AUMA Valve Re-opens Right After Reaching Closed Limit: Troubleshooting Notes

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.

Bottom line: an AUMA motor-operated valve reopens the moment it reaches closed, while the DCS issued no open command, no relay operated, the cabling tests sound, and drying the wet terminals changed nothing — prime suspect: the open-command circuit is being made without a command (damp conduit cabling / tracking), next a welded open-command relay contact. Water ingress is the most common root cause of “valve operates itself” events; “we dried it” is not the same as “the circuit is dry”.

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:

Check point	Method	What it tells you
Open-command circuit insulation	Megger the open-command cores to earth and between cores	Dampness may remain inside the conduit even after the terminal box was dried — falling insulation leaves the open circuit “half-made”
Relay contacts	Inspect the DCS-side open-command relay contacts	A welded contact keeps the loop made after the DCS command is withdrawn
Actuator terminals & plugs	Open the junction box; look for tracking marks and water films between open/close terminals	Moisture inside AUMA internal plugs can also cross-talk channels
Cross-brand evidence	A Rotork normally-open MOV that “closed itself” at another plant	Water in the terminals; dried and re-sealed, fault cleared — command-circuit wetting is the common root of self-operation
Internal control board	Swap the board once the above are cleared	Check the open-direction thyristor/relay output channel

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