Tandem diaphragm brake booster

Claim 1

A tandem diaphragm brake booster which comprises: 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 securing member interconnecting said partition wall with said housing; cylindrical means secured to said first diaphragm and axially slidable therewith, said cylindrical means being made of metal; piston means secured to said second diaphragm and axially slidable therewith; first fluid passage means provided in said cylindrical 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 securing member for fluid communication between said second and fourth chambers; third fluid passage means provided in said 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; and 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 cylindrical means and said piston means and receiving therein said plunger; and a key member disposed in said piston means and extending radially into engagement with both said plunger and said case member to thereby retain said case member in said piston means and to limit axial movement of said plunger, one end of said cylindrical means extending radially inwardly and being disposed and retained between said case menber and said piston means, so as to connect said cylindrical means and said piston means by said key member wherein the other end of said cylindrical means extends radially outwardly and is secured to said first diaphragm.