故障现象是:拖拉机运输时,拖车突然不能提升或不能完全提升。检查时发现外提升臂处于提升位置。将控制油缸油路的截断阀拧出至非截断位置,用力压下外提升臂,排出油缸里的油,再将截断阀拧入到截断位置,液压输出便恢复正常。产生故障的原因是由于截断阀的密封性能较差。在进行液压输出时,高压油会经过截断阀进入油缸, Symptom is: tractor transport, the trailer suddenly can not be promoted or can not be fully upgraded. Inspection revealed that the outer lift arm is in a raised position. Will control the oil cylinder cut off the valve out to the non-cut-off position, the pressure down the outer lift arm, the oil discharged from the cylinder, and then cut off the valve into the cut-off position, the hydraulic output will return to normal. The reason for the failure is due to the poor sealing performance of the cut-off valve. During the hydraulic output, the high-pressure oil will enter the cylinder through the cut-off valve,