Disk and Seat:

To a valve having a bonnet, a disk is the third basic principal pressure boundary. The disk gives the capability for prohibiting and permitting fluid flow. Along With the disk closed, full system pressure is applied across the disk if the outlet side is depressurized.

For this purpose, the disk is a pressure-retaining category. Disks are classically forged and, in a few designs, hard-surfaced to gives good wear features. A fine surface finish of the seating area of a disk is essential for good sealing while the valve is closed. Many valves are named, in component, according to the design of their disks.

The seat or seal rings give the seating surface for the disk. In a few designs, the body is machined to serve as the seating surface and seal rings are not used. Within other designs, forged seal rings are welded or threaded to the body to give the seating surface. For improve the wear-resistance of the seal rings, the surface is frequent hard-faced through welding and then machining the contact surface of the seal ring. A fine surface ends of the seating area is essential for good sealing while the valve is closed. Seal rings are not commonly considered pressure boundary elements since the body has enough wall thickness to withstand design pressure without relying upon the thickness of the seal rings.