A valve housing having a cylindrical fluid passage therethrough; a disc shaped valve body having a hard annular rim of elliptical cross-sectional shape thereon extending in the plane of the valve body rotatable about an axis perpendicular to and intersecting the longitudinal axis of said fluid passage;BUTTERFLY VALVES drive means to turn and lock said valve-body;
a hard annular vavle seat mounted in said housing; Butterfly Valvessaid seat having an inner annular surface of elliptical cross-sectional shape extending in a plane perpendicular to the longitudinal axis of said cylindrical fluid passage corresponding to the periphery surface of an imaginary cylinder having an axis lying at an angle to the longitudinal axis of fluid passage in the direction of rotation of said valve body, said peripheral surface defining a cross-section in said imaginary cylinder of elliptical shape, the axis of said cylinder intersecting the longitudinal axis of said fluid passage at the same point as the axis of rotation of said valve body, BUTTERFLY VALVESsaid rim on said valve body having inclined peripheral surface which in the closed position of the valve corresponds to and seals with the inner annular elliptical cross-sectional surface of said seat.

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