What are Plug Valves Used For?

A plug valve is a right-angle rotary motion manual valve. It uses a cylindrical or conical plug (plug disc) to allow or prevent straight-through flow through the body. Plug valves provide a straight-through passage through a port so that fluid can flow through the open plug with minimal turbulence. Flow can be fully open or fully closed in either direction.

Plug valves have been used in many different fluid services. They perform well in slurry applications. They are used as on/off shutoff valves in airtight service. They are used in air, gas and steam service, natural gas and oil piping systems, food processing, non-abrasive slurries, vacuum, pharmaceutical service, and vacuum to high pressure applications. They are suitable for on-off valves, diverter service and moderate throttling. Originally, plug valves were intended to replace gate valves because, compared to gate valves, plug valves have a quarter-turn action and can be easily opened and closed against the flow.

Plug Valve Principle and structure

Plug valve opening and closing parts is the plug body, through the rotation of 90 degrees so that the valve plug on the channel port and the valve body on the channel port connected or separated, to achieve the opening or closing of a valve. The shape of the valve plug can be cylindrical or conical, in the cylindrical valve plug, the channel is generally rectangular, while in the conical valve plug, the channel into a trapezoid. Suitable for cutting off and connecting the medium as well as shunt applicable.

• Plug valve with through-hole plug body as the opening and closing parts of the valve.
• The plug body with the valve stem rotation, in order to realize the opening and closing action.
• Small plug valve without packing is also known as Cocker.
• Plug valve plug body is mostly cone (also cylinder).
• The valve body of the conical hole surface with the composition of the sealing vice.

Plug valve is the earliest use of a valve, simple structure, rapid switching, low fluid resistance. Ordinary plug valves rely on the finishing of the metal plug body and the valve body to seal the direct contact between the body, so the sealing is poor, opening and closing force, easy to wear and tear, usually can only be used for low (not higher than 1 MPa) and small diameter (less than 100 millimeters) of the occasion. In order to expand the application range of plug valves, many new structures have been developed. Oil lubricated plug valves are an important one. Special grease from the plug body page end into the valve body cone hole and between the plug body, the formation of oil film to reduce the opening and closing torque, improve sealing and service life. Its working pressure up to 64 MPa, working temperature up to 325 ℃, caliber up to 600 mm. Plug valve channel has a variety of forms. The common straight-through type is mainly used to cut off the fluid. Three-way and four-way plug valves are suitable for fluid reversal.

• Plug valve consists of plug, packing gland, packing, valve body.
• It is suitable for frequent operation, rapid opening and closing, lightweight.
• Small fluid resistance.
• Simple structure, relatively small size, light weight, easy maintenance.
• Good sealing performance.
• Not limited by the installation direction, the medium flow direction can be arbitrary.
• No vibration, low noise.

Plug Valve Types 

There are four general categories, each with their own benefits.

• Lubricated Plug Valve

A lubricated valve uses a lubricant usually made up of a base oil and viscosity improver (like amorphous or fumed silica) that is injected under pressure between the plug face and body seat to reduce friction and seal ports. Valve manufacturers generally recommend lubricant suitable for the process fluid, and the valves often must be resealed after only a few cycles, and in some cases. After every cycle. Considered a high maintenance plug valve, they are often used in applications that have infrequent operations. Lubricated plug valves perform well in processes that utilize fluids which carry mildly abrasive particles such as dirty upstream applications. Gas pipeline systems that need bypass valves, and as blow-down valves on valve stations and kicker valves.

• Non-Lubricated Plug Valve

This plug valve features a tapered or cone-shaped design that acts as a wedge, pressing a polymeric sleeve against the body cavity. The sleeve's use reduces friction between the plug mechanism and the body. Non-lubricated plug valves are often preferred over lubricated ones in applications where minimal maintenance is required, such as in special services with Sulphur, hydrogen fluoride, or where liquids could be trapped or solidify and potentially jam the valve. However, non-lubricated plug valves are restricted by the temperature and chemical compatibility of their non-metallic materials. The three main types of non-lubricated plug valves are: lift-type plug valve, elastomer-sleeved plug valve, and fully lined plug valve.

• Eccentric Plug Valve

The design of this plug valve incorporates a half plug, which is beneficial for applications requiring higher seating force with minimal friction from the open to closed position. The torque-seated valves also offer enhanced shut-off capabilities. Eccentric plug valves are versatile and are used for various flow control and isolation applications, including clean and dirty water, sewage, sludge and slurries, air, and other similar services.

• Expanding Plug Valve

This complex plug valve uses multiple components that allow the valve to mechanically expand and give it a true double block and bled function in one valve. The plug valve uses a mechanism that rotates between the open and closed position and protects both seals from the flow path. During rotation there is no contact between body and seals, and slips expand onto the body seat when the valve is closed to avoid causing any wear or abrasion to the seals. They are often used to prevent product contamination in applications that do not require a double isolation.

Plug Valve Applications  

Plug valves are extremely versatile valves that are widely used in low-pressure sanitary and industrial applications, especially in petroleum pipelines, chemical processing and related fields, and power plants. They are high capacity valves for directional flow control, even in medium vacuum systems. They can safely and effectively handle gaseous and liquid fuels as well as extreme temperature flows such as boiler feed water, condensate and similar media. Plug valves can also be used to regulate the flow of liquids containing suspended solids (slurries). Most plug valves are used for:

• For directional flow control, even in medium vacuum systems.
• For efficient handling of gases and liquid fuels.
• For safe handling of flows at extreme temperatures, e.g. boiler feed water, condensate and other such components.
• To regulate the flow of liquids containing suspended solids (e.g. slurries).