A safety valve has movable and immovable valve elements, and a friction unit arranged therebetween for damping vibrations, wherein the friction unit has a plurality of friction members movable radially relative to a valve axis, a pressing member arranged to move the friction members so that their friction surfaces are pressed against a friction countersurface of a movable valve element of the movable valve means and for abutment against a stationary abutment member at their side facing toward a valve closing member, and a pretensioned auxiliary spring acting upon the friction members at their side facing away from the valve closing member and in a valve closing direction, wherein the auxiliary spring has such force and such a smaller resistance that in the event of seizing of the friction members with the movable valve element, the auxiliary spring is compressed within a predetermined opening pressure which does not considerably exceed a response pressure over approximately a valve stroke.