Page 135 - Valve Selection Handbook

122 Valve Selection Handbook

Figure 3-79. High-Performance Butterfly Valve with
Flexible PTFE Lip Seat. (Courtesy ofJamesbury
International Corp.)

minimum rubbing between the seatings. The seat, as illustrated, consists
of a PTFE lip seal with tail, which is clamped between the valve body
and a retainer. Once the disc has entered the seat with slight interference,
fluid pressure forces the lip of the seat into more intimate contact with
the rim of the disc, irrespective of whether the seat is located on the
upstream or downstream side of the disc. This ability of the seatings to
seal in both directions is aided by a small but controlled amount of axial
movement of the disc. The valve is also available with metal and fire-
tested seat constructions.