Tank pressure control system

An apparatus for controlling discharge of fuel vapors from a fuel tank having a filler neck during refueling, the apparatus comprising

• means for conducting fuel vapor between the fuel tank and a distal portion of the filler neck,
• means for selectively blocking flow of fuel vapor through the conducting means, the blocking means being operable between a flow-blocking position and a flow-delivery position, the blocking means including an extension tube extending through the conducting means to communicate with liquid fuel in the fuel tank and valve means coupled to the extension tube for sealingly engaging the conducting means upon movement of the blocking means to its flow-blocking position,
• means for yieldably biasing the blocking means toward its flow-delivery position,
• means for encompassing the valve means to define a venting control chamber therebetween having a volume that expands in response to movement of the blocking means toward its flow-blocking position and contracts in response to movement of the blocking means away from its flow-blocking position, and
• means for using liquid fuel in the fuel tank to develop a pressure head having a pressure in excess of a predetermined threshold level in the venting control chamber to exert a closing force on the valve means in opposition to the biasing means so that the blocking means is moved to its flow-blocking position, thereby permitting discharge of pressurized fuel vapor in the tank to the filler neck through the conducting means.

A system for handling fuel vapors from a vehicle fuel system, the vehicle fuel system including a fuel tank having a filler neck, the system comprising

• means for conducting fuel vapor between the fuel tank and a distal portion of the filler neck,
• means for selectively blocking flow of fuel vapor through the conducting means, the blocking means being actuable between a flow-blocking condition and flow-delivery condition,
• means for containing pressure in a predetermined region communicating with the blocking means and permitting pressure to exert a closure-inducing force on the blocking means causing the blocking means to change to its flow-blocking condition, thereby blocking discharge of fuel vapor in the fuel tank to the filler neck via the conducting means, and
• means for increasing the pressure in the predetermined region in response to accumulation of liquid fuel in the fuel tank in excess of a predetermined volume.