Abstract: In a fuel vapor processing system, a float valve and a check valve are provided in upper parts of a fuel tank to conduct fuel vapor to a canister via a fuel vapor passage. The check valve includes a low set-pressure valve and high set-pressure valve, and operates in two stages so that the internal pressure of the fuel tank can be favorably controlled by the opening of the low set-pressure valve when the fuel tank is being filled to full so that the sensor associated with the fill nozzle can successfully detect a tank full state, and any excessive rise in the internal pressure of the fuel tank typically caused by a high temperature of the surrounding environment can be avoided by the opening of the high set-pressure valve.

Abstract: A fuel tank and a canister are connected to each other by a first evaporated-fuel passage and a second evaporated-fuel passage, and a valve chamber of a float valve separate from the fuel tank is disposed at an intermediate portion of the first evaporated-fuel passage. Thus, there is no limitation in the positional relationship between a filled-up liquid surface in the fuel tank and a valve seat of the float valve. Therefore, it is possible to reduce the vertical dimension of the float valve. Moreover, since the valve chamber is provided separately from the fuel tank, it is unnecessary to define an opening for mounting the valve chamber to the fuel tank.