The plug valve is a rotary valve with a closure element shaped like a plug or plunger. It operates by rotating 90 degrees to either connect or disconnect the passageway opening in the valve plug from the opening in the valve body. The plug can be cylindrical or conical, with cylindrical plugs typically having rectangular channels and conical plugs having trapezoidal channels. These shapes make the plug valve lightweight and ideal for media shut-off, connection, and diversion, although in some cases, depending on the material's properties and the sealing surface's erosion resistance, it can also be used for throttling.
Working Principle of Plug Valve
The plug valve functions with a plug body featuring a through hole as the opening and closing element. The plug body rotates together with the valve stem to achieve the open or closed position. Smaller plug valves without packing are also known as "cocks." The plug body is mostly conical (though sometimes cylindrical), forming a sealing pair with the conical surface of the valve body. Plug valves are among the oldest valve types, offering a simple structure, fast operation, and low fluid resistance. Traditional plug valves rely on direct contact between the finely machined metal plug and the valve body for sealing, which leads to poor sealing performance, higher opening/closing force, and wear. These are typically used in low-pressure (up to 1 MPa) and small-diameter (less than 100 mm) applications.
Advantages of Plug Valves
- Plug valves are suitable for frequent operation and can be opened or closed quickly and easily.
- They have low fluid resistance.
- Simple structure, compact, and easy to maintain.
- Good sealing performance.
- Flexible installation – flow direction can be either way.
- No vibration and low noise during operation.
Installation and Maintenance of Plug Valves
When installing plug valves, the following points should be noted to avoid damage and ensure optimal valve performance:
- Ensure the valve is in the open position. Preheat the pipeline, avoiding direct heating of the valve itself.
- Clean the pipe and cut parts with a wire brush or gauze, avoiding steel wool.
- Make a vertical cut on the pipe, smooth the edges, remove burrs, and measure the pipe diameter.
- Apply flux to the pipe's exterior and the welding cover's interior, ensuring full coverage of the welding surface.
Plug Valve Selection
- For distributing and changing the direction of media flow, where the operating temperature does not exceed 300°C, the nominal pressure is PN ≤ 1.6MPa, and the nominal diameter is no greater than 300mm, it is recommended to use a multi-channel plug valve.
- In the equipment and pipelines of food industries such as dairy, juice, beer, and pharmaceutical factories, it is recommended to use tight-fitting conical plug valves made from austenitic stainless steel.
- In branch pipelines and refining/cleaning equipment used in oilfield and natural gas field extraction, where the nominal pressure does not exceed Class 300 and the nominal diameter does not exceed 300mm, it is recommended to use oil-sealed conical plug valves.
- For branch pipelines and refining/cleaning equipment in oilfield and natural gas extraction, where the nominal pressure does not exceed Class 7500, the nominal diameter does not exceed 900mm, and the operating temperature does not exceed 340°C, it is recommended to use oil-sealed conical plug valves.
- In large-scale chemical industries, for pipelines and equipment with corrosive media requiring fast opening and closing, PTFE-sleeved conical plug valves are recommended for nitric acid-based media, while Crl8Ni12Mo2Ti stainless steel inlaid PTFE-sleeved conical plug valves are recommended for acetic acid-based media.
- For gas, natural gas, and HVAC system pipelines and equipment where the nominal diameter does not exceed 200mm, packed conical plug valves are recommended.
