Sonic Nozzles are also known as “Critical Flow Venturis” or “Critical Flow Nozzles”
What is a Sonic Nozzle?
A “sonic nozzle” (also known as “Critical Flow Venturi” or “Critical Flow Nozzle”) is a flow meter that can be used as a calibration standard for gas flow meters or any flow measurement device.
By design, sonic nozzles are a constant volumetric flow meter. However, with the use of a regulated pressure supply, the sonic nozzle becomes a “state-of-the-art” mass flow meter. Considering both the divergent section design and the flow rate, sonic nozzles may operate with an exit pressure as high as 90% of the inlet pressure.
Advantages of Sonic Nozzles
Internationally Recognized Flow Meters- Mass Flow Varies Linearly with Inlet Pressure
- Minimum Upstream Piping Required
- Long Term Accuracy
- Excellent Repeatability
- No Moving Parts
- Differential Pressure Measurement Not Required
- Flow Rate Is Not Affected by Downstream Flow Disturbances
- Mass Flow is Constant with Varying Downstream Pressure
Common Sonic Nozzle Applications
- Calibration of Gas Flow Meters
- Gas Flow Metering
- Calibration of Turbine Engine Component Gas Passages
- Calibration of Automotive Component Air Passages
- Measurement of Automotive Induction Air
- Automotive Emissions Testing
- Compressor Discharge Capacity Tests
- Valve CV Tests
- Flow Limiting
- Over Speed Protection of Gas Flow Meters
Sonic Nozzles Manufactured by Flow Systems
Flow Systems manufactures a wide variety of sonic nozzles for use as standalone flow meters and as components in complete systems. Nearly every system built by Flow Systems uses sonic nozzles for flow measurement and control.
- Sonic Nozzle design options
- Sonic Nozzle arrays
- Sonic Nozzle schematics and performance charts
- Sonic Nozzle flow calculation software
- Uncertainty analysis reports on Flow Systems test stands built with sonic nozzles
- Sonic Nozzle standard metrology configurations
Learn More About Sonic Nozzles
To learn more information about Sonic Nozzle technology:
- Download the paper “What is the Best Transfer Standard for Gas Flow?” by John D. Wright of the National Institute of Standards and Technology (NIST)
- Refer to a list of bibliographic references of technical papers written by Flow Systems engineers
- Search the Flow Measurement Technical Library for downloadable papers about sonic nozzles
Sonic Nozzles Need Calibration
Without calibration, ASME predictions for flow rate accuracy, assuming the use of reasonably accurate instrumentation, are at best ±1% of reading. Flow calibrations traceable to NIST in conjunction with standard instrumentation packages allow for: ±0.65%, ±0.56%, ±0.29% and ±0.14% of reading accuracy levels. For more information, refer to the technical note titled Uncertainty Analysis in Gas Flow Measurement when using Sonic Nozzles.
Maximum Back Pressure Ratio (MBPR)
Flow Systems provides a MBPR value with all standard size sonic nozzles in most fittings. This will give users a more defined operational range for each sonic nozzle.