Vacuum brake power booster

A vacuum brake power booster for automotive vehicles comprising:

• a booster housing whose interior is subdivided into a vacuum chamber and a working chamber by a movable wall,
• a control housing carrying the movable wall and accommodating a control valve which controls a pressure differential acting upon the movable wall,
• an actuating rod composed of a first sealing seat provided in the control housing and a second sealing seat provided on the valve piston displaceable by the actuating rod, said first and second sealing seats being arranged concentrically in relation to one another, as well as of an elastically deformable valve member,
• a movable third sealing seat being provided which is operable by an electromagnet, which is arranged concentrically in relation to the sealing seats and which permits ventilation of the working chamber irrespective of the position of the actuating rod, wherein the electromagnet, is rigidly coupled to the valve piston and resides in the control housing in a slidable relation therewith (9), wherein the third sealing seat is synchronously movable with the valve piston.