Pneumatic Equipment

NAMUR Solenoid Valve: Working Principle and Selection

Learn how NAMUR solenoid valves mount directly on pneumatic actuators, the difference between 3/2 and 5/2 versions, and their technical data.

ORFA Technical TeamUpdated: Oct 30, 20263 min read

NAMUR solenoid valve mounted directly on a pneumatic actuator

On pneumatically actuated ball and butterfly valves, the component that directs compressed air to the actuator is usually a solenoid valve. A NAMUR solenoid valve (NAMUR actuator valve) is a directional control valve that mounts directly onto a rotary pneumatic actuator through the standard NAMUR interface, with no intermediate tubing or fittings.

This article explains what a NAMUR valve is, how it works, the difference between 3/2 and 5/2 versions, its technical data and its applications.

What Is a NAMUR Solenoid Valve?

A NAMUR valve is a solenoid-operated directional control valve with standard mounting dimensions that sits directly on the air connection face of a rotary pneumatic actuator. By supplying compressed air to the actuator or exhausting air from it, it controls the opening and closing of the valve. Because the NAMUR interface (VDI/VDE 3845) is standardised, actuators and valves from different manufacturers that use it are compatible.

Working Principle

Compressed air supply: Conditioned compressed air is connected to the valve’s supply port.
Actuation: When the coil is energised (or the manual override is used), the spool inside the valve changes position.
Air routing: The spool directs compressed air to the relevant actuator chamber and exhausts air from the other chamber through the exhaust port.
Actuator movement: The actuator pistons move, rotating the valve stem so the valve opens or closes.

3/2 vs 5/2 NAMUR Valves

Valve type	Actuator	Operation
3/2 NAMUR valve	Single-acting (spring return)	When air is supplied the actuator moves; when air is cut off and exhausted, the springs return the valve to its initial position.
5/2 NAMUR valve	Double-acting	In one position air goes to one actuator chamber, in the other position to the opposite chamber; both opening and closing are done by air.

As for coil options, single-coil valves return to their initial position by spring when de-energised, while double-coil valves stay in the last commanded position.

Advantages

Standard compatibility: The NAMUR interface makes it compatible with actuators of different brands that use this interface.
Direct mounting: Mounting directly on the actuator reduces tubing and fittings, simplifies installation and reduces potential leak points.
Compact design: Small dimensions save space.
Fast response: Suitable for applications that require fast opening and closing.
Wide choice: 3/2 and 5/2 functions, single or double coil, various voltages and ATEX (explosion-proof) models.

Tip: For long service life of the NAMUR valve and actuator, the supply air must be filtered and dry. Using a pneumatic air preparation unit at the line inlet prevents spool and seal wear.

Technical Data

Feature	Value
Body	Anodised aluminium
Function	3/2, 5/2
Operating pressure	1.5 – 8 bar
Operating temperature	-5 °C … +80 °C
Coil voltage	12 V DC, 24 V DC; 24 V AC, 110 V AC, 220 V AC
Protection class	IP65
Port size	Mostly G 1/4″ (BSP); high-flow models come in larger sizes
Explosion-proof	ATEX models available

Applications

Process automation
Chemical and petrochemical industry
Food and beverage industry
Water treatment plants
Power plants

Frequently Asked Questions

Which NAMUR valve should be used with a single-acting actuator?

Single-acting (spring return) actuators use a 3/2 NAMUR valve. Double-acting actuators require a 5/2 NAMUR valve.

Can a NAMUR valve be fitted to any actuator?

It mounts directly on actuators with the NAMUR (VDI/VDE 3845) interface. Actuators with a different interface require an adapter or tubed connection.

Can it be used in hazardous areas?

Yes, ATEX-certified explosion-proof models are available for such areas; choose a model that matches the zone classification.

Conclusion

NAMUR valves offer a standard, compact and reliable way to control pneumatically actuated valves. Choosing the right function, coil type and voltage keeps your automation system running smoothly. Browse our pneumatic valves product group, or contact ORFA at [email protected] for technical support.

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