Abstract: A rotary valve for a wind brass instrument comprises, as usual, a housing having a cylindrical wall with four duct connecting pieces fixed thereto about the circumference thereof. It also comprises a rotating member including a continuous metal shaft with end portions forming journals, a middle portion having a core element made of plastic material which does not swell in a wet environment, a metal jacket snugly fitted upon the core element and forming a fluid-tight joint with the cylindrical wall of the housing, and one or more pins engaged in respective bores extending diametrically through the jacket, core and shaft.