​Common Faults and Removal of Mechanical Jack System（1）

Common Faults and Removal of Mechanical Jack System（1）
 Hydraulic mechanical transmission system is mainly composed of hydraulic pumps, control valves, torque converters, transmission and power shift transmission valves, etc. Its faults are usually manifested as inadequate walking or poor engagement of hydraulic clutch. The hydraulic system of working device is mainly composed of hydraulic pump, control valve, hydraulic motor and hydraulic cylinder.  However, the main fault is that the movement or rotation of the motor is weak, and the extension and retraction of the piston of the hydraulic cylinder are slow. The common characteristics of these two system faults are: insufficient system pressure.           
 On-site detection and diagnosis of faults           
 (1)  Preliminary Inspection and Diagnosis on Site             
 Comparing with the hydraulic system diagram, we can not neglect the seemingly simple reasons, nor can we blindly disassemble them in order to avoid unnecessary losses. The following steps should be taken in the specific inspection process.
 (1)  To understand the situation of the driver, the state of the machine and the sound when the fault occurs should be fully understood, so as to avoid making a fuss and turn it into a dilemma. For example, a 966D loader finds that the machine is powerless after changing the oil for the transmission. Torque converter oil temperature is too high. After checking, it was found that the wrong number of transmission oil was added. After finding out the cause of the  fault, the fault could be quickly eliminated.            
 (2)  Conduct necessary specific operations. Sometimes, the driver's statement of the causality of machine failure is not clear, which makes fault diagnosis  difficult. At this time, the necessary field operation will benefit a lot.           
 (3)  Inspection of oil quality and quantity. This content seems simple, but social services are often overlooked. For example, a 966D loader (its walking mechanism is a hydraulic transmission system), the driver has put out the transmission oil during the holidays. When the assistant came to drive after the relocation of the construction site, he found that the machine could not walk. It was thought that there was a big breakdown. However, the maintenance  personnel only listened to the sound and checked the oil gauge on the spot, which solved the problem and avoided the occurrence of major accidents. For example, a Hitachi EX220-2 excavator found that the hydraulic oil was insufficient after repairing the hydraulic cylinder, while the hydraulic oil  purchased on site was regenerated oil extracted by indigenous method, which caused oil pollution after being added to the tank. The deterioration and foaming result in the inability of the machine to move, and the trouble can be eliminated after replacing the hydraulic oil. Therefore, the inspection of oil quality and quantity must be paid enough attention; otherwise, the hydraulic pump will be burnt down and the transmission system will be damaged.           
 (4)  Check all kinds of filters. Oil filter is a cleaning tool of hydraulic system. When fault diagnosis is made, the inspection of oil filter (dirty degree of oil  filter, characteristics of various impurities on filter element, etc.) can provide basis for further analysis of fault. For example, a Garten HD820 excavator was found to be powerless after running for about 4000 hours. When the hydraulic system oil filter was dismantled and inspected, it was found that the filter element was damaged, the oil return outlet was blocked, and the failure was eliminated after the filter element was replaced.