Valve control mechanism

A control mechanism for turbo charged internal combustion engines having a control device responsive to intake manifold vacuum pressure, the combination comprising;

• a housing including a first member forming a valve cavity, said housing including a second member forming inlet, outlet and exhaust ports, said inlet port communicating with a variable source of vacuum, said outlet port communicating with said control device and said exhaust port communicating with the exterior of said housing, valve means including a valve element disposed in said valve cavity and being movable between a normal open position in which said inlet and outlet ports communicate with each other to an operative position in which said inlet port is closed and said outlet port communicates through passage means in said second member with said exhaust port and said control device, a movable wall a third member holding said movable wall relative to said second member and forming a control chamber at one side of said movable wall, the other side of said movable wall being connected to said valve element, a control port connected to said control chamber and being connected to said engine manifold, spring means biasing said movable wall to a first position to maintain said valve element in said normal open position in the presence of a pressure in said control chamber no greater than atmospheric pressure, said movable wall being movable to a second position in the presence of a positive pressure greater than atmospheric pressure to move said valve element to said operative position to isolate said control device.