译文：
在要求较高的应用场合都会对调节阀提出切断要求，因此切断功能是调节阀的一个重要的使用功能和内在质量指标（对切断等级的划分及标准见相关资料）。在现场使用中，往往会出现调节阀切断不好，泄漏大等故障。除因堵卡、允许压差过小而被顶开等原因造成的泄 漏增加外，绝大部分都是由于调节阀的结构缺陷和选型不当造成的。 一、结构型式的选择 双密封类调节阀（如双座阀、双密封套筒阀等）主要的缺点之一就是泄漏大。但上世纪80年代以前，由于当时较盛行套筒阀，然而，不少厂家却在套筒阀上下了很大功夫以改进结 构来降低泄漏量，使其演变成非常复杂的结构。于是，这又带来了许多不足：零件多、可靠性差、备件难、维护难、切断效果不理想等等。实际上，这是设计思路都陷入 了误区，与其在阀体的“心脏”内作如此复杂的改动，倒不如通过外部调整来实现。因此， 应选择单密封类调节阀。这样，密封问题、可靠性问题、维修和备件问题均被一一解决了。 此时，解决矛盾的重点转化为介质对阀的不平衡力增大的问题，解决它仅需配强力活塞执行 机构、加粗阀杆即可。这种通过外部来解决的办法显然比通过内部的复杂改进要容易得多， 与其说这是办法问题，还不如说这是思路问题。 进入到九十年代，人们开始寻找结构更简单、密封更可靠的切断阀。这时，发现角行程 阀比直行程阀（单座阀、套筒阀、闸阀）更具有优越性，于是产生了三偏心切断蝶阀、全功能切断阀、硬密封切断球阀。 二、密封面的选择 （1）面对面密封： 常见的柱塞阀芯，其密封面为60℃的小锥面，阀座也是60℃的小锥面，此小锥面的宽度通 常在0.5mm～2mm之间，要密封好就必须保证两个锥面良好接触。但事实上，它始终受到加工 误差的影响(如同心度、不圆度、倾斜度等)，其密封效果不十分理想。这类阀的泄漏率通常为 10－4，经过精密的研磨可达10－6，只能达到较好的密封等级。 （2）球面密封： 利用阀芯的球面转动与固定的阀座小锥面相切，它们之间为线接触，这就比上述面对面密 封的效果好。华林公司推出的全功能超轻型阀、球面密封蝶阀等就是采用这一思路来制作的，其泄漏率可达10－6～10－8，高性能的三偏心蝶阀可高达10－8，以至零泄漏。 三、密封材料的选择 （1）软密封 除耐腐蚀的衬里阀门外，一般的软密封阀指阀芯或阀座两者之一采用非金属材料（主要为聚四氟乙烯，还有橡胶等）的密封形式的阀。软密封阀密封效果{zj0}，但在管道安装、系 统的清洗中都有可能留下或多或少不干净的杂物（如焊渣、铁屑等），它们流经调节阀时，容易把软密封阀座或阀芯划伤，使泄漏量增加，密封的可靠性差。所以，选择软密封结构必 须考虑介质的清洁和投运前严格冲洗管道。 （2）硬密封 硬密封再堆焊耐磨合金等是切断阀的{zj0}选择。这种方式在考虑密封性的同时也考虑了 使用寿命和可靠性，虽然出厂指标只有10－6～10－8，达不到软密封零泄漏的效果，但足以满足严密切断的要求，而且它经久耐用，从经济的角度考虑更合算。 四、密封可靠性的考虑 （1）软密封，切断效果好，但不适宜用于含颗粒介质，一旦划伤，泄漏会急剧增加。因此，条件允许时尽量选用硬密封。全功能超轻型阀硬密封可达10－7～10－8，三偏心蝶阀可达零 泄漏。 （2）对密封耐磨性的考虑：除选硬密封外，对泄漏要求10－6以上的切断型调节阀，应该(或者说必须)堆焊耐磨合金以提高密封的耐磨性、耐冲蚀、耐划伤的能力，提高阀的寿命。 （3）对高温介质的切断调节阀在室温下组装的，在高温下工作，温度变化几百度。热膨 胀会改变装配时建立的密封比压。过紧，密封面会卡住，运动时会严重擦伤，拉伤；过松， 密封压不够，两种情况泄漏都会急剧增加。解决的{zh0}办法是用弹性阀座来吸收这一变化造 成的差异。通常有三种弹性方案：①弹簧式；②薄片式柔性金属环；③刚柔相济的弹性阀座。 后者{zh0}，即有柔性克服热膨胀，又有刚度并堆耐磨合金来提高耐磨面的可靠性。 （4）对含颗粒的冲蚀介质，要考虑阀芯避让开高速介质的直接冲蚀。直行程阀、蝶阀都 不具备这一功能，而全功能超轻型阀偏心旋转具有这一特点。遇此，应选后二种阀。 （5）对于硬密封，必须有足够的硬度差，同一硬度材料“互不相让”，容易擦伤。 （6）对所配执行机构应增大推力和刚度，使之动作自如。 五、切断阀主要阀型 按上述分析，切断阀的主要阀型如下，选择切断阀应综合考虑泄漏率、介质种类、介质 温度、流量系数等各种参数和xxx。在如下优选秩序中，先考虑硬密封，再考虑软密封。 （1）全功能超轻型调节阀 （2）三偏心金属硬密封蝶阀 （3）双偏心球面密封蝶阀 （4）球阀 （5）偏心旋转阀 （6）单座阀 （7）单座套筒阀 （8）软密封阀 六、高温、高压、大压差、大口径切断阀选择 高温、高压、大压差、大口径切断是一个比较普遍的难题，主要原因是缺少同时具有允 许压差大、切断好、耐高温膨胀卡的阀，如高压蒸汽调节与切断，因压差大（1～3MPa或更 大），口径大（DN200～300），不得不采用平衡式的双密封结构（如双座阀或双密封套筒 阀），经特殊处理，泄漏率可达10－4，再提高就困难了，而全功能超轻型调节阀综合性能好， 可较好的解决这一难题，泄漏率可达10－6～10－7以上。

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原文：
In demanding applications will be made on the control valve off and were therefore cut off the valve function is an important function and the use of internal quality indicators (to cut the division level and standard, see relevant information). In field use, will often appear cut off the bad valve, leakage and large fault. In addition due to lay a trap, allowing the small pressure difference was caused by roof leaks and other reasons to open an increase, the vast majority are due to structural valve defects and improper selection. First, choose the type of structure Double seal type valve (eg, valve seat, double sealed sleeve valve, etc.) is one of the major shortcomings of a large leak. But 80 years ago the last century, was more popular because the sleeve valve, however, many manufacturers are up and down the sleeve valve great effort to improve the structure to reduce leakage, it evolved into a very complex structure. So, this brings a lot to be desired: many spare parts, unreliable and difficult parts, maintenance is