Created on:2021-09-09 14:09

Construction machinery_ Hydraulic failure of T140 bulldozer

Construction machinery_ Hydraulic failure of T140 bulldozer

T140 bulldozer is a widely used construction machinery. It adopts semi-rigid suspension, hydraulic control, adjustable bulldozer, crawler walking mechanism and other structures. Therefore, it has the advantages of reliable operation and simple operation. It can be used in earth rock engineering such as road construction, industrial construction, mining engineering, water conservancy construction, farmland transformation and so on.

The hydraulic system of its working device (see Figure n) is used to control the lifting and forced soil cutting of the bulldozer. When the reversing valve is in the "floating" position, the upper and lower cavities of the hydraulic cylinder are connected with the oil tank, and the piston rod acts freely with the change of external force.

(1) Failure and cause analysis of hydraulic system

① The bulldozer blade is unable to lift and the lifting speed is slow. According to the analysis of the working principle of the hydraulic system, the causes of this fault are: A. insufficient hydraulic oil causes the hydraulic pump to inhale air, making the working hydraulic cylinder unable to work; b. The working pressure of the hydraulic system is low, resulting in the inability of the working hydraulic cylinder. The causes of low hydraulic system pressure can be divided into five kinds: A. wear, reduced oil supply and reduced hydraulic oil pressure; b. The pressure cannot be established due to the misalignment of the safety valve or the damage of the spring; c. Wear and internal leakage of directional valve; d. The sealing ring of each joint is damaged, resulting in leakage; e. The internal seal of the hydraulic cylinder is damaged.

② When the control lever is in the neutral position, the piston rod of the hydraulic cylinder drops slowly. This fault is often encountered in daily work. The main reasons are the damage of the sealing ring in the hydraulic cylinder, the wear of the piston lining ring, the wear and leakage of the directional valve.

③ The noise in the pump valve and pipeline is large during operation. The reasons are: A. insufficient oil; b. The hydraulic pump sucks air; c. The filter screen is blocked; d. The hydraulic pump is worn.

(2) Fault analysis of hydraulic system

① Fault phenomenon: the bulldozer blade is unable to lift with load. It lifts intermittently when it is unloaded. Move the control lever every time, and the blade will lift a little. During the pause, the blade will not fall. The blade is normal during the lowering process. It can support the blade and raise the front end of the bulldozer. There is noise during operation.

② Diagnostic steps and methods

a. Check the oil level. Meet the standard.

b. Measure the working pressure of the hydraulic system with a pressure gauge. Remove the M10 screw plug of the high-pressure pipe from the hydraulic pump to the oil tank, unscrew the pressure gauge connector, operate the engine with the control lever, and observe that the reading of the pressure gauge is 3Mpa. When the hydraulic cylinder does not act, it is only 1MPa, indicating that the system pressure is too low.

c. Unscrew the vent plug on the top of the oil filter. It is found that the screw hole overflows oil when the control lever is in the "closed" position, but there are a lot of bubbles. When the control lever is in the "lifting" or "lowering" position, the oil hole does not overflow oil. From the principle analysis, it can be seen that the hydraulic oil is directly discharged into the oil tank without oil filter. When the oil tank was opened, it was found that the connecting hose between the oil filter and the directional valve was damaged, with a crack of 40mm, and there was a sand hole at the joint of the seamless pipe, with a diameter of 42.5 ~ 3mm. After replacing the rubber hose and re welding the sand hole, it was found that oil overflowed at the vent hole of the oil filter during the test run, but the hydraulic cylinder was still weak.

d. Check the hydraulic oil filter element and bypass valve. The filter element is clean and the bypass valve is normal.

e. Check the safety valve and working condition. Open the side cover of the oil tank, find a plexiglass to make a cover plate, and fix it in the side cover hole with 4 bolts. When the engine does not operate, observe that the oil level is calm. When pulling the control lever to the "up" position of the hydraulic cylinder, it is found that a large amount of oil is injected from the interface of the safety valve block. Therefore, it is judged that the safety valve leaks, causing the pressure drop of the hydraulic system.

f. After disassembling the safety valve, it was found that 2 of the 4 connecting bolts on the right side were loose and a 0-ring between the valve bodies was broken. After replacing the new O-ring, the hydraulic cylinder works normally, but there is still noise at the oil tank. After opening the exhaust plug to exhaust, the noise is eliminated.

(3) Fault cause summary and Prevention

The main cause of the fault is that the two connecting bolts of the safety valve are loose, resulting in uneven compression force of the valve block. Under the action of high pressure, one side of the O-ring is first washed out, and the system pressure is relieved, resulting in the occurrence of the above faults.

Prevention measures: in order to prevent the bolt from loosening again, in addition to tightening according to the specified torque during assembly, loctite glue shall be applied at the thread to completely solve the problem of bolt loosening and prevent similar faults.

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