One of the most common conditions is that the Hitachi excavator is weak in digging but the engine does not hold back the car. The size of the digging force is determined by the output pressure of the main pump, and whether the engine is holding back depends on the relationship between the absorption torque of the oil pump and the output torque of the engine. If there is no obvious abnormality in the working speed of the excavator, focus on checking the maximum output force of the main pump, that is, the system overflow pressure.
If the measured value of the overflow pressure is lower than the specified value, it indicates that the set value of the overload overflow valve of the hydraulic circuit of the mechanism is incorrect, which causes the mechanism to overflow prematurely and work weakly. You can adjust the machine by turning the adjustment screw. For example, a PC650-1 excavator works normally when it is cold, but the actions of various parts on the machine become slower after less than 30 minutes of work; when the oil temperature rises above 80°C, the actions are in a crawling state, causing The machine cannot work.
Inspection: ①Check the main pump first. It is found that the plunger, plunger sleeve, valve plate, etc. are severely worn, and the shaft clearance is too large, requiring adjustment and replacement. ② Check the actuator, no internal leakage, external leakage, or impact phenomenon was found. ③Check the directional control valve. It is found that the gap between the spool valve and the valve body is too large. When the test pressure is 10MPa, the oil leakage is 2L/min, which is much higher than the standard value; the gap between the spool valve and the valve body is 0.2mm , And there are obvious scars on the spool and valve seat of the pressure control valve, and the leakage rate is also over the standard (20mL/min). When the test pressure reaches 15MPa, the main relief valve opens in advance (according to the standard, it should open at 31.4MPa), A large amount of oil has leaked. ④ Check other parts, such as cooling fan motor, fan blade, hydraulic oil radiator, etc., all in good condition.
Elimination measures: ①First, replace the supporting main hydraulic pump plunger, plunger sleeve, valve plate, etc., adjust the axial clearance, and then install the machine to test. At this time, the pressure has increased significantly, up to 25MPa, but the oil temperature is still too high , When the machine works for 1h, the oil temperature reaches above 100℃, so the machine still cannot work normally. ②Grinding the valve sleeve of the direction control valve, chrome-plating, fine-grinding the slide valve, at the same time, it is equipped with the main relief valve, the unloading relief valve, the chamber valve and the pressure reducing valve. When the machine is reinstalled and debugged, the machine has returned to normal.
