| 摘要 |
In a ball valve, valve seats are spring-urged against a valve ball turnable between open and closed position. Each seat has an annular face confronting the ball, the face being a surface of revolution of a line inclined to the said axis. The face is interrupted by an annular groove so as to leave a radially inner annular rib having a radially inner part of the said face. At low pressures there is line contact with the ball nearer the radially outer edge of the inner face part. however, at high pressures elastic distortion of the ball is accompanied by an elastic radially outward flexing of said rib so that said line contact moves nearer the radially inner edge of the inner face part. The contacting surfaces of the ball and the seats are preferably coatings of tungsten carbide. In normal operation the outer face part is clear of the ball but is available for contact with the ball in emergency conditions.
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