NAMUR

What “NAMUR” Actually Means

NAMUR is a German user association for process automation.
In valve automation, “NAMUR” does not mean a brand — it means interface standards that allow components from different manufacturers to bolt together without adapters, machining, or guesswork.

When people say:

“NAMUR solenoid”
“NAMUR switch box”
“NAMUR positioner”

They really mean:

This device complies with NAMUR mechanical and/or pneumatic interface standards and will mount directly to a quarter-turn actuator.

The two most important NAMUR standards in valve automation are:

NAMUR VDI/VDE 3845 → accessory mounting interface
NAMUR VDI/VDE 3847 → solenoid interface (pneumatic pilot valves)

1. NAMUR Solenoid Mounting (VDI/VDE 3847)

What it is

NAMUR solenoid mounting defines a direct pneumatic interface between:

a solenoid valve, and
a pneumatic actuator (rack & pinion or scotch yoke)

The solenoid bolts directly onto the actuator body, eliminating:

external tubing
pipe nipples
fittings
leak points

Mechanical interface (what’s standardized)

Two mounting bolts
Two pneumatic ports aligned with actuator air passages
O-ring sealing between solenoid and actuator face
Fixed port spacing and depth

This means:

Any NAMUR-compliant solenoid fits any NAMUR-compliant actuator
No actuator-specific solenoid models needed

Pneumatic behavior

Typically 3/2-way (single-acting actuator)
Or 5/2-way (double-acting actuator)
Exhaust ports vent internally or externally depending on design

Engineering advantages

Zero external air tubing
Faster response time (shorter air path)
Lower leak risk
Cleaner installation
Simpler maintenance

When NAMUR solenoids are preferred

Hazardous areas (fewer fittings = fewer leaks)
High-cycle service
Skid-mounted systems
OEM valve packages
Anywhere repeatability and speed matter

Important limitation

NAMUR solenoids are pilot valves, not high-flow valves
→ large actuators may still need booster/quick exhaust valves

2. NAMUR Limit Switch Boxes (VDI/VDE 3845)

What it is

A NAMUR limit switch box mounts on top of a quarter-turn actuator and provides:

Valve position feedback
Open / Closed indication
Discrete electrical signals to DCS / PLC

Mechanical interface (VDI/VDE 3845)

Standardized bolt pattern
Standardized shaft height
Standardized drive geometry

This allows:

Any NAMUR switch box to mount on any NAMUR actuator
No custom brackets
No machining
No alignment hacks

Internal sensing technologies

NAMUR does not dictate the sensing method — only the interface.

Common options:

Mechanical limit switches
Inductive proximity sensors (NAMUR sensors)
Magnetic reed switches
Hall-effect sensors

Visual indication

Most NAMUR boxes include:

High-visibility beacon
Adjustable cam system
0–90° visual indication

Electrical side (what engineers care about)

SPDT / DPDT contacts
Intrinsically safe versions (Ex ia)
Explosion-proof housings (Ex d)
Multiple conduit entries
Field-adjustable cams

Why NAMUR matters here

Without NAMUR:

Every actuator needs a custom bracket
Shaft alignment becomes a failure point
Switch timing becomes inconsistent

With NAMUR:

Drop-in replacement
Predictable cam alignment
Faster commissioning

3. NAMUR Positioners (VDI/VDE 3845 + control standards)

What a positioner does

A valve positioner:

Takes a control signal (4–20 mA, HART, fieldbus)
Compares it to actual valve position
Modulates air pressure
Positions the actuator precisely, not just open/close

NAMUR positioner mounting

NAMUR positioners mount directly to the actuator using:

VDI/VDE 3845 bolt pattern
Standardized feedback shaft geometry

No:

Linkage fabrication
Brackets
Lever arm guessing

Pneumatic interface

Output ports align with actuator air passages
Often used with NAMUR solenoids for ESD override
Integrated air routing minimizes lag and hysteresis

Control performance benefits

Faster response
Reduced deadband
Better repeatability
Improved shutoff accuracy
Stable partial-open positioning

Digital NAMUR positioners

Modern NAMUR positioners often include:

Auto-calibration
Valve signature analysis
Partial stroke testing (PST)
HART / Profibus / Foundation Fieldbus
Diagnostics for friction, air leaks, spring health

When NAMUR positioners are used

Modulating control (not just on/off)
Throttling butterfly or ball valves
Emissions-critical services
Safety-instrumented functions (with PST)

How These Three Work Together (System View)

A fully NAMUR-based automation stack looks like this:

NAMUR solenoid → commands motion
NAMUR positioner → controls position (if modulating)
NAMUR limit switch box → reports valve state
All mounted directly to the actuator
No tubing loops
No custom brackets
No alignment risk

This is why NAMUR is so dominant in:

European plants
EPC-designed skids
OEM valve automation packages
Safety-critical services

Engineering Rule of Thumb

NAMUR solenoid → clean, fast, reliable on/off control
NAMUR switch box → standardized, repeatable position feedback
NAMUR positioner → precise, stable, diagnosable control

NAMUR doesn’t make valves better —
it makes automation predictable, interchangeable, and scalable.

