A valve is a device which controls the spritz rate, pressure or the direction. The controlled fluid can be the liquid, gas, the mixture of gas and liquid or the mixture of solid and liquid. The valve usually is well-balanced of body, seat, bonnet, parts for opening or latter, persuasive device, sealing element and so on. The executive function of the valve depends on the persuasive device or the movement of the fluid which drives the sliding, rotating or turning of the parts for opening or latter to transpiration the zone of the spritz passage.

Two thousands years ago, the Chinese people unromantic the bamboo trunk and wooden plug into water pipeline. Then later they unromantic the sluice into the irrigational canal, the plate trammels valve into bellows for smelting and so on. With the minutiae of smelting process and hydraulic machinery, the plug valve made of contumely and lead appeared in Europe. Besides, with the wide using of boiler, in 1681 the unscratched valve with lever and heavy bob came into the world. surpassing the invention of the Watt steam engine, the plug valve and trammels valve were the most important valves. The steam engine leaded the valve into a new field namely mechanical industry.

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