Over-Torque on Electric Actuators: Why It Differs Between Local and Remote, and What to Do About It

Over-torque is the most common alarm on electric actuators, yet many young engineers are unsure where to start. Merging two popular forum threads (27 and 20 replies) — one on "fine locally, juddering at full stroke from remote", one on "how to interpret and handle a torque trip" — this article builds a complete over-torque methodology.

1. The Puzzle: Fine Locally, Juddering at Full Stroke from Remote

Symptom: a desulfurization gas bypass damper actuator (with mid-stop): no juddering in local operation; none in small remote strokes either; only when driving fully open or fully closed from remote does it snag at a few positions — but still pushes through.

The analysis path from the replies:

1. Layer first: the actuator itself is largely cleared. Normal local operation proves the motor, gearing and torque capability; suspicion moves to the remote control path and the mechanical side

2. Check the DCS command type — holding signal or short pulse with local self-holding (stressed twice by several engineers): for a holding signal, check whether the card keeps commanding voltage; for pulses, inspect the local self-holding circuit and confirm the motor stays energized throughout the stroke — mid-stroke power loss can also feel like "snagging"

3. Check the output relay: the only difference between remote and local is the control relay — swap the DCS output relay as a test; if its capacity is too small for the current, add a larger interposed relay. Rotork IQ/AWT/IQM users should also know that changing a main board means changing the 24C12 memory too, and to check the DCS relays

4. Mechanical view: snagging at the ends is most common. Duct corrosion and dust build-up snag dampers at full open/close; bar the valve over by hand to locate the sticking point; raise the torque setting moderately if mechanical, and dismantle for inspection if stubborn

5. Inherent characteristic: an electric actuator's opening torque is inherently higher than the running torque mid-stroke — extra effort near the ends is partly normal and must be distinguished from true snagging

2. After a Torque Trip: Interpretation and Handling

Step 1 — confirm the trip basis (by actuator generation):

• Intelligent types with torque (current) detection show it on the LCD — RAGA, AUTORK, Rotork and similar brands display live torque; compare against the setting in the commissioning menu; older units report fault codes
• Old-style actuators (e.g. YangXiu DZW): after a torque trip the cubicle lamp goes out, and inside the actuator the spring pressing the torque switch visibly tilts — identifiable by eye
• EMG and similar: check the local fault lamp

Step 2 — a four-step routine:

1. Switch to local and stroke open/close once, watching for snagging (take safety precautions first; on small valves the handwheel will tell your hand)

2. Separate electrical from mechanical, as one engineer put it bluntly: lift the actuator off and test it alone; if the actuator is fine, call the mechanical crew — "it is almost always valve snagging"

3. Raise the torque setting moderately if genuinely snagging — but never adjust torque casually; the factory setting has its reasons, and oversized torque harms the valve itself — forcing past a truly seized valve with a big torque setting makes things worse

4. Hand stubborn cases to mechanical for dismantling; intelligent actuators log the torque curve of each trip for later review

3. Quick Reference