The shut-off valve, also called a shut-off valve, is a forced-sealed valve. When the valve is closed, pressure must be applied to the disc to force the sealing surface to not leak. When the medium enters the valve from below the valve disc, the resistance to be overcome by the operating force is the friction between the valve stem and the packing and the thrust generated by the pressure of the medium. The force to close the valve is greater than the force to open the valve. The diameter must be large, otherwise the valve top bending failure will occur. There are three types of connection: flange connection, screw connection and welding connection. After the self-sealing valve appeared, the medium flow direction of the shut-off valve changed from the upper part of the valve disc into the valve cavity. At this time, under the action of the medium pressure, the force to close the valve is small, and the force to open the valve is large, and the diameter of the valve stem can be corresponding To reduce. At the same time, this type of valve is also tight under the action of the medium. China's valve "three chemical supply" has stipulated that the flow direction of the shut-off valve will be used from top to bottom. When the shut-off valve is opened, the opening height of the valve flap is 25% to 30% of the nominal diameter. The flow has reached the maximum, indicating that the valve has reached the fully open position. Therefore, the fully open position of the shut-off valve should be determined by the stroke of the disc.
The opening and closing parts of the stop valve (Globe Valve) are plug-shaped discs. The sealing surface is flat or conical, and the discs move linearly along the center line of the valve seat. The movement form of the valve stem (general name: dark rod), also has the lifting and rotating rod type which can be used to control various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metal and radioactive media. flow. Therefore, this type of shut-off valve is very suitable for shut-off or regulating and throttling. Because this type of valve has a relatively short opening or closing stroke and a very reliable shut-off function, and because the change in valve seat opening is proportional to the stroke of the valve disc, it is very suitable for regulating flow.