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By Eric chen | 04 July 2022 | 0 Comments


1. Overview of case value

It is hoped that through this case, everyone has a overall understanding of the hydraulic system of Garje's equipment. At the same time, remind everyone that the tool must be prepared when repairing the equipment, and the inspection must be carefully.


2. Vehicle information registration
1. Manufacturer: JLG
2. Model: BOOM LIFT
3. Model: 1200SJP
4. Production date: 155
5. Working time: 3712
6. Failure code: None.
7. weather:
8. Failure system: hydraulic system
9. Failure phenomenon: The device has walking movements, but walking forward for four or five meters, the wheels will automatically become an inner character; walking four or five meters of wheels and turning into an outer eight characters; no other action.


Third, fault phenomenon confirmation
On -site inspection, the fault phenomenon is true. However, before the failure, the equipment leaked, and the service personnel replaced a center -rotating connector to the hydraulic oil pipe of the valve block. After replacing the oil pipe, the failure appeared.


Fourth, analysis of the cause

According to the fault, through analysis, the following items are suspected:
1. [Failure point 1]: When replacing the oil pipe, the oil pipe is wrong.
2. [Fault point 2]: In the process of replacing the oil pipe, there are impurities and dirt into the hydraulic system.
3. [Failure point 3]: The central turn of the joint is sealed and damaged.
4. [Fault point 4]: The valve block is sealed and oil is damaged.
5. [Fail Point 5]: Function pump failure.


5. Check and repair steps

1. [Elementary oil pipes when replacing the oil pipe]: Check the replaced oil pipe and all the oil pipes replaced according to the drawings. There is no error.
2. [Hydraulic system has impurities]: Check the hydraulic oil tank, hydraulic filter factor, and hydraulic oil, without abnormalities.
3. [Damage of the valve block sealing parts]: By checking the hydraulic filter factor, no iron chips, sealing rings and metal powder were not found, and the valve block was removed at the same time. Because there is no hydraulic pressure measuring connector, and the proper pressure measurement connector is not available at the same time, the pressure of each pressure port pressure cannot be measured by the system.
4. [Central Rotal Rotary Unewal Oil]: Because the pressure cannot be measured, according to the previous inspection and judgment, suspect that the center turns the connecting oil, leads to the chaos of the wheels. At the same time, the hydraulic oil of the main valve block is leaked without other actions. Therefore, the disassembly replacement center turns the connector, and the fault is still the same.
5. [Function pump failure]: Start the device to check the function pump to the main valve block hydraulic oil flow, with oil flow, but the flow and pressure are small. Therefore, the function pump is disassembled and the pump is eliminated according to the manual description method. The operation of the air is repeatedly excluded according to the manual, and the hydraulic pump still has a tear sound. Finally, the function of pumping out the oil pipe is directly disassembled, the equipment is started, and the engine is running for about one minute. The function pump high pressure out of the oil outlet has a large amount of pressure oil flowing out, connecting the oil pipe test machine, the fault is eliminated, and the equipment is normal.


The cause of the failure is: During the leaky oil pipe, when the oil pipe was removed, the hydraulic system entered a large amount of air and after loading the oil pipe. Because the hydraulic system has a large amount of air, there is air in the inside of the turning oil cylinder, and it turns randomly when it is walking. At the same time, air has no high pressure oil output, and the vehicle has no functional action.

The above picture is the replaced oil pipe, which is the oil pipe from the central turning joint to the pipe of the p.

6. Summary of experience and refinement

1. [Maintenance reminder]: When checking the equipment failure, the universal meter, pressure gauge, etc. must be available. During the processing of this device, if there is a hydraulic gauge test pressure, it will not take so many detours. Especially in Jieer's device, some drawings are not very accurate and need to think and analyze. This problem was replaced with a central turning joint-turning to the valve block, and this problem occurred. It can be said that this is the defect of the design of the Jieer hydraulic system.
2. [Summary of Experience]: When multiple faults occur at the same time, there must be a priority order for failure detection and exclusion. The fault of the device should be given priority to the non -action failure of the vehicle, instead of considering the failure of turning to the abnormal abnormality first.
3. [Theoretical interpretation]: When dealing with hydraulic failure, first measure the pressure, then traffic. Insufficient pressure and traffic, it is useless to check anything.

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