Abstract: A sealing device for a piston that is subjected to the action of a pressure medium and that is arranged in a working cylinder, whereby a piston rod guide is arranged in or on the working cylinder and the rod guide has annular recesses. In addition, elastic sealing rings and a guide are located in the recesses. At least one additional slot provided for accommodating an additional elastic sealing ring is configured in the rod guide or in a cylinder ring connected to the pressure chamber or working chamber, and which surrounds the piston rod in a concentric manner. In addition, a mechanism is provided in order to, if required, apply forces that are directed from the outside in a manner that is radial to the piston rod onto the additional sealing ring, so that the sealing ring is moved or deformed such that it is transferred from a non-sealing position to a sealing position.