Engineering Library
Reference material, not articles. This is where the numbers live: the standards that define control valve engineering, the sizing formulas with every variable named, conversion tables, typical capacity data, pressure classes, materials and actuator data. Use it the way you would use a well-thumbed datasheet folder — look up, confirm, move on. Explanatory writing lives in Articles.
1. Standards & codes
The standards family that governs control valve selection, sizing and testing. When an article on this site cites a clause, it cites one of these.
| Standard | Scope | You use it for |
|---|---|---|
| IEC 60534-1 | Terminology and general considerations | Definitions; the vocabulary every other part builds on |
| IEC 60534-2-1 / ISA-75.01.01 | Flow equations for sizing control valves (liquid and gas, with piping geometry factors) | Cv/Kv sizing, choked-flow checks — the equations the calculators implement |
| IEC 60534-2-3 / ISA-75.02 | Test procedures for flow capacity | How rated Cv is measured and verified |
| IEC 60534-2-4 / ISA-75.11 | Inherent flow characteristics and rangeability | Equal-percentage vs linear curve definitions, rangeability testing |
| IEC 60534-3-1 / -3-2 | Dimensions: face-to-face, end flanges | Envelope dimensions, flange drilling, face-to-face classes |
| IEC 60534-4 / FCI 70-2 | Inspection, routine testing and seat leakage classification | Leakage Classes I–VI and their test conditions |
| IEC 60534-6-1 / -6-2 / -6-3 | Actuator attachment: dimensions and interfaces | Actuator-to-valve mounting, yoke interfaces |
| IEC 60534-7 | Control valve data sheet | The specification sheet format used in enquiries |
| IEC 60534-8-1 / -8-3 / -8-4 | Noise: laboratory measurement, aerodynamic prediction, hydrodynamic prediction | Noise estimates and trim selection for noisy service |
| ASME B16.34 | Valves — flanged, threaded and welding end: pressure–temperature ratings, materials | Pressure class ratings, wall thickness, material groups |
| API 623 | Steel globe valves for petroleum, petrochemical and allied industries | Oil & gas globe valve procurement requirements |
2. Sizing formulas — quick sheet
The core equations from IEC 60534-2-1, in their non-choked form. The Liquid Cv Calculator runs these with the choked-flow check included.
| Quantity | Formula | Units |
|---|---|---|
| Required Cv (liquid) | Cv = Q · √(Gf / ΔP) | Q in US gpm, ΔP in psi |
| Required Kv (liquid) | Kv = Q · √(ρrel / ΔP) | Q in m³/h, ΔP in bar, ρrel relative to water |
| Liquid choked ΔP | ΔPchoked = FL²(P1 − FF · Pv) | abs pressure, psi or bar |
| Liquid pressure-drop ratio factor | FF = 0.96 − 0.28 · √(Pv / Pc) | absolute pressures, same units |
| Gas choked limit | xchoked = Fγ · xT, Fγ = k / 1.40 | x = ΔP/P1; k = isentropic exponent |
| Actuator thrust (unbalanced plug) | F = ΔP · Aseat + Fpack (plus spring force, if any) | ΔP in psi/bar, A in in²/cm² |
Variables: Q = volumetric flow · Gf = specific gravity (water = 1) · P1/P2 = upstream/downstream absolute pressure · Pv = vapour pressure at flowing temperature · Pc = critical pressure · FL = liquid pressure recovery factor (published per trim) · xT = pressure-drop ratio factor (published per trim).
3. Cv ↔ Kv conversion
Cv is US customary (US gpm water at 1 psi drop); Kv is metric (m³/h water at 1 bar drop). They are pure unit conversions of the same idea:
Kv = 0.865 · Cv Cv = 1.156 · Kv
| Cv | Kv | Cv | Kv |
|---|---|---|---|
| 1 | 0.87 | 100 | 86.5 |
| 5 | 4.3 | 150 | 130 |
| 10 | 8.7 | 200 | 173 |
| 25 | 21.6 | 300 | 260 |
| 50 | 43.3 | 400 | 346 |
4. Typical rated Cv by body size
Order-of-magnitude reference for standard globe bodies (single seat, standard trim). Always use the manufacturer's published rated Cv — the actual number depends on trim, port and cage design. Characterized ball and high-performance butterfly valves reach higher Cv at the same size.
| Body size | Typical rated Cv | Body size | Typical rated Cv |
|---|---|---|---|
| 1/2″ | 4–8 | 3″ | 90–180 |
| 3/4″ | 6–14 | 4″ | 150–300 |
| 1″ | 10–24 | 6″ | 350–600 |
| 1-1/2″ | 25–45 | 8″ | 600–1000 |
| 2″ | 40–80 | 10″ | 900–1500 |
5. ASME pressure classes
Class designation vs nominal PN. Actual allowable pressure depends on material group and temperature per ASME B16.34 — a Class 300 carbon steel body at 400 °C carries far less than its cold rating.
| ASME class | Nominal PN | ASME class | Nominal PN |
|---|---|---|---|
| 150 | PN 20 | 900 | PN 150 |
| 300 | PN 50 | 1500 | PN 260 |
| 600 | PN 110 | 2500 | PN 420 |
6. Body & trim materials
The common ASTM designations you will meet on data sheets, and what they are for.
| Material | Family | Typical service |
|---|---|---|
| WCB | Cast carbon steel | The default body: water, steam, oil, gas at moderate temperature |
| WC6 / WC9 | Cast Cr-Mo steel | High-temperature steam (up to ~540 °C with matching grades) |
| CF8M | Cast 316 stainless | Corrosive media, food and pharma-adjacent duties |
| CF8 | Cast 304 stainless | General corrosion resistance, lower alloy cost |
| LCC / LCB | Low-temperature carbon steel | Down to −46 °C (−29 °C for LCB) — LNG-adjacent and cold climates |
| 17-4PH / 316 (trim) | Precipitation / austenitic stainless trim | Standard trim for most services |
| Monel / Hastelloy (trim) | Nickel alloys | Severe corrosion: acids, seawater, sour systems |
| Tungsten carbide (seat/plug) | Hardfacing | Cavitating, erosive or high-ΔP flashing service |
7. Actuator spring ranges
Common diaphragm actuator spring ranges and when each is chosen. The spring range sets the bench set and interacts with fail action — see Fail-Safe Action.
| Spring range | psi | Typical use |
|---|---|---|
| 0.2–1.0 bar | 3–15 | Standard signal range, direct-acting positioner loops |
| 0.4–2.0 bar | 6–30 | Higher thrust needs, stiffer diaphragm cases |
| 0.2–0.6 bar | 3–9 | Small valves, fast stroking, split-range lower half |
| 0.6–1.0 bar | 9–15 | Split-range upper half |
8. Glossary
Every term of art used across this site is defined in the Control Valve Glossary — 34 terms from actuator to cavitation index, each with the standard reference behind it.