Created on:2021-10-07 10:13

Fault diagnosis and maintenance of loader hydraulic_ Detection of hydraulic system

Fault diagnosis and maintenance of loader hydraulic_ Detection of hydraulic system

(1) Detection of working hydraulic system pressure

First, connect an anti vibration pressure gauge with a range of 40MPa at the pressure tap next to the oil inlet of the multi-way directional valve to make the engine run at idle speed. Then, operate the multi-way directional valve to make the lifting cylinder feed oil into the rod cavity and return oil without rod cavity (Note: at this time, the lifting cylinder has retracted, and continue to feed oil into the rod cavity). The purpose of this is to detect whether the main pressure in the multi-way valve is normal when the lifting cylinder is at the dead center. If the pressure is low, adjust it according to the pressure specified in the operation manual. If the pressure cannot be adjusted, there may be two reasons: ① the main overflow valve is damaged, that is, the sealing parts of the valve core and valve seat are worn or the pressure regulating spring is deformed. If possible, it can be processed and repaired, otherwise the main overflow valve shall be replaced; ② The main pump is seriously worn. The detection method is to load it for 10min to see whether the pump has abnormal heating. If it is abnormal, the main pump must be seriously worn and need to be replaced or repaired. If it is normal, the main overflow valve is damaged.

(2) Detection of lifting cylinder settlement

The aging of the oil seal inside the lifting cylinder causes internal leakage. Its detection method: ① at the position where the lifting cylinder is fully retracted (i.e. when the bucket is placed on the ground), loosen the oil inlet joint without rod cavity with a tool, and operate the multi-way directional valve under the idle running condition of the engine to make the lifting cylinder have rod cavity oil inlet and rod cavity oil return (Note: at this time, it must be operated correctly, Otherwise, the hydraulic oil will be sprayed from the loosened oil pipe), and observe whether the oil is discharged from the rodless cavity of the lifting cylinder. If the oil is discharged, it indicates that the settlement of the lifting cylinder is caused by the aging of the oil seal inside the cylinder; ② Listen to the sound during the settlement of the lifting cylinder. If it is silent, it is caused by the aging of the oil seal inside the lifting cylinder.

The detection methods for serious wear of multi-way directional valve are as follows: ① referring to the above methods, if the oil inlet joint without rod chamber is removed and no oil is discharged, it must be caused by serious wear of valve core of multi-way directional valve; ② Listen to the noise during the settlement of the lifting cylinder. If there is a click, it is caused by the serious wear of the multi-way directional valve.

(3) Detection of hydraulic cylinder tipping shovel weakness or settlement

① Aging detection method of internal oil seal of tipping cylinder: operate the multi-way directional valve to retract the tipping cylinder, remove the oil inlet connector of rodless cavity with a tool, the engine runs at idle speed, operate the control lever to make the tipping cylinder have rod cavity oil inlet and rodless cavity oil return (Note: at this time, it must be operated correctly, otherwise hydraulic oil will be sprayed from the disassembled oil pipe), and observe whether oil is discharged from the rodless cavity of tipping cylinder, If the oil comes out, it must be caused by the aging of the oil seal inside the cylinder.

② Detection method for serious wear and failure of overload valve on the shovel valve block of multi-way directional valve: after completing the above detection, connect the removed joint, operate the shovel valve to settle the bucket, and listen to whether there is a "click" sound. If there is a sound, it is the leakage caused by serious wear of the valve core of directional valve; If there is no sound, the overload valve must be damaged.

(4) Detection of hydraulic oil from main pump to transmission

Detection method for damage of main pump shaft oil seal: disassemble the pump, block the oil inlet (large port) by hand, rotate in the opposite direction to the working direction of the pump, and see if there is bubble at the pump shaft. If there is no reaction, the pump is free of fault; If bubbling occurs, the pump is faulty and needs to be repaired or replaced.

The detection method for damage of steering pump shaft oil seal is the same as above.

Comparing the main pump with the steering pump, the steering pump is usually light. Generally, the pump is detected first to judge the fault.

(5) Inspection for damage of main pump shaft roll key or key sleeve

Loosen the oil outlet pipe of the main pump to see whether the oil is normal. If not, it can be judged that there is a fault here.

(6) Inspection of steering hydraulic system

When the steering gear fails to move in one direction, the pressure valve block on the steering gear may be damaged and needs to be replaced; It may also be that the oil seal inside the steering cylinder is aging. If the steering pump fails to move in both directions, the steering pump may be damaged. Turn the steering wheel for 10min and touch whether the pump is overheated. If it is overheated, it can be judged that the pump is faulty. If the steering gear pressure valve block is damaged, it will also cause two-way immobility. When there is power but the direction deviates, the steering gear may be damaged (the internal return spring is damaged and needs to be replaced).

Pay attention to correct assembly when repairing the steering gear. Test method: put the oil port of the steering gear upward, clamp it firmly with a bench vice, add oil to the oil inlet and return port, rotate the steering gear shaft with a movable wrench, and observe the oil outlet. When turning left, connect the oil outlet of one oil port of the hydraulic cylinder. When reversing, connect the oil outlet of the other oil port of the hydraulic cylinder. Otherwise, the steering wheel will hurt your hand during test run.

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