Fuel tank air tightness detection method

The invention relates to a fuel tank air tightness detection method, which includes the steps of pushing a fuel tank from a right roller seat to a workpiece seat, plugging two circular orifices of thefuel tank with plunger plugs, and inserting an internal expansion plug into a ventilation pipe orifice of the fuel tank; and pressing the plunger plugs tightly with a pressure plate to ensure that the fuel tank does not leak air, at the same time, clamping the fuel tank tightly between the pressure plate and the workpiece seat, filling the inside of the fuel tank with air through the internal expansion plug and an air pipe, after the inflation is completed, driving, by the movable frame cylinder, a movable frame and the workpiece seat at the lower part thereof to descend, sinking the fuel tank on the workpiece seat to below the water surface of a water tank, and visually observing whether each fuel tank leaks air. The advantages of the invention are that the detection period is short, andthe production efficiency