Rotary valve of brass instrument

Abstract

A rotary valve is provided for a brass instrument to produce brass sounds of different pitches by changing over a tube length of a resonance tube. Herein, a rotor is inserted in a valve casing. The valve casing has a cylindrical shape whose both ends are openings, wherein ports are formed on a periphery, while the rotor has a cylindrical shape whose outer diameter is slightly smaller than that of the valve casing, wherein two shaft portions respectively project from the end faces of the rotor as its integral parts, and change-over paths are formed on a periphery. An implantation bottom covers one opening of the valve casing, while an implantation upper cover covers another opening of the valve casing. The shaft portions of the rotor are rotatably supported by radial ball bearings respectively. A depression member is inserted between the implantation bottom and radial ball bearing to depress the rotor in its axial direction. An upper cover setscrew fixes the implantation upper cover to the valve casing. In addition, a rotation base is rotatably fixed to the upper cover setscrew. Herein the implantation upper cover functions as a stopper to regulate rotation of the rotation base. Further, a lever is provided in connection with the rotation base. When a human operator manipulates the lever to rotate the rotation base, the rotor is correspondingly rotated to change over connections between the paths of the rotor and the ports of the valve casing. Since a resonance tube and a retractable tube are selectively connected to the ports, it is possible to change pitches of brass sounds by changing over the paths of the rotor. Incidentally, an outer race of the radial ball bearing is provided to engage with an inner peripheral surface of the valve casing in proximity to its opening and is greater than the rotor in outer diameters by 30 .mu.m or so.