The absence of valve response requirements, the need to fill in a leakage class on valve specification forms, an emphasis on minimizing cost and in some cases, pressure drop, and a perception that excess capacity is good for future capability may lead one to think that valves typically designed for on-off service are a good option for throttling control because of lower cost, tighter shutoff, and lower pressure drop.

The efficiency and onstream time of axial and centrifugal compressors is important for many production units and utility systems. Surge, in particular, can cause system downtime and increase energy use. The flow reversals every few seconds cause severe vibrations that can damage compressor seals and shafts reducing compressor efficiency. The loss of forward flow often initiates shutdowns of production lines.

The Proportional-Integral-Derivative controller (PID) is the heart of every control system in the process industry. Given the proper setup and tuning, the PID has proven to have the capability and flexibility needed to meet nearly all of industry’s basic control requirements. However, the information to support the best use of these features has fallen behind the progress of improved functionality.