System for controlling fuel vapor flow discharged from a fuel tank to a

Abstract

A fuel control system includes a valve assembly disposed between a fuel tank with a filler tube and a fuel vapor storage canister. The valve assembly includes a housing having a vapor inlet port for establishing communication with the fuel tank at a level above the full level of fuel contained in the fuel tank, and a vent inlet port for establishing communication with the fuel tank until the full level is reached by fuel contained in the fuel tank. An outlet port is provided for establishing communication with the canister. A conduit is provided for transmiting signal pressure for establishing communication with the filler tube at a level above the fuel level of fuel in the filler tube. First and second check valves are mounted within the housing and respectively include valve seats, valve elements, springs and diaphragms. The diaphragms cooperate with the housing to define a signal pressure chamber communicating with the conduit. The first diaphragm acts on the first valve element against the action of the first spring in response to a difference between the pressure within the signal pressure chamber and the reference pressure. The second diaphragm acts on the second valve element in a direction assisting the action of the second spring in response to a difference between the pressure within the signal pressure chamber and the pressure at the outlet port.