Types and Characteristics of Plug Valves
Plug valves have a simple structure, quick switching, low fluid resistance, and fast angular stroke operation. In emergencies or other urgent situations, they can quickly connect or disconnect pipelines. Compared to gate valves and globe valves, they offer more flexible operation and faster switching. Plug valves use a plug with a through-hole as the opening and closing element. As the plug rotates with the valve stem, it performs the opening and closing actions. Small, unfilled plug valves are also known as "Cock" valves. The plugs of plug valves are mostly conical (although cylindrical plugs also exist) and form a sealing pair with the conical hole surface of the valve body.
Soft-Seated Plug Valves
Soft-seated plug valves are commonly used in harsh environments with corrosive, toxic, or highly hazardous media, as well as in applications where strict leak prevention is required and where valve materials will not contaminate the media. The valve body can be made of carbon steel, alloy steel, or stainless steel, depending on the working medium. Self-lubricating materials such as F4, F46, PVDF, PP, PO, and PE can be used for the valve seats and seals, ensuring good lubrication, low friction coefficients during the entire operation, flexible plug movement, and long service life. The design of the valve body inlet and outlet ports and the double-groove seal ring structure allow for the sealing pair to gradually change the sealing pressure during rotation until sufficient sealing pressure is reached when fully open or fully closed, achieving zero leakage. The double-groove seal ring not only ensures the stability of the liner in the valve body without displacement but also absorbs the slight deformation caused by temperature changes, while generating strong friction between the liner and the plug, thereby automatically cleaning the sealing surface and improving its lifespan. The unique design of the top of the piston, featuring a reverse lip seal, uses a combination of a soft seal membrane, a metal membrane, and adjustment gaskets to adjust the sealing pressure between the sealing surfaces, ensuring flexible plug rotation and sealing at the inlet, outlet, and middle flange connection ends. It is suitable for high-abrasion gas-solid and liquid-solid phase media, such as in PVC, urea, acetic anhydride, caustic soda production units, or media with high external leakage requirements, such as HF and phosgene. The media can flow bidirectionally, and the installation direction is unrestricted, allowing for online maintenance and greater convenience of use. The unique design prevents static electricity, ensuring safety against fire hazards.
Oil-Lubricated Hard-Seated Plug Valves
Oil-lubricated hard-seated plug valves can be divided into conventional oil-lubricated plug valves and pressure-balanced plug valves. Specially formulated grease is injected from the top of the plug into the tapered hole in the valve body, forming an oil film to reduce the valve's opening and closing torque, improve its sealing performance, and extend its service life. They can withstand working pressures of up to 64 MPa, operating temperatures of up to 325 degrees Celsius, and maximum diameters of up to 600 mm.
Conventional Oil-Lubricated Plug Valves
Conventional hard-seated plug valves are installed in the correct position. To reduce friction between the valve body and the plug sealing surface, the valve generally adopts a sealing grease-lubricated seat structure. High-pressure sealing oil injected from the high-pressure oil nozzle forms a high-pressure sealing ring around the plug, creating an oil film between the sealing surfaces of the valve body and the plug that provides both sealing and lubrication, making opening and closing easy. To further reduce the closing torque of the plug valve, the plug diameter is typically reduced, and rectangular flow channels are used. This method, combined with the application of STL alloy material or surface hardening technology at the sealing surface of the plug cone, enhances the wear resistance and corrosion resistance of the sealing surface, resulting in a long service life. The surface of the plug cone is finely ground to a mirror finish, and the sealing surface of the valve body is also ground, resulting in a lower opening and closing torque.
