The present invention is directed to a float actuated shut off valve for terminating the flow of fluid into a storage tank to prevent overfilling of the tank. The valve disclosed, while useful in other applications, is particularly well adapted for controlling the filling of underground fuel storage tanks such as are employed in service stations.
Underground fuel storage tanks utilized by service stations are filled via a fill pipe which extends upwardly from the top of the tank to a supply coupling located in a relatively shallow manhole in the service station apron. A supply hose from a tank truck is coupled to the supply coupling at the upper end of the fill pipe and, upon opening-of a shut off valve on the supply truck, fuel flows by gravity from the truck through the supply hose and fill pipe into the underground storage tank. Typically, neither the tank truck nor the underground storage tank are metered to provide a running indication of how much fuel has been dispensed into the tank during the filling operation. In theory, the delivery man is required to determine how much fuel is in the tank by inserting a dip stick into the tank through the fill pipe before coupling the supply hose to the fill pipe and is prohibited from coupling the fill pipe to a storage compartment in his truck tank which contains more fuel than the underground tank has room for. In practice, this last prohibition is almost universally ignored, and in the past, it was not an unknown practice to continue filling the underground tank until fuel started flowing out of the underground tank vent.
To prevent overfilling, many present day underground storage tanks are provided with a float actuated shut off valve which closes when the level of fuel within the underground tank rises to a preselected level, as, for example, when the tank is 95% full. Closure of these valves stops the incoming flow of fuel, but traps a substantial quantity, typically 25 to 30 gallons of fuel, in the supply hose between the float actuated shut off valve at the fill pipe inlet and the shut off valve on the tank truck. One solution to this problem is to provide an overfill storage container at the upper end of the fill pipe--see, for example, U.S. Pat. No. 4,793,387--into which the supply hose can be drained and the drained fuel subsequently drained from the overfill container into the underground tank when sufficient fuel has been withdrawn from the tank.
The basic problem with float actuated shut off valves is that while they prevent the filling of the underground storage tank beyond its capacity, they do not solve a main problem created by overfilling--namely the trapping of 25 or 30 gallons of fuel in the supply hose between the fill pipe and the shut off valve on the tank truck.
The present invention is directed to a solution to this last problem.