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.

Valve Leakage Class and Rated Capacity

algerrl (Mechanical) (OP)
14 Oct 03 13:33
Some valve specifications, such as ANSI/FCI 70-2, specify an allowable leakage rate through a valve as a percentage of rated valve capacity.  The definition of "rated valve capacity" is vague.  The leakage rate is measured with the valve closed so the pressure differential is the test pressure.  If I use the same test pressure as the pressure differential across the full open valve, I can use the Flow Coefficient of the valve, Cv, to calculate an expected flowrate through the open valve.  This flowrate is huge and will certainly choke.  Is anyone aware of a better definition of rated valve capacity?
bljnv (Mechanical)
15 Oct 03 7:35
Rated valve capacity is the capacity based on the published Cv values for a given valve.
Standards do specify leakage rate as a percentage of rated Valve capacity like 0.01 % and etc..
That means the leak across the valve in its fully closed condition at the test pressure should not exceed this limit.
Normally Cv will be rated for water and test fluid will also be water. No need to take correction on Cv to estimate the allowed leak rates. Standard ASME B16.104 refers leak rates in terms of Valve Cv.
Fog1 (Mechanical)
12 Nov 03 8:29
The way I approach it is this: -

The differential pressure is applied to the sizing equation with the capacity coefficient, Cv value, held fixed at the value specified by the manufacturer at the fully open position.

Using the sizing equations it is then possible to calculate what flow would be expected under the conditions of the test pressure applied.

Example a valve with a Cv of 150, P1 = 3.5 barg, Air at 25 C gives a maximum allowable leakage rate of slightly over 15 L/min

The rated capacity you may have gathered from this is the Cv of the valve at the fully open position.

Fog Jones

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