Butterfly valve body
The butterfly valve consists of only four main components: body, disk, stem and seat.
body Butterfly valves generally have bodies that fit between two pipe flanges. The most common body designs are lug and wafer. The lug body has protruding lugs that provide bolt holes matching those in the pipe flange. A wafer body does not have protruding lugs. The wafer valve is sandwiched between the pipe flanges, and the flange bolts surround the body.
Each type of body has advantages, some of which are listed:
The wafer style is less expensive than a lug style.
Wafer designs do not transfer the weight of the piping system directly through the valve body.
A lug body allows dead-end service or removal of downstream piping.
The flow closure member of a butterfly valve is the disk. Many variations of the disk design have evolved relative to the orientation of the disk and stem in an attempt to improve flow, sealing and/or operating torque.
The disk is the equivalent of a plug in a plug valve, gate in a gate valve or a ball in a ball valve. Rotating the disk one-quarter turn or 90 Degrees opens and closes the butterfly valve.
Stem. The stem of the butterfly valve may be a one-piece shaft or a two-piece (split-stem) design.
The stem in most resilient seated designs is protected from the media, thus allowing an efficient selection of material with respect to cost and mechanical properties.
In high-performance designs, the stems are in contact with the media and, therefore, must be compatible, as well
Seat. The seat of a resilient-seat butterfly valve utilizes an interference fit between the disk edge and the seat to provide shutoff. The material of the seat can be made from many different elastomers or polymers. The seat may be bonded to the body or it may be pressed or locked in.
In high-performance butterfly valves, the shutoff may be provided by an interference-fit seat design or a line-energized seat design, where the pressure in the pipeline is used to increase the interference between the seat and disk edge. The most common seat material is polytetrafluoroethylene (PTFE) or reinforced PTFE (RTFE) because of the wider range of compatibility and temperature range.
Metal seats are also offered in high-performance butterfly valves. These metal seats allow a butterfly valve to be used in even higher temperatures to 1,000 Degrees F. Fire-safe designs are offered that provide the shutoff of a polymer seat valve before a fire, and the metal seal backup provides shutoff during and after a fire.
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