A Rotork electric actuator at one plant started moving on command, but the valve stopped after moving about one percent, paused for roughly 4 seconds, and then continued. The operators suspected the FT (stall-timing) option in the backup settings. This article explains this "move-pause-move" behaviour and its handling.
Symptom
- Actuator starts on command
- Valve moves ~1% and stops, pausing about 4 s
- Then continues by itself, repeatedly
Mechanism Analysis
This is more likely a configured behaviour than a hardware fault:
- Anti-jam start strategy: some imported actuators (Rotork included) implement logic for valves that may be over-tight at the end positions — when starting torque is insufficient, the motor restarts abruptly to boost output torque, appearing as "move a little, pause, move again", helping the valve break away from its seated face
- Stall-timing options: FT-type options in the configuration menu alter the motor's start and run timing
- Dead band and control accuracy: if it occurs while modulating, check the dead-band (Fd) parameter — a mismatch between dead band and required control accuracy makes the actuator cycle between stop and trim
Handling
- First confirm it is a function, not a fault: watch whether the pause always happens at a fixed travel point (near the seat); functional pauses are regular
- Check the current setting of the stall-timing/start-boost options in the configuration menu
- If it degrades modulating control quality, adjust the dead band (Fd); for on-off duty it is harmless and can be left as is
- If still unclear, use the infrared setter/menu to review start counts and the torque profile, distinguishing "insufficient-torque retry" from "parameter cycling"
Takeaway
- For "strange" actuator behaviour, check configuration before hardware — much of a smart actuator's behaviour comes from configured functions, not defects
- Move-pause-move at a fixed travel point is most likely anti-jam/boost design; random occurrence warrants checking torque, dead band and mechanical resistance
Related reading: Rotork 2nd-Gen IQ/IQT: Menu Terminology Annotated & Common Fault Analysis; Rotork IQ Series: Terminal Wiring, Infrared Setter Commissioning & Troubleshooting
