Page 117 - Valve Selection Handbook

104 Valve Selection Handbook

The seat rings of the valve shown in Figure 3-60 are provided with
peripheral slots, which are known as pressure-equalizing slots. These
slots reduce the effect of the upstream pressure on the total valve torque.
This is achieved by letting the upstream pressure filter by the upstream
seat ring into the valve body cavity so that the upstream seat ring
becomes pressure balanced.
The valves shown in Figure 3-62 and Figure 3-63 are also designed to
ensure a preload between the seatings. This is achieved in the valve
shown in Figure 3-62 by supporting the seat rings on metal diaphragms
that act as springs on the back of the seat rings. The seating preload of
the valve shown in Figure 3-63 is maintained by a spring that forces the
ball and seat-ring assembly from the top into wedge-shaped seat ring
back faces in the valve body.

Figure 3-62. Ball Valve with
Floating Ball and Diaphragm-
Supported Seats, with
Sandwich-Split Body.
(Courtesy of Rich. Klinger AG.)

Figure 3-63. Ball Valve with
Wedge Seats Spring-Loaded from
the Top, with One-Piece Top-Entry
Body. (Courtesy of McCanna)