ISA CNTRL VALVES-1998 Control Valves.pdf

1、ControlValvesGuy Borden, EditorPractical Guidesfor Measurement and ControlCopyright 1998 Instrument Society of America67 Alexander DriveP.O. Box 12277Research Triangle Park, NC 27709All rights reserved. Printed in the United States of America.1098765432ISBN 1-55617-636-8No part of this work may be r

2、eproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher.Library of Congress Cataloging-in-Publication DataControl valves / Guy Borden, editor ; Paul Friedm

3、ann, style editor.p. cm. - (Practical guide series) Includes bibliographical references and index. ISBN 1-55617-565-5 1. Automatic control. 2. Control valves. I. Borden, Guy.II. Series. III. Series : Practical guides for measurement and control.TJ223.V3C67 1998621.84-dc21 98-14192CIPiiiAbout This Se

4、riesThis volume is part of the Practical Guide Series developed and published by the ISA, the International Society for Measurement and Control.The Practical Guides were conceived because of a shortage of published material in the field of measurement and control that bridges the gap between theory

5、and actual industrial practice. Many books in the field have catered to the needs of technical students, who need to be oriented to basic control theory and concepts, or college-level readers, who are interested in engineering mainly from a classroom perspective. There are handbooks for practicing e

6、ngineers that cover measurement and control, but these handbooks often devote only a chapter or two to topics that merit more attention. Within the Practical Guides Series, separate volumes address each of the important topics and give them comprehensive, book-length treatments. Each book in the ser

7、ies can be understood and used by technical students, sales engineers, sales personnel, and managers, and relied upon by those who have “real-live” industrial concerns such as correct application, safety, installation, and maintenance.Another unique feature of the Practical Guides is the stress plac

8、ed on the actual experience of measurement and control practitioners. The Practical Guides are overseen by various Volume Editors and a Series Technical Editor, who have extensive experience in measurement and control. The Volume Editors have been selected for their specific expertise in the volume

9、topics, and bring together numerous Contributing Writers with even more specialized knowledge.The Series Technical Editor, who is responsible for general technical consistency within each volume and across all volumes, helps guide the Volume Editors.The Practical Guides capture the hard-earned exper

10、ience of the writers and, by employing examples and recording anecdotal observations, make that experience as applicable for the reader as possible. Case studies, either hypothetical or based on real case histories, are used to illustrate typical situations and show how good planning and practical a

11、pplications made the difference between success and failure. Some of this information has never been documented before.This volume is designed to be at home in a library, in a classroom, or on the plant floor. The comfortable reading style, large pages, and frequent illustrations will contribute to

12、ease of use. The page design uses graphics to “call out” some of the major points of the text, such as crucial safety checks and important examples. Each Practical Guide gathers widely scattered information in a single text, with bibliographies directing the reader to other sources.AcknowledgmentsTh

13、e editors gratefully acknowledge the initial work of Parrish Hirasaki in recruiting many of the initial authors for this volume. Appreciation is also given to Linda Wolffe for support provided during this project. Of course, this volume could not have been completed without the generous contribution

14、s of its authors. For their many contributions, our heartfelt thanks!viiTable of ContentsAbout This Series iiiAcknowledgments vPreface xiiiAbout the Volume Editors xvContributors xviiChapter 1 Introduction to Control Valves 1References 12Chapter 2 The History of Control Valves 15Acknowledgement 23Re

15、ferences 23Chapter 3 Terminology 25Part One: Control Valving Terminology Not Included in ISA Standard 25Part Two: ANSI/ISA S75.05 “Control Valve Terminology” 28References 72Chapter 4 Valve Bodies 73Globe-Style Bodies 73Rotary Valves 82Special-Purpose Valves 91References 92Chapter 5 Control Valve Act

16、uators 93Signals and Power Sources 93Basic Styles 94Motion Conversion 100Linear-to-Rotary Torque/Travel Relationships 100Power Failure Modes 101Actuator/Valve Sizing Factors 101Table of ContentsviiiActuator Accessories 101References 103Chapter 6 Sizing 105Required Calculations 105ANSI/ISA S75.01 Sta

17、ndard “Flow Equations for Sizing Control Valves” 112References 162Chapter 7 Cavitation and Flashing 163Cavitation Fundamentals 164Cavitation in Valves 170Testing 178Cavitation Applications for Control Valves 183Special Fluid Considerations 208Flashing 211Nomenclature and Glossary 216References 220Ch