Pressure-Balanced Plug Valves
To reduce the torque of conventional hard-seated plug valves, pressure-balanced plug valves are often used. In addition to the characteristics of conventional oil-lubricated plug valves, pressure-balanced plug valves have the following features: The installation of the plug cone of the pressure-balanced plug valve is inverted. There is a check valve on the upper part of the plug. When the valve is closed, due to the difference in cross-sectional area between the upper and lower surfaces of the plug cone, the injected high-pressure sealing oil causes the plug to experience an upward lifting force, allowing for better sealing between the plug and the valve body sealing surface. At the moment of valve opening, the pressure in the lower chamber of the valve body balances with the pressure of the medium in the pipeline, while the high-pressure sealing oil in the upper chamber applies a downward thrust to the plug, creating a small gap between the sealing surface of the plug cone and the valve body sealing surface during plug rotation, effectively reducing the torque required for plug rotation. It also protects the sealing pair. Under high-temperature conditions, the thermal expansion of the plug can be absorbed by its lifting and lowering, preventing the sealing pair from jamming. Although oil-lubricated hard-seated plug valves reduce the opening and closing torque to a certain extent, they may contaminate the medium. Therefore, the selection of sealing lubricants should be based on actual conditions. Rising Stem Plug Valves Rising stem plug valves come in various structural forms and are divided into soft-seated and hard-seated types based on the material of the sealing surface. The basic principle is to raise the plug during opening, rotating it 90 degrees to reduce friction with the valve body sealing surface. During closing, the plug rotates 90 degrees to the closed position and then descends to contact the valve body sealing surface to achieve sealing. Double-Seal Rising Stem Plug Valves Double-seal rising stem plug valves are of a soft-seal structure. The plug body is composed of three plates to form a cylindrical plug, with rubber sealing faces embedded on both sides and a cylindrical wedge in the middle. When the valve is opened, the driving mechanism raises the plug, causing the plates on both sides to converge, detaching the composite plug body and the valve body sealing surface, and then rotating the plug body 90 degrees to fully open the valve. When closing the valve, the driving mechanism rotates the composite plug body 90 degrees to the closed position, then pushes the plug body downward. After the plates on both sides contact the bottom of the valve body, they no longer move downward, and the middle wedge continues to descend, pushing the plates on both sides to move inward and outward through the inclined surface, causing the soft sealing faces of the side plates to compress against the valve body sealing surface, achieving sealing. Double-seal rising stem plug valves have double-blocking and discharge functions and are equipped with a pressure balancing device on the valve body to prevent abnormal pressure increases in the system and reduce resistance during valve opening and closing moments. When the sealing ring is compressed and the metal surfaces contact each other, the valve has fireproof capabilities. Maintenance of the valve is very convenient, as the plates can be removed from the valve body for replacement without removing the valve body from the pipeline, simply by removing the end cap at the bottom of the valve body. Therefore, they are widely used in various industries such as petroleum, natural gas, metallurgy, mining, gas engineering, light industry, textiles, shipyards, food, and environmental water treatment for regulating, opening, and closing pipeline fluids.
Hard-Seated Rising Stem Plug Valves
Metal hard-seated rising stem plug valves can seal on both sides of the valve seat sealing surface, and their use is not restricted by the flow direction of the medium. During closing, the sealing surface of the valve seat can be pressurized by the handwheel and the valve stem to achieve better sealing performance. The raised sealing surface of the valve seat facilitates cleaning and prevents the accumulation of crystalline media or solid particles on the sealing surface. They are commonly used in high-temperature environments in chemical plants. Hard-seated rising stem plug valves come in various structures, with two common types:
Handwheel-Operated Rising Stem Plug Valves: The working principle is as follows: When raised, the plug and the valve are fully open. When closing, rotate the handwheel to turn the plug 90 degrees to the closed position, then turn the handwheel of the transmission mechanism to lower the plug to achieve sealing. As the plug separates from the valve seat during valve opening or closing, the operation is very light, and the sealing surface is less prone to abrasion, resulting in a long service life. However, the handwheel driving torque is small, so the nominal size of the valve is usually not large. Handwheel-operated rising stem plug valves have a compact structure, small size, and low fluid resistance.
Mechanical Cross-Arm Transmission Rising Stem Plug Valves: The working principle is as follows: When opening the valve, the transmission mechanism rotates the valve stem's threads to raise the plug. After the plug and the valve body sealing surface are separated, the transmission mechanism rotates the plug 90 degrees to fully open the valve. When closing, the transmission mechanism first rotates the plug 90 degrees to the closed position, and then the plug stops rotating. The driving force of the rotation thread then lowers the plug to contact the valve body sealing surface, achieving sealing. Mechanical cross-arm transmission mechanisms can be connected to cylinders, electric actuators, hydraulic systems, etc., for remote control. Mechanical cross-arm transmission rising stem plug valves overcome the limitation of insufficient input torque of the driving device, allowing valves to be used in larger diameter and higher pressure directions. The plug channel of mechanical cross-arm transmission rising stem plug valves has the same diameter as the pipeline, with low fluid resistance, making it convenient for pipeline cleaning. Their use is increasingly widespread in long-distance pipelines for petroleum and natural gas.
