原文：
选用阀门时： 1、减压阀，平衡阀等必须加旁通; 2、全开全闭{zh0}谁用球阀、闸阀； 3、尽量少用截止阀； 4、阀门的阻力计算应当引起注意； 5、电动阀一定要选好的。 A、按介质通断性质选用阀门 蝶阀 　 蝶阀的蝶板安装于管道的直径方向。在蝶阀阀体圆柱形通道内，圆盘形蝶板绕着轴线旋转，旋转角度为0°~90°之间，旋转到90°时，阀门则牌全开状态。 蝶阀结构简单、体积小、重量轻，只由少数几个零件组成。而且只需旋转90°即可快速启闭，操作简单，同时该阀门具有良好的流体控制特性。蝶阀处于xx开启位置时，蝶板厚度是介质流经阀体时{wy}的阻力，因此通过该阀门所产生的压力降很小，故具有较好的流量控制特性。蝶阀有弹密封和金属的密封两种密封型式。弹性密封阀门，密封圈可以镶嵌在阀体上或附在蝶板周边。 采用金属密封的阀门一般比弹性密封的阀门寿命长，但很难做到xx密封。金属密封能适应较高的工作温度，弹性密封则具有受温度限制的缺陷。 如果要求蝶阀作为流量控制使用，主要的是正确选择阀门的尺寸和类型。蝶阀的结构原理尤其适合制作大口径阀门。蝶阀不仅在石油、煤气、化工、水处理等一般工业上得到广泛应用，而且还应用于热电站的冷却水系统。 常用的蝶阀有对夹式蝶阀和法兰式蝶阀两种。对夹式蝶阀是用双头螺栓将阀门连接在两管道法兰之间，法兰式蝶阀是阀门上带有法兰，用螺栓将阀门上两端法兰连接在管道法兰上。 阀门的强度性能是指阀门承受介质压力的能力。阀门是承受内压的机械产品，因而必须具有足够的强度和刚度，以保证长期使用而不发生破裂或产生变形。 球阀 球阀是由旋塞阀演变而来。它具有相同的旋转90度提动作，不同的是旋塞体是球体，有圆形通孔或, 通道通过其轴线。球面和通道口的比例应该是这样的，即当球旋转90度时，在进、出口处应全部呈现球面，从而截断流动。 球阀只需要用旋转90度的操作和很小的转动力矩就能关闭严密。xx平等的阀体内腔为介质提供了阻力很小、直通的流道。通常认为球阀最适宜直接做开闭使用，但近来的发展已将球阀设计成使它具有节流和控制流量之用。球阀的主要特点是本身结构紧凑，易于操作和维修，适用于水、溶剂、酸和天然气等一般工作介质，而且还适用于工作条件恶劣的介质，如氧气、过氧化氢、甲烷和乙烯等。球阀阀体可以是整体的，也可以是组合式的。 截止阀 截止阀的阀杆轴线与阀座密封面垂直。阀杆开启或关闭行程相对较短，并具有非常可靠的切断动作，使得这种阀门非常适合作为介质的切断或调节及节流使用。 截止阀的阀瓣一旦处于开启状况，它的阀座和阀瓣密封面之间就不再的接触，并具有非常可靠的切断动作，合得这种阀门非常适合作为介质的切断或调节及节流使用。 截止阀一旦处于开启状态，它的阀座和阀瓣密封面之间就不再有接触，因而它的密封面机械磨损较小，由于大部分截止阀的阀座和阀瓣比较容易修理或更换密封元件时无需把整个阀门从管线上拆下来，这对于阀门和管线焊接成一体的场合是很适用的。介质通过此类阀门时的流动方向发生了变化，因此截止阀的流动阻力较高于其它阀门。 常用的截止阀有以下几种：1)角式截止阀；在角式截止阀中，流体只需改变一次方向，以致于通过此阀门的压力降比常规结构的截止阀小。2)直流式截止阀；在直流式或Y形截止阀中，阀体的流道与主流道成一斜线，这样流动状态的破坏程度比常规截止阀要小，因而通过阀门的压力损失也相应的小了。3)柱塞式截止阀：这种形式的截止阀是常规截止阀的变型。在该阀门中，阀瓣和阀座通常是基于柱塞原理设计的。阀瓣磨光成柱塞与阀杆相连接，密封是由套在柱塞上的两个弹性密封圈实现的。两个弹性密封圈用一个套环隔开，并通过由阀盖螺母施加在阀盖上的载荷把柱塞周围的密封圈压牢。弹性密封圈能够更换，可以采用各种各样的材料制成，该阀门主要用于“开

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译文：
Valve selection: 1, valve, balance valve bypass must be added such as; 2, fully open all closed Who is the best use of ball valves, valve; 3, minimize the use of cut-off valve; 4, valve resistance should be calculated to attract attention; 5, the electric valve must be selected for. A, according to the nature of media use on-off valve Butterfly Butterfly valve panels installed on the pipe diameter direction. Cylindrical channel in the valve body, disc-shaped disc around the axis of rotation, rotation angle 0 ° ~ 90 ° between the rotation to 90 °, the valve is open all license conditions. Butterfly simple structure, small size, light weight, only by a few parts. And you can only rotate 90 ° starting quickly, simple, and the fluid control valve has good features. Butterfly valve is fully opened position, the disc thickness is only when the medium flows through the body resistance, thus generated by the valve pressure drop is small, it has a better flow control characteristics. Butterfly valve with elastic metal seal and the sealing of two seal types. Flexible sealed valves, seals can be mounted on the body or attached to the disc periphery. Metal sealing flexible valve seal valve generally higher than long life, but it is difficult to be completely sealed. Metal seal can adapt to high temperature, flexible seal is restricted by temperature, the defects have. If asked to use as a flow control valve, the main choice is the right size and type of valve. Butterfly valve structure principle is particularly suitable for production of large diameter valves. Butterfly not only in oil, gas, chemicals, water treatment, widely used in general industry, but also for the thermal power station cooling water system. Common butterfly valve wafer type butterfly valve and flange type butterfly valve two. Wafer type butterfly valve is the valve stud connection