Kv = Cv × 0.865 | Cv = Kv / 0.865

Choked flow in valves?

Occurs when ΔP ≥ F_L² (P1 - F_F P_v) → flow independent of downstream pressure

Cv / Kv Valve Calculator

Calculate required control valve flow coefficient Cv (US) or Kv (metric) for liquid, gas and steam. Choked flow detection and valve sizing per IEC 60534 / ISA standards.

Required Cv

42.5

Water 100 m³/h, ΔP=2 bar

Control Valve Cv / Kv Sizing

Featured: Liquid • Gas • Steam • Choked Flow

Fluid Type

Flow Rate Q m³/h for liquid/steam, Nm³/h for gas

Specific Gravity SG or Density ρ (kg/m³)

Inlet Pressure P1 (bar g)

Outlet Pressure P2 (bar g)

Temperature T (°C) - Gas/Steam

Valve Opening vs Flow

Typical equal percentage characteristic

Cv / Kv Formulas (IEC 60534 / ISA)

Liquid: Cv = Q √(SG / ΔP)
Gas: Cv = Q √(SG T / (520 x1 P2))
Choked: Use ΔP_choke = F_L² (P1 - F_F Pv)

Enter parameters to calculate Cv/Kv

Valve Sizing Guidelines

Typical Cv Range

1" valve: Cv ≈ 10–20

4" valve: Cv ≈ 150–300

8" valve: Cv ≈ 800–1500

Design Practice

Normal operation: 60–80% open

Max flow: 90% open

Min flow: 10–20% open