Fuel tank pressure-vacuum relief valve

Claim 1

A pressure relief valve for a fuel tank of a motor vehicle equipped with an evaporative emission control system, said valve comprising: a cylindrical hollow casing having end portions said end portions being closed and having an inlet and outlet at said both end portions, respectively, said inlet communicating with the fuel tank and said outlet communicating with the atmosphere; a cylindrical movable valve element coaxially disposed within said cylindrical hollow casing and being in spaced relationship thereto and also in spaced relationship with said both end portions, said cylindrical movable valve element including a cylindrical wall portion, and an annular partition wall portion which is integral with the inner surface of the cylindrical wall portion adjacent one end of said cylindrical movable valve element, the one end being adjacent to one hollow casing end portion having the outlet, the annular partition wall portion having at least one radially outward hole therethrough; a compression spring interposed between the inner surface of the one hollow casing end portion having the outlet and the annular partition wall portion of said cylindrical movable valve element to bias said cylindrical movable valve element in the direction of another hollow casing end portion having the inlet; an annular resilient valve member mounted at its central portion on the annular partition wall portion of said cylindrical movable valve element, said annular resilient valve member having at its peripheral portion a flexible flap portion which is located opposite said compression spring with respect to the annular partition wall portion, the flexible flap portion normally urgingly closing the hole of the annular partition wall portion and opening the hole to introduce atmospheric air therethrough from the outlet of said cylindrical hollow casing to the inlet of said cylindrical hollow casing when fuel vapor pressure in the fuel tank drops bellow zero gage pressure; and a cylindrical resilient valve member securely mounted on the another end of said cylindrical movable valve element adjacent to the inlet of said cylindrical hollow casing, said cylindrical resilient valve member being formed with a central bore therethrough and an annular lip portion which is normally urged by said compression spring into sealingly contact with the inner surface of the another hollow casing end portion having the inlet, said cylindrical resilient movable valve member being moved to a position which unseats the lip portion from the inner surface so as to introduce fuel vapor from the fuel tank through the inlet of said cylindrical hollow casing and around said cylindrical movable valve element to the outlet of said cylindrical hollow casing when the fuel vapor pressure in the fuel tank exceeds a predetermined value.