Three-Way and Four-Way Plug Valves
Three-way and four-way plug valves are suitable for chemical plant applications where it is necessary to change the direction of flow or distribute media. Soft-seated lining or hard-seated rising stem plug valves can be selected according to the requirements of the operating conditions.
Soft-Seated Plug Valves
Soft-seated plug valves are commonly used in harsh environments with corrosive, toxic, or highly hazardous media, as well as in applications where strict leak prevention is required and where valve materials will not contaminate the media. The valve body can be made of carbon steel, alloy steel, or stainless steel, depending on the working medium. Self-lubricating materials such as F4, F46, PVDF, PP, PO, and PE can be used for the valve seats and seals, ensuring good lubrication, low friction coefficients during the entire operation, flexible plug movement, and long service life. The design of the valve body inlet and outlet ports and the double-groove seal ring structure allow for the sealing pair to gradually change the sealing pressure during rotation until sufficient sealing pressure is reached when fully open or fully closed, achieving zero leakage. The double-groove seal ring not only ensures the stability of the liner in the valve body without displacement but also absorbs the slight deformation caused by temperature changes, while generating strong friction between the liner and the plug, thereby automatically cleaning the sealing surface and improving its lifespan. The unique design of the top of the piston, featuring a reverse lip seal, uses a combination of a soft seal membrane, a metal membrane, and adjustment gaskets to adjust the sealing pressure between the sealing surfaces, ensuring flexible plug rotation and sealing at the inlet, outlet, and middle flange connection ends. It is suitable for high-abrasion gas-solid and liquid-solid phase media, such as in PVC, urea, acetic anhydride, caustic soda production units, or media with high external leakage requirements, such as HF and phosgene. The media can flow bidirectionally, and the installation direction is unrestricted, allowing for online maintenance and greater convenience of use. The unique design prevents static electricity, ensuring safety against fire hazards.
Oil-Lubricated Hard-Seated Plug Valves
Oil-lubricated hard-seated plug valves can be divided into conventional oil-lubricated plug valves and pressure-balanced plug valves. Specially formulated grease is injected from the top of the plug into the tapered hole in the valve body, forming an oil film to reduce the valve's opening and closing torque, improve its sealing performance, and extend its service life. They can withstand working pressures of up to 64 MPa, operating temperatures of up to 325 degrees Celsius, and maximum diameters of up to 600 mm.
Conventional Oil-Lubricated Plug Valves
Conventional hard-seated plug valves are installed in the correct position. To reduce friction between the valve body and the plug sealing surface, the valve generally adopts a sealing grease-lubricated seat structure. High-pressure sealing oil injected from the high-pressure oil nozzle forms a high-pressure sealing ring around the plug, creating an oil film between the sealing surfaces of the valve body and the plug that provides both sealing and lubrication, making opening and closing easy. To further reduce the closing torque of the plug valve, the plug diameter is typically reduced, and rectangular flow channels are used. This method, combined with the application of STL alloy material or surface hardening technology at the sealing surface of the plug cone, enhances the wear resistance and corrosion resistance of the sealing surface, resulting in a long service life. The surface of the plug cone is finely ground to a mirror finish, and the sealing surface of the valve body is also ground, resulting in a lower opening and closing torque.
