Page 115 - Valve Selection Handbook

102 Valve Selection Handbook

impose restrictions on fluid compatibility and range of temperature appli-
cation. In addition, elastomers tend to grip the ball, unless the fluid has
sufficient lubricity. For services unsuitable for soft seatings, metal and
ceramic seatings are being used.

Seating Designs

The intimate contact between the seatings of ball valves may be
achieved in a number of ways. Some of the ones more frequently used are:

1. By the fluid pressure forcing a floating ball against the seat, as in
the valves shown in Figure 3-60 through Figure 3-63.
2. By the fluid pressure forcing a floating seat ring against a trunnion-
supported ball, as in the valve shown in Figure 3-64.
3. By relying mainly on the installed prestress between the seats and a
trunnion-supported ball, as in the valve shown in Figure 3-65.
4. By means of a mechanical force, which is introduced to the ball and
seat on closing, as in the valve shown in Figure 3-66.

Figure 3-60. Schematic View of Ball Valve with Floating Ball and Torsion Seats,
Showing Function of Pressure-Equalizing Slots in Periphery of Seats. (Courtesy of
Worcester Valve Co., Ltd.)