Plug Valve 1

 Basic Design
A plug valves is essentially a ported, tapered or cylindrical plug in a housing. Rotation of the plug by 90 degrees (quarter turn) changes the position from open to closed or vice versa. Available sizes are from ½ inch to about 12 inch for nonlubricated valves and up to 30 inch nominal pipe size (NPS) for lubricated valves. The “eccentric plug” valves are a special case and are described separately at the end of this section.

Design Features
All two-way plug valves are bidirectional. However, three-way, four-way and five-way valves have a designated inlet. They require less headroom than most other valves and have a low center of gravity. They are of simple construction and easy to maintain.

Typical Applications

Plug valves are used as bubble-tight, on-off stop valves in a variety of fluid systems including air, gas, oil and liquid slurries, but are not used in steam service. In small sizes they are economically competitive with globe valves, while in large sizes they are more expensive than globe valves.
Because plug sealing methods do not promote “crud traps”, plug valves are frequently used in “slurry” service; however, if throttling accuracy is not important, nonlubricated plug valves can be used when the valves is equipped to hold the plug in position. Lubricated valves, if used in throttling service, will tend to lose sealant from sealant grooves exposed to fluid flow.