Cut-off valve is also known as the section valves, is compulsory sealed valve, so when the valve is closed, must be pressure on the disc to force the sealing surface does not leak. When the media enters the valve under the disc, operating force to overcome the resistance, is the stem and filler friction and by the pressure of the media generated by the force, close the valve than open the force of the valve, so the stem diameter should be large, otherwise it will happen stem top bending fault. According to the connection method divides into three kinds: the flange connection, the silk buckle connection, the welding connection. From the valve after the seal, the media flow of the cut-off valve is changed from the top of the valve into the valve cavity, at this time under the pressure of the media, close the valve force is small, and open the valve of the force, valve stem diameter can be correspondingly reduced. At the same time, in the medium action, this form of valve is also more stringent. China's valve "three to" has stipulated that the cut-off valve flow, all use Top-down. When the cut-off valve is open, the opening height of the disc is the 25%~30% of the nominal diameter. The flow has reached the maximum, indicating that the valve has reached full open position.
Therefore, the full open position of the cut-off valve should be determined by the stroke of the disc. Cut-off valve (Stop valve,globe valve) of the headstock is a plug-shaped disc, sealed above the plane or sea cone, the disc along the center of the seat line for linear motion. The movement of the stem, (general name: Dark Rod), also has the lifting rotary rod can be used to control the air, water, steam, a variety of corrosive media, mud, oil, liquid metal and radioactive medium and other types of fluid flow. Therefore, this type of cut-off valve valve is ideal for cutting off or regulating and throttling. As the valve stem opening or closing of the valve is relatively short, and has a very reliable cutting function, but also because of the valve seat through the mouth of the changes and the disc's journey into a positive proportional relationship, very suitable for the flow of regulation.
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