Symptom
The actuator stops and reports a torque trip, in one direction or both, at the seat or in mid-travel; the valve position stalls; repeated attempts trip at the same place; the fault appears only when the pump runs or after the valve has sat unused.
The short answer
Actuator Torque Fault
An electric actuator measures the torque it delivers and trips when it exceeds the setting, which protects the valve and the actuator from being driven into an obstruction or a seized stem. A torque fault at the end of travel on a valve that should stop on position, such as a butterfly or a ball valve, means the seating mode or the limit is set wrong; a torque fault at the end of travel on a gate valve that seats on torque means the torque setting is too low for the seat or the seat is damaged or fouled; a torque fault in mid-travel means an obstruction, a binding stem, tight packing, a bent stem, or a valve seized by corrosion or disuse; and a torque fault only under flow means the differential pressure exceeds the actuator sizing. The actuator log shows the torque profile and where it tripped, the valve is stroked by hand to feel for the cause, and the fault is reset only after the cause is found, because a torque switch bypassed is a stem or a gearbox destroyed.
Key points
- Where it trips is the diagnosis: at the seat, in mid-travel, or only under flow.
- Gate valves seat on torque closing and position opening; butterfly and ball valves seat on position; the seating mode must match.
- Mid-travel trips are mechanical: obstruction, binding, packing, corrosion, a bent stem.
- Read the actuator torque log; it shows the profile along the stroke and where it exceeded the setting.
- Never bypass the torque switch; it is protecting the drive train from the thing you have not found yet.
Possible causes and what to check
| Possible cause | What to check |
|---|---|
| Seating mode set wrong for the valve type | A butterfly or ball valve set to torque seat trips at every close; the actuator setup shows the seating mode. Set to position seat for those valves per the valve manufacturer. |
| Torque setting below what the seat requires | A gate valve that trips just before it seats; the torque setting against the valve manufacturer seating torque. Raise the setting within the valve rating, never above it. |
| Debris on the seat or a damaged seat | Trips at the seat with the torque setting correct; the valve does not shut off. Inspect and clean or repair the seat. |
| Obstruction in mid-travel | Trips at the same point every time; something in the line or in the valve body. Inspect. |
| Stem binding: packing, corrosion, lubrication | Hard to turn by hand at the trip point; packing overtightened after a repack; a dry or corroded stem. Loosen the packing; clean and lubricate the stem. |
| Valve seized from disuse | A valve that has not been operated in years trips on the first attempt; corrosion between the disc and the seat or on the stem. Exercise by hand carefully; repair if it will not free. |
| Differential pressure beyond the actuator sizing | Trips only when the pump runs or the line is pressurized; the actuator sized for a lower differential. Check the sizing; reduce the differential during operation, or resize. |
| Bent stem or damaged gearing | Trips at a hard spot; the stem visibly bent or the gearbox noisy. Repair. |
| Actuator torque sensor or setting fault | Trips at low torque or at random; the actuator diagnostics show a sensor fault or the setting was changed. Check the setup and the diagnostics. |
| Thermal overload mistaken for torque | The actuator motor thermal trip after repeated strokes, reported alongside a torque fault on some units. Let it cool; check the duty cycle. |
Where it trips
| Trip location | Valve type | Likely cause | Fix |
|---|---|---|---|
| At the closed seat | Gate or globe, torque seated | Torque setting too low; seat fouled or damaged | Raise the setting within the valve rating; clean or repair the seat |
| At the closed seat | Butterfly or ball | Seating mode set to torque; position limit set past the seat | Position seat; set the limit at the seat |
| At the open end | Any | Open limit set past the mechanical stop, or the valve backseating hard | Set the open limit before the stop; check backseat |
| Mid-travel, same point | Any | Obstruction, a damaged disc or gate, a hard spot on the stem | Inspect and repair |
| Mid-travel, varying | Any | Stem binding, packing, corrosion, lubrication | Packing, cleaning, lubrication |
| Only under flow or pressure | Any | Differential pressure beyond the actuator sizing | Resize the actuator, or operate at lower differential |
| First operation after long idle | Any | Seized by corrosion or scale | Free by hand carefully; exercise on a schedule |
Seating modes
A gate valve or a globe valve closes by pushing its disc into a seat, and the seal comes from force: the actuator drives until the torque reaches a setting, which is torque seating. Opening the same valve stops at a position, before the backseat, because driving it open on torque would jam it. A butterfly valve or a ball valve closes to a position; driving it on torque presses the disc into the seat or the stop and damages both. The actuator is configured for each direction on each valve per the valve manufacturer, and a torque fault at the seat on a valve that should be position seated is a configuration finding before it is anything else.
