Fault Characteristics And Diagnosis Of Hydraulic System Of Construction Machinery

The characteristics of the failure of the hydraulic system of construction machinery. The hydraulic mechanical transmission system is mainly composed of hydraulic pumps, control valves, torque converters, transmissions, and power shift transmission valves. Its failures are usually manifested by weak walking or poor hydraulic clutch engagement.

The hydraulic system of the working device is mainly composed of a hydraulic pump, a control valve, a hydraulic motor, and a hydraulic cylinder. Its failure is mainly manifested by the weakness of the motor's walking or turning, and the extension and retraction of the hydraulic cylinder piston. The common characteristics of these two types of system failures are insufficient system pressure.

On-site detection and diagnosis of faults:

(1) Preliminary inspection and diagnosis on site

Find out the relevant situation according to the failure phenomenon, analyze the location of the failure and the preliminary cause against the types of pumps in hydraulic system diagram. Don't ignore the seemingly simple reason, and don't blindly disassemble to avoid unnecessary losses. The following steps should be performed during the specific inspection process.

① Learn the situation from the driver, and make a detailed understanding of the state and sound of the machine when the fault occurs, avoiding trivial problems and making it easy. For example, a 966D loader found that the machine was unable to walk after changing the oil in the transmission. Torque converter oil temperature is too high. After inspection, it was found that the wrong transmission oil number was added. After the cause of the failure was clarified, the failure was quickly eliminated.

② Perform necessary specific operations. Sometimes, the driver's failure to state the cause-effect relationship of the machine failure makes it difficult to diagnose the failure. At this time, the necessary on-site operations will greatly benefit.

③ Inspection of oil quality and quantity. This content may seem simple, but it is often overlooked. For example, a 966D loader (its walking mechanism is a hydraulic transmission system), the driver has completely drained the transmission oil during the holiday. When the assistant came to drive after the relocation of the construction site, he found that the machine could not walk. He thought that there was a major failure, but the maintenance staff at the scene only solved the problem by listening to the sound and checking the oil dipstick to avoid a major accident. For another example, a Hitachi EX220-2 excavator found that the hydraulic oil was insufficient after repairing the hydraulic cylinder, and the hydraulic oil purchased on site was reclaimed oil refined by the soil method, which was added to the fuel tank and caused oil pollution. Deterioration and foaming make the machine weak, and the fault can be eliminated after replacing the hydraulic oil. Therefore, attention must be paid to the inspection of oil quality and quantity; otherwise, the hydraulic pump will be burned and the transmission system will be damaged. Thus, you may need the hydraulic pump spare parts.

④ Check various filter elements. The oil filter is a cleaning tool for the hydraulic system. During fault diagnosis, checking the oil filter (the degree of dirt on the oil filter, the characteristics of various impurities on the filter element, etc.) can provide a basis for further analysis of the failure. For example, a Jiateng HD820 type excavator found that the whole machine was weak after running for about 4000 hours. When disassembling its oil filter of the hydraulic system, it was found that the filter element was damaged and the oil return port was blocked. The fault was eliminated after replacing the filter element.