Tandem brake booster for automotive vehicle

A tandem brake booster for automotive vehicles comprising:

• a housing the interior of which is subidivided into front and rear chambers by means of a partition wall member assembled therein;
• front and rear movable walls respectively assembled within the front and rear chambers and arranged to be connected to each other through said partition wall member, said front movable wall subdividing the front chamber into first constant and variable pressure chambers, and said rear movable wall subdividing the rear chamber into second constant and variable pressure chambers;
• a front cylindrical hub member secured at its front end to the inner peripheral portion of said front movable wall and extending from the first constant pressure chamber into the second constant pressure chamber across said partition wall member;
• a rear hub member secured to the inner peripheral portion of said rear movable wall coaxially with said front cylindrical hub member and being engaged with the rear end of said front cylindrical hub member, said rear hub member being formed with a cylindrical portion which extends into the first variable pressure chamber across said partition wall member and is arranged in surrounding relationship with said front cylindrical hub member, the cylindrical portion of said rear hub member being axially slidably supported by said partition wall in an air-tight manner;
• a cylindrical seal member disposed between said front cylindrical hub member and the cylindrical portion of said rear hub member, said cylindrical seal member being formed in its peripheral wall with a first recess for providing a first passage for commmunication between the first and second constant pressure chambers and with a second recess for providing a second passage for communication between the first and second variable pressure chambers;
• and
• valve means assembled within said rear hub member for interrupting a communication of the second variable pressure chamber with the atmospheric air in a released condition of said brake booster and for establishing the communication of the second variable pressure chamber with the atmospheric air in operation of said brake booster.