A multi-piece valve disk of a sliding and/or seat valve, a ring seal with an elastic sealing ring with an external sealing zone is placed in a ring groove of the valve disk onto a dimensionally stable backup ring, and where an elastic restoring region effectively positioned between the backup ring and the external sealing zone is arranged in the backup ring, the restoring region being embodied in one piece with the sealing ring of its material adjacent to the external sealing zone of the sealing ring.