A method of producing a ball valve which is adapted to be connected to a fluid piping system, and comprises a valve housing, and a ball rotatably contained in the valve housing,
- wherein the valve housing has a pair of openings, which are located in opposed positions so as to be connected respectively to pipes constituting the piping system, and a pair of stem assemblies which are located in opposed positions on a straight line perpendicularly intersecting another straight line, passing through centers of the pair of openings and a center of the ball;
- and
- wherein the ball has a through bore, which can be brought into alignment with the pair of openings to allow the passage of a fluid therethrough, and a pair of recessed portions receiving the pair of stem assemblies, respectively, and the ball is rotatable within the valve housing about a centerline passing through the pair of stem assemblies, characterized in that:
- a pair of housing halves for forming the valve housing, and the ball having the through bore whose opposite open ends are formed to be flat, are prepared, the pair of housing halves being so formed to be mirror-symmetrical bodies of which forms are defined by sectioning the valve housing at the middle between the pair of openings, and the ball being previously provided with a pair of recessed portions;
- annular valve seats, each forming a seal between an outer surface of the ball and an inner surface of the valve housing, are mounted on the pair of housing halves, respectively;
- the pair of housing halves are butted at their open ends, which are opposite to the openings, respectively, so as to enclose the ball, on the other hand, the ball is kept in such a position that the ball is turned by an angle of 90 degrees from a normal operational position of the ball valve, while causing the centerline of the through bore to be in alignment with an operational axis of the ball and to perpendicularly intersect the straight line passing through the centers of the pair of openings and the center of the ball;
- the butted open ends of the pair of housing halves are jointed together by welding, thereby forming the valve housing;
- subsequently, without changing the position of the ball, holes for mounting the pair of stem assemblies respectively, are formed by machining at those positions of the valve housing faced respectively to the both flat open ends of the through bore of the ball so that the centers thereof are located on the operational centerline of the ball valve;
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- the ball is turned by an angle of 90 degrees to be in the normal operational state of the ball valve such that the through bore is aligned with the both openings of the valve housing and that the recessed portions of the ball are aligned with the both holes of the housing, respectively, next, the pair of stem assemblies are attached to the both holes, respectively, and stems are fitted into the both recessed portions, respectively, and subsequently the pair of stem assemblies are welded circumferentially to edge portions of the holes, respectively.