Troubleshooting Guides · Free Tool
Control Valve Fault Finder
Choose the control valve problem and get likely causes in the valve, actuator, positioner or air supply, with checks and fixes.
Not movingHuntingStictionSeat leakage
SymptomValve does not move at all
Most likely causeNo air supply or regulator set too low
First checkCheck supply gauge
Causes in order of likelihood
| Cause | How to check | Fix |
|---|---|---|
| No air supply or regulator set too low | Check supply gauge | Restore air; set the regulator to the rated value |
| No signal at the positioner | Measure mA at the positioner | Repair loop wiring or DCS output |
| Solenoid valve de energised (on/off override) | Check the solenoid state | Reset the interlock or solenoid |
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Before You Start
- Work under a permit, inform the control room and put the loop in manual or bypass the trip before touching a live instrument.
- Check air supply pressure at the positioner and the filter regulator.
- Compare demand signal, positioner feedback and actual stem position.
- Read positioner diagnostics where available.
Control Valve Fault Finder: All Symptoms
Valve does not move at all
| Likely cause | How to check | Fix |
|---|---|---|
| No air supply or regulator set too low | Check supply gauge | Restore air; set the regulator to the rated value |
| No signal at the positioner | Measure mA at the positioner | Repair loop wiring or DCS output |
| Solenoid valve de energised (on/off override) | Check the solenoid state | Reset the interlock or solenoid |
Valve hunts or oscillates
| Likely cause | How to check | Fix |
|---|---|---|
| Controller tuning too aggressive | Put the loop in manual: does it stop? | Retune the controller |
| Valve stiction (stick slip) | Small steps in manual: valve moves in jumps | Adjust or replace packing, service the valve |
| Positioner gain or calibration wrong | Run a step test | Auto calibrate or adjust the positioner |
Valve sticks or moves in jumps
| Likely cause | How to check | Fix |
|---|---|---|
| Packing too tight | Check packing nut torque and friction diagnostics | Adjust or replace packing |
| Damaged stem or guide | Inspect the stem | Repair or replace |
| Undersized actuator | Compare actuator thrust with requirement | Increase supply pressure within rating or resize the actuator |
Passes flow when closed (seat leakage)
| Likely cause | How to check | Fix |
|---|---|---|
| Damaged seat or plug | Leak test or inspect trim | Lap or replace trim |
| Insufficient seat load (bench set) | Check bench set and travel calibration | Adjust bench set; recalibrate zero |
| Debris on the seat | Stroke the valve fully a few times | Flush the line; clean the trim |
Valve noisy or vibrating
| Likely cause | How to check | Fix |
|---|---|---|
| Cavitation in liquid service | Compare ΔP with the choked ΔP | Use anti cavitation trim or change pressure drop |
| High gas outlet velocity | Check outlet velocity | Use low noise trim or a larger outlet |
| Worn guides allowing plug vibration | Inspect trim | Replace worn parts |
Valve does not reach the demanded position
| Likely cause | How to check | Fix |
|---|---|---|
| Positioner out of calibration | Compare signal and travel at 0, 50, 100 % | Recalibrate the positioner |
| Supply pressure too low | Check supply at full travel | Increase supply within rating |
| Mechanical obstruction or travel stop | Check linkage and stops | Adjust linkage and stops |
Key insight: if a loop oscillates with a constant amplitude even after detuning, suspect valve stiction before the controller: test it in manual with small steps.
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Frequently Asked Questions
What is control valve stiction?
Static friction that makes the valve stick and then jump, causing limit cycling in the control loop.
Why does my control valve hunt?
Aggressive tuning, stiction or a poorly calibrated positioner are the usual causes.
How do I check seat leakage?
With a leak test to the specified ANSI/FCI 70-2 class, or by monitoring downstream flow with the valve closed.
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