Smart questions
Smart answers
Smart people
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Member Login




Remember Me
Forgot Password?
Join Us!

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips now!
  • 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!

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

Donate Today!

Do you enjoy these
technical forums?
Donate Today! Click Here

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.
Jobs from Indeed

Link To This Forum!

Partner Button
Add Stickiness To Your Site By Linking To This Professionally Managed Technical Forum.
Just copy and paste the
code below into your site.

Control Valve Leakage CalculationHelpful Member!(3) 

Pruk (Electrical) (OP)
28 Oct 08 5:19
I just read an article about control valve leakage calculation details below.

Cv max = 182, Flow rate at 100% open = 50 MMScfd
The valve is ANSI class IV specification. So design leakage will be 0.01 % at 50 psi(roughly).

Leakage at 50 psi = 0.01/100 * 50 MMScfd = 0.005 MMScfd

If inlet pressure is 1800 psi.
Then, the maximum leakage at 1800 psi differential
                        = 0.005 * sqrt(1800/50)
                        = 0.03 MMScfd

I'm not sure why they have to use sqrt in the equation. If you have any ideas please share them.
Thanks
786392 (Petroleum)
28 Oct 08 7:02
Are you sure that this was not dealing with something else(i.e.pneumatic air leakage etc.)?
If sure then; is it to do with what fluid(gas or liquid)and what is the Control perspective?

Best Regards
Qalander(Chem)

Helpful Member!(2)  JimCasey (Mechanical)
28 Oct 08 7:42
FCI 70.2 (Was once called ANSI B16.104) Class IV specifies allowable leakage up to 0.01% of rated Cv when tested on air or water at nominally 50 psi differential to atmosphere.  This is at ambient temperature.

Extrapolating the leakrate to other pressures or other fluids is not meaningful.  

If a valve leaks 1 scfh at 50 psi on air, you can't predict what it will leak at, for example, 1000 psi on steam.  

70.2 is a standard that allows comparison of fit and finish, but not much else.   
Pruk (Electrical) (OP)
28 Oct 08 20:35
As JimCasey say that 70.2 doesn't allows us to compare to real process. So, if we like to know leakrate at other pressure, how can we compute then?
In this calculation, he tried to compute optimum flare rate. So he have to know normal leakrate from all control valves which connected to flare knockout drum at operating condition. The problem is I never seen any standard talk about control valve leakrate at operating pressure. Please feel free to share your ideas.
Helpful Member!  NGiLuzzu (Mechanical)
29 Oct 08 6:10
       For more information, please take also a look at thread408-76110: FCI 70-2-2003 and thread408-122060: ANSI/FCI 70-2 Control Valve Leakage within this website.
       Up-to-date reference standards are now FCI-70-2-2006 of April 2006 and equivalent IEC 60534, Part 4, 3rd Edition of June 2006.

       The latter, in a NOTE to paragraph 4.2 about Seat leakage test, explicitly says that "this part of the standard cannot be used as a basis for predicting leakage when the control valve is installed under actual operating conditions".
       A similar statement should be present also in the "American version" of the standard, in paragraph 2.2, if I remember well...


       For the particular application, I would suggest to contact the Valve Manufacturer and ask for their own flow calculation method and/or computer program, for instance.


Hope this helps,     'NGL

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!

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close