Conical Plug Valves: Structure, Operation & Applications

 
Conical plug valves represent an important evolution of cylindrical plug valves, characterized by their unique structural design and diverse functionality. These valves are designed to meet various operational and fluid control requirements by adjusting the sealing gap between the plug and the valve seat to achieve reliable sealing and fluid control. Based on different designs and applications, conical plug valves can be classified into several types, including fixed-type, packing-type, oil-sealed, pressure-balanced inverted conical, metal hard-sealed lifting, and sleeve-type. Each type has its specific features related to structure, operation, and suitability for different applications. This article provides a detailed overview of the structural characteristics, working principles, and applications of these conical plug valves.

Fixed-Type Conical Plug Valve

 
The fixed-type conical plug valve is the simplest in structure, consisting only of a valve body and a plug. The sealing is achieved by adjusting the pressure of the plug against the valve seat using a nut, without the use of packing. The lower end of the plug extends out of the valve body and is threaded; tightening the securing nut pulls the plug down, pressing it against the valve body. This design relies on direct metal-to-metal contact for sealing, requiring high surface roughness and geometric accuracy of the plug and valve seat. Fixed-type conical plug valves are easy to maintain and clean, as the plug can be easily removed from the valve body for servicing. Due to their simple structure, they are typically used in low-pressure applications and are less common today.

Packing-Type Conical Plug Valve

 
The packing-type conical plug valve builds upon the fixed-type design by incorporating packing and a gland to enhance sealing performance. By tightening the gland nuts, the packing is compressed, which in turn tightens the plug against the valve seat to achieve a reliable seal. This type of valve usually employs non-lubricated metal sealing, which limits the sealing load due to higher friction between sealing surfaces. Although the leakage gap of the sealing surface is relatively larger, it can be used for sealing wet gases with higher viscosity liquids or added sealing grease. This valve type offers good sealing performance and is especially suitable for applications with a nominal pressure of 10 bar.

Oil-Sealed Conical Plug Valve

 
The oil-sealed conical plug valve has a similar structure to the packing-type valve but includes an oil injection mechanism. It features transverse and longitudinal oil grooves on the sealing surface of the plug. By injecting sealing grease into the valve body, an oil film forms to provide lubrication and sealing, significantly reducing operating resistance. If the plug becomes immovable due to prolonged inactivity or lack of lubrication, oil injection can restore its rotation. The oil-sealed conical plug valve is easy to operate, provides reliable sealing, and requires less effort to open and close, making it suitable for a wide range of applications.

Pressure-Balanced Inverted Conical Plug Valve

The pressure-balanced inverted conical plug valve is more complex in structure, consisting of the valve body, valve stem, plug, bottom cover, and oil-injection valve. The plug's position is adjusted using screws within the bottom cover, and balance holes are provided at the plug's end to allow medium pressure to enter the cavities on both sides of the plug, preventing it from being pushed into the valve seat by the medium pressure. This design makes the valve suitable for high-pressure conditions, ensuring smooth operation of the plug even under high pressure. Sealing between the plug and valve body is achieved through the injection of sealing agent, which also provides lubrication. This type of valve is commonly used in natural gas pipelines and station control systems.

Metal Hard-Sealed Lifting Conical Plug Valve

 
The metal hard-sealed lifting conical plug valve is a newer type that has developed rapidly in recent years. Its design features a lifting operation before opening and closing, which significantly reduces the valve's opening and closing torque. The valve usually has a circular channel design, resulting in low fluid resistance and suitability for high-temperature and high-pressure conditions, expanding the range of plug valve applications. When the valve opens, the plug is first lifted away from the valve seat, then rotated 90° to open. As the plug and seat are separated during operation, the sealing surface is less prone to damage, leading to a longer valve life and reliable sealing performance. This valve is suitable for a wide range of pressures and temperatures and is not restricted by fluid flow direction. It also allows for adjustment of the sealing pressure through a handwheel when closed, further enhancing sealing effectiveness.

Sleeve-Type Conical Plug Valve

 
The sleeve-type conical plug valve uses PTFE liners as sealing material, which are embedded in the valve body and pressed in place to prevent leakage between the body and liner. This valve does not require sealing grease that might contaminate the medium, resulting in lower plug torque and good sealing performance. It is suitable for bidirectional flow applications. The sealing surface is protected by a unique 360° metal lip to prevent direct contact and avoid seizing of the sealing surface. This valve type is widely applicable, especially for small and medium-sized plug valves. During rotation, the sealing pressure of the sealing pair gradually changes, ultimately achieving zero leakage and ensuring excellent sealing performance.
 
Conical plug valves meet various sealing and operational requirements through diverse designs and structures. Whether it is the fixed-type, packing-type, oil-sealed, pressure-balanced inverted conical, lifting-type, or sleeve-type conical plug valve, each type has its unique advantages and characteristics, making it suitable for low-pressure, high-pressure, high-temperature, and other conditions. When selecting a suitable conical plug valve, it is essential to consider its sealing performance, operation mode, and applicable pressure and temperature ranges to ensure efficient operation and long-term reliability of the fluid control system.