Abstract: A sealing apparatus for applying seals, such as valves, over a pressure relief passage of a container. Displaceable retention members, positioned next to a platen having an applicator surface, releasably secure one or more seals adjacent the applicator surface prior to attachment to the container. A seal attachment element moves the applicator surface toward and into a seal attachment position adjacent the container. As the applicator surface moves, the displaceable retention members release to, in turn, effectuate attachment of the seals over the pressure relief passage. A retraction element operatively attached to the platen causes return movement of the applicator surface and, in turn, return of the displaceable retention members back into a seal retaining position.