选用时须考虑的因素   选择阀门是根据操作和及经济的合理性，综合平衡比较的经验结果。在选择阀门之前必须提出下述原始条件:1.1 物 性 (1) 物料状态 a.气体物料的物料状态包括有关物性数据，纯气体还是混合物，是否有液滴或固体微粒，是否有易凝结的成份。 b.液体物料的物料状态包括：有关物性数据，纯组份或混合物是否含易挥发组份或溶解有气体(压力降低时可析出形成二相流)，是否含固体悬浮物，以及液体的粘稠度、凝固点或倾点等。 (2) 其它性质:包括腐蚀性、毒性、对阀门结构材料的溶解性，是否易燃易爆等性能。这些性能有时不只影响材质，还会引起结构上的特殊要求，或需要提高管道等级。

　　The factors to consider when selecting valves are based on the rationality of operation, safety, and economy, and the empirical results of comprehensive balance comparison. Before selecting a valve, the following original conditions must be proposed: 1.1 Physical properties (1) Material state a. The material state of gas materials includes relevant physical property data, whether it is pure gas or mixture, whether there are droplets or solid particles, and whether there are easily condensable components. b. The material state of liquid materials includes: relevant physical property data, whether pure components or mixtures contain volatile components or dissolved gases (which can precipitate into two-phase flow when pressure decreases), whether they contain solid suspensions, as well as the viscosity, solidification point or pour point of the liquid. (2) Other properties: including corrosiveness, toxicity, solubility in valve structural materials, flammability and explosiveness. These properties sometimes not only affect the material, but also cause special structural requirements or require an increase in pipeline grade.

　　1.2 操作状态下的工作条件 (1) 按正常工作条件下的温度和压力，还需结合开停工或再生时的工作条件。 a.泵出口阀应考虑泵的关闭压力等。 b.当系统再生温度高出正常温度很多，而压力却有所降低，对这种类型的系统，要考虑温度和压力综合的影响。 c.操作的连续程度：即阀门开闭的频率，也影响到对耐磨损程度的要求，开关较频繁的系统，应考虑是否安装双阀。 (2) 系统允许的压力降 a.系统允许压力降较小，或允许压力降不小但不需要进行流量调节时，则应选用、压力降较小的阀型如闸阀、直通的球阀等。 b.需要调节流量，则应选择调节性能较好，具有一定压力降的阀型(压力降占整个管道压力降的比例与调节的灵敏度有关)。 (3) 阀门所处的环境:在寒冷地区的室外，特别是对化学物料，阀体材质一般不可用铸铁而应选用铸钢(或不锈钢)。

　　1.2 Working conditions under operating conditions (1) The temperature and pressure under normal working conditions should also be combined with the working conditions during start-up, shutdown, or regeneration. a. The pump outlet valve should consider the maximum closing pressure of the pump, etc. b. When the regeneration temperature of the system is much higher than the normal temperature, but the pressure decreases, the combined effects of temperature and pressure should be considered for this type of system. c. The continuity of operation: that is, the frequency of valve opening and closing, also affects the requirements for wear resistance. For systems with frequent opening and closing, the installation of dual valves should be considered. (2) When the system allows for a small pressure drop, or allows for a significant pressure drop but does not require flow regulation, valve types with small pressure drops such as gate valves and straight through ball valves should be selected. b. If flow regulation is required, a valve type with good regulation performance and a certain pressure drop should be selected (the proportion of pressure drop to the entire pipeline pressure drop is related to the sensitivity of regulation). (3) The environment in which the valve is located: outdoors in cold regions, especially for chemical materials, the valve body material should generally not be cast iron but should be cast steel (or stainless steel).

　　1.3 阀门功能 (1) 切断：几乎所有的阀门都具有切断功能。单纯用于切断而不需调节流量则可选用闸阀，球阀等，要求迅速切断时，则以旋塞、球阀、蝶阀等较为适宜。截止阀则既可调节流量又可切断。蝶阀也可适于大流量的调节。 (2) 改变流向：选用两通(通道为L形)或三通(通道为T形)球阀或旋塞，可以迅速改变物料流向，且由于一个阀门起到两个以上直通阀门的作用，可简化操作，使切换准确无误，并能减少所占空间。 (3) 调控：截止阀、柱塞阀可满足一般的流量调节，针形阀可用于微量的细调；在较大流量范围进行稳定(压力、流量)的调节，则以节流阀为宜。 (4) 止回：需防止物料倒流时可选用止回阀。

　　1.3 Valve Function (1) Cut off: Almost all valves have a cut-off function. If it is only used for cutting off without adjusting the flow rate, gate valves, ball valves, etc. can be selected. When rapid cutting is required, plug valves, ball valves, butterfly valves, etc. are more suitable. The shut-off valve can adjust the flow rate and cut off the flow. Butterfly valves can also be suitable for regulating large flow rates. (2) Changing the flow direction: By using two-way (L-shaped channel) or three-way (T-shaped channel) ball valves or plugs, the material flow direction can be quickly changed. Moreover, since one valve serves as a direct passage for two or more valves, the operation can be simplified, the switching can be accurate, and the occupied space can be reduced. (3) Regulation: Globe valves and plunger valves can meet general flow regulation requirements, while needle valves can be used for micro fine adjustments; A throttle valve is suitable for stable regulation (pressure, flow) within a large flow range. (4) Check valve: When it is necessary to prevent material backflow, a check valve can be used.

　　(5) 不同生产过程可以选择有附加功能的阀门，如有带夹套、带排净口和带旁路的阀门，有用于防止固体微粒沉降的带吹气口阀门等。

　　(5) Valves with additional functions can be selected for different production processes, such as valves with jackets, discharge ports, and bypass ports, as well as valves with blowing ports to prevent solid particle settling.

　　1.4 开关阀门的动力  就地操作的阀门绝大多数用手轮，对与操作带有一定距离的，可采用链轮或加长杆。一些大口径的阀门因启动力矩过大在阀门设计时已带有电机。在防爆区内要采用相应等级的防爆电机。  遥控阀门：采取的动力种类有气动、液压、电动等，其中电动又可分为电磁阀与电机带动的阀。应根据需要和所能提供的能源来选择。

　　1.4 Power for opening and closing valves: The vast majority of locally operated valves use handwheels. For valves that are at a certain distance from the operation, chain wheels or extension rods can be used. Some large-diameter valves are designed with motors due to excessive starting torque. Corresponding grade explosion-proof motors should be used in the explosion-proof area. Remote control valve: The types of power used include pneumatic, hydraulic, electric, etc. Among them, electric can be further divided into solenoid valves and motor-driven valves. The selection should be based on the needs and available energy.

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