An actuator (4) is connected, on one side, to a valve needle (3), and on the opposite side, to a hydraulic piston (6) pertaining to a hydraulic length compensator. A working chamber (5) is divided by a tight separating membrane (9), into an actuator chamber (10) containing the actuator (4) and a fluid chamber (11) which can be filled with the fluid to be dosed in a pressurized manner while the actuator chamber (10) and the hydraulic chamber (7) are filled with a hydraulic fluid. A base pressure can be produced in the hydraulic fluid by means of the pressure of the fluid to be dosed, which is transmitted through the separating membrane (9).