Specifying Control Valve Performance to Achieve Process Performance Goals

A significant amount of time is often spent specifying the proper control valve for the application.  These specifications typically includes such aspects as material of construction, erosion and corrosion specification, shutoff classification, fugitive emissions requirements, etc.  While these aspects are important, other performance metrics such as dead band, resolution, process gain and step response time are vital to the good performance of the control loop that manipulates the control valve.  The definition and importance of these performance metrics will be explained and field examples will be provided.  These techniques can be used to specify and select control valves that will enable control loops to perform as required.  And, they can be used to diagnose and improve existing control valve performance that limits control loop performance.  The benefits include longer valve life, reduced process variability and improved process performance.