Fuel dispensing nozzle after starting, members of the fuel dispensing nozzles switch, oil through the main valve hole, the text's pipe, outlet valve and output after the barrel.Refueling, due to the oil rapidly through the venturi, between the venturi tube and vice seat sealing cavity form the low pressure area, all the way to the trachea to barrel front-end gas mouth, until the self-control membrane cavity. When the fuel dispensing nozzle oil containers or bubble has yet to reach gas mouth, fuel dispensing nozzles low pressure area for gas mouth ventilation big release;Gas oil or foam flooding gas mouth, the mouth is gas pump nozzles blocked, in self-control membrane cavity form the negative pressure, make automatic film up, gas pump nozzles steel ball slide.