Stop valve are forced sealing valves, so when the valve is closed, pressure must be applied to the disc to force the sealing surface not to leak. When the medium enters the valve from below the disc, the resistance to be overcome by the operation force is the friction force of the stem and packing and the thrust generated by the pressure of the medium. The force of closing the valve is greater than the force of opening the valve, so the diameter of the valve stem is large, otherwise the fault of the stem top bend will occur. According to the connection mode, it is divided into three kinds: flange connection, wire connection and welding connection. From the emergence of the sealing valve, the flow of the
stop valve by the valve disc above the valve chamber, then under the medium pressure, the force of closing the valve is small, and the force of opening the valve is large, the diameter of the valve stem can be reduced accordingly. At the same time, under the action of the medium, this form of valve is also tight. China's valves "three to" once stipulated, the flow of cut-off valve, all from top to bottom. When the globe valve is opened, the opening height of the disc is 25% ~ 30% of the nominal diameter. Flow has reached the maximum, indicating that the valve has reached the full open position. So the full open position of the globe valve should be determined by the stroke of the valve disc.
The opening and closing parts of the stop valve are plug shaped disc, seal above the plane or sea cone, disc along the center line of the seat for linear motion. The movement form of the stem, (common name: dark rod), there are also lifting rotary rod type can be used to control the flow of air, water, steam, various corrosive media, mud, oil, liquid metal and radioactive media and other types of fluid. Therefore, this type of cut-off stop valve is ideal for cutting or regulating as well as throttling. Due to this kind of valve stem open or close stroke is relatively short, and has a very reliable cut off function, and due to the change of the valve seat through the stroke of the disc is proportional to the relationship, very suitable for flow regulation.
