​Common Faults and Removal of Mechanical Jack System（2）

Common Faults and Removal of Mechanical Jack System（2）
 Before I told you about the first common failures and troubleshooting methods, now we are the second. If failures can not be eliminated after the above preliminary inspection, more detailed testing should be done with the help of instruments.           
 (2)  Instrumental Diagnosis of Hydraulic System           
 In general on-site detection, because of the difficulty of flow detection, and the failure of hydraulic system is often manifested as insufficient pressure, so in on-site detection, the method of measuring system pressure is more used. For example, when a 966D loader is running for 6000 hours, it is found that it is weak to walk, and the pressure values at the inlet and outlet of the converter are normal. When the power shift transmission valve is operated and the pressure of the directional clutch is measured, the pressure is only 0.5 MPa, that is, the normal pressure cannot be established. It was found that the oil seal in the oil channel of the directional clutch was damaged, resulting in hydraulic oil leakage, and the fault was eliminated after replacing the oil seal. Another example is an EX220-5 excavator, running 3000 hours after the current running deviation, detection of the walking system pressure found that the left side is 32 MPa, the right side is only 26 MPa, after adjusting the right-walking safety valve pressure, the fault can be eliminated.           

 (3) Computer Diagnosis           
 With the wide application of Electromechanical-hydraulic integration in engineering machinery, single pressure test can not meet the needs of on-site testing. Now more and more imported engineering machinery, its fault diagnosis needs to be completed by special testing computer, which has abundant data, small size and easy to carry. For example, a Hitachi EX220-2 excavator, the hydraulic system of the working device is weak, when operating the excavator handle, accompanied by a sound change and smoke. When using the computer to test, it is found that there is no significant change in the flow rate of hydraulic pump, and the engine changes when the pressure rises. Through analysis, it is considered that the flow rate of hydraulic pump is too large to adjust the flow rate of swash plate. When the servo valve of the hydraulic pump is disintegrated, it is found that the connecting pin of the servo valve and the flow adjusting swash plate of the hydraulic pump is broken, and the fault is eliminated after replacing the pin shaft.           
 (4)  Other diagnostic methods           
 On-site maintenance often adopts the method of exchange diagnosis without instrument, which is often used in the overall test of different types of machines. That is, if there is no detection instrument on-site or the components being inspected are more precise and not suitable for disassembly, other components on the same type of machine can be replaced for inspection, which can quickly diagnose whether there is a fault. If a CAT320L excavator works less than 500 hours, the hydraulic system of the working device is weak, and there is no testing instrument on the spot, the main safety valve is initially judged to be faulty according to experience; but when the main safety valve is disintegrated on the spot, it is found that there is no obvious wear and tear on the cone surface of the pilot needle valve, so another 320L excavator of the same type will be on the same site. The main safety valve was replaced with the safety valve, and the fault was eliminated after the test. This method is simple and feasible, but it must be judged accurately.