A valve element may be configured to be mounted in an air intake passage of a container. The valve element may be at least partially elastically deformable. The valve element may include a valving member configured such that, when vacuum pressure inside the container is less than a predetermined threshold differential from atmospheric pressure, the valving member is in sealed contact with a seat formed on the container. The valving member may also be configured such that the valving member moves away from the seat when the predetermined threshold differential is reached, so as to allow air to be taken into the container. By elastic return, the valving member may return to a position in sealed contact with the seat when the vacuum pressure inside the container drops back to less than the predetermined threshold differential. The valve element may be placed in a functional configuration via an elastically irreversible modification thereof during mounting.