"Travel-open, torque-close" is the classic setting for modulating valve actuators, yet few newcomers can explain why — or what pitfalls follow. Merging three popular SIPOS threads (11~18 replies), this article covers the principle and three real fault cases.

1. Why Travel-Open, Torque-Close?

The clearest forum answer: whether the valve opens to 100% or 80% only affects valve wear — so the open limit is travel-based; the closing direction must seat tightly for safety and energy reasons, so it is torque-based: the actuator stops when the sensor "feels it cannot turn further", compressing internal leakage — critical for fan blade-pitch duties and the like. Rotork, SIPOS and all major brands follow the same logic.

A counter-case proves it: a SIPOS control valve set to a travel (limit) close tuned perfectly cold — the limit so tight it could not be hand-cranked past it; after startup the valve could never reach its cold-state position again. A travel limit cannot cope with thermal distortion; only a torque close suppresses leakage.

There is also a hidden option: set Close tightly = yes on the SIPOS control board, complementing the torque close.

2. Case 1: Closes to 0%, Bounces Back to 3%, Endlessly

Symptom: after mechanical re-machining of the plug, a spray-water SIPOS5 actuator bounces from 0% back to 3% on closing; re-setting limits, changing closing torque/travel all failed; from remote with 0% command it cycles 0%~3%. Defining 3% as zero stops the cycling — but the internal leakage cannot then be eliminated (torque-close 48, open 54 untouched).

Directions from the replies:

• Try Close tightly = yes (the first reply nails it — directly tied to tight seating)
• Try switching to travel-close mode; or raise the closing torque a notch
• Check the signal-gear (ratio gear) meshing at the closed end for firmness
• Board-motor matching: mismatched main-board and motor models, or a non-original replacement actuator head, cause motor hunting; "the unit probably memorized its pre-maintenance position — set both limits a few more times"
• Redefining 3% as zero only masks the symptom — the leak's root lies in the closing mode and gear meshing

3. Case 2: One Direction Only, No Alarm

Symptom: a SIPOS professional-type control valve on the fourth extraction line closes fully but opens only 5%, no alarm; after a power cycle it opens fully but closes only to 94%; re-setting the limits succeeds in one direction only; torque already at 90%.

Directions from the replies:

• Main-board firmware mismatch — the final answer: SIPOS main boards look identical but carry many internal program variants, each matched to a specific inverter type; read out the actuator data with the software to verify the board match; a matched board cured it
• Aging power board and the inverter module remain on the suspect list
• Before any of that, do the basics: confirm no snagging or over-torque, re-zero and re-span, prove full local travel before handing to remote

4. Quick Reference