Industrial Non‑Return Valves (NRVs) for Gas Safety and Process Efficiency

EN ISO 5175‑2 Compliance

WITT non-return valves conform to EN ISO 5175‑2, the global standard governing gas non-return devices. This standard defines safety requirements, leakage limits, functional criteria, and testing procedures for check valves used with technical gases. Compliance ensures:

• Safe prevention of gas backflow
• Suitability for industrial fuel gases and oxidants
• Verified leak‑tightness and endurance under defined test conditions

Extremely Low Opening Pressure and Very Low Leakage

Thanks to the WITT valve design and sealing system, the valves achieve:

• Opening pressures as low as approx. 4 mbar
• Exceptionally low leakage rates due to elastomer sealing systems
• Durable performance even under low operating pressures used in thermo‑process and biogas applications

Suitable for a Wide Range of Industrial Gases

WITT non‑return valves are suitable for a broad range of technical gases, including carbon dioxide (CO₂), argon (Ar), helium (He), town gas, ethylene (E), natural gas and LPG, hydrogen (H), nitrogen (N₂), carbon monoxide (CO), oxygen (O) and compressed air. Their elastomer‑based sealing systems are designed for high gas‑tightness, while optional inlet filters protect against contamination.

Clear User Benefits

WITT non‑return valves provide measurable advantages for system designers and operators: compact size, low weight, high flow capacity, low pressure drop and quiet operation, enabling more efficient burner and thermal‑process systems. The extremely low pressure drop allows smaller nominal pipe diameters, reducing both investment and operating costs. For some applications, the high performance of WITT NRVs can eliminate the need for an additional flashback arrestor (depending on model and application), resulting in lower costs and more compact installation.

ULTRA Series – High‑Performance for Thermo‑Process and Biogas Applications and much more

The ULTRA series offers:

• Extremely low opening pressure (~4 mbar)
• Minimal pressure drop with flow‑optimised geometry
• Quiet operation due to reduced flutter
• Built‑In Filter for Extended Service Life
• Material options: brass, stainless steel, aluminium
• Seal options: FPM, EPDM, FFKM
• G/NPT connections from 1/2'' to 2 1/2'' depending on model
• 100% tested before delivery
• Oxygen‑cleanable versions ready for O₂ service
• Suitable for EN 746‑2 thermo‑process applications

Modular Configuration Options

WITT NRVs offer extensive modularity: housing materials such as stainless steel, brass or aluminium, sealing materials including FPM, EPDM or FFKM, optional inlet filters, and a full range of G or NPT connections from ½″ to 2½″. Temperature‑, media‑ and corrosion‑specific configurations can be tailored precisely to the requirements of OEMs and system integrators. All oxygen‑service versions are cleaned according to EIGA guidelines, and elastomers are BAM‑approved for oxygen use.

Orientation‑Independent Installation

WITT non‑return valves can be installed in any orientation (model dependent), simplifying system design and integration for OEMs. This flexibility is especially valuable in compact burner systems and biogas skids.

Thermoprocessing and Burner Applications

Thermal process equipment often operates with several gases simultaneously — for example natural gas, hydrogen, nitrogen or process gas mixtures. In these systems, WITT non‑return valves prevent the formation of hazardous gas mixtures inside furnace supply lines, safeguarding upstream gas‑mixing and metering equipment.

Their very low opening pressure (~4 mbar) supports stable flow even at low operating pressures, while the orientation‑independent installation simplifies integration in compact furnace layouts.  Thanks to gas‑tight elastomer sealing and optional inlet filters, WITT NRVs ensure reliable protection in continuous furnaces, roller hearth furnaces, kilns and other thermo‑process systems where multiple gases are used in parallel.

Biogas Applications

Biogas requires careful handling due to its methane content and the introduction of air or oxygen for desulphurisation. WITT stainless‑steel non‑return valves ensure that aeration air enters in one direction only, preventing hazardous gas mixtures in digesters. They offer very low opening pressures (~4 mbar) for low‑pressure biogas systems, minimal leakage thanks to high‑quality elastomer seals, and optional inlet filters for contamination protection. WITT NRVs are easy to retrofit, orientation‑independent, and help reduce compressor energy and maintenance costs due to their low pressure drop and robust construction.

Industry‑Wide NRV Types 

Several NRV categories are available on the market, such as poppet, lift, inline and modular check valves. WITT specialises in gas‑specific NRVs optimised for low‑pressure operation and high‑flow stability.

OEM Benefits

• Orientation flexibility
• Modular configuration of housing and seals
• Low pressure drop ideal for low pressure applications
• Compact design enabling smaller nominal diameters
• Long service life
• ISO 9001 certified quality 

Safety & Quality Assurance

• Cleaned for oxygen service according to EIGA/CGA
• Elastomers BAM‑approved
• 100% individually performance tested 

Frequently Asked Questions FAQs

Q: What is the opening pressure? 
A: As low as approx. 4 mbar depending on model.

Q: Are the valves suitable for oxygen? 
A: Yes, oxygen‑cleaned versions available.

Q: Can WITT NRVs be installed in any orientation? 
A: Yes, depending on the type.

Flyer: Non-return valves in biogas plants Flyer: Non-return valves in thermal processing plants

Practical Example: Non-return Valves in Heat Treatment