ANSI/FCI 70-2-2006 Control Valve Seat Leakage Standard Clarification

[brillntblk92]

Under table 1, class IV, the maximum seat leakage rate is "0.01% of rated valve capacity". Under para 5.1.2, the standard states "pressure of test medium shall be 45-60 psig...". Flow capacity of a valve is based on Cv and pressure differential. How would flange class effect the maximum seat leakage rate? Would I calculate the "rated valve capacity" based on the test pressure of 60 psig, or does my maximum seat leakage rate increase as flange class increases from 150# to 2500#, which in turn allows more leakage at a standard of 60 psig test pressure?

Thanks.

 

[Raaden]

Yes you recalculate your Cv based upon the test pressure you will be using (60 psig) and multiply that with 0.01%.

It's only if you had a valve with leakage class V that the pressure class would start to matter since that test uses the maximum operating differential pressure across the valve as test pressure and the allowed leakage rate is based upon dp and seat diameter instead of the rated capacity.

 

[brillntblk92]

Great, thank you. That "rated valve capacity" was confusing, but it didn't make sense.