Precise Flow · Calibration · Test Equipment

Critical micro nozzles according to DIN EN ISO 9300

Critically operated micro-nozzles have very small throat diameters between 18 and 1000 µm and they are cylindrical up to 170 µm. A Venturi form can only be realized starting from a throat diameter of 170 µm. Micro-nozzles have hardly any pressure recovery. They can only be critically operated with a critical pressure ratio between inlet and outlet of 2 : 1.


Flows of air or gases can be adjusted with very high stability by critical nozzles. Therefore, they are perfect for the calibration of all kind of mass flow and volume flow measuring devices for air and gases, as, e.g., gas meters, LFEs, mass flow meters and all other kind of flow meters.

Micro nozzles
Micro nozzles

Product features include:

  • Nozzle throat diameter d of 20 μm up to 170 μm
  • Inlet diameters of DN 4 up to DN 18
  • Connection by adapter or clamp
  • Suction or pressure operation
  • Short response time and high accuracy
  • Very good long-time stability, no moving parts

Calibrating options

  • Type: Calibration in pressure and suction operation
  • Medium: air or pure gases
  • Certificate: factory calibration, DAkkS-DKD calibration or PTB calibration

Operating instructions

Suction operation is the preferred operation mode for these nozzles, since the atmospheric density is very constant at the inlet. For pressure operation a very stable pressure control should be used. Optimally free and undisturbed incoming flow is observed at high-capacity conditions at the inlet section of the nozzle: No barrier gets closer to the nozzle axis and the inlet level than 5 times the nozzle diameter.

Venturi nozzles
of the series CFO

for critical operation

More information and technical details can be
found in the data sheet

Additional information
on this subject:


Flow calibration

Flow element software

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