ISO 5211:2026: What a Part-Turn Actuator Interface Standard Does—and Does Not—Decide

ISO 5211 defines a mechanical interface, not a complete actuator selection. Its fourth edition, published in February 2026 as a 27-page replacement for the 2023 edition, specifies the flange dimensions, driving-component dimensions and reference torque values needed to attach part-turn actuators to industrial valves. It also records a focused technical revision: Figure 2 and Table 2 were updated for through bolting, alongside editorial changes. The rest of the standard's value lies in knowing where that interface stops.

What changed in the 2026 edition?

ISO identifies a technical update to through bolting in Figure 2 and Table 2, plus editorial changes; it does not describe a redesign of the entire interface system.

The fourth edition cancels and replaces ISO 5211:2023. That makes the edition relevant to new specifications, but the documented change is narrower than a new flange family or a new torque philosophy. Through bolting is the named technical revision, and it is the only hardware-specific change identified in the public foreword.

The consequence for a specification review is straightforward. Check the through-bolting arrangement against the 2026 figures and table when that attachment method is used. Do not claim that every interface dimension or every torque reference changed; ISO's own revision note does not say that.

What does ISO 5211 define?

The standard defines how a part-turn actuator attaches to an industrial valve, either directly or through an intermediate support, including versions with or without gearboxes.

Three groups of mechanical information sit inside that interface:

• Flange dimensions needed to attach the actuator to the valve or to an intermediate support.
• Driving-component dimensions needed to connect the actuator's output to the driven component.
• Reference torque values for interfaces and couplings having the dimensions specified in the document.

For control valves, use of the standard's attachment requirements is subject to agreement between supplier and purchaser. That qualification prevents the document from being read as an automatic control-valve selection rule. It remains an attachment standard whose application to that valve class can require an explicit agreement.

What makes an actuator “part-turn”?

A part-turn actuator transmits torque through one revolution or less and does not have to withstand axial thrust; a multi-turn actuator transmits torque for at least one revolution and may also withstand thrust.

Those definitions separate two mechanical jobs. The part-turn interface is concerned with rotary motion and torque transfer without requiring the actuator to carry axial thrust. The multi-turn interface has a different motion and load case and is handled by ISO 5210.

ISO 5211 also allows for combinations. A multi-turn actuator combined with a separate part-turn gearbox uses ISO 5210 for the multi-turn attachment to the gearbox. A combination supplied as a part-turn actuator with an integral part-turn gearbox follows the part-turn arrangements in ISO 5211. The interface therefore follows the actual mechanical chain, not just the label on the actuator catalogue.

Torque itself is defined as the turning moment transmitted through the mounting flanges and connection components, expressed in newton-metres. This is a property of the mechanical connection. It is not, by itself, the torque required to operate the valve under process conditions.

Why are reference torques not a sizing answer?

The standard's torque values belong to specified interfaces and couplings; they do not establish the valve's operating torque or prove that an actuator is adequate for a service.

That distinction separates two checks that can share the same units. One asks whether the flange and coupling can transmit a reference torque. The other asks how much torque the valve requires at its actual differential pressure, temperature, seat condition and operating point. ISO 5211 addresses the first. The second belongs to the valve and actuator engineering records.

A matching flange designation therefore proves geometric compatibility only within the standard's scope. It does not prove that the actuator can open and close the valve throughout its duty, and it does not establish a safety factor. No such factor should be inferred from an interface table.

What does an intermediate support change?

An intermediate support adds another mechanical connection, but ISO 5211 does not govern the support's attachment to the valve.

The standard covers the actuator-side attachment to the valve or intermediate support. The connection between the intermediate support and the valve is expressly outside its scope. A mounting arrangement can therefore conform to the actuator-side interface while still leaving a separate engineering question at the valve-side joint.

The bibliography points to related documents rather than pretending that ISO 5211 covers the whole assembly. ISO 5640 concerns mounting kits for part-turn valve actuator attachment. ISO 22153 covers electric actuators for industrial valves, and ISO 22109 covers valve gearboxes. ISO 5115 addresses part-turn valve actuation. Each document answers a different part of the assembly problem.

For ball and butterfly valves, the practical reading is modular: valve interface, support, drive coupling, actuator and gearbox may each bring their own requirements. A single ISO 5211 designation does not collapse those checks into one certificate of compatibility.

