Abstract: A pressure control valve for controlling vapor pressure in a fuel tank has an inlet line from the fuel tank, a pressure sensing line from the filler pipe, and an outlet line to a canister for handling the fuel vapor. Fuel vapor flow through the valve is controlled by ambient pressure from the filler pipe and tank pressure from the fuel tank, with those pressures acting on two diaphragms within the valve to alternately allow flow through the valve during normal vehicle operation and to prevent flow during refueling. A pressure relief valve is connected between the filler pipe line and the canister outlet line to prevent tank overpressurization should the valve malfunction.