Numerous apparatuses have been proposed for preventing overfilling of fuel tanks. The most common used method is an automatic cut-off within a nozzle. Typically this automatic cut-off uses a vapor path from the nozzle outlet back to a venturi around the fuel flow path within the nozzle. A sufficiently high pressure must be maintained at a point within this path to indicate that vapor is being drawn into the vapor path rather than liquids. When liquids enter the vapor path, the pressure drop in the path increases, and the pressure at the sensor point will decrease. When this pressure decreased below a threshold pressure, the fuel flow is cut-off, usually by a mechanical trip. When a vapor recovery system that seals the fuel inlet is incorporated in a fuel dispenser, this automatic fuel cut-off will not function properly because pressure at the pressure sensor is subject to variations due to variations in the vapor recovery system. Such variations result in the shutoff not having sufficient consistency.
An electo-mechanical fuel cut-off switch is disclosed in U.S. Pat. No. 5,131,441. This switch includes an electromagnetic clutch that enables the trigger of a nozzle to close. When fluids are detected by a fluid actuated switch located in the nozzle spout, electrical energy to the electromagnetic clutch is interrupted, and the fuel valve is closed. This mechanism is said to be quick-acting, and therefore minimizes splash-back losses to the environment. An optical liquid sensor is suggested as the fluid actuated switch. The fluid actuated switch is located within the nozzle in the fuel dispenser of '441. The location of the switch within the nozzle relies on the fluid level raising within the nozzle. Because vapor is trapped within the closed volume of the nozzle, liquid will not necessarily back-up in the nozzle, but could raise outside the nozzle and be drawn into the vapor recovery system. Liquids could therefore be exiting the fuel tank into the vapor recovery system before the fuel flow is cut off by the mechanism of patent '441.
It is therefore an object of the present invention to provide a method and apparatus for cutting off fuel flow in a fuel dispensing nozzle wherein a vapor recovery system having a seal around a vehicle's fuel inlet can be utilized without effecting the fuel cut-off.