Flowseal® High Performance Butterfly Valves

 

Principle of Seat Sealing


Principle of Soft Seat Sealing

Flowseal Soft Seated HPBV Sealing Principle Figure 1


Disc Open


In Figure 1, the disc and seat are not engaged. In this position, the shoulders of the seat are forced against the cavity shoulders by the compression of the o-ring.


The seat is recessed inside the seat cavity and acts as a gasket in the anchoring groove area. The seat cavity is sealed from exposure from the process fluid and protects the seat from abrasion and wear. The o-ring, which is completely encapsulated by the seat, is also isolated from exposure to the process fluid.

Flowseal Soft Seated HPBV Sealing Principle Figure 2


Disc Closed, Self-Energized Seal


In Figure 2, the Flowseal disc and seat are engaged, and the process fluid is under low pressure. The edge of the disc, with a larger diameter than the seat tongue, directs movement of the seat radially outward, causing the seat to compress against the convergent sidewalls of the cavity. The elastomeric o-ring imparts a mechanical pre-load between the disc and seat tongue as it is compressed and flattened by the disc; this is the self-energized mode for sealing at vacuum-to-60 psig.


As the seat moves radially outward, the seat shoulders move away from the cavity shoulders and open the cavity to the process media.

Flowseal Soft Seated HPBV Sealing Principle Figure 3


Disc Closed, Pressure-Energized Seal (Seat Upstream)


As line pressure increases, the process fluid enters the sidewall area and applies a load against the parallel-spaced sidewall and convergent sidewall of the seat. The seat and cavity design permits the seat to move axially to the downstream sidewall, but confines the movement and directs the movement radially inward towards the disc; the higher the line pressure, the tighter the seal between the disc and seat. Because the o-ring is elastic, it is able to flex and deform under loads and return to original shape after removal of the load; it is the rubber which deforms, not the thermoplastic material.


This dynamic seal, patented by Flowseal, is totally unique among high performance butterfly valves.

Flowseal Soft Seated HPBV Sealing Principle Figure 4


Disc Closed, Pressure-Energized Seal (Seat Downstream


The Flowseal valve is bi-directional (in some instances, modifications may be required to operate this arrangement for dead end service). The cavity and seat sidewalls are symmetrically designed to permit, confine, and direct movement of the seat to the disc to dynamically seal with line pressure in the reverse direction. The disc edge is the segment of a sphere, and the seat is angled towards the disc edge to seal with pipeline pressure in either direction.


Recommended installation direction is “SUS” (seat upstream), as in Figure 3.


Metal Seat Principle of Sealing

Flowseal Metal Seated HPBV Sealing Principle Figure 1


Principle of Metal Seat Sealing


Metal-to-metal sealing is accomplished by the "line contact" between a spherical surface and conical surface. Figure 1 illustrates a typical globe control valve seat and plug. The plug seating surface is the segment of a sphere; when engaged against the seat ring, a line contact seal is achieved.


In a metal seat design, it is necessary to apply enough force per linear inch to maintain a tight metal-to-metal contact between the sealing members; however, high linear thrust can cause a collapse of the seating members ("bearing failure").

Flowseal Metal Seated HPBV Sealing Principle Figure 2


Disc Closed, Self-Energized Seal


In Figure 2, the Flowseal disc and seat are engaged, and the process fluid is under low pressure. The spherical edge of the disc, with a larger diameter than the conical seat tongue, imparts a thrust of approximately 600 pounds per linear inch against the seat. The mechanical properties and shape of the Inconel® seat allow it to both flex and maintain a constant thrust against the disc.


This controlled loading prevents the occurrence of bearing failure and reduces the leakage and wear between the components.

Flowseal Metal Seated HPBV Sealing Principle Figure 3


Disc Closed, Pressure-Energized Seal (Seat Upstream)


As line pressure increases, the process fluid enters the sidewall area and applies a load against the parallel-spaced sidewall and convergent sidewall of the metal seat. The seat moves towards the downstream sidewall while being supported axially by the support ring, as shown in Figure 3. The cavity shape confines the seat movement and directs the movement radially inward towards the disc; the higher the line pressure, the tighter the line contact between the disc and seat. The Inconel® seat, shaped by a special hydroforming process, is able to flex under these loads and return to its original shape after removal of the loads.


