Valve CV curve

[Proc84]

dear all
good day , i have only cv / kv value for valve. how can use this value to make new curve depend on the flowrate and CV / kv due to i dont have the actual curve for this valve from the supplier which is give me the valve open position with flowrate

regards

 

[BigInch]

There is no Cv curve. Cv is one value. If you plot it, it is a point.

Using the Cv value for a valve you can make a pressure drop curve, with flowrate as the dependent variable. [Δ]P = (Q/Cv)^0.5

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[ione]

Proc84,

You've received a good input from BigInch. Maybe you're looking for a Cv vs valve position curve. In this case the manufacturer should be capable to provide this information. What kind of valve are you talking about? Please consider there are valves conceived to work fully open or closed, and in this case the question becomes meaningless unless you want to perform a transient analysis.

 

[Proc84]

i have 2 options
1- ball valve
2- butterfly valve

im searching about the curve showing the relation between the valve position (% opening ) and flow rate
what is available with me only CV Value

can i make this cure or only i can get from the supplier

im thinking to take % of KV = (Q = FLOWRATE ) (D/1000 DALAT P )force 1/2 to calculate (Dalta p) after that keep this value constant and try for different % kv i will get different flow rate ( its ok but is that right to keep the pressure drop constant in different positions ) i dont think so pressre drop will increase olso when the cluser be more

 

[BigInch]

Don't make that one up. Get it from the mfgr, or find one for a similar valve, a very similer valve. It's much easier to find a template of a similar valve than it is to make one from scratch. You will have to do quite a bit of streamline modeling. As an example, a FO ball valve will experience 90% of the total pressure drop going from 10% to 0% open.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[JLSeagull]

Perhaps your application is for a large line for selecting butterfly or ball valve. Differentiate a butterfly or ball type valve designed for throttling from the typical examples for on/off use.

Start with globe style control valve literature. You can find the curves for control valve position and Cv % based upon the trim selection for equal percentage (normal throttling), linear or fast open. Fewer selection choices exist for most butterfly or ball valve models. If not a throttling valve a high percentage open Cv likely exists at a low percentage of opening travel. Knowing the approximate Cv (Kv) for a valve based upon the percentage travel is required to calculate flow based upon inlet pressure valve pressure drop etc. BTW you could find liquid easier to calculate than vapor.

 

[sspeare]

BigInch, for a liquid, isn't the formula as follows:

Delta P = SG x (Q/Cv)^2

SG = specific gravity.
Q = flow, GPM.
Cv = flow coefficient.

The exponent is 2, not 0.5. Am I right, or have I lost my mind?

 

[hacksaw]

my two cents, standard ball valves are quick opening with very little modulation, characterized ball valves have almost an exponential, ok parabolic, rise with % open

 

[xnuke]

The exponent is 2.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[BigInch]

Yes it is 2. Evidence of another neuron having crossed over. Sorry.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus