NAMUR

Valve Actuation Reference

NAMUR — VDI/VDE 3845 & 3847 Accessory Interface

The mounting and interface standards that let solenoids, positioners, and limit switch boxes from any manufacturer bolt directly to any compliant pneumatic actuator. What NAMUR is, what each standard covers, and how it ties into the broader ISO 5211 and SIL-rated ESD architectures.

What NAMUR Is

NAMUR stands for Normen-Arbeitsgemeinschaft für Mess- und Regeltechnik in der Chemischen Industrie — the standards working group for measurement and control technology in the chemical industry. It originated in Germany in 1949 as a user association of the major chemical and pharmaceutical operators. NAMUR itself does not publish standards directly — it works through the German engineering and electrical bodies VDI (Verein Deutscher Ingenieure) and VDE (Verband der Elektrotechnik), which jointly issue the actual standard documents. In valve actuation, two of these have become global de facto standards for accessory mounting.

The reason NAMUR matters in your daily life: Because of these standards, you can buy a pneumatic actuator from one manufacturer, a solenoid from another, a positioner from a third, and a limit switch box from a fourth — and they will all bolt together correctly without custom brackets or adapters. That is the entire point of NAMUR.

VDI/VDE 3845 — Accessory Mounting

VDI/VDE 3845 defines the mechanical interface on top of a pneumatic rotary actuator for mounting accessories: solenoid valves, limit switch boxes, position transmitters, and positioners. The standard defines:

  • Bolt pattern on the actuator top (typically 30 mm or 80 mm hole spacing depending on actuator size).
  • Coupling shaft dimensions (height, diameter, slot orientation) that drive the position feedback mechanism.
  • Bracket size codes: sizes 1 through 5, mapped to actuator output torque ranges.

Bracket Size Reference

Size Bolt Spacing (mm) Typical Actuator Range
1 30 × 80 Small actuators, low-torque applications
2 30 × 80 Medium-small actuators
3 30 × 80 / 130 Mid-size actuators — most common
4 30 × 130 Larger actuators
5 30 × 130 / 200 Largest scotch-yoke and rack-and-pinion actuators

Side-Mount Solenoid Interface

The standard also defines a side-mounted solenoid interface with a defined port pattern: supply, exhaust, and two cylinder ports machined into the actuator body. A NAMUR solenoid bolts directly to the actuator side, eliminating tubing entirely between the solenoid and the actuator. This is the configuration that gives NAMUR-compliant systems their characteristic compact, tube-free appearance.

NAMUR side-mount solenoid on pneumatic rotary actuator NAMUR-compliant valve assembly

VDI/VDE 3847 — Extended Interface (Positioners)

VDI/VDE 3847 extends the NAMUR concept to digital positioners and smart valve controllers, addressing a gap in the original 3845 standard. Where 3845 was written for simple on/off solenoids and switch boxes, 3847 defines:

  • Combined supply & exhaust port pattern on the actuator side, suitable for high-flow digital positioners that combine pilot and main spool functions.
  • Solenoid override interface — the ability to mount a redundant solenoid behind the positioner for partial-stroke testing or ESD service without disturbing the positioner's calibration.
  • Maintained backward compatibility with the 3845 mounting pattern, so 3847-compliant devices can still mount on a 3845 actuator.
NAMUR-compliant positioner on actuator
Field detail: A 3847-style "combined" positioner with integrated solenoid override is becoming the standard for new safety-related modulating service. It lets you stroke the valve fully for an ESD demand while still maintaining throttling control during normal operation — on a single mounted assembly.

NAMUR Limit Switch Boxes

Limit switch boxes — sometimes called switchboxes or position monitors — mount to the NAMUR pattern on top of the actuator. They confirm actual valve position by sensing the rotation of the actuator coupling shaft.

NAMUR limit switch box exterior NAMUR limit switch box internal cam mechanism NAMUR limit switch box wiring and sensors

What's Inside

  • Two adjustable cams on the coupling shaft — one for the open limit, one for the closed limit.
  • Sensors — mechanical lever switches, inductive proximity sensors, reed switches, or Hall-effect — depending on the duty rating, cycle life, and hazardous area requirement.
  • Visual position indicator dome on top (red/green or similar), giving a walk-up indication of valve position without opening the box.
  • Conduit entry — M20 metric or 1/2 NPT, with Ex d or Ex e gland appropriate to area classification.

For higher-precision feedback, NAMUR-mounted position transmitters replace the discrete switches with a continuous 4–20 mA output sensing the shaft rotation, used both for control room indication and for partial-stroke test analysis.

For more on the sensing technologies inside switch boxes, see Solenoids & Pneumatic Control Components → Limit Switches section.

How NAMUR Ties Into ISO 5211

NAMUR (VDI/VDE 3845/3847) and ISO 5211 are two complementary standards that govern different interfaces on the same valve assembly. People often confuse them because they appear together in every specification.

Stack diagram showing how NAMUR sits above ISO 5211 in the valve assembly
AccessoriesSolenoid valve · Positioner · Limit switch box
VDI/VDE 3845 / 3847 (NAMUR)Defines the mechanical interface between actuator and accessories
Pneumatic actuatorRotary or linear · spring return or double acting
ISO 5211Defines the mechanical interface between actuator and valve
ValveBall · butterfly · plug · or other quarter-turn

The two interfaces operate independently. ISO 5211 lets you bolt any actuator to any compliant valve. NAMUR lets you bolt any accessory to any compliant actuator. Together they define a fully modular automation stack — the underlying reason the global valve automation supply chain works the way it does.

