An actuator for axially displacing an object includes an actuator piston disc and an actuator piston rod, which together form an actuator piston, a cylinder volume, the actuator piston disc dividing the cylinder volume into a first part and second part and being displaceable in the cylinder volume between an inactive and active position, a pressure fluid circuit arranged for controllable fluid communication with the first part, and a first hydraulic circuit including a liquid-filled space, the actuator piston rod being disposed to be axially displaced in relation to the liquid-filled space in connection with axial displacement of the actuator piston disc in the cylinder volume. The actuator piston includes a second hydraulic circuit, the liquid-filled space being in fluid communication with an inner cavity in the second hydraulic circuit when the actuator piston disc is in the inactive position, the inner cavity partly being delimited by a positioning piston.