Vacuum Controlled Orifice Tank Vapor Valve

Some vehicles use this valve (VCOTVV) in the fuel tank vent line, between the fuel tank and vapor canister, to retain the fuel vapor within the tank until tank pressure reaches a predetermined level. With the engine off, when the tank vapor level reached that predetermined level, the valve opens, allowing the vapor to flow to the vapor canister. With the engine running and manifold vacuum connected to the valve's signal port, the valve is open, allowing vapor to flow to the canister.