Pneumatic servo booster

Claim 1

In a pneumatic servo booster of the type including a housing, a movable wall partitioning the interior of said housing into two chambers, a valve body connected to said movable wall, and a valve mechanism including a poppet valve, a valve seat formed on said valve body and another valve seat formed on a plunger which is slidably fitted in said valve body, said valve mechanism communicating said two chambers when said poppet valve is spaced from said valve seat on said valve body and engages with said valve seat on said plunger, and said valve mechanism intercepting communication between said two chambers when said poppet valve engages with said valve seat on said valve body and is separated from said valve seat on said plunger, the improvement comprising: return movement restricting means for restricting directly the extent of return movement of said plunger with respect to said housing when said valve body returns to its return position during return movement of said valve mechanism to said non-actuated position of the servo booster, said return movement restricting means comprises a member which, when said servo booster is in said non-actuated position, has a first surface axially abutting said plunger and a second surface axially abutting a surface of said housing, thereby axially positioning said plunger with respect to said housing, said member comprising a portion extending through a radial passage in said valve body, and said passage partially providing communication between said two chambers when the servo booster is in said non-actuated position.