BALL VALVE AND SEAT ASSEMBLY

A ball valve having an improved relationship between the ball and associated seat rings and an improved seat ring design. The ball is mounted for selective rotation and limited axial movement in a valve body passageway. Seat rings disposed on diametrically opposite sides of the ball about valve inlet and outlet openings each include a ball engaging surface having an arcuate contour. At a relaxed preassembly reference position, the radius of curvature of the ball engaging surface is greater than the radius of curvature of the ball. Frusto-conical disc springs interposed between each seat ring and an associated valve body shoulder additionally urge the seat rings into engagement with the ball. A reinforcing ring disposed at the forward end of each seat ring acts as a rigid bearing surface. Component sizing is such that in the assembled valve, the seat rings are slightly rotatably flexed in response to the engaging surfaces thereof engaging the ball such that the surfaces are distorted to have a mating relationship with the ball. At the same time, the disc springs are compressed while continuously urging the seat ring ball engaging surfaces into ball engagement.