the vent line 11 leading to the adsorption canister fig2 a 2b and 2c describes details of the valve 10 from fig1 the filler neck 13 forms the mounting for the valve fastened into the filler neck is the liner 14 which contains threads to engage the filler cap not shown the liner has a hole 15 slightly larger in diameter than the fuel dispensing nozzle 16 to guide the nozzle restrict fuel splashback and to prevent larger nozzles from being inserted the nozzle is of the type which automatically shuts off when fluid begin to back up in it around filler neck 13 is a collar 17 for mounting the filler neck to the vehicle structure attached to the end of the filler neck 13 is the fill tube 3 covering hole 15 is a flapper 18 made of thin resilient metal which swings away from hole 15 when nozzle 16 is inserted and which seals against hole 15 when nozzle 16 is withdrawn the liner 14 hole 15 and flapper 18 are widely used with filler neck 13 and fill tube 3 in production vehicles to prevent larger diameter leaded fuel nozzles or funnels from being used to fuel the vehicle flapper 18 is fabricated with folded over extensions 19 forming sockets 20 for attachment of pivots 21 at the end of the valve stem 22 the folded over extensions.