How does control valve sizing affect control loop performance?

Proper valve sizing is critical for control performance. Oversized valves: operate at small opening where small position changes cause large flow changes (high gain, sensitive to stiction), poor rangeability, and control valve hunting. Undersized valves: limit maximum flow capacity, operate near wide-open with little control authority. Target: valve operates at 60-80% open at normal conditions with capacity for upsets. Cv calculation must account for pressure drop variation with flow. Installed characteristic differs from inherent due to system pressure drop distribution.