“The tank is overflowing!” Not a nice thought, but that could be a result of a system out of control due to a poor choice of the valve characteristic. Selecting the proper valve characteristic is the easiest way to ensure process stability at all loads. So what valve characteristic to use? This article makes recommendations for the four basic process controlling variables: liquid level, pressure, flow, and temperature. These recommendations are based on a complete dynamic analysis of the process and serve as “rules of thumb” to be used as part of valve selection. The “valve characteristic” refers to the relationship between the position of its flow-controlling element (e.g. valve plug) and its resulting flow. Graphi- cally, this is normally plotted with the valve’s resulting flow on the vertical axis vs. the valve plug’s travel on the horizontal axis. The shape of the resulting output vs. input curve describes the type of valve characteristic.
HEADLEY, MICHAEL (2003) Guidelines for Selecting the Proper Valve Characteristic