一次作业中,我们遇到了这样一例故障,有一台上海-50型拖拉机发动机突然工作无力,经查是喷油泵低压油路中有空气。排除空气后工作半小时左右故障又出现,如此重复多次,故障始终不能排除。面对此疑难故障,我们仔细地进行了分析,怀疑喷油泵上回油阀有问题。拆下回油阀后,发现回油阀弹簧过松,钢球顶不紧, A homework, we encountered such a failure, a Shanghai -50 tractor engine suddenly work weakness, the investigation is the fuel pump low pressure oil in the air. After excluding air for about half an hour or so failure appears again, so repeated several times, the fault can not be ruled out. In the face of this difficult fault, we carefully conducted an analysis, suspected fuel pump return valve problems. Remove the oil return valve and found the return valve spring is too loose, the ball is not tight,