What is a lubrication plug valve?
Lubrication plug valves are also known as reverse pressure balanced lubrication plug valves. This valve is a metal seated valve with tight closing (0 leakage) seal. The valve shall be lubricated regularly with appropriate grease.
Oil lubricated hard seal plug valves can be divided into conventional oil lubricated plug valves and pressure balanced plug valves. Special grease is injected from the top of the plug body between the conical hole of the valve body and the plug body to form an oil film to reduce the opening and closing torque of the valve and improve the sealing performance and service life. The working pressure can reach 64MPa, the maximum working temperature can reach 325 degrees, and the maximum diameter can reach 600mm.
1. Conventional oil lubricated plug valve
A. For conventional hard seal plug valve, the installation method of plug cone is positive installation. In order to reduce the friction between the valve body and the sealing surface of the cock, the valve generally adopts the sealing structure of lubricating the valve seat with sealing grease. The high-pressure sealing oil injected from the high-pressure oil nozzle forms a high-pressure sealing ring around the cock, that is, there is an oil film between the valve body and the sealing surface of the cone of the cock, which can be closed and lubricated, and it is easy to open and close.
B. In order to further reduce the opening and closing force of the plug valve, the method of reducing the plug diameter is usually adopted, so the plug valve usually adopts a rectangular flow channel. This method not only reduces the opening and closing torque of the plug valve, but also increases the fluid resistance of the plug valve
C. The sealing part of the plug cone is overlaid with STL alloy material or surface hardening technology to enhance the wear resistance and corrosion resistance of the sealing surface and long service life
D. The surface of the plug cone is finely ground to the mirror surface, and the sealing surface of the valve body is ground to have lower opening and closing torque.
2. Pressure balanced plug valve
In order to reduce the torque of conventional hard seal plug valves, pressure balanced plug valves are often used. In addition to the characteristics of conventional oil lubricated plug valves, pressure balanced plug valves also have the following characteristics:
A. The plug cone of pressure balanced plug valve is installed upside down. The upper part of the plug cone is provided with a check valve.
When the valve is closed, due to the difference between the upper and lower cross-sectional areas of the plug cone, the injected high-pressure sealing oil makes the plug body subject to upward lifting force, so that the sealing surface of the plug body and the valve can be better sealed.
B. At the moment of opening the valve, the pressure in the lower chamber of the valve body is balanced with the medium pressure of the pipeline. The high-pressure sealing oil in the upper chamber pushes the plug body downward, resulting in a small gap between the plug cone and the sealing surface of the valve body, and the torque when rotating the plug body will be effectively reduced. It can also protect the sealing pair.
C. Under high temperature conditions, the thermal expansion of the cock can be absorbed through its rise and fall to avoid the wedging of the sealing pair.
Oil lubricated hard seal plug valve, although the use of oil lubrication can appropriately reduce the opening and closing torque, it may pollute the medium. Therefore, the sealing lubricating oil is selected according to the actual working conditions.
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