In the exhaust state, the pontoon pulls down one end of the lever due to the gravity. At this time, the lever is in the inclined state, and there is a gap at the contact part between the lever and the exhaust hole, and the air is discharged from the exhaust hole through this gap. 

With the discharge of air and the rise of water level, the float floats upward under the buoyancy of water. The sealing end face on the lever gradually presses against the exhaust hole until the whole exhaust hole is completely blocked, and the exhaust valve is completely closed at this time. 

This is the working principle of the complete exhaust valve, which is widely used at present and will be used in many pipe exhaust to solve the pipe exhaust problem in life.