Fault Finding Guides · Free PDF

Control Valve and Positioner Fault Finding Guide

A one page guide to control valve and positioner problems: movement, stability, leakage, speed and noise.

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A one page A4 guide to print for the workshop or keep on your phone in the field. The full content is also shown below.

Symptom	Likely causes	Checks and fixes
Does not move	No air, failed I/P or positioner, seized stem, no signal	Check supply, signal, positioner status, manual override
Hunting or cycling	Stiction, high positioner gain, loose feedback arm, oversized valve	Check signature; tune; tighten linkage
Passing when closed	Seat wear, wrong bench set, low thrust, debris	Check bench set and thrust; inspect trim
Slow stroking	Small tubing, blocked exhaust, booster or solenoid limits	Check air path; fit booster or quick exhaust
Cannot fully open	Low supply pressure, travel limits, wrong spring range	Check supply and settings
Noise or vibration	Cavitation, flashing, high velocity	Check pressure drop and σ; consider trim change
Air leak	Diaphragm, fittings, positioner	Soap test; replace parts

Status	Meaning	Action
F Failure	Output invalid	Repair or replace; check loop goes to safe state
C Function check	Simulation, calibration or maintenance active	Finish the work, return to normal mode
S Out of specification	Operating outside limits or uncertain	Check process conditions and sensor
M Maintenance required	Still valid but degrading	Plan maintenance before failure

Why does my valve hunt?

Stiction, loose feedback arm or too high positioner gain are typical causes.

Why is my valve passing?

Seat damage or insufficient seat load from wrong bench set or low supply.

What is a valve signature?

A plot of actuator pressure against travel that reveals friction and spring range.

Control valve passing causes

A practical guide on instrumentationblog.in with more background on this equipment.