difficult, and so cut off the result is not satisfactory. In fact, this is the design ideas are misunderstanding, rather than in the body of the "heart" in making such complex changes, it would be better achieved through external adjustment. Therefore, we should choose a single seal type valve. In this way, sealing problems, reliability problems, maintenance and spare parts were to solve the problem. At this time, resolving contradictions into a media focus on the imbalance force increases valve problem, solve it only with a strong executive body piston, valve stem can be bold. This means external to solve the complex clear through internal improvements than the much easier, so much the problem is way than to say that this is a thinking problem. Into the nineties, people began to look for structure is more simple, more reliable shut-off valve closed. At this time, found for rotary valve stroke than a straight valve (single seat valve, sleeve valve, gate valve) has more advantages, then had to cut off the three eccentric butterfly valve, all-off valve, hard seal off valve. Second, the choice of sealing surface (1) face to face sealing: Common plunger valve, the sealing surface of the small cone was 60 ℃, 60 ℃ seat is a small cone, the width of this small cone is usually between 0.5mm ~ 2mm to seal well to guarantee that the two a cone of good contacts. But in fact, it is always affected by processing errors (like heart degrees of roundness, inclination, etc.), the sealing effect is not very good. Usually this type of valve leakage rate of 10-4, after precision grinding up 10-6, only to achieve a better seal level. (2) spherical seal: Spool of spherical rotation using a fixed seat with a small cone tangent, line contact between them, and this effect than the good face seal. Waring has introduced full-featured ultra-light valve, spherical valve seal is used to this thinking, such as produced by the leakage rate up to 10-6 ~ 10-8, high performance butterfly valve can be as high as 10-8 even zero leakage. Third, the choice of sealing materials (1) soft sealing In addition to the lining of corrosion-resistant valves, in general, the soft-sealing valve spool or valve seat means one of two non-metallic materials used (mainly PTFE, as well as rubber, etc.) form the valve seal. Soft sealing valve seal is best, but in the pipe installation, the system of cleaning that could have left more or less does not clean debris (such as welding slag, iron, etc.), they are flowing through the valve, it is easy to Soft sealing valve seat or scratch, an increase of leakage, seal the reliability of the difference. So, choose medium soft sealing structure must be considered before operation for cleaning and flushing pipelines strict. (2) seal Seal re-surfacing of wear-resistant alloys such as shut-off valve is the best choice. This approach in considering the tightness of taking into account the service life and reliability, although the factory index only 10-6 to 10-8, fail soft seal zero leakage effect, but enough to meet the rigorous requirements to cut off, and it durable, from the economic point of view is more cost-effective. 4, sealing reliability considerations (1) soft sealing, cutting effect, but not suitable for medium containing particles, once scratch, leakage would increase drastically. Therefore, conditions permitting, to make full use seal. Full-function ultra-light valve seal up 10-7 to 10-8, three eccentric butterfly valves up to zero leakage. (2) wear resistance of the seal to consider: In addition to seal the election, the demands on the leakage of more than 10-6 to cut off type control valve, it should be (or must) wear-resistant alloy to improve the seal welding the wear-resistant erosion, scratch-resistant ability, to improve valve life. (3) to heat the medium at room temperature, cut off valve assembly, work at high temperatures, temperature several hundred degrees. Thermal expansion will change the seal assembly to establish specific pressure. Too tight, sealing surface will be stuck, movement will be severely bruised, strained; too loose, seal pressure is not enough in either case, leakage would be increased dramatically. The best solution is to use elasticity to absorb the changes in the valve seat caused by the difference. Usually there are three flexible options: ① spring-type; ② Flexible sheet metal ring; ③ hardness and softness of the flexible seat. The latter is best, that is flexible to overcome the thermal expansion, but also the stiffness and wear-resistant alloy to improve wear heap surface reliability. (4) medium containing particles of the erosion should be considered open spool avoid direct high-speed media erosion. Linear actuator valves, butterfly valves do not have this feature, and full-function ultra-light eccentric rotary valve with this feature. In such, should be after the election, two kinds of valves. (5) for the seal must have sufficient hardness difference, the same hardness material "to each other," easy bruising. (6) on the ticket enforcement agencies should increase thrust and stiffness, so that action freely. 5, the main valve-type shut-off valve By the above analysis, the main valve shut-off valve type as follows, select the shut-off valve leakage rate should be taken into account, media types, media temperature, flow coefficient and other parameters and cost-effective. In the following preferred order, first consider the seal, and then consider the soft seal. (1) full-featured ultra-light valve (2) three eccentric metal seal butterfly valve (3) spherical double eccentric butterfly valve seal (4) Ball (5), Eccentric rotary valve (6) Single-seat valve (7) single-seat sleeve valve (8) Soft Seal Valves 6, high temperature, high pressure, big pressure, large diameter shut-off valve selection High temperature, high pressure, big pressure, large diameter cut is a relatively common problem, mainly due to the lack of pressure also has allowed large, cut off a good, high temperature valve expansion cards, such as high pressure steam conditioning and cut off, due to large pressure (1 ~ 3MPa or greater), diameter large (DN200 ~ 300), have adopted balanced double seal structure (such as two-seater double-sealed sleeve valve or valves), with a special treatment, leak rate of up to 10-4 , further increase the difficulty, while the all-comprehensive performance ultra-light control valve, and can be a better solution to this problem, the leakage rate can reach more than 10-6 to 10-7.