Abstract: A vehicle on board system for recovering fuel vapors from the fuel tank both during filling of the fuel tank with volatile hydrocarbon liquid fuel and operation of the vehicle engine. A control unit in the fuel tank has a valve assembly actuated by a float to control the flow of fuel vapors from the top of the tank into a receiving canister with activated charcoal for absorbing the fuel vapors which can be purged from the canister by operation of the engine. The valve assembly has a valve seat, a flexible elastomeric closure received on a pivotally mounted carrier plate movable to open and closed positions relative to the seat, and a stripper plate encompassing the seat, overlying the closure and pivotally movable by the float to disengage the closure from the seat to open the valve.