原文：
选购气动换向阀应注意的问题： 一、气动换向阀是气动系统中的控制元件，用来控制系统中流体的流向，其式样类型很多，用户可根据自己的需要进行选择。 换向阀的常见类型有如下几种： 按出气口分：二通、三通、四通和五通; 按工作位置分：二位和三位。 按控制方式分：气控和电控、直动式和先导式; 按被控介质分：流体阀和气体阀; 按功能分：常闭和常开、中封和中泄及中间供气; 按结构分：有截止阀和滑阀; 二、在选购气动换向阀时，应注意以下几点： 1.换向阀的螺纹接口：换向阀的公称通径与气口螺纹并不一一对应，因此，选用换向阀时应注意接口螺纹。 2.换向阀的安装尺寸：相同型号、功能的换向阀因生产厂家不同其外形和安装尺寸不尽相同。 3.换向动作是否干脆利落，不拖泥带水。进口泵 阀门 4.电磁阀特别是交流电磁阀应注意其绝缘性能。以保证 操作者的人身安全。 5.换向阀应无外泄漏，内泄漏越小越好。否则，会影响系统的正常工作，并浪费能源。 6.注意阀的出厂日期，换向阀放的时间太长，其润滑油脂会老化，影响换向阀的正常工作。

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译文：
Optional pneumatic valve should pay attention to the problem: 1, pneumatic valve control system is pneumatic components to control the flow of fluids in the system, many types of its style, users can choose according to their needs. Valve There are several common types: Divided by outlet: Two-, three, four-way and five-pass; Divided by the working position: two and three. Control points by: pneumatic and electric control, direct-action and Pilot; Divided by charged media: Fluid valve and gas valve; By function: Normally closed and normally open, the seal and the vent and the middle gas; Divided by the structure: a cut-off valve and slide valve; Second, in the purchase pneumatic valve, should note the following: 1. Valve thread interface: the nominal valve diameter and the air intake is not thread-one correspondence, therefore, should pay attention to interfaces used valve thread. 2. Valve installation dimensions: the same type, valve function by different manufacturers to install its shape and size vary. 3. For the action is crisp, not muddy. Import pump valve 4. Solenoid valve solenoid valve in particular, the exchange should be noted that the insulation performance. To ensure operator safety. 5. Valve should be no external leakage, internal leaks as small as possible. Otherwise, will affect the normal operation of the system, and a waste of energy. 6. Note valve manufacture date, valve amp for too long, the grease will aging affect the normal operation of valve.