FieldEngineersKitEngineering Reference & ASME Code Basis
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)
ISA-75.01.01 & IEC 60534-2-1 Control Valve Sizing Equations
This valve sizing calculator returns US Cv for liquid and simplified gas screening. 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. Use SpecRoutes /liquid and /gas; run FL cavitation in the Control Valve Choked Flow sister tool.
- 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. Sizing Rules Matching This Calculator
The valve sizing calculator computes required Cv and compares it to catalog Cv,sel. Choked-flow FL checks live in the sister Choked Flow tool; Fp and noise remain site / vendor steps.
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).
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.
Matches the Quick Reference row and the calculator defaults (with Cv,sel = 100 → adequate). SpecRoute /liquid.
Same Q with a lower ΔP — used in the ISA guide with the cavitation sister-tool check (ΔP_cav ≈ 4.84 bar).
FL / FF choked checks → Control Valve Choked Flow tool. Piping geometry Fp and equal-percentage lift maps → vendor sheet.
Quick Reference Lookup Table
| 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. Body / Trim Notes (Selection Context)
Material choice is outside the Cv equation but governs whether the calculated ΔP is serviceable.
| Group / Regime | Range / Condition | Limit / Criterion | 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. FL choked ΔP → Control Valve Choked Flow. Fp, aerodynamic noise, and stem-lift curves remain vendor / site steps.
- 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 VerificationShowHide
Worked example — valve sizing calculator liquid default
Reproduce the app default liquid valve-sizing 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 on SpecRoute /liquid.
Convert to US units (as the engine does)
Metric inputs are converted before the US Cv equation.
Compute required Cv
Matches the calculator hero for the default liquid case.
Compare to catalog Cv,sel
If Cv,sel were 45 (older demo), the app would flag Undersized.
Optional 25% selection margin
Margin is guidance only; enter the actual manufacturer Cv in 1.2.
Cavitation / site checks
Gas cases need absolute P1/P2 and are screening-only here — use SpecRoute /gas.
5. How to use the valve sizing calculator
- 1
Choose liquid or gas
Open SpecRoute /liquid or /gas. Liquid uses US Cv after unit conversion. Gas needs absolute P1/P2 (gauge + 1 atm) and temperature.
- 2
Enter Q, P1, P2
Q in m³/h (Nm³/h gas), P1/P2 in bar g. ΔP must be positive.
- 3
Open 1.2 for SG, T, Cv,sel
Water SG = 1. Set catalog Cv,sel to check Cv ≤ Cv,sel headroom.
- 4
Read hero Cv and export
If Undersized, raise Cv,sel or reduce required capacity. Run FL cavitation next in the Choked Flow tool when ΔP is high.
6. Frequently Asked Questions & Technical References
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A valve sizing calculator computes the required US Cv from process flow and differential pressure, then checks whether catalog Cv,sel is adequate (Cv ≤ Cv,sel). FEK’s tool follows ISA-75.01 / IEC 60534 screening ($F_P = 1$). Open SpecRoute /liquid or /gas. Cavitation uses the separate Control Valve Choked Flow calculator.
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.
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).
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.
Not inside this calculator. FL / FF choked ceilings are screened in Control Valve Choked Flow. Treat the Cv result as non-choked capacity screening and confirm severe-service cases on a vendor IEC 60534 worksheet.
The liquid US Cv screening equation uses Q, SG, and ΔP only. Temperature is shown for documentation and is required for gas sizing.
Same Q = 120 m³/h water, different ΔP: docs cooling-water duty uses 2.5 bar (Cv ≈ 87.7); the calculator default uses 3 bar (Cv ≈ 80.1). Both use the same US Cv engine path.