Page 85 - Valve Selection Handbook

72 Valve Selection Handbook

Figure 3-26. Scrap View of Parallel Gate Valve
Showing Double-Disc Closure Member with
Wedging Mechanism. (Courtesy of Pacific
Valves, Inc.)

Figure 3-27. Parallel Gate Valve with Scrap
View of Seating Arrangement Showing
Spring-Loaded Floating Inserts in Disc.
(Courtesy of Grove Valve and Regulator
Company.)

parallel slide gate valves may be used also for many other services such
as water in particular boiler feed water—and oil.
A variation of the parallel slide gate valve used mainly in the U.S. is
fitted with a closure member such as the one shown in Figure 3-26. The
closure member consists of two discs with a wedging mechanism in
between, which, on contact with the bottom of the valve body, spreads
the discs apart. When the valve is being opened again, the wedging
mechanism releases the discs. Because the angle of the wedge must be
wide enough for the wedge to be self-releasing, the supplementary seat-
ing load from the wedging action is limited.
To prevent the discs from spreading prematurely, the valve must be
mounted with the stem upright. If the valve must be mounted with the stem
vertically down, the wedge must be appropriately supported by a spring.
The performance characteristic attributed to parallel slide gate valves
also applies largely to this valve. However, solids carried by the flowing