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Development And Use Of Valves
Jul 20, 2017

Valves are devices used to control fluid flow, pressure, and flow. Controlled fluids can be liquids, gases, gas-liquid mixtures or solid-liquid mixtures.

Valves are usually composed of valve body, bonnet, valve seat, headstock, drive mechanism, sealing piece and fasteners. The control function of the valve depends on the driving mechanism or the fluid driving the headstock to lift, slip, swing or rotate the movement to change the size of the runner area.

The use of valves is very wide, it is closely related to People's daily life, for example, faucet for water pipe, pressure reducing valve used for LPG cooker are valves. Valves are also a variety of machinery and equipment such as internal combustion engines, steam turbines, compressors, pumps, pneumatic actuators, hydraulic actuators, vehicles, ships and aircraft indispensable components.

BC 2000 years ago, the Chinese people in the pipeline used bamboo and wood plug valve, and later in the irrigation channel using the sluice, in the smelting of the bellows using the plate check valve, in the salt mining aspect using bamboo and plate check valve extraction brine.

With the development of smelting technology and hydraulic machinery, copper and lead plug valves appear in Europe. With the use of boilers, in 1681, the lever-heavy-hammer relief valve appeared. Prior to the advent of the 1769 watt steam engine, plug valves and check valves have been the main valves.

The invention of the steam engine brought the valve into the mechanical industry. In addition to using the plug valve, safety valve and check valve on the Watt's steam engine, the butterfly valve is used to regulate the flow. With the increase of steam flow and pressure, the use of plug valve to control the steam engine's intake and exhaust has not been able to meet the needs, so there is a sliding valve.

Around 1840, the successive emergence of a threaded stem of the cut-off valve, and with trapezoidal threaded stem wedge gate valve, which is a major breakthrough in the development of the valve. The appearance of these two kinds of valves not only satisfies the requirement of increasing pressure and temperature of various industries at that time, but also satisfies the requirement of flow regulation. Since then, with the development of power industry, petroleum industry, chemical industry and shipbuilding industry, various high pressure valves have been developed rapidly.

After the Second World War, with the development of polymeric materials, lubricating materials, stainless steel and cobalt-based cemented carbide, the old plug valves and butterfly valves were newly applied, and the ball valves and diaphragm valves developed rapidly. The cut-off valve, gate valve and other valve varieties increase, the quality is improved. Valve manufacturing has gradually become an important sector of the machinery industry.

Valves according to the use of functions can be divided into cut-off valves, regulating valves, check valves, shunt valves, safety valves, more than six categories of valves.

Truncation valve is mainly used to truncate the fluid path, including the cut-off valve, gate valve, plug valve, ball valve, butterfly valve diaphragm valve, pinch valve, etc. the regulating valve is mainly used to regulate the pressure and flow of the fluid, including the regulating valve, throttle valve, pressure valve and floating ball regulating valve; Check valve is used to prevent the reverse flow of the fluid; the shunt valve is used for distributing the flow path of the fluid, or separating the two-phase fluid, including the slide valve, the multi-channel valve, the steam trap and the emptying valve; The pressure vessel or pipeline is damaged by overpressure; multi-use valve is a valve with more than one function, such as stop check valve can not only play the role of cut-off and start and return.

Industrial piping valves can be divided into vacuum valves according to nominal pressure, low pressure valve, medium pressure valve, high pressure valve, ultra-high pressure valve; the valve can be divided into normal temperature valve, medium temperature valve, high temperature valve and low temperature valve according to the working temp. The valve can also be classified according to the type of drive device, the connection mode of the pipe and the use material of the valve Valves may be named individually or in combination according to various classification methods, or by the structural characteristics or specific uses of the headstock.

The basic parameters of the valve are working pressure, working temperature and caliber. For a large number of valves used in industrial pipelines, common nominal pressure and nominal path as the basic parameters. Nominal pressure refers to the valve of some kind of material, under the specified temperature, allow the maximum working pressure to withstand. Nominal diameter refers to the nominal inner diameter of the valve body and the end of the pipe joint.

Valves according to their types and uses have different requirements, mainly sealing, strength, regulation, circulation, opening and closing performance. In the design and selection of valves, in addition to the basic parameters and performance considerations, but also to consider the performance of fluids, including fluid phase (gas, liquid or solid particles), corrosion, viscosity, toxicity, inflammable and explosive, precious rare degree and radioactivity, etc.

Sealing performance and strength performance is the most basic and most important performance of all valves. The valve seals the seal and the outer seal two parts. The inner seal is the seal between the disc and the valve seat, and the outer seal is the seal between the movement part of the stem and the bonnet, between the valve body and the bonnet and between the valve body and the pipe joint part. Valve in use not only requires good sealing performance, but also must ensure safety.

If leakage due to poor sealing or damage due to insufficient strength, will cause different degrees of economic loss, such as transportation of toxic, inflammable and explosive or strong corrosive fluids, but also may lead to serious safety accidents. In order to ensure the sealing and strength of the valve, in addition to the need to comply with the relevant standards to carry out reasonable structural design, to ensure the quality of the process, but also must be correctly selected materials.

Usually, the valves used for low pressure non corrosive fluids use cast iron or cast copper; high and medium pressure valves with cast steel or forged steels; high-temperature or high-pressure valves using alloy steel; valves for corrosive fluids are made of stainless steel, plastics, corrosion resistant alloys (such as copper-nickel-molybdenum alloys, titanium alloys, lead alloys, etc.) or by cast iron, cast steel liner corrosion resistant materials.

Usually, the sealing surface of low pressure valve mostly uses brass or bronze, high, medium pressure valve uses stainless steel most, require high, medium pressure valve or high temperature valve to use cobalt base cemented carbide. Polymeric materials have been widely used in the valve, such as the valve seat of the ball valve mainly using PTFE plastic, butterfly valve seals and diaphragm valves using a variety of rubber materials. These materials have better sealing properties than metals in the range of temperatures available.

With the development of modern nuclear industry, petrochemical industry, electronic industry and aerospace industry, and the development of process process automation and long-distance fluid transportation, the development of modern cryogenic valve, vacuum valve, nuclear industrial valve and various regulating valves has been promoted. There are more and more applications for valve drives for long distance control and programming.

Future valve Development will expand product parameters, development of energy saving, labor and automatic valve, improve the structure, the use of new materials and technology to improve the service life of the valve, as well as the development of special valve series such as the development of such as liquid oxygen, liquid hydrogen and liquefied natural gas, such as low-temperature valves, vacuum valves, nuclear industrial valves, safety valves, regulating valves, traps and valve drive devices.