An improved BUTTERFLY VALVES of the type wherein a disc mounted for rotation about a nondiametric axis and having a continuously convergent circumferential sealing surface which cooperates with a wall-mounted annular flexible seat is disclosed. The inwardly projecting nature of the flexible seat subjects it to highly erosive forces when fluid is throttled between it and the disc when the disc is opened to a throttling position, i.e. approximately 15° from the closed position or greater.Butterfly Valves To protect the seat from such erosive forces, the rigid wall of the fluid flow channel is projected inwardly on both sides of the seat to provide a far more erosion-resistant surface for throttling operation. These same inward projections can also be employed to provide a scraping lip which will remove solids buildup from the sealing surface of the disc as it is rotated toward the seat. A manner of affixing the disc to the shaft without providing a leak path across the disc and whereby the forces imposed by fluid pressure upon the disc are transmitted directly to the shaft is also disclosed. Butterfly ValvesThis entails passing the shaft through a shaft bore in an integrally formed gudgeon in said disc and passing tapered pins parallel to the surfaces of the disc through the gudgeon and shaft in such a manner that a majority of, but not the entire circumference of, the tapered pin lies within the circumference of the shaft. Rotation of the disc beyond the desired one-quarter turn from the fully closed to the fully open position and displacement of the disc along the direction of the axis of the shaft are prevented by lugs extending into the fluid flow channel from the valve body.

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