Trouble removal of hydraulic system on QY8 truck crane (two)

On the hydraulic system may cause low pressure on the reasons, in accordance with the "first easy after difficult" principle, itemized investigation. First of all, the branch valve 3 to push the stem to make the leg hydraulic system work position, to control the leg control valve (outrigger relief valve set pressure 21MPa), the results confirmed that the plunger pump 1 and oil filter 2 work properly.

Then, 3 shunt valve stem is pulled out, the car hydraulic system, operating luffing handle, adjusting the set pressure relief valve of the car at the same time, it is found that the pressure is low, so the car dismantling the relief valve 6, found no problem; then built on the control valve 7, also found no problem. Finally, to determine the reasons for possible failure in 3 shunt valve, the shunt valve 3 after the disintegration of the body, a right side seal ring leakage (see Figure 2), which is on the right side of the valve body sealing step by hydraulic oil shock, the surface layer due to seal failure. When pulled out 3 shunt valve stem, plunger pump oil at P by P2 and all the car flow hydraulic system, but because the shunt valve 3 valve leakage, resulting in a large number of hydraulic oil leaked to P1 and the flow of outrigger hydraulic system, and the support leg control valve (M type three four valve position is unloading function) directly back into the tank, causing the volume low pressure hydraulic system. After the bypass valve 3 is replaced, the fault is eliminated.