Cv Flow Rate Calculator
Valve Flow Coefficient Calculator
Pressure Conditions
Gas Properties & Conditions
Valve Properties
Air - Molecular Weight: 28.97 g/mol
Specific Heat Ratio (γ): 1.4
Standard Density: 1.293 kg/m³
Specific Heat Ratio (γ): 1.4
Standard Density: 1.293 kg/m³
Cv Flow Rate Calculator - Theory & Applications
Low Pressure Drop (P₂ > ½P₁)
q = N₂CᵥP₁(1 - 2ΔP/3P₁)√(ΔP/(P₁GᵧT₁))
Used when outlet pressure is greater than half the inlet pressure. Accounts for gas expansion effects.
High Pressure Drop (P₂ < ½P₁)
q = 0.471 N₂CᵥP₁ √(1/(GᵧT₁))
Used for choked flow conditions. Flow becomes independent of downstream pressure due to sonic velocity limit.
Key Parameters:
- q: Flow rate in SCFM (Standard Cubic Feet per Minute)
- N₂: Numerical constant for units (1360 for SCFM, psig, and °R)
- Cᵥ: Flow coefficient - the flow rate of 60°F water that produces 1 psi pressure drop
- P₁: Upstream absolute pressure (PSIA)
- P₂: Downstream absolute pressure (PSIA)
- ΔP: Pressure drop (P₁ - P₂)
- Gᵧ: Specific gravity of gas (relative to air = 1.0)
- T₁: Upstream absolute temperature (°R)
Applications:
- Control Valve Sizing: Determine proper valve size for required flow rates
- System Design: Calculate expected flow rates through existing valves
- Process Control: Predict valve performance under varying conditions
- Safety Analysis: Assess maximum flow rates during emergency conditions
Critical Flow (Choked) Conditions:
When P₂ ≤ ½P₁, the gas reaches sonic velocity at the valve throat. Further reduction in downstream pressure does not increase flow rate - this is the "sound barrier" for gas flow through valves.
Engineering Accuracy: These calculations are based on standard ISA/ANSI valve flow equations widely used in process industries. Results are typically accurate within ±5% for most engineering applications when proper Cv values are used.