Abstract: Disclosed is a subunit consisting of a hollow cylinder (1) which is provided with an opening on at least one face and in which a spring bearing (2) is arranged on the inside of said face, a first valve spring (3) resting against said spring bearing (2). A shaft that is guided within the spring bearing (2) is disposed in the first valve spring (3) so as to be reversibly movable in the direction of the longitudinal axis of the hollow cylinder (1). A thrust bearing (5) for the first valve spring (3) is located at the end of the shaft (4), which faces away from said face of the hollow cylinder (1), said thrust bearing (5) being connected to the shaft (4). A second valve spring (6) is placed between the thrust bearing (5) and the interior on the opposite face (1a) of the hollow cylinder (1).