Abstract: A sealing structure capable of various uses and particularly in butterfly valves having a body with a flow passage and a movable valve disc in the flow passage and having a sealing surface. The sealing structure is mounted in the body to engage the disc in the closed position of the latter to provide a high performance (i.e. bubble-tight) seal. The sealing structure includes an annular seal retaining cavity with a slot opening to the flow passage. The structure includes a seal ring of Teflon, PFA or the like retained in the cavity and sealing one axial side of the ring from the other. It also has a tongue-like extension projecting through the slot into the passage and having a seat at its end engageable with the sealing surface of the disc. The seal and cavity structures have shoulders normally (in open position of the valve) abutting each other to seal the interior of the cavity (the abutment occurring from expansion of the seal ring into place in the cavity).