Brake booster with simplified airflow

At rest the rubber sealing element (15,16) is not in contact with the piston seating (26) and the low pressure zone (8) is connected to the rear (9) of the piston (4,7). The plunger seating (20) is in contact with the sealing element and prevents atmospheric air from entering the rear piston zone. In operation when the braking control rod is pushed the reverse situation obtains and atmospheric air flows through a radial passage (37) to operate the piston.