Importance

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Abstract

A ball or plug valve comprises a ball or plug having a through bore which is rotatable in a metal body to control the flow of fluid through a passage in the body. The ball can be rotated from the exterior of the body by means of a metal stem which is rotatably received in an opening in the metal body. The opening is stepped so as to define a first shoulder which faces the passage in the body, and the stem is correspondingly stepped to define a second shoulder which faces the first shoulder. Under normal operation of the valve, the shoulders are spaced apart slightly and a sealing ring is interposed therebetween. In the event that the sealing ring fails, the pressure of fluid in the passage presses the shoulder on the stem into contact with the shoulder on the body to create a metal-to-metal seal which prevents the escape of fluid to atmosphere through the opening. To make the seal reliable, the shoulders are shaped so that they contact each other only over the outer periphery of the stem shoulder. For example, the shoulders can be mutually tapered, or one of the shoulders can have a raised rim on its outer periphery.

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First Claim