JPH0375791B

This invention is intended to solve such problem that a valve casing for use in a butterfly valve formed by press working is advantageous in the aspects of productivity, thickness and weight, but has a serious disadvantage of breakage or deformation lowering in sealing performance due to getting out or ageing of the seal ring when the valve is mounted on pipe line and clamped from both sides. From this point of view, a valve casing according to this invention is formed into a double structure composed of an inner shell and an outer shell, the inner shell comprising a cylindrical part defining a bore and seal ring receiving portions formed on both ends with their diameters enlarged larger than the cylindrical part, substantially forming a S-shape in section the outer shell defining a space by surrounding a whole outer periphery of the inner shell, and the inner shell and the outer shell being superposed each other at both end of the valve casing.