If it is confirmed through troubleshooting that the bucket overturning is normal due to the hydraulic system fault and only the boom lifting is slow and weak. This shows that the working pump and the main safety valve are working normally. It also shows that the oil quantity and quality of the pipeline and oil filter at the oil inlet end of the pump as well as the oil tank are all right. At this time, it is only necessary to check the boom spool valve, boom oil cylinder, boom oil pipe and its seals. When the boom cylinder piston retracts to the limit, remove the oil pipe without rod chamber, so that the rod chamber of the boom cylinder can continue to be filled with hydraulic oil. If there is a large amount of oil leaking from the oil pipe port without rod cavity, it indicates that the hydraulic cylinder has internal leakage. You can also observe the sinking speed of the boom by filling the bucket with load and lifting it to the limit position, placing the boom control lever in the middle position and stopping the engine. Then place the boom control lever in the RAISE position. If the boom sinking speed is obviously accelerated at this time, internal leakage occurs in the hydraulic cylinder. If the sinking speed does not change significantly, the cause of internal leakage is the boom spool valve.
