Plug Valve: Overview, Classification, Characteristics and Industrial Applications

A plug valve is a type of rotary valve. By rotating a perforated plug 90° around the valve stem, it can achieve rapid opening and closing. It operates through the cooperation between a plug valve core with a through hole and the sealing pair of the valve body. The main function is realized by rotating the plug to cooperate with the valve seat. It features a simple structure, low flow resistance, and quick opening and closing, and is widely used in low and medium pressure, medium and low temperature, and high viscosity working conditions.

The valve body serves as the outer shell of the valve, responsible for withstanding medium pressure and providing a flow channel for the medium. Common materials include cast iron, cast steel, stainless steel, and special alloys. The selection of materials depends on the corrosiveness of the working conditions and the pressure level.

The plug (valve core) is the core component for opening and closing the valve. It is mostly conical or cylindrical in shape, with a through hole in the center, and is divided into two structures: full bore and reduced bore. The valve can be opened or closed by rotating it 90°.

The sealing system is mainly divided into two types: soft seals and hard seals. Soft seals use sealing materials such as PTFE and rubber, featuring low leakage, and their applicable temperature range is generally from -20℃ to 180℃; hard seals are metal-to-metal fits lubricated by seal grease, with excellent high-temperature and high-pressure resistance, capable of withstanding temperatures up to around 450℃.

The central hole of the plug is perfectly aligned with the axis of the pipeline, allowing the medium to flow in a straight line, resulting in the minimum flow resistance.
Fully Closed State
The valve stem rotates 90°, making the through hole perpendicular to the pipeline. The sealing surfaces fit closely, blocking the flow of the medium.

Non-lubricated Plug Valves: Suitable for corrosive media and working conditions with strict leakage requirements, such as the chemical and food industries.

Pressure balance lubricated plug valves: Seal grease reduces friction and improves sealing performance. They are suitable for high-temperature, high-pressure conditions, as well as applications involving heavy oil, gas, etc.

Straight-through Plug Valves: Only used for on-off control of a single pipeline and are the most widely used type.
Three-way/Four-way Plug Valves: Can realize medium flow direction switching, diversion, or confluence, and are mostly used in gas distribution and fluid direction change systems.
Lubricated Plug Valves: Reduce friction by injecting seal grease to improve sealing performance, suitable for high-temperature, high-pressure, heavy oil, gas, and other working conditions.lubricated

Extremely fast opening and closing: Rotating only 90° is sufficient to complete the switching operation, which is much faster than a globe valve and suitable for emergency shutdown.
Low flow resistance: Suitable for high-viscosity and particle-containing media, such as mud and syrup.
Easy maintenance: The oil-sealed type can extend its service life by adding grease, and the soft sealing components are easy to replace.

Plug valves have a fast opening and closing speed and extremely low flow resistance, but their regulating capacity is relatively weak, making them suitable for quick cutoff and reversing. 
Gate valves have slow opening and closing speed and medium flow resistance, but high regulating accuracy. 
Ball valves also open and close with a 90° rotation, with slightly higher flow resistance than plug valves, but they have stronger sealing reliability and a wider application range.

In summary, the plug valve is a type of shut-off and reversing valve characterized by rapidity, simplicity, and low flow resistance. It has obvious advantages in working conditions involving low pressure, medium temperature, high viscosity, and particle-containing media. For high-precision regulation or ultra-high temperature and high-pressure working conditions, other types of valves should be selected as appropriate.