Book excerpt: This up-to-date work on final control elements presents theoretical and practical information in an easy, conversational style, which makes it an excellent reference for experienced instrument and process engineers as well as students who are new to the field. The book begins with a basic explanation of the function and purpose of control valves, explaining the various types of valves that are available along with their features and limitations. It also provides: * Directions for selecting the best valve for a given service and the right flow characteristics * Simplified equations for sizing control valves for liquids and gases under normal and special conditions, such as flashing and laminar flow * Directions for minimizing environmental problems, such as noise produced by turbulent or cavitating fluids and aerodynamic noise * Solutions to dynamic instability problems * Methods for improving control loop stability * Discussion on related safety issues such as "fail-safe" action and cybersecurity Many reference tables provide information that will be invaluable in valve selection, such as valve materials, temperature ratings, and valve dimensions. Also, for the benefit of international readers, examples and equations are presented in metric as well as U.S. customary terms and measurements.