Confusion Regarding Flow Coefficient?

[WheyProtein]

From my understanding, coefficient of flow basically determines how easily a fluid flows through a valve. How does one determine the Cv value though? For example, I’ve checked the manufactures specs for a regulator and it states that the Cv=1.2. However, wouldn’t this value of Cv vary depending on the inlet/outlet pressure, flow rate and the type of fluid (since specific gravity changes) that flows through? How can the Cv stay constant at 1.2?

http://www.idealvalve.com/pdf/Flow-Calculation-for-Gases.pdf

https://www.spectron.de/spectron_de...flaschendruckregler/fm51/en/DES_FM51_1115.pdf

 

[WheyProtein]

Hello Everyone,

I did more research into this, and it seems that the calculated Cv value is used as a preliminary value to determine the most suitable type of valve/regulator for its application (depending on the valves/regulators Cv). Is this correct?

 

[WheyProtein]

Hi Everyone,

I seem to understand it now. However, does anyone seem to know what formula this website uses to calculate the Cv value?

https://www.swagelok.com/en/toolbox/cv-calculator

Cheers!

 

[moideen]

flow/sqrt of pd=cv
ex: flow=125 gpm
inlet= 45 psig
outlet =35 psig
delta p - 10 psig
sqrt of delta P=3.16

then Cv=39.5

 

[RVAmeche]

Cv is typically determined empirically thru testing but there are also equations.

For control valves, the Cv curve has given "inherent characteristic" which relates to how rapidly Cv changes with open percentage (linear, equal percentage, and quick opening). In real life once the valve is installed in a system, you see an "installed characteristic" that varies depending on the system.

 

[LittleInch]

https://www.engineeringtoolbox.com/flow-coefficients-d_277.html

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