18、apter 8 Control Valve Noise 223Introduction 223Valve Noise Sources 227Valve Noise Prediction 233User Caveat 235Valve Noise Categories 236Possible Solutions 237Conclusion 266References 266Chapter 9 Control Valve Trim 269Selection of Valve Trim Material 269Characterizing of Valve Plugs or Cage Ports 2

19、71Seat Leakage 273Soft Seat Trim Design 278Seating of Rotary Valves 283Low Flow Trim 285Trim for Abrasive-Erosive Service 288Plug Guiding 294Dynamic Torque of Rotary Valves 301Bistable Flow and Plug Instability 308Elastomeric Trim 310References 310Chapter 10 Control Valve Features 313Process Conditi

20、ons that Influence Valve Design 314Piping End Loadings that Influence Valve End Connection Design 315Valve End Connection Concerns 316Valve End Connection Types 317Table of ContentsixBonnets 327Fluid Solidification Protection 333Freeze Protection (Cryogenic Service) 335High Temperature Protection 33

21、6Valve Stem Sealing Features 337Valve Packing 337Live Loading 345Flow Straightening Devices 347Traps, Strainers and Filters 347Hydraulic Snubbers 350Valve Features to Reduce Noise 352Fire Safe Treatment 356Fire Safe Pneumatic Actuators with Fusible Elements 357Evaluating the Need for Bypass and Bloc

22、k Valves 358Valve Bypasses 359Chapter 11 Materials for Control Valves 363Material Properties 363Environmental Considerations 365Materials of Construction 380Materials for Pressure Retaining Parts 382Coatings 391Trim Material Selection 393Valve Packing 401Gaskets 403Sealants 405Paint and External Coa

23、tings 406Trademarks 408References 408Chapter 12 Control Valve Applications 411The Application Categories 412Valves in Parallel 423Valves in Series 432Frequent Application Problems 434References 446Chapter 13 Safety 449Automated Valve Selection 449On-Off Valves 449Materials of Construction 450Valve P

24、iping 451Valve and Actuator Sizing and Selection 452Valve Positioners, Transducers, Position Transmitters, and Accessories 453Valve Failure Modes 456Other Safety Considerations 458References 458Table of ContentsxChapter 14 Control Valve Selection 459Safety 461Process Containment 464Valve Performance

25、 467Control Performance 470Control Valve Design 472Accessories 476Specialized Valves 478Bypass Manifolds 479Prepare Plans 480Develop Specifications 482Putting It All Together 490References 492Bibliography 494Chapter 15 Accessories 495General Considerations 496Device Descriptions 499Device Operation

26、501Networked Valves 511The Future 539References 540Chapter 16 Installation 543Planning 543Receiving-Inspection 546Installing in the Piping 547Paperwork 549Testing After Installation 551Type Specifics 553References 558Chapter 17 Control Valve Troubleshooting 561Control Valve Troubleshooting 561Preven

27、tion Rather than Cure 562Types of Problems Encountered 566Methods for Analyzing Problems and Diagnosing Potential Causes 567Functional Problems 567Operational Problems 574Use of Diagnostic Tools to Aid in Troubleshooting 582References 582Chapter 18 Case Histories 585Specification and Selection 585Ma

28、terials 590Installation and Location 591Testing 595Table of ContentsxiOperation and Maintenance 595External Causes 596Multiple Problems 599Stupidity 599References 599Chapter 19 Maintenance 601Philosophy 601Warranty 601Planning 602Safety 602Instructions 603Maintenance Choices 604What Goes Wrong with

29、Control Valves? 606Alternatives to Repair 614References 616Chapter 20 Control Valve Testing 619Part One: Manufacturers Testing 619Less Common Tests 626Conclusions for Manufacturers Testing 629Part Two: Field Testing Of Installed Valves 630Diagnostic Testing 630Other Control Valve Tests 649Motor-Oper

30、ated Valves: Diagnostic Testing 651Summary of Post-installation Testing 657References 658Chapter 21 Codes and Standards 659Definitions and Descriptions 659Subjects of Codes and Standards 663References 669Chapter 22 Computerized Control Valve Sizing 671The Development of Valve Sizing Aids 671Importan

31、t Features 673Valve Sizing Worksheets 674Gas and Vapor Sizing Worksheet 675Liquid Sizing Worksheet 684Two-Phase Sizing Worksheet 692Valve Sizing Procedure 696References 698Chapter 23 Everything You Ever Wanted to Know About Regulators 699Operation 699Performance 701Designs 702Table of ContentsxiiSiz

