By-pass valve

摘要

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.