Precise Flow · Calibration · Test Equipment

SAO Inlet nozzle

SAO nozzles (Smooth Approach Orifice) are inlet nozzles for free suction of air. They are first choice with applications, where only a low pressure drop may occur during the measurement. They are designed according to VDI/VDE 2041 similar to standard Norm DIN EN ISO 5167 part 3.


SAO nozzles are suitable for the measurement of large flows of air at free suction of atmosphere, particularly if short total lengths and low remaining pressure drops are required. Due to their efficient pressure recovery they have a very low remaining pressure drop. It depends on the type of inlet and the outlet cone.

Product features include:

  • Throat diameter d of 5 up to 500 mm
  • Diameters of DN 10 up to DN 500
  • Straight outlet: min. 2 x DN
  • Connection by flanges
  • Suction operation for free suction of atmosphere
  • Quick response time and good accuracy
  • Very good long-time stability, no moving parts


SAO nozzles consist of an inlet venturi nozzle followed by a cylindrical throat as well as an outlet cone with a full angle of 8 – 15°. If the throat diameter is equal to the outlet tube diameter, an outlet cone is not required. SAO nozzles are mostly turned and welded of aluminium or stainless steel.


The plus pressure measurement is taken in the atmosphere. The minus pressure tapping is carried out in the throat in the tube wall by one or several single bores. It is recommended to connect them by a ring line in case of larger diameters.

SAO inlet nozzles:

Suction air measurement with
low pressure drop

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

Data sheet:

Data sheet SAO

Additional information
on this subject:


Flow calibration

Flow element software

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