原文：
用以控制流体（液体、气体、气液或固液混合体）流量、压强和流向的装置。简称阀。通常由阀体、阀盖、阀座、启闭件、驱动机构、密封和紧固件等组成。阀门的控制功能是依靠驱动机构或流体驱使启闭件升降、滑移、旋摆或回转以改变流道面积的大小来实现的。广泛用于工农业生产和日常生活器具中。 公元前2000年前，中国就在输水管道上使用了竹管和木塞阀，以后又在灌溉渠道上使用水阀，在冶炼的风箱上使用板式止回阀，在井盐开采方面使用竹管和板式止回阀提取盐水。随着冶炼技术和水力机械的发展，欧洲出现了铜、铅制旋塞阀。1681年出现了杠杆重锤式安全阀。1769年出现了蝶阀。不久又出现了滑阀。1840年前后，相继出现了带螺纹阀杆的截止阀和带梯形螺纹阀杆的楔式闸阀。随后由于电力、石油、化工和造船工业的发展，各种新型材料的应用，各种阀门相继问世并得到迅速发展，阀门制造业也逐渐成为机械工业的一个重要部分。 阀门种类繁多。按使用功能可以分为：①截断阀。用于截断或接通介质流，包括闸阀、截止阀、隔膜阀、旋塞阀、球阀、蝶阀等。②调节阀。用于调节流体的流量和压力等，中国制造的阀门包括调节阀、节流阀、减压阀等。③止回阀。用于阻止流体倒流。④分流阀。用于分配、分离和混合流体，包括滑阀、多通阀、疏水阀等。⑤安全阀。用于超压安全保护，防止锅炉、压力容器或管道等的破坏。另外，按工作压力可分为真空阀、低压阀、中压阀、高压阀、超高压阀；按工作温度可分为高温阀、中温阀、常温阀、低温阀；按驱动方式可分为手动阀、电动阀、气动阀、液动阀等；按阀体材料又可分为铸铁阀、铸钢阀、锻钢阀等；按使用部门特点可分为船用阀、水暖用阀、电站用阀等。 阀门的基本参数是工作压力、工作温度和口径。工业管道的各种阀门，常用公称压力pN（在规定温度下允许承受的{zd0}工作压力）和公称通径DN（阀体与管子联接端部的名义内径）作为基本参数。阀门主要有密封、强度、调节、流通、启闭等性能，其中前二者是一切阀门最基本最重要的性能。为了保证阀门的密封和强度，除了必须遵守有关标准规定合理地进行结构设计、确保工艺质量外，还必须正确地选用材料。用以控制流体（液体、气体、气液或固液混合体）流量、压强和流向的装置。简称阀。通常由阀体、阀盖、阀座、启闭件、驱动机构、密封和紧固件等组成。阀门的控制功能是依靠驱动机构或流体驱使启闭件升降、滑移、旋摆或回转以改变流道面积的大小来实现的。广泛用于工农业生产和日常生活器具中。

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译文：
Used to control the fluid (liquid, gas, liquid or solid-liquid mixture) flow rate, pressure and flow devices. Referred to as valves. Usually by the valve body, valve cover, valve seat, opening and closing parts, drive mechanism, seals and fasteners and other components. The control valve drive mechanism, or rely on fluid movements driven hoist parts, sliding, rotating or revolving swing to change the size of the flow area is achieved. Widely used devices in industrial and agricultural production and daily life. 2000 BC, China has used in the water pipe valve bamboo and cork, and later use the valve in the irrigation channels, in refining the use of bellows plate check valve, the use of bamboo in the well salt mining and salt extraction plate check valves. With the smelting technology and hydraulic machinery, Europe emerged copper, Lead plug. 1681 heavy hammer safety valve lever occurred. 1769 butterfly emerged. Appeared soon after sliding valve. 1840, there have threaded stem of the cut-off valve and with a trapezoidal wedge gate valve threaded valve stem. Then as electricity, petroleum, chemical and shipbuilding industries, the application of a variety of new materials, all kinds of valves one after another, and rapid development of the valve manufacturing industry is also becoming an important part of the mechanical industry. Various valves. By using the function can be divided into: ① cut-off valve. Used to cut or connect media streams, including the gate valve, globe valve, diaphragm valves, plug valves, ball valves, butterfly valves and so on. ② valve. For regulating the fluid flow and pressure, the Chinese-made valve including control valve, throttle, valve and so on. ③ check valve. Used to prevent fluid backflow. ④ shunt valve. For distribution, separation and mixing fluids, including the slide valve, multi-valve, traps and so on. ⑤ safety valve. Overpressure protection for safety, to prevent the boiler, pressure vessel or piping damage. In addition, by working pressure can be divided into the vacuum valve, low pressure valve, the pressure valve, high pressure valves, high pressure valve; by operating temperature can be divided into high-temperature valve, the temperature valves, temperature valve, cryogenic valve; by drivers can be divided into manual valves, electric valves, pneumatic valves, hydraulic valves, etc.; according to body material can be divided into cast iron valve, cast steel valve, forged steel valves, etc.; according to characteristics of the user department can be divided into marine valves, plumbing valves, valves for power station and so on. The basic parameters of the valve is working pressure, temperature and diameter. Industrial pipeline valves, commonly used PN pN (the prescribed temperature to allow maximum exposure to work stress) and nominal diameter DN (body connected with the pipe diameter end of the name) as basic parameters. Main valve seal, strength, conditioning, circulation, open and close and other properties, of which the first two are fundamental and most important of all valve performance. In order to ensure the valve seal and strength, in addition to observe the standard of reasonable structural design requirements to ensure process quality, but also must be properly selected materials. Used to control the fluid (liquid, gas, liquid or solid-liquid mixture) flow rate, pressure and flow devices. Referred to as valves. Usually by the body, the valve cover, valve seat, opening and closing parts, driving mechanism, composed of seal and fasteners. The control valve is driven to rely on drive mechanism or fluid lift hoist parts, sliding, rotating or rotary pendulum to change the flow area and the size to achieve. Widely used devices in industrial and agricultural production and daily life.