Plug valves, also called cock or stop-cock valves, date back to ancient times, where they were developed for use in citywide Roman plumbing systems. Today, they remain one of the most widely used valves for both on/off and throttling services. Their design is fairly simple; the body is comprised of three main parts: body, cover and plug. The plug is a cylindrical, tapered, or generally cone-shaped device that can be raised or lowered within the seat to maintain, restrict or completely shut off flow. The valve is opened by rotation, with the plug itself being the only element that is capable of movement.
Early models of plug valves used metal-to-metal seals that were nonlubricated. This design is still used, but problems with galling and sticking limit their usefulness. The use of lubricant between the plug face and the seat eliminates most of these problems. The lubricant helps to control leakage around the plug, reduces wear between the valve contact surfaces, and slightly lifts the plug to reduce the operating torque required to operate the valve.
Nonlubricated-plug valves may use a tapered plug with a mechanical lifting device that unseats the plug before it is turned to reduce the operating torque required. Or it may have an elastomeric sleeve or plug coating with a low coefficient of rubbing friction.
Plug valves are extremely versatile valves that are found widely in low-pressure sanitary and industrial applications, especially petroleum pipelines, chemical processing and related fields, and power plants. They are high capacity valves that can be used for directional flow control, even in moderate vacuum systems. They can safely and efficiently handle gas and liquid fuel, and extreme temperature flow, such as boiler feed water, condensate, and similar elements. They can also be used to regulate the flow of liquids containing suspended solids (slurries).
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Butterfly valves control flow through a circular disc or vane by turning the valve's pivot axis at right angles to the direction of flow in the pipe. They are normally used as throttling valves to control flow.
Check valves are self-activating safety valves that permit gases and liquids to flow in only one direction, preventing process flow from reversing. They are classified as one-way directional valves.
Globe valves are linear motion valves with rounded bodies, from which their name is derived. They are widely used in industry to regulate fluid flow in both on/off and throttling service.
Needle valves are small valves used for flow control in liquid or gas services. The fine threading of the stem and the large seat area allow for precise resistance to flow.
Pinch valves include any valve with a flexible elastomer body that can be pinched closed, cutting off flow, using a mechanism or fluid pressure.
Solenoid valves are devices that use a solenoid to control valve activation.
Solids valves are used to control or regulate the flow of powder, granular and other bulk solid materials along a process line, or to and from process units, storage bins, conveyors and product packaging.