Disc가 Wedge Type경우에는 고온고압에서 밸브를 닫은상태에서 열팽창이나 내부 압력으로 인해 Disc가 body seat에 고착되어 작동하지 않는 경우가 있다. 이런 경우를 방지하기 위해 최근에는 발전소에서는 고온고압 배관에서 사용하는 것으로 유체를 차단하는 것이 주된 용도이다. 기본적으로 긴급하거나 빈번한 개폐 조작을 중요시 하지 않는 배관에 사용된다. Disc가 평행하여 고착현상이 없으며 밸브 개폐하는 힘도 적게 든다.
■ YOKE SLEEVE
The upper portion of the Yoke Sleeve is hexagonally tapered to fix the handwheel. The standard material of the Yoke Sleeve is Nodular Ni-resist D2 with over 1150℃ (2100℉) dissolution point in accordance with API Std. specifications.
The bonnet is of a steel forging identical to the body to insure high reliability. The bonnet has a perfect body-bonnet seal and both ease of dismantling and reassembly are ensured. The bodies and bonnets of the valve are machined by special purpose machines to achieve perfect coaxiality and eliminate any misalignment which may damage the stems.
The machined forged stem comes with a T-shape head, which connects the slot of the wedge. The contacting surface of the head is spherically shaped. thereby giving it greater strength and durability. It is heat treated to give it adequate mechanical properties and surface hardness. Accurate machining and lapping insure minimized friction during opening and shutting.
■ SEAT RING
The Stellite 6 surface of the seat ring is integrally applied to the body by means of welding in all valve sizes.
Lapping applied to the seating surface ensures perfect mating with the wedge surfaces.
■ PARALLEL DISC
The parallel disc designed to absorb thermally-induced body distortion, thereby making it ideal for high temperature steam or water supply piping. A Stellite 6 layer is applied to the seating surface, and this deposit is subjected to a special heat treatment to secure required hardness and soundness. The lapped finish then insures perfect mating with the seats
The valve body is cylindrically shaped to prevent distortion or undue stress during extreme working conditions.
Inaddition, adequate padding helps to achieve a sound cast structure in critical area. The wall thickness is
greater than, or in accordance with API, ANSI and ASME requirements. The contact surfaces ensure that a minimum specific pressure is achieved. The close tolerances of the inside diameter of this area are attained by accurate machining and honing finish.