An AUMA valve at one plant behaved strangely: operations reported "not fully closed"; local inspection found the closing-torque trip. After reset, the DCS close command closed the valve normally — but the moment it reached the closed limit, the valve opened by itself. The DCS had issued no open command, the interposing relay had not operated, the cable checked out, and a small amount of water was found inside the terminal strip; after drying, the fault persisted. This article compiles the troubleshooting approach and a parallel case.

Symptom Highlights

• Closing-torque trip (resistance in the closing direction)
• After reset, remote closing works — but the valve opens right at the closed limit
• No open command from DCS, interposing relay unoperated, cable normal
• Some water in the terminal strip; fault persists after drying — the water clue was not confirmed

Troubleshooting Approach

"Reverses at limit" with no open command: focus on whether the open circuit is being bridged without a command:

• Open-circuit insulation: measure the open-command wiring to earth and between cores — drying the strip does not remove moisture inside the conduit; degraded insulation makes the open circuit "half-connected"
• Relay contacts: check the DCS-side open-command relay for welded contacts (command withdrawn but circuit still made)
• Actuator-side terminals and plugs: open the wiring box and inspect the open/close command terminals for tracking marks or water films; damp internal plugs on AUMA can cross-couple channels
• A parallel case: another plant's Rotork normally-open valve "closed by itself"; the terminal strip was found wet, and drying plus re-sealing cured it — water bridging the command line is a common root cause of self-action
• If all the above are excluded, check the actuator's internal control board (open-direction triac/relay channel), verifying by board replacement if necessary

Recommendations

• Dry the terminal box thoroughly: clear water, replace damp terminals, add sealing glands and desiccant — priority for outdoor or damp areas
• Re-test open-circuit insulation before re-energizing, then observe several close-open cycles
• The closing-torque trip is a second clue: closing-direction resistance (tight seat or jammed guides) needs mechanical confirmation, so "over-tight seating" and "false opening" are not conflated

Takeaway

• For self-acting valves, suspect a non-command bridge in the open/close circuit first — water ingress is a frequent root cause; "the strip is dry" does not mean all moisture is gone
• Split overlapping symptoms: this case has both a torque trip (mechanical) and re-opening (electrical); verify the two lines separately

Related reading: AUMA Actuator Runs Locally but Not Remotely: Hunting a Recurring Fuse Failure