US Patent 7951474 Gas release valve

A gas release valve to be mounted in an access port of a battery cell includes a housing, the upper side of which is closed by a lid. The lower side of the lid has an opening leading into the battery cell and is in communication, via degassing passageways closed by an elastic sealing element, with at least one vent provided in the lid. The elastic sealing element is a preloaded non-return element, the inner surface of which is urged into sealing contact with a seat provided in the housing by it s own elasticity and, in addition, by a pressure differential with the outer pressure that acts through the vent against the outer surface of the sealing element.