Flowserve Cast Flex Wedge Gate Valve - Manual (Page 8)

Cast Flex Wedge Gate Valves FCD ADENIM0010-02
8
1.0 VALVE DESCRIPTION
(Continued)
1.3
Design Features
1.3.1 BONNET SEALS
Anchor/Darling flex-wedge valves are supplied with two basic types of body-bonnet closure: bolted bonnet or
pressure seal bonnet. The bolted bonnet closure (Fig. 2) is a bolted flange tongue and groove joint with spiral-wound
stainless steel gasket and graphite filler. The seal depends upon the bolt preload to maintain sufficient compressive
force on the gasket. Pressure seal type closures (Fig. 3) utilize a tapered soft metal ring or graphite gasket for
sealing. The gasket is contained within the body neck bore by a retaining ring. The tapered inner surface of the
gasket bears against a mating annular surface on the valve bonnet. Under internal pressure, the bonnet is forced
against the pressure seal gasket, wedging it against the body neck wall. A slight interference angle produces a line
contact and high sealing pressure. The greater the valve pressure the tighter the metal-to-metal seal. No bolting is
required to maintain the seal although the bonnet is initially drawn into contact with the pressure seal by cap screws.
Figure 2 Figure 3