Abstract: A sealing device for containers which forms a valve for automatic elimination of overpressurized gases that may form with the container is provided. The device is composed of a rigid cap having a flat crown and depending skirt, an elastic disk sector in contact with the underside of the flat crown and an inner cap having a circular crown with a circular cutout and raised circular rim on an upperside thereof. A flat circular protuberance on the underside surface of the disk sector, when the device is in use fits into and is surrounded by the circular crown portion, both of which are adapted to fit vertically over the orifice of the container. When in use, the circular crown exerts a crushing pressure on the upper portion of the elastic disk sector while at the same time the flat circular protuberance remains sufficiently elastic to allow gases overpressurized to vent from the container.