What is your approach to troubleshooting a control valve problem?

Valve troubleshooting methodology: define problem (slow response, oscillation, passing, noise), verify controller output and valve position (positioner feedback), check air supply (pressure, quality), observe valve operation (stroke valve manually), check positioner calibration and diagnostics, inspect actuator (diaphragm, seals, connections), and if needed, remove and inspect trim. Common problems: sticking (high friction, packing too tight), poor response (positioner issue, low air supply), passing (worn seat, improper shutoff force), and noise (cavitation, high velocity). Document findings and corrective actions.