Lubricated plug valve can be divided into conventional lubricated plug valves and pressure balanced plug valves. The special grease is injected from the top of the plug body between the valve cone hole and the plug body, forming an oil film to reduce the valve opening and closing torque, imcrease sealing and service life. The operating pressure can be up to 420MPa, with a maximum operating temperature of 325℃ and a maximum size of 600mm.
1. Conventional oil lubricated plug valve
A. For conventional metal seat lubricated plug valve, the installation position of the plug cone is positive. In order to reduce the friction between the valve body and the sealing surface of the plug, the valve generally uses the sealing structure of the sealing grease lubrication seat. The high-pressure sealing oil injected from the high-pressure oil nozzle forms a high-pressure sealing ring around the plug, that is, there is a layer of oil film between the valve body and the sealing surface of the plug cone, which can be sealed and lubricated, and easy to open and close.
B. In order to further reduce the opening and closing torque of the lubricated plug valve, usually the method of reducing the diameter of the plug is used, therefore the lubricated plug valve usually uses a rectangular flow path. This method increases the fluid resistance of the plug valve while reducing the opening and closing torque of the plug valve.
C. The sealing part of the plug cone is welded with STL alloy material or adopts surface hardening technology to enhance the wear and corrosion resistance of the sealing surface, and the service life is long.
D. The surface of the cock cone is finely ground to the mirror surface, and the sealing surface of the valve body is ground, which has a lower opening and closing torque.
2. Pressure balanced lubricated plug valve
In order to reduce the torque of conventional metal seat lubricated plug valves, pressure balanced lubricated plug valves are often used. In addition to the characteristics of conventional oil ubricated plug valves, the pressure balanced plug valves also have the following characteristics:
A. The plug cone of the pressure balanced lubricated plug valve is mounted in an inverted position. There is a check valve on the upper part of the plug cone. When the valve is closed, due to the difference in the upper and lower cut area of the plug cone, the injected high-pressure sealing oil causes the plug body to be lifted upwardly, so that the plug body and the valve sealing surface can be better sealed.
B. At the moment when the valve is opened, the pressure in the lower chamber of the valve body is balanced with the medium pressure in the pipeline. The high-pressure sealing oil in the upper chamber causes the plug body to be pushed downward, and a slight gap appears between the plug cone and the sealing surface of the valve body, the torque of the rotating plug body is effectively reduced.
C. In high temperature conditions, the thermal expansion of the plug can be absorbed by its rise and fall. Oil lubricated plug valve, although the use of oil lubrication can appropriately reduce the opening and closing torque, but it may form pollution of the medium. Therefore, the sealed lubricant is selected for the actual operating conditions.