Page 95 - Valve Selection Handbook

82 Valve Selection Handbook

Figure 3-38. Wedge Gate with Plain
Solid Wedge, Bolted Bonnet, and
External Screw. (Courtesy of Crane Co.)

Figure 3-39. Wedge Gate with Plain Solid
Wedge, Welded Bonnet, External Screw,
Bellows Stem Seal, and Auxiliary Stuffing
Box Seal. (Courtesy of Pegler Hattersley
Limited.) ->

Variations of Wedge Design

The basic type of wedge is the plain wedge of solid or hollow con-
struction, as in the valves shown in Figure 3-34 through Figure 3-39.
This design has the advantage of being simple and robust, but distortions
of the valve body due to thermal and pipeline stresses may unseat or jam
the metal-seated wedge. A failure of this kind is more often experienced
in valves of light-weight construction.
The sealing reliability of gate valves with a plain wedge can be
improved by elastomeric or plastic sealing elements in either the seat or
the wedge. Figure 3-40 shows a seat in which the sealing element is a
PTFE insert. The PTFE insert stands proud of the metal face just enough
to ensure a seal against the wedge.