Valve is used to open and close the pipeline, control the flow direction, adjust and control the parameters (temperature, pressure and flow) of the conveying medium. According to its function, it can be divided into shut-off valve, check valve, regulating valve and so on. The valve is a control component in the fluid conveying system. It has the functions of cut-off, regulation, diversion, prevention of reverse flow, stabilization, diversion or overflow and pressure relief. Valves used in fluid control systems, from simple shut-off valves to various valves used in complex automatic control systems, have a wide range of varieties and specifications. If divided by function and purpose, as follows:
　　 One, shut off the valve.　　
　　 This kind of valve is used for opening and closing. Standing on the inlet and outlet of cold and heat sources, equipment inlet and outlet, and pipeline branch lines (including standpipes), it can also be used as a drain valve and a vent valve. Common shut-off valves include gate valves, globe valves, ball valves and butterfly valves. Gate valves can be divided into open rod and concealed rod, single gate and double gate, wedge gate and parallel gate, etc. The closing tightness of the gate valve is not good, the large diameter gate valve is difficult to open, the valve body size along the water flow direction is small, the flow resistance is small, and the gate valve has a large nominal diameter span. According to the flow direction of the medium, the shut-off valve is divided into three types: straight-through, right-angle and direct-flow.
　　 The closing tightness of the globe valve is better than that of the gate valve. The valve body is long, the flow resistance is large, and the nominal diameter is DN200. The spool of the ball valve is a round ball with an opening. The valve stem is fully opened when the sphere opening is facing the axis of the pipeline by moving the valve stem, and it is fully closed when it is turned 90°. The ball valve has a certain adjustment performance and closes tightly. The valve core of the butterfly valve is a circular valve plate, which can rotate along a vertical axis perpendicular to the pipeline axis. When the plane of the valve plate is consistent with the axis of the pipe, it is fully open; when the plane of the gate is perpendicular to the axis of the pipe, it is fully closed. Butterfly valve has a small body length and low flow resistance, which is more expensive than gate valves and globe valves.
What are the types of valves
　　 Two, check valve.
　　This kind of valve is used to prevent the medium from flowing back, using the kinetic energy of the fluid itself to open by itself, and automatically close when flowing in the reverse direction. Standing at the outlet of the water pump, the outlet of the steam trap and other places where the reverse flow of fluid is not allowed. There are three types of check valves: swing type, lift type and wafer type. For the swing check valve, when the fluid can only flow from left to right, it will automatically close when it flows in the reverse direction. For the lift check valve, when the fluid flows from left to right, the valve core is lifted to form a passage, and when the flow is reversed, the valve core is pressed to the valve seat and closed. For the wafer check valve, when the fluid flows from left to right, the valve core is opened to form a passage. When the flow is reversed, the valve core is pressed to the valve seat and closed. The wafer check valve can be multiple positions Installation, small size, light weight and compact structure.
　　 Three, control valve.
　　 The pressure difference between the front and back of the valve is constant. When the opening of the ordinary valve changes within a larger range, the flow rate does not change much. When it reaches a certain opening, the flow rate changes sharply, that is, the regulation performance is poor. The regulating valve can change the valve spool stroke according to the direction and size of the signal to change the resistance of the valve, so as to achieve the purpose of regulating the flow of the valve. Regulating valves are divided into manual regulating valves and automatic regulating valves, and manual or automatic regulating valves are divided into many types, and their regulating performance is also different. Automatic control valves include self-operated flow control valves and self-operated differential pressure control valves.
　　 Fourth, vacuum class.
　　 includes vacuum ball valve, vacuum baffle valve, vacuum charging valve, pneumatic vacuum valve, etc. Its function is to change the direction of air flow, adjust the size of air flow, and cut off or connect the pipeline in the vacuum system. The vacuum system components are called vacuum valves.
　　 5. Special purpose category.
　　 includes pigging valve, vent valve, drain valve, exhaust valve, filter, etc. The exhaust valve is an indispensable auxiliary component in the pipeline system, which is widely used in boilers, air conditioners, oil and gas, and water supply and drainage pipelines. It is often installed at high points or elbows to remove excess gas in the pipeline, improve the efficiency of pipelines and roads, and reduce energy consumption.
　　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 (201, 304, 316, etc.) according to their materials, chromium molybdenum steel valves, chromium molybdenum vanadium steel valves, duplex steel valves, plastic valves, non-standard customized valves, etc.