Valves are devices used to regulate the rate, pressure, and direction of flow of a fluid. The regulated fluid can be a liquid, a gas, a gas-liquid mixture or a solid-liquid combination. Valves normally consist of a body, cover, valve seat, opening and closing elements, drive mechanism, seals and connectors.
The control function of the valve is achieved by means of a drive mechanism or fluid which drives the lifting, sliding, oscillating or rotating movement of the opening and closing elements to regulate the size of the passage section.
The use of the valve is very wide, it is closely related to people’s daily life, for example, the tap water pipe and the PRV used in the liquefied petroleum gas stove are valves.
Valves are also essential components of a wide range of mechanical machinery, such as internal combustion engines, steam engines, air compressors, pumps, pneumatic transmission systems, hydraulic transmission machinery, ships and planes.
Before the year 2000 BC, the Chinese used bamboo pipes and cork gates on the water pipeline system, then sluice gates on the irrigation canals, check valves return to plate on foundry bellows, and collected brine using bamboo pipes and plate check valves in pit salt mines, and appeared in Europe with the introduction of the technology of melting and hydraulic machines.
Lead and copper faucet. The lever safety valve was created in 1681 for boiler use. Plug valves and check valves were still the main valves until the arrival of Watt’s steam engine in the 18th century. The invention of a steam engine led to valves entering the engineering industry.
In addition to ball valves, safety valves, and Watt’s steam engine valves, butterfly valves were often used to control flow.
The increase in steam flow and pressure means that the use of a shut-off valve to regulate the inlet and outlet of steam from the steam engine no longer meets the needs, so that the valve appears.
From 1840, threaded stem stop valves and trapezoidal threaded stem globe valves follow each other, which is an important progress in valve production.
The introduction of these two types of valves has not only met the demands of different industries to increase point pressure and temperature, but also ultimately satisfied the requirements of flow control.
Since then, with the growth of electrical industry, petroleum industry, chemical industry and shipbuilding industry, various forms of high and medium pressure valves have rapidly evolved.
Since World War II, older poppet and butterfly valves have seen new applications through the production of polymeric materials, stainless steel, lubricating materials, and cobalt-based cemented carbide. Ball valves and diaphragm valves have evolved rapidly.
Globe valves, gate valves and other valves have improved and enhanced their efficiency.
The valve manufacturing
The valve manufacturing industry has become an increasingly important area of the machinery industry. Valves can be divided into six categories: valve used for shut-off, regulation, check valve, shut-off valve, safety valve and general purpose valve function.
Shut-off mechanism is mainly used to interrupt the flow of fluid, such as gate valve, plug valve, ball valve, diaphragm butterfly valve, pinch valve, etc. Control valve is mainly used to adjust fluid pressure and speed, such as throttle valve, pressure relief valve and floating ball valve, etc.
The check valve is used to prevent reversal of fluid flow; the diverter valve is used in the valve.
Two-phase fluid passage or fluid isolation, including slide valve, multi-port valve, drain valve, and air purge valve; the safety valve is mainly used for safety protection to prevent the furnace, pressure vessel or pipeline from being broken by overpressure;
valve is a valve with several features, such as a shut-off valve, both of which can be used as a pressure relief valve.
Industrial pipeline valves can be classified into vacuum valve, low pressure valve, medium pressure valve, high pressure valve and ultra-high pressure valve according to the rated pressure, and the valve can be further divided into standard temperature valve.
Medium temperature valve, high temperature valve and low temperature operating temperature valve, and the valve can also be classified by type according to how it is operated.
Valves can be named individually or in combination according to different classification methods and can also be named according to structural properties or particular uses of the opening and closing components.
The process requirements of the valve are working pressure, working temperature and calibration. Valve ratings and nominal diameters are widely used as standard specifications for separate valves used in industrial pipelines.
Pressure rating is the average operating pressure of the material valve at the specified temperature. The nominal diameter is the nominal inside diameter of the connection end of the valve body and the pipe.