The lift plug valve has a variety of structural forms, and the lift plug valve is classified into a soft seal and a hard seal according to the material of the seal face. The basic principle is that when the opening is opened, the cock is raised, and the cock is rotated by 90 degrees until the valve is fully opened to reduce the friction with the sealing surface of the valve body; when the valve is closed, the cock is rotated 90 degrees to the closed position and then the valve body is sealed. The surface contact reaches the seal.
1. Double sealed lift plug valve
The double-sealed lift plug valve is a soft seal structure. The plug body is a cylindrical plug body composed of three plates, the rubber plates on both sides are inlaid with rubber sealing faces, and the middle is a cylindrical wedge plug.
When the valve is opened, the transmission mechanism raises the cock, and the two sides of the plate are closed, so that the combined plug body and the valve sealing surface are separated, and then the plug body is rotated by 90 degrees to the fully open position of the valve.
When the valve is closed, the transmission mechanism rotates the combined plug body by 90 degrees to the closed position, and then pushes the plug body down. After the two side plates contact the bottom of the valve body, the lower wedge plate does not move down, and the middle wedge plug continues to descend, pushing the two side plates through the inclined surface. The inlet and outlet ends are moved so that the soft sealing surface of the side plate is compressed by the valve body sealing surface to be sealed.
The double-sealed lift plug valve has double blocking and discharging functions, and the valve is provided with a pressure balance device to prevent abnormal pressure rise of the system and reduce the resistance of the valve when opening and closing. Since the metal faces are in contact with each other after the sealing ring is compressed, the valve has a fireproof function. The maintenance of the valve is very convenient. The two side plates can be removed from the valve body by removing the end cover of the bottom of the valve body without removing the valve body from the pipeline. Therefore, it is also widely used in oil, natural gas, metallurgical mining, gas engineering, light industrial textiles, ship docks, food and environmental water treatment industries to regulate and open and close pipeline fluids.
2, hard seal lift plug valve
The metal seat seal lift plug valve can be sealed on both sides of the seat sealing surface, and the use of the valve is not limited by the flow direction of the medium. When the metal hard seal lift plug valve is closed, the valve seat sealing surface can be pressurized by the hand wheel and the valve stem. By increasing the seal specific pressure, the plug valve can have better sealing performance. The sealing surface of the valve seat is convex, which is convenient for cleaning the sealing surface, and the sealing surface is not easy to accumulate crystal medium or solid particles. Solid is often used in high temperature applications in chemical plants. There are many types of hard seal lift plug valves, and two are common.
A. Handwheel-operated lift plug valve, working principle: rise, make the cock and valve fully open. When closing, turn the handle to rotate the cock 90 degrees to the closed position, then turn the transmission handwheel to lower the cock to seal.
When the valve is opened and closed again, the cock is separated from the valve seat, so the opening and closing of the valve is very easy, and the sealing surface is not easy to be scratched during the opening or closing process, and the valve has a long service life. However, the handle drive torque is small, so the nominal size of the valve used is usually small. The handwheel lift lift plug valve is compact, small in size and low in fluid resistance.
B. Mechanical cross drive lift plug valve, the working principle is: when the valve is opened, the transmission rotates the thread of the valve stem to raise the plug body. After the cock and the sealing surface of the valve body are disengaged, the cock is driven to rotate 90 degrees until the valve is fully opened. When the transmission is turned off, the cock is rotated 90 degrees to the closed position, the cock is no longer rotated, and the driving force turns the thread to lower the cock, and contacts the sealing surface of the valve body to achieve sealing.
The mechanical cross drive mechanism can be connected to cylinders, electric devices, hydraulic systems, etc. for remote control.
The mechanical cross drive lift plug valve solves the limitation of insufficient input torque of the drive device, and makes the valve develop toward large diameter and high pressure.
The diameter of the cock of the mechanical cross drive lift plug valve is the same as the diameter of the pipe, and the fluid resistance is small, which is convenient for pigging. The development of oil and natural gas long-distance pipelines is growing.
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