Valve is used to control fluid flow, pressure and flow devices. Controlled fluid can be liquid, gas, gas-liquid mixture or the solid-liquid mixture. Usually by the valve body valve, valve cover, valve seat, hoist parts, drive mechanism, such as seals and fastener components. The control valve is the rely on the drive mechanism or fluid movements driven hoist parts, sliding, spinning or turning motion before to change the size of area of flow is achieved. SAFETY VALVES uses a wide range of people's daily lives and it is closely related to, for example, the tap water works, liquefied petroleum gas stoves are used in the valve pressure relief valve. Valve is also a variety of mechanical equipment, such as internal combustion engines, steam engines, compressors, pumps, pneumatic actuators, hydraulic transmission vehicles, ships and aircraft components indispensable. BC Two thousand years ago, the Chinese people in the water using a bamboo pipe and valve Muse, after the use of irrigation canals in the lock, used in refining the use of bellows plate check valve, in the use of bamboo Well Salt Mining extraction tube and check valveplate with the brine smelting technology and the development of hydraulic machinery, have emerged in Europe and leaded copper plug valves. With the use of boilers, in 1681 there was a lever-type safety valve weights. Watt steam engine in 1769 appeared before the plug valves and check valve has been the main valve. The invention of the steam engine so that the valve into the field of machinery industry. Watt's steam engine in addition to the use of plug valves, safety valve and check valve, but also the use of the butterfly valveto regulate flow. As the steam flow and pressure increases, the use of plug valves control the steam engine into the exhaust gas and can not meet the needs, then a slide valve.

Before and after 1840, have emerged one after another with the valve stem thread, trapezoidal screw thread and with the wedgegate valvestem, which is a valve in the development of a major breakthrough. The emergence of these two types of valves, not only to meet a variety of industries at the time of pressure, temperature rising demands, and the initial adjustment to meet the requirements of the flow. Since then with the electric power industry, petroleum industry, chemical industry and shipbuilding industry, a variety of high and medium pressure valve has been developed rapidly.

After World War II, as a result of polymeric materials, lubrication material, stainless steel and cobalt-based hard alloy development, the old plug valves and butterfly valves to obtain a new application, the ball valve and the valve has been developed rapidly. Cut-off valve, gate valve and other valves to increase variety, quality. Valve manufacturing machinery industry has gradually become an important sector. Valve-per-use features can be divided into the cut-off valve, control valve, check valve, diversion valve, safety valve, six multi-purpose valve.

Cut-off valve for cutting off the main fluid pathway, including the cut-off valve, gate valve, plug valves, ball valve, butterfly valve, control valve, such as folder; the main control valve for regulating the fluid pressure, flow, etc., including control valve, section flow valve, relief valve and the float valve, etc.; non-return valve for preventing reverse flow of fluid; shunt valve fluid channel for the distribution of the future, or two-phase separation, including the slide-valve, multi-way valve, hydrophobic emptying valves and valves, etc.; the main safety valve for the security protection to prevent the boiler, pressure vessel or pipeline and the damage due to overpressure; multi-purpose valve is a valve in more than one function, such as the cut-off from a non-return valve can stop Back to the role while the role of start-stop.

Industrial pipe valve can be divided into a vacuum by the nominal pressure valve, low pressure valves, medium pressure valve, high pressure valves, high pressure valve; valve by operating temperature can be divided into normal temperature valves, temperature valve, high temperature valve, cryogenic valve; valve doors can also be driven by the type of device, with the pipeline and valve means connected to the use of classified materials. Valve can be a variety of classification methods, either individually or in combination to name headstock can also be pieces of the structural characteristics or specific purposes named.

The basic parameters of the valve is working pressure, working temperature and diameter. For large-scale use in a variety of industrial pipeline valves, commonly used nominal pressure and nominal diameter as the basic parameters. Nominal pressure of a material refers to the valves, the temperature required to allow the maximum working pressure to bear. DN is the valve body and connected to the end of the tube diameter of the name.

Valves in accordance with their types and uses have different requirements, there are sealing, strength, conditioning, circulation, such as the performance of headstock. In the design and selection of valves, in addition to considering the basic parameters and performance, but also consider the performance of fluid, including fluid phase (gas, liquid or solid particles containing), corrosion resistance, viscosity, toxic, flammable easy burst, and precious and so rare and radioactive.

Sealing performance and intensity of performance is the most basic of all valves, the most important performance. Since the beginning of the sealing valve seals and seal the two parts apart. Is sealed between the valve seal and SAFETY VALVES seat; outside the sealed parts of the stem movement and between the valve cover, valve body and valve cover and valve body and pipeline between the connection between the sealed parts. Valve not only requires the use of good sealing performance, and security must be guaranteed.

If due to bad seal leakage or insufficient strength of parts is damaged, it will result in different levels of economic losses, such as transportation of toxic, flammable or corrosive fluids are strong, but also may lead to serious security incidents. In order to ensure the strength of seals and valves, in addition to the provisions of the relevant standards must comply with a reasonable structure design, to ensure that the process quality, it is also necessary to choose the correct materials.

Typically, non-corrosive fluid low-pressure valves used in the use of cast iron or bronze; high pressure valve in cast steel or forged steel; the use of high-temperature alloy steel or high-pressure valve; valves for corrosive fluids of stainless steel, plastics, corrosion resistant alloys (such as copper-nickel molybdenum alloys, titanium alloys and lead alloys, etc.) or cast iron, cast steel liner corrosion resistance material.

Typically, low-pressure valve sealing surface of most of the use of brass or bronze, high pressure valves are mostly used in stainless steel, the higher the high, medium pressure valve or valves, such as the use of high-temperature cobalt-base hard alloy. Polymeric materials in the valve has been widely used, such as the main seat of the ball valve using Teflon plastic, butterfly valve of the diaphragm seals and various rubber materials. These materials can be used in the temperature range with a better seal than metal.

With the modern nuclear industry, petrochemical industry, electronic industry and aerospace industry, as well as the process automation technology and the development of long-distance transmission fluid, and promote a modern low-temperature valve, vacuum valve, the nuclear industry with a variety of valves and control valve. For remote control and valve control applications drive more and more.

The future development of valve products to expand the parameters, the development of energy-saving, labor-saving and self-control valves, to improve the structure, the use of new materials and new techniques to improve the service life of valves, as well as the development of special valves series, such as using in liquid oxygen, liquid hydrogen and liquefied natural gas cryogenic valves, vacuum valves, nuclear industrial valves, safety valves, regulating valves, steam trap and valve-driven devices.