Abstract: A sealing mechanism particularly for a rotary valve wherein a recess around the valve body carries a resilient seal ring engageable with a sealing surface on the valve closure member. The resilient seal has a narrow sealing portion which extends through the narrow opening of the recess and a wider body portion which normally seats on shoulders within the recess. A pair of flexible lips extend radially from the body portion to engage and seat against converging recess walls. In closed position of the valve the body portion of the seal ring is forced away from the recess shoulders and the radial lips are forced into firm engagement with the converging walls to provide static seals on the valve body. Fluid on the high pressure side of the seal ring deflects the upstream lip away from the tapered walls and enters the recess cavity to force the downstream lip against the tapered wall and biases the seal ring into firmer sealing engagement.