between two pipe flanges, flange type butterfly valve is a valve with a flange with bolts on both ends of the valve in the pipe flange connection method Lan on. Strength properties of the valve is the valve the ability to withstand the pressure medium. Valve is subjected to inner pressure of mechanical products, and therefore must have sufficient strength and rigidity to ensure the long-term use without the risk of rupture or deformation. Ball Evolved from the plug valve. It has the same movement raised 90 degrees, is the cock body is different sphere, round through-hole or the channel through its axis. The ratio of the sphere and the openings should be such that when the ball is rotated 90 degrees, the import and export office should be fully present sphere, thus cutting off the flow. Only need 90 degrees ball valve operation and a small rotation torque can be closed tightly. Full equality for the medium body cavity to provide a little resistance, through the flow channel. Generally considered the most suitable valve opening and closing used directly to do, but the recent development has been designed to make it a throttle valve and flow control purposes. The main characteristics of ball valve itself compact, easy operation and maintenance for water, solvents, acids, and natural gas general working media, but also to poor working conditions of media, such as oxygen, hydrogen peroxide, methane and ethylene . Ball valve can be integral, it can be modular. Valve The stem valve seat sealing surface and the vertical axis. Valve stem to open or close the relatively short trip, and have very reliable cutting action, making this valve is suitable for medium-conditioning and cutting off or use. Cut-off valve in the open position when the valve flap, and its seat and disc sealing surface is no longer between the contacts and have very reliable cutting action, and combine this valve is suitable for medium cut or regulation and throttle use. Once the valve is turned on, its seat and disc sealing surface contact between the longer, so it's sealing surface mechanical wear small, as most of the cut-off valve seat and disc easily repaired or replaced seals without having to remove the whole valve from the pipeline to which valves and pipes for welding into one of the occasions are very applicable. Medium through the valve when the flow direction of such a change, so the higher the flow resistance valves in the other valve. Commonly used cut-off valves are the following: 1) angle-type valve; in the angle-type valve, the fluid change only one direction, so that the pressure drop through the valve structure than conventional globe valves. 2) DC-type valve; in the DC-type or Y-shaped valve, the valve body and the main channel flow into a slash, so the damage flow state is smaller than the conventional cut-off valve, so the pressure losses through the valve accordingly smaller. 3) The plunger-type valve: This form of cut-off valve is a variant of conventional valves. In the valve, the valve disc and seat are usually designed based on the plunger principle. Polished into a flap valve connected between the plunger and valve stem seal is set in the plunger on the realization of the two elastomeric seals. Two elastic rings separated by a ring, and through the valve cover nut load exerted on the valve cover seals around the plunger pressure prison. Elastic ring can be replaced, you can use variety of materials, the valve is mainly used for "open