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Valve is a pipeline accessory used to open and close the pipeline, control the flow direction, regulate and control the parameters of the transported medium (temperature, pressure and flow). According to its function, it can be divided into shut-off valves, check valves, regulating valves, etc.

Valve is a control component in the fluid delivery system, with functions such as shut-off, regulation, flow guidance, prevention of backflow, pressure stabilization, diversion or overflow pressure relief. Valves used in fluid control systems, from the simplest shut-off valve to the most complex automatic control system used in a variety of valves, its variety and specifications are quite large.

Valves can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, slurry, oil, liquid metal and radioactive media. Valves are also divided into cast iron valves, cast steel valves, stainless steel valves (201, 304, 316, etc.), chromium-molybdenum steel valves, chromium-molybdenum-vanadium steel valves, duplex steel valves, plastic valves, non-standard customized valves, etc. according to the material.

Valve is a device used to control the direction, pressure and flow of fluid in the fluid system, is to make the medium (liquid, gas, powder) in the pipeline and equipment flow or stop and can control its flow.

Valve is a control part of the pipeline fluid delivery system, used to change the cross section of the pathway and the direction of media flow, with the function of inflow, cut-off, throttling, check, diversion or overflow pressure relief. Valves for fluid control, from the most simple shut-off valve to the most complex automatic control system used in a variety of valves, its variety and specifications, the nominal diameter of the valve from the very small instrumentation valve to the diameter of up to 10m industrial pipeline with valves. Can be used to control the flow of water, steam, oil, gas, slurry, a variety of corrosive media, liquid metals and radioactive fluids and other types of fluids, the working pressure of the valve can be from 0.0013MPa to 1000MPa ultra-high pressure, the working temperature can c-270 ℃ ultra-low temperature to 1430 ℃ high temperature.

Valve control can be used in a variety of transmission methods, such as manual, electric, hydraulic, pneumatic, turbine, electromagnetic, electro-hydraulic, electro-hydraulic, gas-hydraulic, spur gear, bevel gear drive, etc.; can be under the action of pressure, temperature or other forms of sensing signals, according to the predetermined requirements of the action, or do not rely on sensing signals and simple opening or closing, the valve relies on drive or automatic mechanism to open and close the lifting, sliding, swinging or rotary movement, The valve relies on the drive or automatic mechanism to make the opening and closing parts for lifting, sliding, swinging or rotary motion, thereby changing the size of its flow channel area to achieve its control function.

According to the role and use

(A) shut-off valve

This type of valve is to open and close the role. Often set up in the cold, heat sources, inlet and outlet, equipment inlet and outlet, pipeline branch lines (including risers), can also be used as a water release valve and bleed valve. Common shut-off valves are gate valves, globe valves, ball valves and butterfly valves.

Gate valve can be divided into open and concealed stem, single gate and double gate, wedge gate and parallel gate, etc. Gate valve closing tightness is not good, large diameter gate valve opening difficulties; along the water flow direction valve body size is small, small flow resistance, gate valve nominal diameter span.

Gate valve according to the media flow direction is divided into straight-through, right-angle type and DC type three, there are open stem and concealed stem. Globe valve closing tightness is better than the gate valve, the valve body is long, large flow resistance, the maximum nominal diameter of DN200.

The spool of the ball valve is a round ball with an open hole. The plate moves the stem so that the ball opening is facing the axis of the pipeline for the full open, turn 90 ° for the full closed. The ball valve has certain adjustment performance and closes more tightly.

The spool of butterfly valve is a circular plate, which can be rotated along the vertical axis of the vertical pipe axis. When the valve plate plane is in line with the pipe axis, it is fully open; when the gate plate plane is perpendicular to the pipe axis, it is fully closed. Butterfly valve body length is small, the flow resistance is small, and the price is higher than gate valve and globe valve. [1]

(B) check valve

These valves are used to prevent the backflow of media, using the fluid's own kinetic energy to open itself, reverse flow automatically closed. Often set in the outlet of the pump, water evacuator outlet and other places where the reverse flow of fluid is not allowed. Check valve is divided into three types of swing, lift and clamp type. For swing check valve, the fluid can only flow from left to right, and automatically close when the reverse flow. For lift check valves, the spool lifts when the fluid flows from left to right, forming a pathway, and closes when the spool is pressed against the valve seat in reverse flow. For the clamp check valve, the spool is opened to form a pathway when the fluid flows from left to right, and is closed when the spool is pressed onto the seat in reverse flow. The clamp check valve can be installed in many places, small in size, light in weight and compact in structure. [1]

(C) adjustment valve

Valve before and after a certain pressure difference, the opening of the ordinary valve in a wide range of changes, the flow rate does not change much, and to a certain opening, the