Actuation device for a hydraulic system

The actuating device (1.1) has a volume displacement element (3.1) that is arranged partially in a working volume of a hydraulic cylinder (2.1). The hydraulic cylinder and volume displacement element are movable relative to each other. An actuating element (9.1) is arranged around an axis parallel to longitudinal axis of hydraulic cylinder. A translation assembly is provided to convert rotational movement of actuating element into axial movement of hydraulic cylinder or volume displacement element. An independent claim is included for brake system.