Hardware knowledge: general equipment valve development and principle

Valve usually by valve, valve cover, valve seat, open and close parts, drive mechanism, seals and fasteners and other components. The control function of the valve is driven by the drive mechanism or fluid to drive the hoist and lift, slip, swing or rotary movement to change the size of the flow passage area to achieve.
Valve is widely used, it has a close relationship with people's daily life, such as the tap water pipe, liquefied petroleum gas stove valves are used in valve. Valve is also a variety of mechanical equipment such as internal combustion engine, steam engine, compressor, pump, pneumatic transmission device, hydraulic transmission device, vehicle, ship and aircraft in the indispensable parts.
BC 2000 years ago, Chinese people is in the pipeline used valve bamboo and cork, and later use in irrigation channels gate, in refining the use of bellows using plate check valve, in the well salt mining the use of bamboo tube and plate check valve salt extraction.
With the development of smelting technology and hydraulic machinery, copper and lead plug in europe. With the use of boilers, in 1681 and the emergence of lever type safety valve. 1769 before the advent of the Watt steam engine, plug and check valve has been the main valve.
The invention of the steam engine valve into the field of machinery industry. On Watt steam engine in addition to using the plug valve, safety valve and check valve, but also used the butterfly valve, to adjust the flow. With the increase of the steam flow and pressure, the use of plug valves control steam engine inlet and exhaust gas can not meet the need, so there is a slide valve.
Before and after 1840, the valve has emerged with threaded stem, and with trapezoidal threaded valve stem wedge gate valve, which is a major breakthrough in the development of the valve. The emergence of these two types of valves, not only meet the various industries at the time of the pressure, temperature rising requirements, and initially meet the requirements for traffic regulation. Since then, with the development of power industry, oil industry, chemical industry and shipbuilding industry, all kinds of high pressure valve developed quickly..
After the Second World War, due to the development of polymer materials, lubricating materials, stainless steel and cobalt based alloy, the old plug valves and butterfly valves won the new application, ball valves and diaphragm valves get rapid development. Valve, gate valve and other varieties of the increase in quality to improve. Valve manufacturing industry has gradually become an important sector of the machinery industry.
Valve according to the function can be divided into the cut-off valve, control valve, check valve, diversion valve, safety valve, multi-purpose valve six categories.
The cut-off valve is mainly used for cut off fluid pathways, including cut-off valve, gate valve, plug valve, ball valve, butterfly valve, diaphragm valve pinch valve; the valve is mainly used for adjusting the pressure of the fluid flow, including control valve, throttle valve, pressure relief valve and the float valve; check to prevent reverse flow of fluid valve; valve for the distribution of fluid pathways whereabouts, or two-phase flow separation, including slide valve, multi valve, drain valve and air exhaust valve; safety valve is mainly used for security protection, prevent the boiler, pressure vessel or pipeline overpressure due to the damage; multi valve is a valve with more than one function such as the cut-off valve, drying both can play a role and can play the role of check.
Industrial pipe valve according to nominal pressure can be divided into the vacuum valve, low pressure valve, pressure valve, high pressure valve, super high pressure valve; valve according to the working temperature can be divided into valve at room temperature, the temperature valve, high temperature valves, cryogenic valves; valves can also be classified as a type of driving device, and the pipe connection mode and the body of the use of materials. Valve can be classified by various classification alone or in combination, can also be the structure of the opening and closing parts or specific purpose named.
The basic parameters of the valve is working pressure, working temperature and caliber. For various valves used in industrial pipes, nominal pressure and nominal diameter are used as basic parameters.. Nominal pressure refers to the valve of a material, at the specified temperature, allowable maximum working pressure. Nominal diameter refers to the nominal diameter of valve body and pipe joint end.
Valve according to its type and purpose have different requirements, the main sealing, strength, adjustment, circulation, opening and closing performance. In the design and selection of valves, in addition to considering the basic parameters and performance, but also consider the fluid properties, including fluid phase (gas, liquid or solid particles containing), corrosive, viscosity, toxic, flammable and explosive of, precious rarity and radioactive.
Sealing performance and strength of the valve is the most basic, the most important performance. The sealing part of the valve seal and the outer sealing part two. Inside seal is the valve between the valve and valve seat seal between the valve stem movement and valve cover, between valve cover and valve body and pipe joints between the sealing. Valve in the use not only requires good sealing performance, but also must ensure safety.
If the result of bad sealing leaks or damage due to insufficient strength leaving part, will result in different degree of economic loss, such as the transmission of toxic, inflammable, explosive or corrosive fluids, can also lead to serious safety accidents. In order to ensure the valve seal and strength, in addition to comply with the relevant standards and regulations to rationally design and ensure the quality of the process, it must also be the correct selection of materials.
Usually low non corrosive fluid valve cast iron or cast copper; high, medium pressure valve made of cast or forged steel; high temperature or high pressure valve use of alloy steel; used for corrosion fluid valve with stainless steel, plastic, corrosion resistant alloys (such as copper nickel