Several coal-mill seal-air dampers at one plant are driven by Ruiji RJ on/off actuators, and within days multiple units developed the same fault: the remote open command did nothing, with F-15 shown on the panel, and no conventional means could reset it. The value of this case: instead of gambling on board swaps, the crew designed a full set of simulation experiments and completely clarified both the alarm mechanism and the root cause.
1. Remote open command did nothing; the panel showed F-15;
2. Neither the stop position nor the local position reset the alarm;
3. Local electric operation to open also failed; the alarm persisted;
4. Engaging the hand-jack clutch and hand-turning the valve open "a tiny bit" (the display still read 0%) made the alarm vanish immediately;
5. After that, local electric opening worked — until F-15 reappeared after 5 seconds of commanded travel; releasing the knob cleared it again;
6. After hand-turning to 5% or more on the display, local open/close worked perfectly, full travel with no sticking, and remote control was normal again;
7. One actuator had its internal boards replaced, yet the fault returned days later; the valve hand-turned freely, ruling out valve sticking.
The crew took one damper, simulated remote control, and artificially created four abnormal conditions while commanding motion, observing which could trigger F-14/F-15:
| Simulated condition | Behavior | Alarm raised |
|---|---|---|
| Valve stuck (won't move) | motor audible for several seconds, then stops | F-11, F-12 (over-torque) — **not** F-14/F-15 |
| Clutch not engaged | motor audible for several seconds, then stops | **F-14, F-15** |
| Position potentiometer failed | motor audible for several seconds, then stops | **F-14, F-15** |
| Motor fault | motor silent, stops after seconds | **F-14, F-15** |
Combined with the manual's definition — F-14/F-15 means "no position change detected" — the conclusion fell into place: whenever the motor runs but the position-detection path shows no change (clutch not engaged, potentiometer dead, motor protection circuit open), F-14/F-15 results. True valve sticking travels the F-11/F-12 over-torque path — a completely different channel.
The experiments also mapped the motor wiring: five leads, all terminated on the relay board — three are the three-phase power leads (380 V AC measurable during motion), and two are motor-protection leads fed from the relay board (about 3.3 mV DC measurable during motion). If that circuit is open, the motor will not run at all; the protection leads are embedded in the stator winding, presumably a thermal switch.
The final finding: the torque switch sits beneath the relay board inside the motor compartment — a mechanical, adjustable torque switch. The recurring F-15 corresponded to "motor runs but no position change detected" within the initial stroke of the open direction — exactly matching the observation that hand-turning a tiny bit reset the alarm and passing 5% restored everything. After inspecting and adjusting the related components (clutch engagement, position detection, torque switch), the fault was eliminated.
1. When facing an unfamiliar alarm code, design a set of simulation experiments to reproduce it under controlled conditions — comparing which conditions trigger it and which do not reveals the mechanism;
2. F-14/F-15 (no position change detected) and F-11/F-12 (over-torque) are two different protection channels — valve sticking and detection-circuit faults must be diagnosed separately;
3. Details like "hand-turning a tiny bit resets it" are gold: they lock the fault onto the detection path of the initial stroke instead of a vague "the actuator is broken."
