01
Choked flow: definition and engineering context
Sonic flow. Condition where mass flow no longer increases by lowering downstream pressure at fixed upstream conditions.
The term belongs to the flow & valves context. Its exact limits can depend on the cited standard, catalog convention, unit system, reference state, and component configuration.
02
Why Choked flow affects pneumatic selection
Increasing component conductance or upstream pressure may be needed for more flow.
- SCFM: Always confirm the reference temperature, pressure, and humidity convention.
- NL/min: Normal conditions vary by convention; record the supplier basis.
- ANR: Keep ANR values tied to the catalog's stated reference definition.
- Qn: Compare only when pressure conditions and measurement conventions match.
03
How to evaluate Choked flow in a catalog or replacement project
Read the value together with its unit, test basis, operating pressure, temperature, circuit state, and manufacturer definition.
For replacement work, compare the complete datasheet and drawing. A matching abbreviation or nominal size does not by itself prove functional or dimensional interchangeability.
- Standard cubic feet per minute: Volumetric flow referenced to stated standard conditions.
- Normal litres per minute: Volumetric flow normalized to a stated reference condition.
- Atmosphère Normale de Référence: Reference-air condition used by some pneumatic catalogs for normalized flow.
- Nominal or normalized flow rate: Catalog flow value defined under a stated test condition.
Selection checklist
What to verify before selection
- 01
Increasing component conductance or upstream pressure may be needed for more flow.
- 02
Always confirm the reference temperature, pressure, and humidity convention.
- 03
Normal conditions vary by convention; record the supplier basis.
- 04
Keep ANR values tied to the catalog's stated reference definition.
Application caution
Common mistakes
- Treating Choked flow as a universal definition without checking the manufacturer or standard context
- Mixing gauge and absolute values, incompatible units, or different reference conditions in one comparison
- Selecting a component from the term or nominal value alone without checking the complete operating point and drawing
FAQ