Non-Return Valve NV400 intermediate flange version

Non-return valve (intermediate flange version) for the prevention of unintended gas mixtures, for flow rates up to 8100 m³/h (air), up to 16 bar, for use in thermal processing plants, certified to EN746-2, DN 40/50

  • with welding neck flanges for simple installing and removing
  • safety element: non-return valve [NV]
  • every non-return valve 100% tested
  • ultra-low opening pressures (approx. 3 mbar), ultra-low pressure drop
  • ideal for biogas desulphurisation systems
  • dirt filter (100 μm) on gas inlet

This model is also available in Stainless Steel


Ficha técnica Descargas
Solicitud de oferta


WITT non-return valves for reliable protection against dangerous reverse gas flow. Now available also with welding neck flanges for simple installing and removing. Every non-return valve 100% tested.


  • a spring loaded non-return valve prevents back feeding of gases which could lead to unwanted gas mixtures
  • low pressure drops – using complex valve assembly with low opening pressure – approx. 3.0 mbar
  • no leaks – using of a spring loaded valve assembly with elastomer sealing
  • stainless steel filter (100 μm) in the gas inlet protects the non-return valve against dirt contamination, extending the service life
  • dirt filter in gas inlet are replaced quickly and easily
  • diverse applications – useful for many technical gases
  • reduce installation costs – the spring loaded valve is not affected by gravity and may be installed in any orientation
  • non-return valve as „intermediate flange version“ guarantees quick and uncomplicated removal and installation at replacement and annual testing
  • maximum flexibility – screwed non-return valve as well as installed between flanges. Complete (non-return valve + flange-set) or as add-on kit available
  • spacer tubes around threaded rods (M16) for secure centering of non-return
  • flange connection with weld-on connecting according to EN 1092-1 Type11
  • equal length in brass and stainless steel non-return valves for optimal interchangeability and combination with flange kits (as well as DN40 and DN50)

Operation / Usage

  • non-return valves are used to protect equipment and pipelines against dangerous reverse gas flow. Use is possible for applications in accordance with EN 746-2
  • non-return valves are proved in accordance with DIN EN ISO 5175-2
  • WITT non-return valves may be mounted in any position / orientation
  • the maximum ambient / working temperature is 70 °C / 158 °F


  • annual testing of the non-return valve, body leak tightness and flow capacity is recommended
  • WITT is happy to supply special test equipment
  • non-return valves are only to be serviced by the manufacturer.The dirt filter may be replaced according to model by competent staff

Company certified according to ISO 9001 and PED 2014/68/EU Module H
CE-marked according to PED 2014/68/EU
Cleaned for Oxygen Service according to EIGA IGC Doc 13/12/E: Oxygen Pipeline and Piping Systems