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Basic Concepts > General > Fluid Basics Español
 
Concepts
Flow Coefficient CV and Kv
Flow Coefficient comparative
Flow coefficient for ball valve
Flow coefficient for butterfly valve
Discharge Coefficient
Reynolds Number
Flow Equations - Online Calculation
Flow Coefficient (Cv and Kv)
Pressure drop Coefficient zeta (ζ)
Discharge Coefficient (C)
Flow Rate (Q)
Flow velocity (v)
Head drop (Δh)
Pressure drop (ΔP)
Cavitation Number
 
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Flow Coefficient Definition

When flow goes through a valve or any other restricting device it loses some energy. The flow coefficient is a designing factor which relates head drop (Δh) or pressure drop (ΔP) across the valve with the flow rate (Q).

flow coefficient, flow rate, pressure drop(liquids)
Q: Flow rate
ΔP: Pressure Drop
Sg: Specific gravity (1 for water)
K: Flow coefficient Kv or Cv
flow coefficient schem


Go to online calculation of the Flow coefficient Cv and Kv


Each valve has its own flow coefficient. This depends on how the valve has been designed to let the flow going through the valve. Therefore, the main differences between different flow coefficients come from the type of valve, and of course the opening position of the valve.

Flow coefficient is important in order to select the best valve for a specific application. If the valve is going to be most of the time opened, probably there should be selected a valve with low head loss in order to save energy. Or if it is needed a control valve, the range of coefficients for the different opening positions of the valve should fit the requirements of the application.

At same flow rate, higher flow coefficient means lower drop pressure across the valve.


Depending of manufacturer, type of valve, application the flow coefficient can be expressed in several ways. The coefficient can be non-dimensional or with units if parameters such as diameter or density are considered inside the coefficient or just in the equation.

Most of valve industry have standardized the flow coefficient (K). It is referenced for water at a specific temperature, and flow rate and drop pressure units. Same model valve has different coefficient for each diameter.

Kv is the flow coefficient in metric units. It is defined as the flow rate in cubic meters per hour [m3/h] of water at a temperature of 16º celsius with a pressure drop across the valve of 1 bar.
Cv is the flow coefficient in imperial units. It is defined as the flow rate in US Gallons per minute [gpm] of water at a temperature of 60º fahrenheit with a pressure drop across the valve of 1 psi.

Kv = 0.865 · Cv
Cv = 1,156 · Kv

(Equivalence between flow coefficients Kv and Cv)


At valves which discharge the flow directly into the environment it is used the non-dimensional Discharge Coefficient(C).

Flow coefficient C Cv Kv Comparative

Flow Coefficient References
Tipo de válvulaCoeficiente de Caudal (válvula toda abierta)
C

[-]
Cv
[gpm]
[psi]
Kv
[m³/h]
[bar]
Referencia
Annular valve÷÷÷-
Ball valve (Full bore)4.751004370Jamesbury series 9000 6" dn
Butterlfy valve÷÷÷-
Diaphragm valve (Weir)0.64690597ITT Dia-Flo Plastic Lined 6" dn
Diaphragm valve (Straightway)1.314001211ITT Dia-Flo Plastic Lined 6" dn
Gate valve÷÷÷-
Globe valve÷÷÷-
Fixed Cone valve0.8637003200Henry Platt 12" dn
Needle valve÷÷÷-
Plug valve÷÷÷-
Pinch valve÷÷÷-
Rubber Duck-Bill check valve1.043003700EVR CPF/CPO 300mm dn
Spherical valve÷÷÷-
Tilting disc check valve0.9311601003Val-matic 6" dn
(*) Water density reference (1000kg/m3) to calculate C and Cv KV equivalencies
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