Before resetting
- 1
Read the log
The actuator event and torque log: the position where it tripped, the torque profile along the stroke, and whether it was the torque switch or the thermal.
- 2
Check the setup
Seating mode in each direction, torque settings, limit positions, against the valve data.
- 3
Declutch and feel
Stroke the valve by hand through the trip point. A hard spot, a stop, a jerk, or a seize is felt; note where.
- 4
Look
The stem for bending, corrosion, and lubrication; the packing gland; the seat if the line can be opened; the line for debris.
- 5
Correct
The setting, the seat, the stem, the packing, or the sizing.
- 6
Reset and stroke
Reset the fault and stroke the valve under observation, watching the torque profile on the actuator display if it has one.
Preventing the next one
- Exercise valves that are rarely operated, on a schedule, by hand or by the actuator with the torque profile recorded.
- Record the torque profile at commissioning; a stroke whose torque has doubled has a stem or a seat problem coming.
- Set the torque per the valve manufacturer, not by trial, and record it on the valve data sheet.
- Lubricate stems and check packing on the maintenance schedule.
- Size actuators for the worst differential the valve will see, not the normal one.
Frequently asked questions
- The actuator trips on torque at the seat but the valve still leaks.
- The seat is fouled or damaged, so the torque is reached against debris before the disc seals. Cleaning or repairing the seat is the fix; raising the torque presses the disc into the debris harder and damages the seat.
- Can I raise the torque setting?
- Up to the valve manufacturer rating for the valve, and only when the setting is below what the valve needs. Above the rating, the actuator can break the valve. The rating is on the valve data sheet; if it is not, ask the manufacturer before touching the setting.
- The valve trips on torque when the pump starts.
- The pump raises the differential across the valve beyond what the actuator can overcome, usually on a valve that is closing against the pump or opening against a head. Sequence the valve to move before the pump builds pressure, or resize the actuator.
- How do I free a seized valve?
- By hand, with the actuator declutched, gently in both directions, with penetrating lubricant on the stem, never with a cheater bar that bends the stem. A valve that will not free by hand is repaired or replaced, not forced by the actuator.
Related topics
- Valve Will Not Reach PositionA valve commanded to a position that stops short: an obstruction or a seat the actuator cannot push through, travel limits or a positioner span set wrong, a stem binding, an actuator undersized or out of air, or a command signal that does not span.
- Valve Slow to RespondA valve that takes far longer to move than it should: a pneumatic supply restricted or leaking; a positioner tuned slow; an electric actuator whose speed is fixed; a stem binding in cold or packing; or a rate-limited output. Measuring the stroke time.
- Position Feedback WrongThe HMI says one position and the valve is at another: a feedback potentiometer worn or miscalibrated, a linkage that slipped, scaling that does not match, a reversed signal, limits set wrong, or noise. Comparing indicator, feedback, and process.
- SequencersStep-based control for operations that always run in the same order: backwash, pump and valve startup, batch makeup, membrane cleans. What every step needs, three ways to implement one, handling faults and power loss mid-sequence, and what the HMI shows.
- High Service PumpsThe pumps that carry finished water into distribution: types, the pump curve against the system curve, best efficiency point, the affinity laws and where a drive pays, parallel operation, valves, protection, and the efficiency monitoring that shows wear.
- Interlocks and PermissivesA permissive lets you start. An interlock stops you. Confusing the two produces equipment that either will not run or will not protect itself.
Direct contact
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