such as nitrile rubber nbr is movable by the stroke movement h from the closed position fig1 into the fully opened position fig3 by means of the armature 3 against the force of the spring 4 in the opened position the shutoff body 2 bears against the lower edge of the abutment ring 5 the edge serving as an abutment 5 b for the shutoff body 2 in order to avoid noise in that situation the friction brake 6 as shown in fig2 comes into operation when the shutoff body 2 is still a friction distance r 1 at a spacing from the abutment 5 b more specifically at that moment the lower abutment flange 6 b bears against the annular hub which serves as a control body 5 a if the friction brake 6 were non displaceably connected to the stem 3 c then the shutoff body 2 could not reach its blocking position in order to make that possible the force of the drive body 3 urges the shutoff body out of the position shown in fig2 into the position shown in fig3 when that happens the friction brake 6 rubs along the friction surface 3 a whereby the abutment forces of the shutoff body 2 against the abutment 5 b are substantially.