Valve Selection
* Data based on typical manual valve coefficients from major
manufacturers. Actual Cv may vary by brand/trim. Use for
estimation only.
Flow Coefficient
Valve Cv
-
Valve Kv:
-
(Kv = 0.865 Γ Cv)
Typical coefficient; manufacturer variation commonly Β±10β20%.
Confirm final values with vendor datasheet.
Select a valve to begin
Flow Rate (Q):
-
Technical Notes & Engineering Logic
Variable Definitions
-
Cv: Valve Flow Coefficient (US gpm
of water @ 60Β°F with 1 psi ΔP).
- Q: Volumetric Flow Rate (US gpm).
-
ΔP: Differential Pressure drop across
valve (psi).
-
SG: Specific Gravity of fluid (Water = 1.0).
Formulas (ISA 75.01 / FCI)
-
To Find Flow: Q = Cv ×
√(ΔP / SG)
-
To Find Drop: ΔP = SG × (Q /
Cv)Β²
-
Assumes: Turbulent flow, non-choked, Newtonian fluid (liquid).
Notes & Constraints
-
Values assume fully open valves unless an opening angle is
specified (throttling datasets).
-
Typical Cv/Kv values compiled from common
industrial valve curves published by major manufacturers;
individual products/trim may vary.
-
Equations assume incompressible liquid,
non-choked conditions and
turbulent flow (typically Re > 10,000).
-
Does not evaluate cavitation, flashing, or choked flow (these
are primarily control-valve checks per ISA/IEC methods).
-
For viscous / laminar regimes, additional Reynolds-number
(viscosity) corrections are requiredβconfirm with vendor or
detailed sizing software.
-
Use for preliminary engineering estimation.
Final selection must be confirmed with vendor-certified
datasheets.
Standards Referenced
-
IEC 60534-2-1 / ISA-75.01: Control/valve sizing
equations (basis for Cv, Kv relationships
and liquid flow equations).
-
FCI (Fluid Controls Institute): Typical valve
coefficient data practices.
-
ASME B16.x: Valve pressure class conventions
(150#β2500#).
-
Manufacturer Catalogues: Typical published
coefficients for manual valves (used for estimation).