Control Valve Commissioning & Troubleshooting

Stroking a valve moves the process. Agree every test with operations, isolate and depressurise where needed, and keep hands clear of the stem and linkages. Positioner menus and settings vary by make: follow the manufacturer's manual.

Pre-checks

Nameplate vs datasheet: tag, size, rating, trim, Cv, fail action (fail open / closed / last), actuator type and air supply range.
Flow direction arrow matches the line.
Air supply: filter regulator set to the actuator's rated pressure (from the nameplate), clean dry air, drain the filter.
Tubing tight; no leaks at fittings (listen and use leak spray).
Mechanical: stem connector tight, travel indicator and scale correct, linkage/feedback arm secure.

Positioner calibration

Check the action setting: direct (4 mA = closed) or reverse (4 mA = open), as the loop requires.
Run the positioner's automatic calibration (auto-stroke) with the valve isolated from the process or agreed with operations. It finds the end stops.
Check the tuning (gain / speed) the auto-calibration chose. A valve that overshoots or hunts may need a lower gain.
Set any travel cut-offs (tight shut-off below e.g. 1 %) only if the process needs them, and record them.
Save and record the configuration.

Stroke test

Apply 4, 8, 12, 16 and 20 mA going up, then back down, and record the actual travel at each step:

Signal	Expected travel (direct)	Typical tolerance
4 mA	0 %	± 1 % of travel
8 mA	25 %	± 1–2 %
12 mA	50 %	± 1–2 %
16 mA	75 %	± 1–2 %
20 mA	100 %	± 1 %

The difference between the up and down readings at the same point is the hysteresis / deadband. Small steps (0.5–1 %) show whether the valve moves smoothly or jumps.

The Valve Stroke Check app builds the table and pass/fail for you; see also Valve Stroke Testing.

Fail-action, limit switches and solenoids

Air failure: isolate the air supply. The valve must go to its fail position in the expected time.
Signal failure: disconnect the mA signal. Most positioners drive to the fail position too.
Solenoid (trip) valve: de-energise it and check the valve trips; time the stroke if the safety requirements specify it. The Solenoid Coil Check app helps confirm the coil is energised.
Limit switches: set the open and closed switches so they change state just before the end of travel, and check the indication in the DCS.

Troubleshooting in service

Symptom	Likely cause	Check / fix
PV cycles in a slow sawtooth, controller output a square wave	Stiction (static friction): packing too tight, damaged stem or trim	Small step test in manual; adjust packing per manufacturer; service trim
Valve hunts around setpoint	Positioner gain too high, or controller tuning	Put loop in manual: if it stops, it's tuning; if not, positioner
Won't fully close / passing	Seat damage, travel not reaching seat, wrong bench set	Stroke to 0 % and check travel; seat leakage test
Slow to move	Low air supply, blocked filter, small tubing, booster setting	Supply pressure at the positioner during stroking
Moves but wrong position	Feedback linkage loose or slipped	Re-fit linkage and re-calibrate
Packing leaking	Packing worn or loose	Tighten evenly per manual or replace; don't over-tighten (stiction)
Noise, vibration, damage downstream	Cavitation or flashing (liquids) or high velocity	Check sizing: see the Control Valve Cv app

Field example: level loop cycling every 3 minutes
A level loop cycled continuously, even after the controller was detuned. In manual, a 0.5 % output step didn't move the valve; a 2 % step made it jump 1.5 %. The packing had been over-tightened during maintenance. After the packing was re-adjusted to the manufacturer's value, the valve followed 0.5 % steps and the loop settled.

Seat leakage

Seat leakage is specified by class (ANSI/FCI 70-2): for example Class IV for metal seats in general service, Class V for tighter metal-seated shut-off and Class VI for soft-seated (bubble-tight) valves. Check the class on the datasheet before deciding a valve is "passing": a Class IV valve is allowed a small leak.