Abstract: A diaphragm-activated control valve and system for both refuel and running loss venting of a fuel tank to a vapor trap. The control valve is connected to fill control and rollover valves in the fuel tank, and defines a separate venting flow path for each valve to the vapor trap. The control valve is responsive to pressure conditions at the filler pipe inlet to alternately open and close the flow paths. During refueling the control valve vents the tank through the fuel-level responsive fill control valve. When the filler pipe inlet is closed, the control valve switches to vent the tank through the rollover valve. In a preferred form, the control valve includes a liquid fuel drain to prevent its being disabled by fuel entering from the filler pipe inlet via the signal pressure line during refueling. The drain includes a reverse flow check valve to prevent vapor venting out the drain path to the atmosphere during refueling.