Ball의 상하를 고정점으로 하여 Trunnion과 Bearing에 의해 지지되며 고압과 대형사이즈에 적용된다. Upstream 쪽의 Seat가 Ball쪽으로 말려 Sealing되는 구조이다.

■ STANDARD

SINGLE PISTON EFFECT (SELF-RELIEVING SEATS) Fluid pressure, both upstream and downstream, creates a resultant thrust that pushes the seat rings against the ball. Fluid pressure acting in the body cavity creates a resultant thrust that pushes the seat rings away from the ball. The single piston design permits the automatic release of any overpressure in the body cavity when the valve is in the fully open or fully closed position, therefore the seat rings are “self-relieving”

■ OPTIONAL

DOUBLE PISTON EFFECT Fluid pressure, both upstream and down-stream, as well as in the body cavity creates a resultant thrust that pushes the seat rings towards the ball. Valves with double piston effect seat rings require a relief valve in order to reduce the build-up of overpressure in the body cavity.

■ SEAT SEALING

Soft seats are standard. Seat inserts of synthetic material such as Nylon, PTFE, RTFE or Peek are contained within a one-piece metal seat ring. With no or very low line pressure. sealing between the seats and ball is achieved by seat springs. With higher line pressure, the line pressure, in conjunction with the spring load, forces the upstream seat ring against the ball, which results in tighter sealing.

■ SELF RELIEVING SEAT

This standard feature is designed to prevent excessive pressure buildup within the valve by automatically relieving pressure when body cavity pressure exceeds the spring load on the seats. Double Piston Seat is also available as an option.

■  SEAT RING SEALING

Two o-rings or one each of an o-ring and graphite ring are used for pressure classes 150 through 600. One lip seal with an o-ring or graphite ring is used for the pressure class 900 up to 2500.

■  SEALANT INJECTION FITTING

This feature is standard except in sizes 2”-4” for pressure classes 150, 300 and 600. In case of seat ring damage, sealant injection provides a fast, reliable way to restore tight sealing. This injection system can also be used for routine flushing or the seat ring area while in service.