A fuel tank vent valve disposed between the tank and a carbon canister to provide high volume venting between the tank and the canister under normal operating conditions. A diaphragm type control element within the valve pulls an internal valve plate against a seat when the filler pipe cap is removed thereby to close off the vent between the tank and the canister. The system operates with a filler pipe door seal of the type which is opened by the introduction of a filler nozzle. The vent valve is primarily constructed of molded plastic parts.