Separable Flange – The separable flange (see Figure 33) is another variation of a raised-face flange. In this construction, the flange is manufactured independently of the valve body. Split rings are required to secure the flange to the body and to transmit the bolting force to the gasket and the mating connection. When an expensive body material is specified, separable flanges may result in some economy, because the flanges can be made of a more economical material such as carbon steel. Some companies prefer separable flanges because a standing inventory of control valves can be adapted to several different piping configurations by simply installing the appropriate flange.
Ring-Type Joint – Also known as RTJ, this flange design (see Figure 33) is well suited for extremely high pressure applications. Matching grooves in the body and pipe flanges retain a solid metal seal ring. As the line bolting is tightened, the ring deforms and conforms to the grooves. This seal is pressure-assisted because, as the pressure increases, the ring pushes against the groove, making the seal tighter.