01
Kv: definition and engineering context
Metric flow coefficient. Metric coefficient convention commonly used for valve flow capacity.
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 Kv affects pneumatic selection
Cv and Kv are related conventions but are not numerically identical.
- C: Use with critical pressure ratio and absolute pressure conditions.
- b: Needed with sonic conductance for standardized pneumatic flow calculations.
- Choked flow: Increasing component conductance or upstream pressure may be needed for more flow.
- SCFM: Always confirm the reference temperature, pressure, and humidity convention.
03
How to evaluate Kv 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.
- Sonic conductance: ISO 6358 flow characteristic representing conductance in choked flow.
- Critical pressure ratio: ISO 6358 ratio marking transition between choked and subsonic flow behavior.
- Sonic flow: Condition where mass flow no longer increases by lowering downstream pressure at fixed upstream conditions.
- Standard cubic feet per minute: Volumetric flow referenced to stated standard conditions.
Selection checklist
What to verify before selection
- 01
Cv and Kv are related conventions but are not numerically identical.
- 02
Use with critical pressure ratio and absolute pressure conditions.
- 03
Needed with sonic conductance for standardized pneumatic flow calculations.
- 04
Increasing component conductance or upstream pressure may be needed for more flow.
Application caution
Common mistakes
- Treating Kv 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