plane in a preferred embodiment of the present invention the radial extension of the surface section located on the inside is considerably smaller than the radial extension of the conical surface section located radially on the outside or than the wall thickness of the pole tube in this area fig1 shows part of a longitudinal section through a pole tube 1 of a proportionally adjustable actuation magnet with a pressure tight construction the pole tube 1 consists essentially of a pole piece 2 a spacer ring 4 and a tube piece 6 in the solution presented here the spacer ring 4 has been manufactured by means of build up welding in principle however this spacer ring 4 can also be prefabricated as a separate component and then joined to the pole piece 2 and to the tube piece 6 for instance by means of thermal joining together these three components form an armature space 8 in which an armature 10 is arranged with an air gap so as to be axially movably a tappet 12 that passes through the pole piece 2 in the axial direction and that is directly or indirectly connected to a control stem of a valve for purposes of actuating the latter is affixed to the armature 10 it is also possible for the tappet 12 to be configured as a separate component so that the armature 10 strikes against the tappet 12 in the end section shown on the right hand side of fig1 the pole tube 2 has a central thread 14 by means of which it can be screwed into a valve hole of a valve housing so that the tappet 12 is in operative connection with the control stem of the valve the tappet 12 u2014 which.