How NAMUR Ties to ISO 5211 Actuator Mounting

The short version

ISO 5211 and NAMUR solve different but complementary problems:

Standard	What it standardizes
ISO 5211	Actuator ↔ valve mounting interface
NAMUR (VDI/VDE 3845 / 3847)	Actuator ↔ automation accessories

They are designed to stack.

ISO 5211: actuator to valve

ISO 5211 defines:

Mounting flange size (F03–F25)
Bolt pattern
Drive geometry (square / DD)
Torque envelope of the interface

ISO 5211 answers:

“Can this actuator physically and mechanically drive this valve?”

NAMUR: accessories to actuator

NAMUR standards define:

Solenoid mounting (VDI/VDE 3847)
Switch box / positioner mounting (VDI/VDE 3845)
Pneumatic port alignment
Shaft height and rotation reference

NAMUR answers:

“Can automation components bolt directly to this actuator without custom work?”

How they work together (stacked interfaces)

Control System

│

NAMUR Solenoid / Positioner / Switch Box

│ ← NAMUR (VDI/VDE 3845 / 3847)

Pneumatic Actuator

│ ← ISO 5211

Valve

Engineering takeaway

ISO 5211 = torque + mechanical integrity
NAMUR = automation repeatability + interchangeability

If an actuator is ISO 5211 and NAMUR-compliant:

Any valve (same ISO size) fits
Any NAMUR solenoid fits
Any NAMUR switch box fits
Any NAMUR positioner fits

That’s why EPCs quietly demand both, even if they only write one in the spec.

NAMUR Solenoids vs Tubing-Mounted Solenoids

Mechanical difference (the real story)

Feature	NAMUR Solenoid	Tubing-Mounted Solenoid
Mounting	Direct to actuator face	Panel / bracket mounted
Pneumatic path	Internal	External tubing
Fittings	None	4–8 typical
Leak points	Very low	High
Installation time	Minutes	Hours
Replacement	Drop-in	Re-plumb

Pneumatic behavior (why NAMUR is faster)

NAMUR solenoid exhausts directly at actuator
No hose volume
No compression lag
No fitting restriction

Result:

Faster stroke times
More consistent ESD closure
Less variability across temperature

Tubed systems:

Add pneumatic “springiness”
Increase hysteresis
Delay emergency shutdown

Reliability comparison (field reality)

NAMUR

Fewer parts
Fewer failure modes
Easier FAT/SAT
Cleaner hazardous-area installations

Tubed

Tubing cracks
Fittings loosen
Water accumulates
Mis-plumbing errors common

This is why NAMUR dominates:

Skid packages
OEM valve automation
European plants
SIL loops

When tubing is still used (fair comparison)

Tubing-mounted solenoids still make sense when:

Actuator has no NAMUR pad
High-flow pilot required
Custom logic (multiple pilots)
Very large scotch-yoke actuators

Even then, NAMUR is often used with boosters.

Mapping NAMUR Hardware into ESD / SIL Architectures

Why NAMUR is almost universal in ESD valves

Emergency shutdown valves demand:

Fast response
Predictable failure mode
Low probability of common-cause failure
Simple proof testing

NAMUR directly supports all four.

Typical ESD valve stack (single-acting, fail-close)

SIS / Safety PLC

│ (24 VDC)

NAMUR Solenoid (de-energize to trip)

│

Spring-Return Actuator

│

Valve (Fail-Close)

Why NAMUR helps SIL

Direct mounting = fewer failure points
Known pneumatic volume
Repeatable trip time
Easier SIL verification

Redundant solenoids (SIL 2 / SIL 3)

SIS

├── NAMUR Solenoid A

└── NAMUR Solenoid B

│

Pneumatic Actuator

Either solenoid can vent air
Common architecture for SIL-rated ESDs
Much harder with tubing

NAMUR + Positioner for Partial Stroke Testing (PST)

Control System

│

Digital NAMUR Positioner (PST logic)

│

NAMUR Solenoid (ESD override)

│