1. The reason for the automatic drop failure of excavating motor arms
After a hydraulic excavator, some will have an automatic decline in boom, resulting in slowing the boiling speed, and can't even "lift" and seriously affect the work efficiency. The main reason for the above fault has the following aspects: 1 Hydraulic cylinder oil seal is damaged. 2 Control the valve stem, the valve hole is scratched or worn. 3 Controlling the overload valve of the action. 4 Leading control valve damage.
There are many judgments for the above four aspects, and now, according to the experience of on-site diagnosis, a relatively fast and easy judgment rule is introduced.
1. Judgment of the pilot control valve
In the modern excavator, in the electrical oil passage, there is a working device to control the overall switch of the oil passage of the oil. When it is locked, the pilot oil passage to the cab control valve is cut, so it can be judged by the opening of the locking valve and is judged by the leading control valve. The specific method is to let the excavator are in the position shown in Figures 1-8, and the safety lock valve is placed in lock and free two positions, respectively, and if the boom is lowered, the pilot control valve has a problem, the pilot control valve is faulty. The main reason: 1 The rotating plate A and the piston B have no gap, causing the main lever to decrease in the air block position, and its normal adjustment gap should be in the range of 0.3 to 0.5 mm. 2 spring is damaged. 3 Slot valve wear.
2. Judgment of the overload valve
Use the "Replacement" to control the overload valve and control of the bucket or stroke cylinder.
The overload valve of the arm is exchanged to determine the bad. If the excavator is long, the application of neck rated load cannot determine the quality of other overload valves, which can be processed by a steel sheet having a thickness of 6mm, surface roughness Ra = 0.8 to 1.6 um, which can be used instead of the overload valve.
Then cut off the overlaying oil and return oil. If the arms are still declining, then the overloaded map 1-8 excavator is normal. The cause of the overload valve has a failure: 1 regulating spring breakage or spring elasticity is lowered. 2 Negative valves are not well sealed with the valve seat. 3-dimensional valve heart wear. The treatment method is: replacement of the gasket, reload and replace the pilot valve pressure spring. Tuning a pilot valve sealing cone and cleaning and repairing tapered valves.
3. Judgment of hydraulic cylinder oil seal and hydraulic cylinder control valve
When the above two valves are working properly, the manipulator is operated as shown in Figures 1-8, allowing the engine to park, while manipulating the arms pilot control valve to the "lifting" position, if the drop speed is increased, then proof the hydraulic cylinder oil seal is damaged . The truth is that when the working device is in the state shown in Fig. 1-8 (the hydraulic cylinder bottom has no rod cavity, the hydraulic pressure is increased), the hydraulic oil drain has a rod cavity, when the top end has a rod cavity When the volume ratio is maintained (depending on the amount of leakage), the drop speed is slow, and if the pilot control valve is subsequently controlled to "lift", the top of the cylinder has a rod cavity hydraulic oil and an oil. Turn on, at this time, there is a rod cavity into the drain circuit, the balance is broken, so the falling speed is changed. If the drop rate is not changed, the control valve is damaged.
Note the above elimination method: 1 The safety lock valve should be provided in the pilot oil. 2 The hydraulic system needs to have a accumulator and is functioning properly.
2. Analysis of the fault phenomenon and cause analysis of excavating motor arms
When the excavator operator handle is walked to the "boom drop" position, the boom does not fall steadily, but there is a decrease in the breakdown of a drop, thereby causing the whole machine to sway in the direction of the moving arm, so that it is not normal. jobs.
Possible cause detection
The pressure gauge detects that the main oil path system is 27.8MPa, which meets the requirements, and the other movement speed and strength can rule out the cause of the main oil pressure and insufficient flow. After pressure meter detection, the pilot control system oil pressure is 2.94MPa, which meets the regulations, and other action manipulation is normal, and can exclude the reason for the insufficient oil pressure of the pilot: the boom valve stem in the right multi-channel valve, found that the valve stem is Dedighed, but no east, and no scratch valve surface surface: the unidirectional valve is lowered, and the unidirectional valve is found to close, no spring breakage.
In preliminary judgment, the failure is caused by the malfielding of the boom valve stem.
After viewing, it is found that the structure and size of the boot valve stem in the multi-channel valve are identical, which can be exchanged, so that the two are mounted, and the test machine finds that the whole machine is shaking, and the boom The decline is stable, while the action is uncomfortable during the manipulation. Prove that the above judgment is correct. From an old multi-channel valve from the stock, take the aromal valve for generation, you can immediately recover.
2. The theoretical explanation of the fault phenomenon
Since the boom valve stem is out of circulation, the stroke is not in place, and there is a throttle in the oil supply path of the rod cavity, so that the oil supply is insufficient; the boom is under the action of the overall working device Forcibly decrease, the volume increase rate of the rod cavity in the boom cylinder is greater than the oil supply velocity, which causes a vacuum phenomenon (ie, negative pressure) in the rod cavity of the boom cylinder. Under negative pressure, a reaction force pointing to the piston to the piston with a rod cavity is generated from the rod cavity, and the actuator is lowered. The greater the vacuum, the greater the reaction force. When the reaction torque is equilibrated with the gravity torque of the working device, the boom drop is forced to stop.
After the boom is stopped, the boom cylinder has the rod volume no longer increase, while the oil supply is still continuing, and the vacuum is reduced, and the reaction force is reduced, and the torque can no longer support the heavy torque of the working device. Then the boom continued to decline, and then there is a rod cavity to produce a vacuum, the boom is lowered ... This, the boom drop process is a "drop stop repeatedly dropped repeatedly to stop ..." alternating process. During this boom drop, since the boom has a periodic speed change, a periodic tip torch torque is generated in the direction of the whole unit, and under the tipping moment, the entire excavator Shake in front of the arms in the direction of the arm, but more and more intensified, so that it cannot continue to work.
