Ball Valves are already known in the prior art. The known ball valves comprise of valve body, a stem, a ball, seats, a pair of seat carriers, connecting sleeves and union nuts. The valve body has a cylindrical hole extending therethrough which forms the valve chamber. Ball ValvesThe stem extends laterally into the central portion of the valve body, with one end thereof projecting into the valve chamber. The ball has a bore diametrically extending therethrough and is inserted in the valve chamber and engages the end of the stem such that it is rotatably held in the valve chamber The ball must be able to be inserted into the valve body for assembling, and for this purpose the ball has a groove on the top thereof to receive and engage the end of the stem. Thus, the ball can be removed from the valve body when the ball is turned sideways, that is, in the state when the bore crosses the valve chamber in the valve body i.e., in the closed position.

A seat carrier is located on at least one side of the ball and, usually two seat carriers are located one on each side of the ball The seat carrier is provided with a ball seat on the end facing to the ball in close contact with the ball to set the ball in position and to allow the ball to rotate freely. BALL VALVESIf the ball seat is abraded by the rotation of the ball, after a period of use and a gap may be formed between the ball seat and the ball. The seat carrier is designed to be able to move towards the ball in the valve body to eliminate the gap. Thus, most of the conventional ball valves have not been designed to firmly secure the seat carrier to the valve body.

In order to prevent the seat carrier from moving out of the valve body, a connecting sleeve is provided in contact with the seat carrier and joined to the valve body by a union nut. Thus the ball seat is pressed against the ball via the seat carrier and the connecting sleeve by the force exerted by the union nut and this prevents the ball from coming out of the valve body. Therefore, if the ball seat is worn, it gives rise to play between the ball and the seat, and then the union nut must be further rotated to advance the connecting sleeve inwardly to bring the ball seat into close contact with the ball.

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