may be made of metal since the housing shell 9 of the actuator 7 is thin walled and not made of a ferromagnetic material the carriage 70 is entrained when the piston 8 is adjusted inside the actuator 7 in the process the length of the capacitor varies accordingly in this embodiment the lifting element is the piston 8 directly the special advantage of the seventh embodiment consists in that the displacement sensor 14 can be retrofitted with comparatively little effort it is only necessary to provide the piston 8 with the metal ring 76 and the displacement sensor 14 with the carriage 70 has to be mounted on the outer surface of the actuator 7 fig1 shows an eighth embodiment the same reference numbers are used for the parts known from the preceding embodiments and reference is made to the above explanations in this respect the essential difference between the eighth embodiment and the preceding embodiments consists in that in the eighth embodiment one end of the capacitor 16 is attached to the valve spindle 5 the latter is adjusted by a linear drive 80 the linear drive 80 is fastened to a component which follows the linear movement and to a stationary component in particular the linear drive 80 includes an electric motor 81 which drives a spindle nut 82 that is fixed in the axial direction the spindle nut 82 is arranged on a spindle rod 84 adjusting the latter in the axial direction when the spindle nut 82 is rotated in the eighth embodiment too the elongation of the capacitor 16 is proportional.