The 442 overfill prevention device series is a prevention system designed to avoid liquid leaking out of tank during filling. This device is a valve based on the action an external float in contact with the fluid to close the flow and prevent to overfilling the tank. As the liquid rises, the float also rises with the liquid and, through a mechanism of levers, activates a plate in order to close the valve.
There are two types of valves in the series; the float in the first one has a vertical movement while the float of the second one has a side movement to close the plate. All overfill valves are two stage except the 442S-80 AL and 4420R-80 AL models which are single stage.