อัปเดต 2026-09-07

Control Valve Cv Sizing

ISA-75.01.01-2012 (R2020) / IEC 60534-2-1:2011

Liquid-service control-valve Cv sizing with choked-flow detection, cavitation-regime classification, piping-geometry correction Fp, valve authority, installed characteristic, Reynolds factor, and a preliminary hydrodynamic-noise estimate.

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Solves in dependency order: choked-flow ΔP threshold and FF (Eq 4/5) → cavitation σ-index regime → Eq 1 Cv at Fp=1 (seed) → iterative Fp (50/50-relaxed fixed point on the implicit Cv↔Fp coupling) → final Cv at converged Fp → valve authority N → installed Cv/Q characteristic → Reynolds factor FR (Annex C) → Baumann noise estimate.

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Master Cv sizing equation (Eq 1, turbulent liquid)

C_{v} = \frac{Q}{N _{1} F _{P} Δ P / G _{f}}

ISA-75.01.01-2012 (R2020) Eq 1; N₁=1.00 (GPM, psi), Gf = ρ/ρ_water,60°F, Fp = piping-geometry factor (reducers/expanders).

Choked-flow pressure-drop limit

Δ P_{c h o k e d} = F_{L}^{2} (p_{1} - F_{F} p_{v}), F_{F} = 0.96 - 0.28 p_{v} / p_{c}

ISA-75.01 Eq 4 & 5; FL = liquid pressure-recovery factor (trim-dependent, e.g. 0.90 globe vs 0.55 butterfly). ΔP beyond this yields no extra flow.

Cavitation index σ

σ = \frac{p _{1} - p _{v}}{p _{1} - p _{2}}

ISA-75.13 / ISA-RP-75.23; higher σ = more margin from vapor pressure. Regimes bounded by σ_mr (damage) / σ_c (constant) / σ_i (incipient).

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