What is Cv,sel and when is the valve “Adequate”?

Cv,sel is the manufacturer full-open catalog Cv entered in Advanced 1.2. The result is Adequate when calculated Cv ≤ Cv,sel. The gauge fill is calculated Cv / Cv,sel (a capacity proxy, not a true stem-lift curve).

Are P1 and P2 gauge or absolute?

UI inputs are gauge (bar g / psig). Liquid sizing uses the gauge ΔP directly. Gas sizing adds 1 atm to each pressure before the simplified gas equation.

Does the app check choked flow or cavitation?

No. FL / FF choked ceilings and cavitation indices are not computed. Treat the result as non-choked screening and confirm severe-service cases on a vendor IEC 60534 worksheet.

Why doesn’t liquid Cv use temperature?

The liquid US Cv screening equation uses Q, SG, and ΔP only. Temperature is shown for documentation and is required for gas sizing.

Valve Cv Sizing Calculator | FieldEngineersKit

1. Core Formula & Variable Definitions

ISA-75.01.01 / IEC 60534-2-1 (Flow Equations for Sizing Control Valves) — screening use · ISA-75.02.01 / IEC 60534-2-3 (Control Valve Capacity Test Procedures) · ASME B16.34 (Valves — Flanged, Threaded, and Welding End)

C_{v} = Q_{gpm} \cdot \frac{S G}{Δ P _{psi}}

K_{v} = Q_{m^{3} / h} \cdot \frac{S G}{Δ P _{bar}}

C_{v} \approx 1.156 \cdot K_{v}

Δ P_{max} = F_{L}^{2} \cdot (P_{1, abs} - F_{F} P_{v}) [choked ceiling; absolute pressures]

ISA-75.01.01 & IEC 60534-2-1 Control Valve Sizing Equations

Liquid Cv = Q_gpm √(SG/ΔP_psi)1 m³/h 4.403 GPM1 bar 14.504 psiAdequate Cv ≤ Cv,sel

This calculator returns US Cv. Liquid mode converts metric Q (m³/h) and ΔP (bar) to gpm/psi, then Cv = Q_gpm √(SG / ΔP_psi). P1/P2 are gauge; liquid ΔP is the gauge differential. Gas mode converts gauge to absolute with +1.01325 bar (+14.696 psi) and applies a simplified non-choked screening equation — not a full IEC 60534-2-1 purchase calculation with xT / Fγ. Enter catalog Cv,sel to check headroom (adequate when calculated Cv ≤ Cv,sel). Temperature is used for gas only.

Cv (Required US Flow Coefficient) — Hero output — US gpm of 60 °F water at 1 psi ΔP capacity needed for the process case.
Cv,sel (Catalog / Selected Cv) — Manufacturer full-open rated Cv (Advanced 1.2). Gauge fill ≈ Cv / Cv,sel. Adequate when Cv ≤ Cv,sel.
Q (Volumetric Flow Rate) — Liquid: m³/h or GPM. Gas: Nm³/h or SCFH.
P1 / P2 (Upstream / Downstream Pressure) — Gauge inputs (bar g or psig). Liquid uses ΔP = P1 − P2. Gas converts each to absolute before sizing.
ΔP (Valve Differential Pressure) — P1 − P2 (must be > 0). Same magnitude in gauge or absolute for liquid.
SG (Specific Gravity) — Liquid: relative to water (= 1.0). Gas: relative to air (= 1.0 for air).
T (Fluid Temperature) — Used in the gas equation. Documented for liquid but not used in the liquid US Cv formula.

2. Allowances, Tolerances & Standards

The app computes required Cv and compares it to catalog Cv,sel. Choked-flow, Fp, and noise checks remain site / vendor steps.

Catalog Headroom (this app)Adequate when Cv ≤ Cv,sel

Enter the manufacturer full-open Cv as Cv,sel. The result gauge shows calculated Cv as a fraction of Cv,sel (travel proxy, not true stem lift).

Typical Selection PracticeCv,sel ≈ 1.25–1.30 × normal Cv

Field practice often sizes catalog Cv about 25–30% above normal calculated Cv so normal travel sits near mid-range. Not auto-applied — set Cv,sel yourself.

Default Liquid CaseQ = 120 m³/h, ΔP = 3 bar → Cv ≈ 80.1

Matches the Quick Reference row and the calculator defaults (with Cv,sel = 100 → adequate).

Out of Scope HereFL choked ceiling · Fp · noise · true lift curve

FL / FF choked checks, piping geometry Fp, and equal-percentage lift maps are not solved in-app. Confirm on the vendor sizing sheet before purchase.

