Pneumatic control system and pressure responsive valve assembly therefor

Claim 1

A pneumatic control system comprising a carburetor having a vacuum inlet; a device for advancing the spark timing of an engine; and a pressure responsive valve assembly comprising a housing which includes an inlet port communicated with said vacuum inlet and an outlet port communicated with said advancing device, a diaphragm dividing the interior of said housing into a first chamber communicated with said vacuum inlet through said inlet port and a second chamber communicated with atmospheric air, a power piston secured to said diaphragm for unitary movement therewith, a first spring disposed within said first chamber for urging said power piston to move in one direction, said power piston being moved in the other direction against an exerting force of said first spring when a vacuum is applied to said first chamber, a valve member operatively associated with said power piston and cooperative with a valve seat to control the admission of atmospheric air to said advancing device from said second chamber via said outlet port, and a second spring disposed between said power piston and said valve member and having a smaller exerting force than said first spring, thereby urging said valve member to rest on said valve seat when said power piston is being moved in said one direction.