fresh air component of the vapors is expelled into the atmosphere via canister vent valve 240 when controller 12 determines that conditions for canister purge e g the end of engine adaptive learning cycle ambient temperature barometric pressure etc are met it sends a signal to the valve assembly to enable fuel vapor purge from canister to engine valve assembly preferably couples engine to canister only during purging and fuel tank to canister only otherwise to store fuel vapors referring now to fig3 an example of the valve assembly components is described in detail a purge control valve 270 is located on the engine side of the fuel vapor purge control system and is selectively turned on and off by controller 12 alternatively the purge control valve may be continuously controlled thus varying the opening area of the communication passage 132 tank control valve 250 is used to isolate the fuel tank and is selectively turned on and off by controller 12 when the internal pressure of the tank exceeds a predetermined value the controller 12 sends signals to close purge control valve 270 and open tank control valve 250 in order to store fuel vapors in the carbon canister in addition when canister purge needs to be performed controller 12 sends a signal to open purge control valve 270 and close tank control 250 thus isolating the fuel tank with the purge control valve 270 open intake manifold vacuum draws fresh air from the atmosphere into the charcoal canister thus purging the vapors from the canister into the engine where they are burned with fresh air alternatively the opening area of the purge control valve.