The separating piston (4) which divides the inside of the work cylinder (2) into two pressure chambers (5,6) contains at least one additional flow path which connects these two chambers together. This additional flow path runs past the piston seal (3) which projects at least partially into this additional flow path and in order to open and close same is designed as a sliding part displaceable in the separating piston (4). The piston seal is set displaceable in a ring-shaped outwardly open circumferential groove (8) of the separating piston whose axial longitudinal extension is greater than that of the piston seal.