This dynamic seal, patented by Flowseal, is totally unique among high performance butterfly valves.

Flowseal Metal Seated HPBV Sealing Principle Figure 4


Disc Closed, Pressure-Energized Seal (Seat Downstream


The Flowseal valve is bi-directional (in some instances, modifications may be required to operate this arrangement for dead end service). The cavity and seat sidewalls are symmetrically designed to permit, confine, and direct movement of the seat to the disc to dynamically seal with line pressure in the seat downstream direction, as in Figure 4. Recommended installation direction is "SUS" (seat upstream), as in Figure 3.


The stainless steel back-up ring interacts dynamically with the metal seat for axial support in seat sealing. Additionally, this ring effectively restricts corrosion and particulate build-up in the cavity.


Principle of Fire Flow Seat Sealing

Flowseal Fire Flow HPBV Sealing Principle Figure 1


Disc Open, Normal Operation


In Figure 1, the disc and seat assembly are not engaged. In this position, the metal seat acts to keep the soft seat inside the seat cavity while the soft seat shoulders seal the cavity from exposure to the process fluid. (The o-ring is under tension and imparts a load against the soft seat.)


The soft seat is protected from abrasion and wear because it is recessed inside the seat cavity area. The o-ring is isolated from exposure to the fluid because it is completely encapsulated by the seat tails which act as a (soft) gasket in the anchoring groove area. The metal seat gaskets add further high temperature protection past the anchoring grooves.

Flowseal Fire Flow HPBV Sealing Principle Figure 2


Disc Closed, Normal Operation


In Figure 2, the disc and seat assembly are engaged; both the metal seat and the soft seat are in contact with the disc. Under little to no pressure conditions, both seats are self-energized. The disc edge, with a larger diameter than the seat tongues, moves the seats radially outward; the metal seat shape, with a mechanical and dynamic flexibility, is designed to be hoop-loaded and impart a spring force against the disc, while the soft seat o-ring is stretched and flattened (without deformation of the material) and imparts a mechanical pre-load against the disc.


With increased line pressure, the process fluid enters the cavity sidewall area and applies loads against the seat sidewalls. The cavity design allows the seats to move toward the downstream sidewalls, but confines and directs the movement radially inward towards the disc; the higher the pressure the tighter the seal. The symmetrical shape and angle of the cavity permit the seal to be bi-directional.

Flowseal Fire Flow HPBV Sealing Principle Figure 3


Disc Closed, After Fire (Seat Upstream)


After a fire, with partial or complete destruction of the soft seat, the metal seat maintains metal-to-metal contact with the disc and restricts leakage of the process fluid in conformance to industry fire-safe requirements.


With little or no line pressure, the spring force and hoop load of the metal seat maintain a "line contact" seal against the disc edge. Under higher pressures, the process fluid enters the cavity sidewall areas and applies loads against the seat sidewalls (Figure 3). The geometry of the metal seat permits the seat to move axially, but directs the movement radially inward toward the disc. The higher the pressure, the tighter the line contact seal.


Graphite gaskets, on both sides of the metal seat tail, seal the anchoring groove and prevent leakage of the process fluid.

Flowseal Fire Flow HPBV Sealing Principle Figure 4


Disc Closed, After Fire (Seat Downstream


The Flowseal Fire-Flow™ valve is bi-directional; however, modifications are required to operate for bi-directional dead end service. The angle and shape of the cavity and metal seat maintains metal-to-metal contact in the event of partial or complete soft seat destruction with line pressure in the reverse direction (Figure 4).


While the preferred flow direction is "seat upstream" (SUS), the bidirectional seat design is both self-energized and pressure-energized if the flow direction is "seat downstream" (SDS).


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