This 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 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 engineers 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 series 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 placed 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 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 experience 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 applications 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 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. |
TABLE OF CONTENTS Preface
Control 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 information 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 contradictions, 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 author's experience may be directed to a particular industry, perhaps omitting ideas important to other industries. An effort has been made to cross-reference 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 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 communication, 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. |
