Troubleshooting for weak lifting cylinder and falling shovel of bulldozers

During the operation of a D85 bulldozer, a fault occurred where the bulldozer blade quickly and automatically dropped after being lifted, and the vehicle did not respond when the bulldozer blade or loosening device was used to support the vehicle, that is, the vehicle could not be lifted.

Fault Analysis and Elimination

First, eliminate the fault that the vehicle cannot be started. When a bulldozer is working normally, it is a piece of cake to lift the vehicle with a bulldozer blade or a soil loosener. However, this vehicle cannot lift the vehicle when using the above-mentioned operation tools. Based on experience, it is judged that the pressure of the hydraulic system is insufficient. Upon inspection of the hydraulic filter, rubber debris and some small rubber pieces were found inside, but no metal impurities. It can be initially determined that the metal parts such as the hydraulic pump and hydraulic cylinder are not damaged. The fault may occur on the main safety valve. So the hydraulic oil tank was disassembled to inspect the main safety valve, and it was found that the valve core of the main safety valve was stuck. Clean the main safety valve, reinstall it and then conduct a test run. The vehicle can be supported by both a soil loosening tool and a bulldozer. At the same time, the vehicle can also be supported by both a bulldozer and a soil loosening tool. The fault of weak hydraulic system has been eliminated.

2. Troubleshooting the problem of the bulldozer shovel falling off. When the soil loosening device is lifted, it can remain at any position without sinking automatically. After the bulldozer shovel is lifted, the control lever returns to the center position. The bulldozer shovel sinks rapidly, and the sinking speed of the left hydraulic cylinder is slightly faster than that of the right one. Based on the analysis of the inspection of the hydraulic filter, it is initially determined that the left piston seal is damaged. When disassembling the left hydraulic cylinder, it was found that all the piston seals were damaged. After replacing the new seals and reinstalling the vehicle, the bulldozer shovel still sank. According to the working diagram of the vehicle and the hydraulic system that can be lifted by a bulldozer blade alone, it can be known that after the bulldozer blade is lifted, it will have a tendency to fall due to its own weight. Assuming that the seal of the right hydraulic cylinder also fails, when the control lever is in the middle position, the hydraulic oil in chamber 1 of the right hydraulic cylinder will enter chamber 2 through the gap between the piston and the inner wall of the cylinder. Then, it enters the left hydraulic cylinder 4 chamber along pipeline 3, and the hydraulic oil in the left hydraulic cylinder 5 chamber will enter chamber 1 along pipeline 6, causing the hydraulic oil to circulate, making the upper and lower chambers of the hydraulic cylinder communicate and causing the bulldozer to sink. Even if the piston seal fails when supporting the vehicle with a bulldozer shovel, the upper and lower chambers are connected. Since the upper chamber is a rod-free chamber and the lower chamber is a rod-filled chamber, the amount of oil discharged from the upper chamber cannot be contained in the lower chamber (V up =V down +V rod, V up >V down). Therefore, when supporting the vehicle with a bulldozer shovel, the vehicle cannot sink. So, the right hydraulic cylinder was disassembled for inspection. It was found that the piston seal was severely worn. After replacing it with a new seal and conducting a test run, everything worked normally.

Based on the above troubleshooting process, I believe that when eliminating faults in the hydraulic system, one should first review the hydraulic system flow chart, start from the vulnerable parts for analysis and inspection, and also combine common structural principles for analysis to avoid detours and reckless disassembly, which is conducive to the rapid elimination of faults.