ISO 5211 defines an attachment interface for part-turn actuators and industrial valves. A matching flange code is a starting point for assembly, but it does not prove that the actuator will fit the valve stem, transmit the required torque or provide the required operating and failure response.
For a replacement or a new assembly, compare the actual mounting and drive drawings, then check the load through the complete connection. Two components marked F07, for example, can still need different drive bushes or couplings. The mounting holes may align while the drive connection does not.
What ISO 5211 Covers
As checked in October 2026, the ISO 5211 publication record lists ISO 5211:2026, fourth edition, as published and the 2023 edition as withdrawn. Use the edition required by the project and resolve any difference between the purchase specification and the supplied drawings.
The published scope covers attachment flange and drive dimensions, plus reference torques for the specified interfaces and couplings. It includes part-turn actuators with or without gearboxes. Application to control valves is subject to agreement between supplier and purchaser. The connection from an intermediate support to the valve is outside this scope.
This is an attachment standard, not approval of a complete actuated valve. It does not establish process suitability, seat tightness, actuator duty, a safe failure position or the performance of a particular bracket. Those decisions require the selected components and their operating conditions.
Check the Flange and the Drive Separately
Codes such as F05 and F07 identify mounting flange types. They do not uniquely identify the valve shaft, drive bush or coupling needed for the assembly. Read the full drawing designation and revision on each side of the connection.
Pitch circle diameter, or PCD, is the diameter of the circle through the bolt-hole centers. A matching PCD alone is insufficient: hole count, angular orientation, hole or thread form, usable thread engagement and any locating features also have to agree. Use the specified edition and approved drawings for dimensions and tolerances; a general dimension chart cannot replace the actual assembly drawing.
| Connection detail | What to compare | What a mismatch can cause |
|---|---|---|
| Mounting flange | Flange designation, PCD, hole count and angular orientation | Holes do not align or the actuator sits in the wrong orientation. |
| Fasteners and threads | Thread form, diameter, pitch, engagement and specified fasteners | Bolts appear to fit but do not provide the intended joint. |
| Locating surfaces | Any spigot or recess, seating faces and required clearances | The faces cannot seat correctly or the drive is forced out of alignment. |
| Drive connection | Stem and socket shape, dimensions, key details where used, and orientation | The flange fits but torque cannot be transmitted correctly. |
| Axial engagement | Stem projection, coupling length, socket depth and specified clearance | The drive can bottom out or engage too little of the shaft. |
| Travel and closing direction | Valve position, actuator position, coupling phase and permitted stops | The indication or stop position can disagree with the actual valve position. |
Consider two assemblies with the same flange pattern but different stem projection. A coupling suitable for the first can bottom out in the second before the mounting faces meet. Tightening the bolts to pull the parts together does not correct that mismatch. Confirm engagement and clearance from the supplied drawings instead.
Keep Four Torque Checks Distinct
Valve torque demand
Obtain the torque required to break the valve away, move through its travel and reach the specified seated position, in both directions where applicable. Pressure differential, temperature, seat friction, deposits and time between operations can change that demand. Do not select the actuator from valve diameter or one normal operating torque alone.
Actuator torque available
Compare available output with valve demand across the required travel. For a pneumatic actuator, use the minimum available supply during movement; for spring return, check the spring stroke separately from the air stroke. For an electric actuator, use the rating and operating conditions for the required duty. Apply the supplier’s documented sizing allowance for the service, rather than a universal percentage.
Allowable torque through the connection
Check the allowable loads of the stem, drive bush, coupling, mounting flange and any bracket. The actuator must have enough output to move the valve, but the torque it can transmit must also remain within the approved limits of that chain. Review the highest relevant output and any protective settings with the assembly supplier. An oversized actuator is not automatically a safer match.
An interface reference torque is not the valve’s required operating torque and does not establish the capacity of every custom coupling or support. Keep the source, conditions and scope of each rating attached to the component it describes.
Fastener tightening torque
The torque used to tighten a mounting bolt is a separate value from the rotary torque transmitted by the actuator. Do not use an interface torque table as a bolt-tightening instruction. Follow the assembly manufacturer’s fastener specification, tightening values and sequence, including the specified thread condition, lubrication and washers.
Direct Mounting and Bracket Mounting
Direct mounting removes the separate support bracket only when the valve top and actuator base are designed to mate. A drive bush, insert or coupling may still be required. A dual-pattern mounting pad offers alternative bolt patterns; it does not make every drive size or actuator orientation compatible.
With bracket mounting, inspect the whole path: actuator base, upper bracket interface, bracket structure, lower attachment, coupling and valve stem. Verify alignment, stiffness, fastener access and allowable load. An ISO marking on the actuator side does not approve the lower bracket connection or a locally made adapter.
The mounting arrangement also affects clearance around pipework and access to the handwheel, cable entries, air fittings and adjustments. If a stand-off is used for a thermal or access reason, confirm that the selected length and construction meet that purpose without exceeding the assembly’s load limits.
Replacing a Legacy or Different-Standard Mount
Do not treat an ISO flange code, an MSS designation or a similar-looking bolt pattern as a universal cross-reference. Compare the actual drawings and thread specifications. Metric and inch fasteners are not interchangeable merely because a bolt starts to enter a hole.
Where an adapter is needed, it needs a defined drawing, material, connection details and verified load capacity. Enlarging holes, forcing alignment or substituting a coupling by appearance can create a new weak point. Refer required modifications to the valve and actuator suppliers before machining or assembly.
For a replacement, retain the old assembly identification and record what changes: drive orientation, output torque, operating time, stops, supply and feedback. A mechanically fitting replacement may behave differently in the control system.
Installation and Functional Verification
Install under the plant’s approved isolation procedure and the selected equipment instructions. Account for process pressure, electrical and pneumatic supplies, and stored spring energy. Do not remove an actuator from an in-service valve or disturb a spring module merely to check the mounting pattern.
Before tightening the assembly, confirm that valve and actuator are in the corresponding specified position, the drive is correctly engaged and the mounting faces seat without being pulled into alignment by the bolts. Set travel stops and control limits using the valve and actuator instructions; do not use excessive torque to overcome a mechanical stop or a misfit.
During the approved functional check, compare actual valve movement with the command, end-position indication and any continuous feedback. Check for binding, unexpected movement or bracket deflection. An unloaded workshop cycle verifies only that test condition; it does not establish operation at the project’s maximum differential pressure or minimum utility supply.
Verify each required failure event against the actual circuit and assembly. The air, power and signal failure comparison explains why an interface match cannot establish the fail position. Record the tested conditions and acceptance result separately from the dimensional inspection.
A Matching Interface Is Only One Acceptance Check
Accept the mount when both the geometry and the load path have been verified for the supplied assembly. Accept the operating function when the complete package meets its specified duty and test conditions. For the separate choice of power source, use the electric and pneumatic ball valve comparison. Neither decision can be made from an F-code alone.