how does a float type air vent work
Automatic bleeding valve If the valve body is filled with water, the float moves upwards and closes the valve. If air collects in the valve body, the waterline lowers, as does the float, and the valve opens to release it.[3] To give more sealing force on the valve, the float generally works the valve through a lever. A greater movement of the float gives a shorter, but more forceful, movement of the valve. This lever mechanism may be simply, almost crudely, made of a pressed steel strip which acts as a bending hinge.[4]