| 摘要 |
A two stage float actuated shutoff valve for preventing overfilling of an underground storage tank has a first float actuated valve flapper movable to a closed position to block a major portion of the fuel inlet passage of the underground tank when the level of fuel in the tank rises to a first predetermined level. Closure of the first valve blocks a first portion of the flow passage while maintaining a second portion of the flow passage open to permit a reduced flow of fuel through the flow passage, thereby generating an observable water hammer effect signalling that the filling operation should be terminated. If the incoming flow is not terminated, the continued rise of the level of fuel in the tank will in time actuate a second float controlled valve to completely close the fuel inlet passage. The incoming fuel is supplied from a delivery truck tank, fuel flowing gravitationally from the truck tank through an operable shutoff valve on the tank, a delivery hose and a drop tube into the underground tank. Once closed, the second float controlled valve will remain closed as long as the truck tank shutoff valve is open, upon closure of the truck tank shutoff valve the resulting reduction of the hydraulic head on the second valve is reduced to a head which can be overcome by a spring biasing the second valve to its open position to so that fuel can be drained from the delivery hose and drop tube into the underground tank.
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