Quick Reference Lookup Table

Liquid Cv screening (SG = 1.0) — same conversion as the calculator (Q m³/h, ΔP bar → US Cv)
Q (m³/h)	ΔP 1 bar	ΔP 2 bar	ΔP 3 bar	ΔP 5 bar
10	11.56	8.17	6.67	5.17
20	23.12	16.35	13.35	10.34
50	57.80	40.87	33.37	25.85
80	92.49	65.40	53.40	41.36
120	138.73	98.10	80.10	62.04
150	173.41	122.62	100.12	77.55

Non-choked incompressible screening only. Default calculator case Q = 120 m³/h @ ΔP = 3 bar → Cv ≈ 80.1. Gas mode uses a simplified absolute-pressure form — apply full IEC 60534-2-1 with xT for purchase.

3. Material & Code Limitations

Material choice is outside the Cv equation but governs whether the calculated ΔP is serviceable.

Material Group	Temperature Range	Allowable Stress / Limit	Engineering Notes
ASTM A216 WCB / WCC (Cast Carbon Steel)	-29 °C to 425 °C (-20 °F to 800 °F)	ASME B16.34 class rating for the body	Common for non-corrosive water, hydrocarbons, and utility steam.
ASTM A351 CF8M / CF3M (Cast 316 / 316L)	-196 °C to 538 °C (-320 °F to 1000 °F)	Corrosion + cryogenic / hot service per class	Chemicals, amine, sour gas, LNG.
Hardened / Stellite Trim	Per trim OEM	High ΔP / flashing / slurry erosion	Use when ΔP is large or flashing is expected — Cv alone does not select trim.
Cr-Mo Alloy Bodies (WC9 / C12A)	Elevated steam / hydroprocessing	Creep-resistant class ratings	Boiler feedwater and high-temperature steam headers.

Code Applicability & Safety Boundaries

Calculator scope: liquid US Cv and simplified gas Cv, plus Cv ≤ Cv,sel headroom. It does not compute FL choked ΔP, Fp, aerodynamic noise, or stem-lift curves.
If P2 < Pv (flashing) or ΔP approaches choked limits, use anti-cavitation / severe-service trim — not covered here.
Avoid chronic operation at very low opening fractions; set Cv,sel so normal Cv/Cv,sel stays in a controllable band.

4. Step-by-Step Worked Example

Field VerificationShow

Step-by-Step Worked Example: Match the Calculator Liquid Path

Reproduce the app default liquid case: Q = 120 m³/h water (SG = 1.0), P1 = 10 bar g, P2 = 7 bar g (ΔP = 3 bar), catalog Cv,sel = 100. Confirm required Cv and adequacy.

Fluid:Liquid water, SG = 1.00Flow rate (Q):120 m³/h (≈ 528.3 GPM)Inlet / Outlet:P1 = 10 bar g, P2 = 7 bar gDifferential (ΔP):3.00 bar (≈ 43.51 psi)Catalog Cv,sel:100 (Advanced 1.2)

1

Convert to US units (as the engine does)

Q_gpm = 120 × 4.402867655 = 528.34 GPM. ΔP_psi = 3 × 14.5037738 = 43.51 psi.

Result:Q = 528.34 GPM, ΔP = 43.51 psi

Metric inputs are converted before the US Cv equation.

2

Compute required Cv

C_{v} = Q_{g p m} \cdot S G /Δ P_{p s i}

Cv = 528.34 × √(1.00 / 43.51) = 528.34 × 0.1516 ≈ 80.08.

Result:Cv ≈ 80.1

Matches the calculator hero for the default liquid case.

3

Compare to catalog Cv,sel

C_{v} \leq C_{v, se l}

80.1 ≤ 100 → Adequate. Travel proxy ≈ 80.1 / 100 = 80%.

Result:Adequate (Cv / Cv,sel ≈ 80%)

If Cv,sel were 45 (older demo), the app would flag Undersized.

4

Optional 25% selection margin

1.25 × 80.1 ≈ 100.1 — a catalog Cv near 100–115 is a common pick for this normal case.

Result:Cv,sel ≈ 100–115 typical

Margin is guidance only; enter the actual manufacturer Cv in 1.2.

5

Site checks outside the app

Confirm non-choked service with FL / Pv, noise, and equal-percentage lift on the vendor sheet before purchase.

Result:Export / copy the sizing sheet

Gas cases need absolute P1/P2 and are screening-only here.

Conclusion: For Q = 120 m³/h water with ΔP = 3 bar, required Cv ≈ 80.1. With Cv,sel = 100 the calculator reports Adequate at ~80% of catalog capacity — the same path as the live default case.

5. Frequently Asked Questions & Technical References

Show

US Cv only. Metric inputs are converted to gpm/psi (or SCFH/psia) before the equation. The relationship Cv ≈ 1.156 × Kv is reference context — the app does not display Kv.