of the valve housing 1 a shell type core 7 of ferromagnetic material is inserted into the interior 5 of the valve housing 1 the core 7 has a diameter smaller than that of the interior 5 and rests with a shoulder 8 on an inner step 9 of the valve housing 1 the side of the shoulder 8 remote from the inner step 9 is engaged by a spacer ring 10 which is followed by a guide diaphragm 11 and a nozzle carrier 12 a crimped edge 13 partially surrounds the end face of the nozzle carrier 12 engaging it and exerting axial tension thereon so as to assure the positional fixation of the shell core 7 the spacer ring 10 the guide diaphragm 11 and the nozzle carrier 12 a conventional shell core available on the market from siemens and known as t 26 can be used for the shell core 7 this element has an annular outer core 15 and an annular inner core 17 connected therewith via a crosspiece 16 a magnetic winding 18 may be at least partially enclosed by an insulating carrier body 19 which together with the magnetic winding 18 is inserted into the annular space of the shell core 7 formed between the outer core 15 and the inner core 17 and is connected in a positively engaged manner for instance by rivets 20 or a releasable snap connection with the crosspiece 16 the supply of current to the magnetic winding 18 is efficaciously accomplished via contact prongs 22 only one of which is shown and which are embedded in an insulation insert 23 of glass for example the insulation insert 23 may be surrounded by.