Butterfly valve

Claim 1

Butterfly valve comprising a valve housing having a a valve seat therein, throttle means located in said housing for movement between an open position and a shut-off position, a stem around which the throttle means rotates, seal face means on the throttle means for pressing against the valve seat when the throttle means is in the shut-off position to close the valve against flow of material therethrough, said seal face means defining a plane said seal face means including two opposite, essentially spherical shaped sections intersected by a symmetry plane through the throttle means coinciding with the torsional axis of the throttle means said plane of said seal face means being offset from said torsional axis, the said essentially spherical shaped sections being essentially the shape of a sphere having a radius R which is equal to one-half of the distance between the points of contact of the essentially spherical shaped sections of the seal face means with the valve seat when the throttle is in the shut-off position, said seal face means also including two essentially conically shaped sections on each side of said symmetry plane, said conically shaped sections being portions of a cone having a top rake between 10° and 40° and each essentially conically shaped section being located on said seal face means between said essentially spherically shaped sections, each said essentially spherically shaped section and each said essentially conically shaped section successively merging into each other, said essentially conically shaped sections and said essentially spherically shaped sections being in sealing engagement with a significant portion of said valve seat when said throttle means is in said shut-off position.