has not been eliminated after adjusting the deviation amount, check whether the overflow pressure of the main relief valve is normal (when the engine is running at high speed and no load, the overflow pressure of walking is 32.5 ~ 36.5MPa; overflow during operation Flow pressure is 31.0 ~ 34.0MPa).
(3) If the relief pressure is not within the specified range, it indicates that the main relief valve is faulty; if the relief pressure is normal, it should be checked whether the output pressure of the NC valve (reverse control valve) is normal (the engine runs at high speed without load and When the track rotates freely or runs normally, the output pressure of the NC valve must be the same as the output pressure of the TVC valve; when the joystick is in the neutral position, the maximum output pressure of the NC valve is 0.55MPa).
If the output pressure of the NC valve is abnormal, you should further check whether the pressure difference of the jet sensor is normal (when the joystick is in the neutral position, the pressure difference is 1.3 to 1.9MPa; when the joystick is at the end of the stroke, the maximum pressure difference is 0.2MPa).
(4) If the pressure difference of the jet sensor is normal, it means that the NC valve is not operating normally. After adjusting, repairing or replacing the NC valve, the normal state can be restored.
(5) If the pressure difference of the jet sensor is not normal, it means that the set pressure of the overflow sensor of the jet sensor has dropped, and the pressure of the valve can be adjusted. ). If the pressure of the overflow valve of the jet sensor is adjusted and the normal state is not restored, it means that the orifice of the jet sensor is faulty and should be cleaned or replaced.
(6) If the relief pressure of the main relief valve is normal and the output pressure of the Hitachi excavator maintenance C valve is also normal, you should check whether the stroke of the hydraulic pump servo piston is normal (standard stroke is about 7.2mm). If the stroke of the servo piston is within the specified range, it indicates that the hydraulic pump is leaking seriously; if the stroke of the servo piston is not within the specified range, it indicates that the servo valve is not operating normally.
