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 Chapter 3 - Terminology
This chapter is offered in two parts. This first part addresses the terms useful to those involved with control valves but not deemed appropriate for the ISA Standard, ANSI/ISA S75.05, "Control Valve Terminology." The second part is a complete reproduction of that ISA standard. Standard terminology is important in any technical activity. Control valve users are encouraged to use and communicate in accord with these entries. Appendix B of this volume lists the acronyms of organizations (as well as their names and addresses) that are important in control valving. Part One: Control Valving Terminology Not Included in ISA Standard Terminology Av Flow coefficient in the International System of Units (SI) system; AOV Air-operated valve. This is not a preferred designation, but it follows the similar designation, MOV (motor-operated valve). ANSI Class A strength designation for valves of arbitrary class numbers from which tables were developed by the American Society of Mechanical Engineers (ASME) for a variety of materials in standards ANSI/ASME -B16.1, -B16.34, and -B16.42 [Refs. 1-3]. These tables show the maximum pressures at various temperatures at which a valve can be expected to work safely and continuously. ANSI is the American National Standards Institute. ARC A self-operated automatic recirculation valve for pump protection (not a valve controlled by an instrument signal). Belleville Springs Cupped washers that maintain bolt tension (live loading) when they are compressed between a flange and the nut on the bolt. Choked Flow With upstream pressure and valve opening constant, lowering the downstream pressure will result in increased flow until the ability to turn pressure drop (compression energy) into velocity (kinetic energy) is hindered by partial vaporization of liquid - occurs both with flashing and cavitation. With gases choked flow is attained when the downstream velocity becomes sonic - approximately when the downstream pressure is about half the upstream pressure or less. CWP Cold working pressure, sometimes used for pressure ratings, infrequently for control valves. |
