Valves are pipe accessories used to open and close pipelines, control flow direction, and adjust and control the parameters (temperature, pressure, and flow) of the conveying medium. According to their functions, they can be divided into manual shut-off valves, automatic control valves, etc.Valves are control components in fluid conveying systems, with functions such as shut-off, regulation, diversion, prevention of backflow, pressure stabilization, diversion, or overflow pressure relief. Valves used in fluid control systems, from the simplest shut-off valves to various valves used in extremely complex automatic control systems, have a wide variety of varieties and specifications.Valves can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metal, and radioactive media. Valves are also divided into cast iron valves, cast steel valves, stainless steel valves (304, 316L, etc.), chrome-molybdenum steel valves, chrome-molybdenum-vanadium steel valves, duplex steel valves, plastic valves, non-standard custom valves, etc. according to their materials.The control of the operating valve can adopt a variety of transmission methods such as manual, electric, hydraulic, pneumatic, worm gear, electromagnetic, electromagnetic hydraulic, electro-hydraulic, gas-hydraulic, spur gear, bevel gear drive, etc.; it can act according to the predetermined requirements under the action of pressure, temperature or other forms of sensor signals, or simply open or close without relying on sensor signals. The valve relies on the drive or automatic mechanism to make the opening and closing parts move up and down, slide, swing or rotate, thereby changing the size of its flow area to achieve its control function.Main technical parameters of the valve:Nominal pressure:(1) Vacuum valve: refers to a valve with a working pressure lower than the standard atmospheric pressure.(2) Low-pressure valve: refers to a valve with a nominal pressure PN ≤1.6Mpa.(3) Medium-pressure valve: refers to a valve with a nominal pressure PN of 2.5Mpa, 4.0Mpa, 6.4Mpa, 10.0Mpa, and 16.0Mpa.(4) High-pressure valve: refers to a valve with a nominal pressure PN of 16.0Mpa~42.0Mpa.(5) Ultra-high pressure valve: refers to valves with nominal pressure PN ≥ 42.0Mpa.Working temperature:(1) Ultra-low temperature valve: valves used for medium working temperature -29℃~<-196℃.(2) Normal temperature valve: valves used for medium working temperature -29℃<~<120℃.(3) Medium temperature valve: valves used for medium working temperature +120℃<~<425℃.(4) High temperature valve: valves used for medium working temperature +>425℃.Drive mode: manual, electric, hydraulic, pneumatic, worm gear, electromagnetic, electromagnetic hydraulic, electro-hydraulic, gas-hydraulic, spur gear, bevel gear drive, etc.Drive mode can be divided into: manual valve type, automatic valve type, self-controlled valve type, power drive valve type, etc.Nominal diameter:(1) Small diameter valve: valve with nominal diameter DN ≤ 50mm.(2) Medium-diameter valve: valve with a nominal diameter of DN 50 to 300 mm.(3) Large-diameter valve: valve with a nominal diameter of DN 350 to 1200 mm.(4) Extra-large diameter valve: valve with nominal diameter DN ≥ 1400mmStructural features:The structural features of valves can be divided into the following types according to the direction in which the closing part moves relative to the valve seat:(1) Gate-shaped: the closing part moves along the center of the valve seat; such as stop valves, etc.(2) Plug and ball-shaped: the closing part is a plunger or a ball that rotates around its own center line; such as plug valves, ball valves, etc.(3) Gate-shaped: the closing part moves along the center of the vertical valve seat; such as gate valves, gates, etc.(4) Swing-shaped: the closing part rotates around the axis outside the valve seat; such as swing check valves, etc.(5) Butterfly-shaped: the disc of the closing part rotates around the axis inside the valve seat; such as butterfly valves, butterfly check valves, etc.Connection methods:(1) Threaded valve: the valve body has internal or external threads and is connected to the pipe threads.(2) Flange-shaped valve: the valve body has a flange and is connected to the pipe flange.(3) Welded valve: the valve body has a welding groove and is welded to the pipe.(4) Clamp-connected valve: The valve body has a clamping mouth and is connected to the pipe clamp.(5) Sleeve-connected valve: The valve body is connected to the pipe with a sleeve.(6) Wafer-connected valve: The valve and the two pipes are directly clamped together with bolts.Valve body material:(1) Metal valve: The valve body and other parts are made of metal materials. For example: cast iron valve, cast steel valve, stainless steel valve, alloy steel valve, titanium alloy valve, monel alloy valve, etc.(2) Non-metal valve: The valve body and other parts are made of non-metal materials. For example: plastic valve, enamel valve, ceramic valve, fiberglass valve, etc.