32、ing 711Performance Comparison with Control Valves 711References 714Appendix A Units Conversion 717Appendix B Organizations That Sponsor Codes, Standards and Recommended Practices 719Appendix C Bibliography of Control Valve Standards 725ISA 725IEC 727ASME 729API 729ASTM 730FCI 731IEEE 731ISO 731MSS 7

33、32UL 733Miscellaneous 734Index 735xiiiPrefaceControl valves consist of body assemblies, actuators, and accessories. There have been so many innovations in all of these areas since the Second Edition of the ISA Handbook of Control Valves was published in 1976 that it was thought important to bring in

34、formation about the subject devices and techniques up-to-date.In the presentations in their chapters, authors have written based on their own experience as well as those of their associates. Most chapters overlap several others. If differences of opinion or technique become apparent, seeming contrad

35、ictions, it is because each author has had success with his or her particular technique, not that others are wrong. It should be recognized that each authors experience may be directed to a particular industry, perhaps omitting ideas important to other industries. An effort has been made to cross-re

36、ference chapters so that the reader may be aware of other points of view.Many valves are called “control valves” without fitting the definition shown in the ISA Terminology Standard S75.05. There are a number of control valves that fit the definition, but are so specialized that they are not covered

37、 in this volume.Of the problems experienced with procuring and using control valves, the major ones seem to be caused by lack of knowledge of installed process conditions (design versus actual) and lack of good communication between the buyer and seller. With high quality process data and good commu

38、nication, poor installation practices still will account for some dissatisfaction. Experienced valve practitioners say that ten percent of their control valves give ninety percent of their problems.xvAbout the Volume EditorsGuy Borden, Jr., the volume editor, has over forty years involvement with co

39、ntrol valves including twenty with control valve manufacturers Black, Sivalls a little noisy, perhaps; but operating in a good throttling position.Introduction to Control Valves3The comprehensive sizing equations of ANSI/ISA S75.01 are readily solved on a computer, allowing alternatives to be review

40、ed very quickly. But reliable basic process data are difficult to obtain. It seems that there is no money to develop basic data before the project is authorizedand no time afterward. In those sage words from computerland: “Garbage ingarbage out.” Research, investigation, and even questions beyond th

41、e nominal flowsheet are required to assure reliable data Ref. 11. Fuzzy data cause the process engineer to inflate flows; then the instrument engineer adds a factor, sizes the valve for 50% open and goes to the next higher Cvin the manufacturers table. The resulting oversized valve incurs penalties

42、in both cost and rangeability.A checklist that can be used to verify that all the data necessary to select the valve are available in ISA Form S20.50, Rev. 1, from ISA S20-1981. With this form, a valve can be selected and purchased. This ISA form requires that all necessary mechanical and process in

43、formation be entered and, because of its organization, eases the selection process.So, valve selection and sizing can be compared to the familiar three-legged stool. The leg that represents the comprehensive sizing procedures is by far the strongest. Regrettably, the basic data leg is the weakest. F

44、ield testing and computer time to close complex mass balances are extremely expensive: thus, the necessity for a strong third legjudgmentto support the stool.An important selection parameter that is difficult to assess is valve rangeability. It is defined in Table 1-1. The definition emphasizes one

45、of the dangers of oversizing. The minimum controllable flow remains constant for a given valve. Thus, as the maximum required flow decreases, rangeability decreases. Quite obviously, a choked or sonic flow condition that is unrealized during sizing will also limit rangeability Ref. 12.Table 1-1. Ter

46、minology Used in Control Valve Selection Ref. 11.Valve TerminologyInherent flow characteristic of a valve is defined as the relationship between fractional valve lift and the relative flow through the valve at a constant pressure drop.Installed characteristic is the actual lift-vs-flow characteristi

47、c under system operating conditions where pressure drop is not constant, and is unique to each specific installed system.and Kv= the slope of the valve characteristic curve.where Pv= valve pressure drop;PL= system friction losses (piping and other)RangeabilityMaximum controllable flowMinimum control

48、lable flow-=TurndownNormal maximum flowMinimum controllable flow-=Valve GainKvChange in flowChange in stem position-=Valve pressure drop ratioPvPvPL+- PR=Introduction to Control Valves4The weakness of the definition of rangeability is a working understanding of minimum controllable flow. Lovett has

49、pointed out that it is limited by seat leakage and the ability of the actuator to maintain stem stability at a near-closed position Ref. 13. Hetz observes vibration as the plug approaches the seat Ref. 14; and Schuder suggests a limit on change in valve gain for rangeability Refs. 15 and 16. Shinskey offers a technique for making a smooth transition