I believe a two port canister would use a control valve like the one in the picture below with that valve controlled by the engine computer.
The vent valve lets air into the tank when cruising down the road so that you get fuel flow to the engine.
Otherwise you would be creating a vacuum on the fuel tank. NOT GOOD.
The Vent Valve would close when the engine is off, keeping the fumes trapped in the canister.
The purge valve would open at a given point in the engine cycle and the vent valve would open and remove gas vapors from the canister and excess gases from the fuel tank. then the valves would switch back into normal vent mode to the fuel tank.
Tom V.
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"Engineers do stuff for reasons" Tom Vaught
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Last edited by Tom Vaught; 06-28-2020 at 07:05 PM.
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