an expanding room by using a clapboard arranged in the top of the fuel tank to space out fuel gas from fuel;

a canister arranged in the expanding room and having two guiding pipes communicated respectively with an entrance of an engine and the environment;

a fuel control valve arranged in the expanding room and adjacent to the canister, the fuel control valve being communicated with the expanding room; and

a double-lane valve arranged between the canister and the fuel control valve, the double-lane valve having an entrance communicated with the fuel control valve, an exit communicated with the canister, a first valve and a second valve arranged between the entrance and the exit, the second valve withstanding a spring and arranged on the first valve,

wherein the first valve opens to recycle the volatized fuel gas of the expanding room into the entrance of the engine through the fuel control valve when the first valve detecting an expanding press produced by volatilized fuel gas larger than a press produced by the spring and closes to prevent the fuel gas recycling when the expanding press being less than the press produced by the spring, the second valve opening to compensate air into the fuel tank through the canister when the second valve detecting a vacuum press of the fuel tank larger than the air press and closes to prevent the air entering into the fuel tank when the second valve detecting the vacuum press of the fuel tank less than the air press.