Impact of Control Valve Performance on Control Performance

A significant amount of time is often spent specifying and selecting the proper control valve for the application.  However, this effort is generally focused on the physical properties of the valve such as metallurgy, erosion and corrosion specification, shutoff classification, fugitive emissions requirements, actuator type, positioner type, etc.  While these aspects are critical to the performance of a control valve, there are other performance metrics that are vital to the good performance the control loop that manipulates the control valve.  These include such metrics such as dead band, resolution, travel gain and step response time.  Often poor performance in these areas can significantly reduce the performance of the control loop, sometimes even preventing operation in the automatic mode.  The definition and importance of these valve performance metrics will be explained and field examples will be provided.