Pneumatic brake booster

A pneumatic brake booster comprising a housing (10) which is divided into a vacuum chamber (14) and a working chamber (12), in which

• a dual valve arrangement (20) having a first valve means (24, 26) between the vacuum chamber (14) and the working chamber (12) and a second valve means (24', 26') between the ambient atmosphere (A) and the working chamber (12) is arranged at the housing (10), in which
• the valve arrangement (20)
• in an inoperative position, allows having pressure levels in the vacuum chamber (14) and in the working chamber (12) separate from the atmosphere (A),
• in an operative position, keeps the vacuum chamber (14) sealed off and allows communication between the atmosphere (A) and the working chamber (12),
• in normal operation, the first valve means (24, 26) and the second valve means (24', 26') are adapted to be actuated by a common actuating rod (34), and
• in a controlled operation, when the actuating rod (34) effects an opening of the first valve means (24, 26), an electromagnetic actuator (40, 46) which is independent of the actuating rod (34) prevents communication between the vacuum chamber (14) and the working chamber (12) by a sealing element (64) coupled to the electromagnetic actuator (40, 46), the electromagnetic actuator (40, 46) so preventing said communication by moving the sealing element (64) into a position preventing a passage through the first valve means (24, 26).