×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Valve CV curve

Valve CV curve

Valve CV curve

(OP)
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

RE: Valve CV curve

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.  ΔP = (Q/Cv)^0.5

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

RE: Valve CV curve

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.


 

RE: Valve CV curve

(OP)
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

 

RE: Valve CV curve

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

RE: Valve CV curve

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.

RE: Valve CV curve

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?

RE: Valve CV curve

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

RE: Valve CV curve

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: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Valve CV curve

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

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources