过程装备与控制工程专业英语阅读材料翻译.docx

1、过程装备与控制工程专业英语阅读材料翻译四种类型的阀门回转阀毫无疑问，回转阀是人类构想的第一种截断流体的器具。它满足人类使用超过两千年，由于它的结构简单，还会将继续使用。使用的时候通常是通过旋转塞子打开或者关闭四分之一，如图5.13所示。通过旋转使得塞子与阀体的相对位置发生改变，形成互补，达到各自打开和闭合的目的。这种阀门源自早期罗马工人的的智慧，并由有兴趣的工人及工程师流传下来。将锥形塞紧密塞于锥形壳或壳里中做成锥形阀使之保持紧密的想法，但不会太紧密，是其发明者的一个突破。对于敞开的铅制金属管，老练的管子工会环状滚压，折叠成近似圆弧状，并用其将管道纵向封住。回转阀的设计主要是凭经验，而不是靠理

2、论确定。塞子的坡口角度一般是10，如果角度过小，会导致塞子和阀体卡住或者难以开闭。闭锁式自由阀虽然，相对于已经使用两千多年的回转阀，闭锁式自由阀算是新东西。但实际上，它是在钳的基础上改进而成的。它最初是由我们所知道的历史上两件大事相关联，螺纹车床的发明（17951800年）及特里维西克、瓦特的蒸汽机应用。直到1768年，由于瓦特发明的循环蒸汽机要求锅炉要变得要求更高，普通的旋转阀已经很快不能满足快速增长的蒸汽压强的要求（相对现在的标准说来只能算接近大气压）。 闭锁式自由阀的外观上存在不同，有的采取球形截流阀及环绕封闭的形式，有的却采取水平或直线形式。这样的截止阀连结点，可以使得主管道流动方向进

3、行九十度的改变，或者导致锅炉的竖向积压，或作为一个可控给水止回阀。其中活门并不是安装在中轴上（由其中轴控制）以进行单向流动。只有外螺纹螺旋阀，是面与面相贴紧的，各部分的几何位置使得它们之间产生固定挤压。楔式闸阀由詹姆斯在1839年发明，它的重要性超过了水管栓旋塞（来源已经不明），历史记载楔式闸阀是由于供水系统阀门的不足启发了内史密斯，希望他能发明出更可靠的东西来代替。这些流体控制设备有着共同的特点，但是，由于都是依靠楔作用而达到面与面贴近的效果，所以会影响到密封问题，这种阀门一个面是平面，另一个面为圆锥状或圆周面，都经过了一定时效处理，在依照详细设计及所需材质合理改进的。下面仅对楔式闸阀进行介

4、绍。如图5.14简图所示的阀门，我们发现两个活门同时关闭，这使得防渗漏有双重保险，这正是这种詹姆斯发明的阀的优点。达到双重封闭需要满足如下条件：（a）两个活门同时关闭并且是平行横切的。（b）由轴提供的轴向力必须能够克服活门受到的表面压力（压强及冲力）以及活门所受阻力。（c）活门必须完整，完全封闭等等。双重阻挡面不是这种类型的阀门绝对必要的，反而，只要能阻挡面能防止流体六国，就可以算严格意义上的“活门”了。无论是何种旋式截止阀或是平行闸阀（弹簧片类型），采用的都是单面关闭形式双密封的活门是相当理想的，但在以下设计条件得到满足时，才可以用单活门来阻挡流体流动。根据安装条件的不同，阀门有时也须详细检

5、测，并与大口径的阀门进行工作对比测试。安全泄压阀安全泄压阀可以防止压力容器内的压力超出限定的压力范围，例如蒸汽锅炉或接受器，而其他压力容器则较少要求使用这种保护。安全和泄压有着同一个意义，尽管“安全”普遍是说阀门防止压力容器爆炸，造成生命危险，而后者则是指压力容器内装非膨胀性物体，消除偶尔的爆发，防止过压，进而防止爆炸。比如，为了防止不必要的阀门过度的压力水管会被称为一个安全阀。忽略它们的类别，这些阀门的设计原则基本是相同的，这些阀门必须独立运作（尽管在某些设计中，在阀门处的测试操作杆有时必须脱离其基座，以便测定效率或者清除污垢），总之，阀门必须独立操作，在超压时要及时打开，在排气后回到正常压

6、力并及时关闭，但基于具体的压力情况，阀门往往不能及时关闭。安全和泄压阀可以分为四种基本类型（如果包括已经逐步淘汰的弹簧阀的话则可以分为五类），近年来有许多由国外引进的新型阀门，我们对这些阀门不做讨论。这四种类型是：（1） 杠杆型（2） 重力型（3） 弹簧型（4） 扭力杆型Reading Material 25Primary Sealing ComponentsThe primary sealing components，designated as the seal seat and seal head，characterize entire design configuration in a

7、mechanical end face sealThe seal head generally，although not always，rotates with the shaftIn most designs the seal seat is in a stationary position，but sometimes the seal seat is in a rotating position，rotating with the shaft，and the seal head is stationary The geometry of the primary seal component

8、s is governed by a multitude of factorsBoth types of primary seal components have distinct design configurationsThe design geometry of the rotary seal head is usually the result of the degree of dynamic balance to be utilized to control the hydraulic force activitiesThe secondary seal components gre

9、atly influence the shape of the glandLast，but not least，the selection of the pusher springs is another influential factor in determining the configuration of the seal head ring The geometry of the seal seat ring is determined primarily by the environmental control methods chosento be discussed in de

10、tai11Design of the Seal Head The seal head is the predominant constituent of any mechanical end face sealAs Fig515 and Fig516 indicate，the seal head represents a unit consisting of several parts required to provide the interface functionThe seal head must be designed to achieve optimal flexibility，a

11、dequate loading in conjunction with suitable pressure balance，uniformity in the circumferential distribution of the automatic pushing forces，supplied by compatible spring action，and a guarantee of proper positive drive facilities for the seal head ring when subject to rotation with the shaft The sec

12、ondary seal components play a significant role in head ring geometry and are next to the most decisive factor of hydraulic fluid balancing2Design of the Seal SeatThe mating partner of the primary seal head，the seal seat，can be designed to be equipped with either one or two seal facesThe second seal

13、face is usually machined to be used after the initial front face has been worn beyond repairThe seal seat generally functions in a stationary position The seat ring design is governed primarily by the configuration of the gland，which satisfies one or the other of several diversified environmental co

14、ntrol methods，such as flushing，quenching，cooling，or a combination of severalThe second significant factor determining the shape of the seal seat ring is the selection of the secondary seal componentsThese can be of many types as，for example，a cup ring or a Vring or even metallic gaskets of the flexo

15、tallic type The factors governing the design of primary seal seats by environmental control methods are discussed in detail in references Seal seat design must incorporate simple components，simplicity of installation，ease of replacement and maintenance，and a secondary sealing component that permits

16、flexibility of the seat ring，providing optimal seal effectivenessA pressedin design is not favorable，although this method is found in a variety of design configurations In seal design in which the seat rotates with the shaft，the seat arrangement with regard to the shaft can either be rigid or elasto

17、mers in the form of highly elastic 0-rings with drive pin attachment for positive driveThey provide some flexibility，which allows compensation for irregularities in the shaft motionSome of the conventional drive methods are pressfit，pins，set screws，dents，and many others For rotating primary seat rin

18、gs a fixed attachment to the shaft is sometimes preferred to assure positive drive action Seal seats frequently consist of brittle or fragile materials，such as carbon，ceramics, and the likeSuch materials are very sensitive and，therefore，susceptible to stress. particularly tensile stressesThis must b

19、e considered when seal seats are attached solidly to the rotating shaftIf 0-rings are used，the elastomer must be chosen from a group of materials that provide optimal resiliency and freedom from swellingSwelling O-rings develop tensile stresses in the ring cavity against the mating ring wall，leading

20、 finally to destruction of the seat ringAccurate information on the swelling characteristics of elastomer O-rings is mandatory if failures are to be avoided When using standard gland ring plates without builtin environmental control devices great care must be taken in attaching the gland ring to the

21、 housingIt is important that the gland ring be properly aligned with the housing to secure appropriate location of the seal seat ring in relation to the shaftThe use of adequate gland pilots provides a means for achieving reliable gland centeringGland pilots can be designed in many different ways，pa

22、rticularlysince they do not create any problem With the solution of alignment of the pump gland ring plates to the housing，other problems in seal assembly are not critical，except for uneven bolting in fastening As is discussed in a later section in connection with seal balancing，perfect alignment of

23、 the seal seat with the seal head on the shaft should be the aim of assemblyThe pilot centering device of the gland ring plates facilitates this requirement；it also represents the simplest way at minimum cost It is common experience that the elastomeric O-ring as a secondary sealing component for th

24、e stationary seal seat represents an elegant possibility to compensate for rotational irregularities of the seal head on the shaft3Springs for Face LoadingSteady contact between the rubbing faces of the primary seal rings to ensure proper seal performance is accomplished by using elastic springs，whi

25、ch permit a steady automatic pushing actionThis activity is further assisted by the hydraulic fluid pressure provided by the pumpSystem fluid pressure and spring selection must be closely balanced against each otherA wide range of springs is available and in practical use 密封分类 物件的分类，无论是技术的还是非技术的，都是为

26、了确定分类，是为了分析他们问题更容易。因此密封可以分为两大类，静态的和动态的。 静态密封由三个密封件组成，它们包括垫片密封、密封胶密封、和直接接触密封。 动态密封可以被细分为两个基本的密封，一种是针对轴的密封，另一种是针对往复密封。在数量上，这两种密封占了工业的绝大多数，而主要的定做密封的设备需要进行特殊考虑，动密封的分类需要用商标来确定设备的不同分类。这些商标必须使用，这是因为没有其他任何来精确区分设备。 根据旋转轴密封和径向密封。界面密封提出了工业密封式这个大家族，主要是密封件和旋转轴之间有着接触。 间隙密封包括了四个不相同种类的家族。与旋转轴成比例的部件。密封元件允许部分泄露来控制流体在

27、外力控制下可以通过间隙。 间隙密封的功能是在被密封的流体上产生一个压降，同时允许在自由运动部件中存在相对运动。间隙密封在机器内部与环境之间产生一个压力差，不同于见面密封，移动的部件之间没有主动接触。将摩擦降低到一个最小值作为一种控制方式来限制流体，当然，必须允许稍微的流动。间隙密封的例子是黏胶密封，速度密封和轴封。铁磁流体是一个例外，磁铁介质充满间隙，在一个磁场或多或少的帮助下，使得磁介质约束在间隙内。建立一个密封机械部件不必要，因为间隙密封没有滑动接触，因此运动部件之间的摩擦或磨损全部被消除。作为轴向密封的设备的机械端面密封。与垫片密封相比，端面密封属于机械密封，使用独特的不同的密封原则，机

28、械密封第一次被大规模使用在汽车工业中，用于发动机冷却液和给水系统。现在使用的国家众多也证明了对一种工业的重要性。在化工、石油化工、公共事业、机关事业，随着密封以及密封配件技术和用于密封配件的结构材料不断地改进，机械密封体现出很大的价值。除了转速的要求提高以及的温度和压力的要求不断增长，现代密封设计者要不断扩大视野和知识。机械端面密封的原理机械密封目前的技术水平已经发展到如下的程度，从十的负五次方托到五千磅每平方英寸的高真空度都能处理。新型材料，尤其是金属波纹管，使得机械密封的使用范围到达以前度不能达到的允许范围内。周转速度的旋转达到50000RPM成为可能机械密封很复杂，包括一系列单一组件的设

29、计，主要通过两个带有贴片的密封环来防止泄露达到密封。重要密封环连在轴上并且随它一起转动，另一个密封环沿着固定环的密封面摩擦，因此这两个密封环相当于轴承一样工作，而且受摩擦力磨损，任何流体泄露时都流过这个表面。因为作用在轴线方向的力使得摩擦接触的限制存在。轴向推力可能是机械力也可能是水压力。在很多设计中两者有相同作用。推力的建立是保持在周部件的连续接触并形成界面。稳定的接触防止了或最小化了摩擦区域的泄露。在固体接触不断摩擦作用产生的热和磨损的存在下。热量会积累并最终导致摩擦区域的破坏。为了防止这种情况，应用具有双重性的润滑剂，首先将摩擦接触产生的热带走进而减少热量的积累，其次，介质上覆盖一个润滑

30、剂微小薄膜从而减少摩擦同时建立紧密的密封。润滑剂流体可以是泵系统流体，也可以是其他流体，可以被输送并与任何其他液体相协调。很薄的润滑膜是我们机械断面密封面密封产生良好密封性的关键，但作用依然是个谜。对一个机械断面来说，轴的可靠性分析是不可能的。这因为每一个机械密封都是在一个纯经验主义基础上设计发展而来的，任何新的密封设计都必须以经验为主进行测试，因为对密封特性而言没有可靠理论基础只能对最后表现进行预测。Reading Material 26Introduction to Process Control ()4. The Control Loop Control in one form or a

31、nother is an essential part of any chemical engineering operation. In all processes there arises the necessity of keeping flows, pressures, temperatures, compositions, etc., within certain limits for reasons of safety or specification. Such control is most often accomplished simply by measuring the

32、variable it is required to control (the controlled variable), comparing this measurement with value at which it is desired to maintain the controlled variable (the desired value or set point) and adjusting some further variable (the manipulated variable) which has a direct effect on the controlled variable until the desired value is obtained.In order to design such a system to operate not only automatically but efficiently, it is necessary to obtain both the steady-state and dynamic (uns