Pressure-Balanced Plug Valves
To reduce the torque of conventional hard-seated plug valves, pressure-balanced plug valves are often used. In addition to the characteristics of conventional oil-lubricated plug valves, pressure-balanced plug valves have the following features: The installation of the plug cone of the pressure-balanced plug valve is inverted. There is a check valve on the upper part of the plug. When the valve is closed, due to the difference in cross-sectional area between the upper and lower surfaces of the plug cone, the injected high-pressure sealing oil causes the plug to experience an upward lifting force, allowing for better sealing between the plug and the valve body sealing surface. At the moment of valve opening, the pressure in the lower chamber of the valve body balances with the pressure of the medium in the pipeline, while the high-pressure sealing oil in the upper chamber applies a downward thrust to the plug, creating a small gap between the sealing surface of the plug cone and the valve body sealing surface during plug rotation, effectively reducing the torque required for plug rotation. It also protects the sealing pair. Under high-temperature conditions, the thermal expansion of the plug can be absorbed by its lifting and lowering, preventing the sealing pair from jamming. Although oil-lubricated hard-seated plug valves reduce the opening and closing torque to a certain extent, they may contaminate the medium. Therefore, the selection of sealing lubricants should be based on actual conditions. Rising Stem Plug Valves Rising stem plug valves come in various structural forms and are divided into soft-seated and hard-seated types based on the material of the sealing surface. The basic principle is to raise the plug during opening, rotating it 90 degrees to reduce friction with the valve body sealing surface. During closing, the plug rotates 90 degrees to the closed position and then descends to contact the valve body sealing surface to achieve sealing. Double-Seal Rising Stem Plug Valves Double-seal rising stem plug valves are of a soft-seal structure. The plug body is composed of three plates to form a cylindrical plug, with rubber sealing faces embedded on both sides and a cylindrical wedge in the middle. When the valve is opened, the driving mechanism raises the plug, causing the plates on both sides to converge, detaching the composite plug body and the valve body sealing surface, and then rotating the plug body 90 degrees to fully open the valve. When closing the valve, the driving mechanism rotates the composite plug body 90 degrees to the closed position, then pushes the plug body downward. After the plates on both sides contact the bottom of the valve body, they no longer move downward, and the middle wedge continues to descend, pushing the plates on both sides to move inward and outward through the inclined surface, causing the soft sealing faces of the side plates to compress against the valve body sealing surface, achieving sealing. Double-seal rising stem plug valves have double-blocking and discharge functions and are equipped with a pressure balancing device on the valve body to prevent abnormal pressure increases in the system and reduce resistance during valve opening and closing moments. When the sealing ring is compressed and the metal surfaces contact each other, the valve has fireproof capabilities. Maintenance of the valve is very convenient, as the plates can be removed from the valve body for replacement without removing the valve body from the pipeline, simply by removing the end cap at the bottom of the valve body. Therefore, they are widely used in various industries such as petroleum, natural gas, metallurgy, mining, gas engineering, light industry, textiles, shipyards, food, and environmental water treatment for regulating, opening, and closing pipeline fluids.
Hard-Seated Rising Stem Plug Valves
Metal hard-seated rising stem plug valves can seal on both sides of the valve seat sealing surface, and their use is not restricted by the flow direction of the medium. During closing, the sealing surface of the valve seat can be pressurized by the handwheel and the valve stem to achieve better sealing performance. The raised sealing surface of the valve seat facilitates cleaning and prevents the accumulation of crystalline media or solid particles on the sealing surface. They are commonly used in high-temperature environments in chemical plants. Hard-seated rising stem plug valves come in various structures, with two common types:
Handwheel-Operated Rising Stem Plug Valves: The working principle is as follows: When raised, the plug and the valve are fully open. When closing, rotate the handwheel to turn the plug 90 degrees to the closed position, then turn the handwheel of the transmission mechanism to lower the plug to achieve sealing. As the plug separates from the valve seat during valve opening or closing, the operation is very light, and the sealing surface is less prone to abrasion, resulting in a long service life. However, the handwheel driving torque is small, so the nominal size of the valve is usually not large. Handwheel-operated rising stem plug valves have a compact structure, small size, and low fluid resistance.
Mechanical Cross-Arm Transmission Rising Stem Plug Valves: The working principle is as follows: When opening the valve, the transmission mechanism rotates the valve stem's threads to raise the plug. After the plug and the valve body sealing surface are separated, the transmission mechanism rotates the plug 90 degrees to fully open the valve. When closing, the transmission mechanism first rotates the plug 90 degrees to the closed position, and then the plug stops rotating. The driving force of the rotation thread then lowers the plug to contact the valve body sealing surface, achieving sealing. Mechanical cross-arm transmission mechanisms can be connected to cylinders, electric actuators, hydraulic systems, etc., for remote control. Mechanical cross-arm transmission rising stem plug valves overcome the limitation of insufficient input torque of the driving device, allowing valves to be used in larger diameter and higher pressure directions. The plug channel of mechanical cross-arm transmission rising stem plug valves has the same diameter as the pipeline, with low fluid resistance, making it convenient for pipeline cleaning. Their use is increasingly widespread in long-distance pipelines for petroleum and natural gas.
Three-Way and Four-Way Plug Valves
Three-way and four-way plug valves are suitable for chemical plant applications where it is necessary to change the direction of flow or distribute media. Soft-seated lining or hard-seated rising stem plug valves can be selected according to the requirements of the operating conditions.