Why do flange and drive dimensions have to agree?

A flange match establishes the mounting geometry, while a drive-component match establishes how torque passes between actuator and valve; an assembly needs both checks.

The flange determines whether the actuator can be attached to the valve or support. The driving components determine whether the actuator's output can engage the part that turns the valve. One interface can fit while the other does not, so a flange designation alone is not a complete mechanical description.

Through bolting belongs to the attachment side of that problem. The 2026 revision's focus on Figure 2 and Table 2 does not remove the need to inspect the drive connection. It updates one named attachment method, not every way torque is transmitted.

The standard also points to ISO 273 for fastener clearance holes. That normative reference reinforces the mechanical nature of the document: bolt holes, flange patterns and driving components are specified as engineering interfaces, not as procurement adjectives.

Which related documents cover other parts of the assembly?

The surrounding documents cover fasteners, splines, mounting kits, actuation, electric actuators and gearboxes rather than duplicating ISO 5211's interface role.

ISO 4033 appears in the bibliography for hexagon high nuts, and ISO 4156-1 for straight cylindrical involute splines. These references show that attachment hardware and drive geometry may draw on their own standards. ISO/R 773 is listed as withdrawn, which is a reminder to check document status before invoking an old key or keyway reference.

ISO 5640 addresses mounting kits, ISO 5115 part-turn valve actuation, ISO 22153 electric actuators and ISO 22109 valve gearboxes. ISO/DIS 23097, listed as under preparation at publication, concerns pneumatic part-turn actuators. Each belongs to a different layer of the assembly record.

The practical boundary is documentary as well as mechanical. ISO 5211 can identify the actuator-to-valve interface, but it cannot supply the requirements of every component around that interface. The invoked assembly specification has to name the companion documents where needed.

What does an interface designation leave undocumented?

An interface designation leaves the valve's process duty, required operating torque, materials, actuator energy supply and control functions to be documented elsewhere.

The valve still has to be identified by type and service, and its required operating torque has to come from the valve record. The actuator's motive energy and control behaviour also sit outside the flange-and-drive description. ISO 5211 explicitly allows for electric, pneumatic, hydraulic or manual energy in its actuator definition, so the interface does not choose among them.

Environmental and functional requirements are separate again. A flange drawing cannot establish hazardous-area suitability, enclosure protection, fail-safe action, position feedback or control-valve performance. Those subjects require their own specifications and, where applicable, the related actuator documents named in the bibliography.

This is why an assembly record should not stop at “ISO 5211 mounting.” The designation is useful only when the remaining mechanical and functional requirements are documented alongside it.

Where does the public record stop?

The public record stops at the normative dimension tables and the detailed through-bolting requirements; the free preview does not make the whole standard public.

ISO's catalogue establishes the edition, publication month, status and page count. The public preview supplies the foreword, introduction, scope, terms and bibliography. The detailed flange dimensions, coupling dimensions and reference torque tables belong to the invoked standard text and should be read there rather than reconstructed from a secondary chart.

The edition named in a purchase specification is also decisive. Publication of ISO 5211:2026 does not retroactively alter an assembly specified to the 2023 edition, and it does not make an undocumented “ISO mounting” claim traceable.

What does the revision add up to?

The 2026 edition is a maintenance revision with a named mechanical target: through bolting. It leaves intact the standard's central engineering discipline — define the interface, state the relevant dimensions and reference torques, and leave valve duty and actuator suitability to their own evidence.

That makes the standard useful precisely because it does less than a selection guide. It can establish that two mechanical parts are intended to fit. It cannot establish that the assembled valve and actuator will perform the required work.

What this article does not cover

Note that this article does not reproduce flange or coupling dimensions, calculate valve torque, size an actuator, specify a mounting kit, or assess any valve–actuator assembly. It records the public scope and revision structure of ISO 5211:2026 and is not a conformity determination.

Where the next constraint sits

The valve-side decision comes before the mounting interface: Ball vs Gate vs Globe Valves: The Three-Way Comparison sets out the functional differences among the three architectures.

The procurement layer for a pipeline ball valve — what an owner specification adds beyond the base product standard — is covered in IOGP S-562 Version 4.0: The Owner Overlay Reaches the Pipeline's Commonest Valve.

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