For the valve-to-actuator interface details, see ISO 5211 →.

NAMUR Solenoids vs. Tubed Configurations

The NAMUR side-mount eliminates tubing between solenoid and actuator — but it is not always the right answer. There are real cases where you tube the solenoid back to a remote-mounted manifold instead.

Factor NAMUR Side-Mount Tubed (Remote Solenoid)
Tubing & leak points Eliminated between solenoid and actuator 4–8 fittings per actuator — meaningful at plant scale
Stroke speed Fast — ports are short and direct Slower — tubing volume and pressure drop add to stroke time
Hazardous area service One Ex d enclosure per actuator One Ex d enclosure shared across a manifold — lower total cost for skids
Solenoid maintenance access Requires shutting the actuator station down Solenoid can be isolated and serviced while the valve holds position
Large scotch-yoke actuators Solenoid usually too small for required flow; not viable Standard — high-flow remote-mounted solenoid feeding tubed lines
Cold / arctic service Solenoid sees full ambient swing; coil heating may be needed Solenoid mounted in heated enclosure; tubing to actuator can be heat-traced
NAMUR side-mount vs tubed solenoid configurations
Practical rule: Small to mid-size on/off valves in benign environments → NAMUR side-mount. Large scotch-yoke ESD valves, arctic service, and skid-mounted manifold installations → tubed configuration with appropriately-sized remote solenoid.

Mapping NAMUR Hardware into ESD & SIL Architectures

For Emergency Shutdown (ESD) service in safety-instrumented systems (SIS), NAMUR-mounted hardware shows up in nearly every architecture. NAMUR itself is not a safety standard — that is the role of IEC 61508 and IEC 61511 — but the modular, well-defined interface NAMUR provides makes it dramatically easier to assemble certified hardware into validated loops with known failure rates.

Typical SIL-Rated ESD Valve Architecture

SIL-rated ESD valve architecture with NAMUR-mounted hardware Partial stroke test arrangement on NAMUR-mounted positioner Redundant solenoid voting architecture for SIL 3 service

How the Pieces Map

Function Typical NAMUR-Mounted Hardware Role in SIL Loop
De-energize-to-trip signal Side-mount 3/2 solenoid, continuous-duty coil, certified to IEC 61508 Final element actuation. PFDavg contribution dominates the SIF.
Position feedback NAMUR-mounted limit switch box or 4–20 mA position transmitter Confirms valve actually reached safe position; required for diagnostic coverage credit.
Partial Stroke Test Smart positioner (VDI/VDE 3847) with PST capability, or dedicated PST controller Tests valve travel without disrupting process. Improves diagnostic coverage; allows longer proof test intervals.
Higher-SIL voting (e.g., SIL 3) Redundant NAMUR-mounted solenoids in 1oo2 (one-out-of-two) or 2oo3 voting configuration Reduces probability of dangerous failure on demand; required for SIF target above what single solenoid can achieve.
What NAMUR contributes to SIL: NAMUR does not give you a SIL rating. What it does is reduce the failure modes that come from custom brackets, ad-hoc mounting, and proprietary interfaces — every one of which is a path to a systematic failure that is not captured by random-failure-rate math. The standardized interface is a meaningful contributor to systematic capability under IEC 61508, even though it does not appear directly in the PFDavg calculation.

Specification Checklist

For ordering NAMUR-mounted hardware, the data points that prevent rework are:

  • Actuator make and model — needed to confirm NAMUR size code (1 through 5) and 3845 / 3847 compliance.
  • Shaft height and coupling type — not all actuators ship to standard shaft height; verify against the accessory's reach.
  • Solenoid configuration — 3/2 spring return, 5/2 dual coil, or 5/3 center blocked; coil voltage; hazardous area certification.
  • Switch box sensing type — mechanical, inductive proximity (most common), reed, or Hall-effect; quantity of switches (typically two).
  • Position feedback — discrete only, or 4–20 mA transmitter for continuous feedback and PST.
  • Positioner (if modulating) — 4–20 mA, HART, or fieldbus; intrinsically safe or explosion-proof; PST capability if needed.
  • Area classification — Class / Div / Group, or Zone, plus enclosure (IP65 / IP67 / NEMA 4X).
Related references: For the valve-to-actuator interface, see ISO 5211 →. For solenoid sizing and pneumatic accessory selection, see Solenoids & Pneumatic Control Components →. For broader pneumatic actuation context, see Pneumatic Actuation →. For the parent hub, see Valve Actuation →.

Specifying a NAMUR-Mounted Assembly?

Send the actuator make/model, required solenoid configuration and voltage, position feedback type, area classification, and whether the application is on/off or modulating. We'll come back with a complete NAMUR-mounted package — solenoid, switch box or positioner, brackets, and certifications.

281.664.8000 Email sales@e4industrial.com ← Back to Valve Actuation Hub

NAMUR Hardware Procurement

For NAMUR side-mount solenoids, limit switch boxes, position transmitters, and positioners, E4 Industrial supports procurement through our e-commerce arm at Watermain Supply.

Shop at Watermain Supply
E4 Industrial LLC is a Houston, TX-based industrial distributor. Watermain Supply is the e-commerce arm of E4 Industrial.