The typical BUTTERFLY VALVES heretofore known comprises an approximately cylindrical casing having an annular valve seat on its inner peripheral surface, a valve stem rotatably extending through the casing, a valve disk attached to the valve stem by a stem mount portion and having an outer peripheral edge portion opposed in its entirety to the valve seat when the disk is in its closed position, and an annular valve seal fixedly attached to the outer peripheral edge portion so as to be in pressing contact with the valve seat when the valve disk is in its closed position. With this butterfly valve, the valve seat, the valve stem, the valve disk and the valve seal must be prepared with high precision, and the valve stem, the valve disk and the valve seal need to be installed in place also with high precision. Butterfly ValvesOtherwise, it is impossible to assure a uniform pressure (seal pressure) of contact between the valve seat and the valve seal over the entire circumference when the valve disk is closed. Accordingly butterfly valves of this type which are satisfactory in performance are invariably expensive to make.

To overcome the above drawback, a butterfly valve has been proposed which includes clamp means at the outer peripheral edge portion of the valve disk for holding an annular valve seal. The valve seal is adjustably deformed by being compressed by the clamp means to realize the desired seal pressure despite the dimensional errors of the parts concerned and errors involved in installation. The butterfly valve nevertheless has the drawback that the valve seal breaks within a short period of time owing to fatigue deterioration because the seal is used as deformed by compression.

An object of the present invention is to provide a butterfly valve which is inexpensive to make and in which when the valve is closed, required uniform seal pressure can be obtained between the valve seat and the valve seal without entailing the problem of life.

In order fulfill the above object, the present invention provides a butterfly valve comprising a substantially cylindrical casing having an annular valve seat on its inner peripheral surface, valve stem means rotatably extending through the casing, a valve disk attached to the valve stem means by stem mount means and having an outer peripheral edge portion opposed in its entirety to the valve seat when the valve disk is in its closed position, and an annular valve seal attached to the outer peripheral edge portion of the valve disk so as be in pressing contact with the valve seat when the valve disk is in its closed position, the butterfly valve being characterized in that a) the valve disk is formed in the outer peripheral edge portion with an annular groove in communication with a resin injection channel, and that b) the valve seal is partially fitted in the annular groove and adapted for pressing contact with the valve seat and anchored in the annular groove by a resin injected into the groove through the resin injection channel at a predetermined pressure.

According to the construction described above, the valve seal is adapted for pressing contact with the valve seat by the resin which is cured after having been injected into the annular groove through the resin injection channel at the site.Butterfly Valves Consequently, the seal pressure between the valve seat and the valve seal can be set to a predetermined constant value over the entire circumference of the valve disk without excessively deforming the valve seal and regardless of the dimensional errors of the valve seat, stem, disk and seal and of the errors involved in installing these components.

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