Abstract: An air valve for an internal combustion engine, said air valve comprising a valve body (10,19), a passage (27) in said body, valve means adapted to normally close said passage (27) to prevent egress therethrough of spent combustion products from said engine and to open on creation of a pressure drop within the engine to permit air to flow through the passage (27) into the engine. The valve means comprises a flexible valve element (18) engageable with a valve seat (26) associated with said passage (27), and means (17,22) for tensioning said flexible valve element (18) to assist effective operation of the valve element (18).