Tandem brake booster

Claim 1

A tandem diaphragm brake booster comprising: a housing; first and second diaphragms disposed in said housing in spaced relation to each other; a partition wall disposed between said first and second diaphragms within said housing for defining first, second, third and fourth chambers within said housing; a first piston means secured to said first diaphragm and axially slidable therewith; a second piston means secured to said second diaphragm and axially slidable therewith; first fluid passage means provided in said first piston means for fluid communication between said first and third chambers, said first chamber being in communication with a vacuum source; second fluid passage means provided in said partition wall for fluid communication between said second and fourth chambers; third fluid passage means provided in said second piston means for fluid communication between said third and fourth chambers; valve means disposed in said third fluid passage means for preventing fluid communication between said third and fourth chambers and introducing atmospheric pressure into said fourth chamber, thereby creating pressure differentials between said first and second chambers and said third and fourth chambers, respectively; an operator-operated means for actuating said valve means in response to manual operation; said valve means including a plunger operatively engaged with said operator-operated means and axially movable within said piston means; a case member disposed in said first and second pistons and receiving therein said plunger; and a key member disposed in said second piston means and extending to said plunger and said case member, thereby to retain said case member to said second piston means, one end of said first piston means being disposed between said case member and said second piston means, thereby connecting said two piston means by said key member.