Abstract: An improved by-pass valve (1) for use in the exhaust system of an internal combustion engine has control means (69) responsive to engine vacuum for exposing a chamber (27) to engine vacuum. The control means is responsive to an abrupt change in engine vacuum such as occurs during engine decelerations for spoiling the vacuum in the chamber and causing a vacuum responsive means (19) to close a first valve (15) and open a second valve (17). The control means reestablishes the vacuum in the chamber after a predetermined time interval causing the vacuum responsive means to open the first valve and close the second valve. The controlled opening and closing of the first and second valves prevents engine backfires. Means (117) overrides operation of the control means when engine temperature reaches a predetermined value whereby the vacuum responsive means maintains the first valve closed and the second valve open.

Abstract: A forced air control valve for an air injection system in an internal combustion engine is shifted during cold engine operation to divert air flow to the exhaust manifold upstream of a catalytic converter bed to supply air to the exhaust gases for further combustion prior to entry in the catalytic converter. A diaphragm operated main valve is responsive to a vacuum from the intake manifold for diverting air to the exhaust manifold and a temperature activated vacuum switch shuts off the vacuum when the engine warms up. Upon deceleration during cold engine operation the control valve is shifted to divert air away from the exhaust manifold.