Class V vs Class VI Leakage Rates

[Sid89]

While comparing the leakage rates of ANSI FCI 70-2 Class V against Class VI, I realized that Class V has lower allowable leakage than Class VI. For example: 2" Class 150 metal seated valve with Class V rating has a leakage rate = 0.285ml/min while the same valve with soft seats and Class VI rating has a leakage rate = 0.45ml/min. Why is Class VI leakage more than Class V (shouldn't class VI soft seats offer better shut-off than class V metal seats)? I always believed that Class VI valves have a better (tighter) shut-off than Class V but the leakage rates are stating otherwise. Can someone shed light on this?

 

[bcd]

Have you figured it out yet? Your Class V leak rate is with water and Class VI leak rate is with gas.

 

[moideen]

yes, it is confusing. when checking BELIMO control valves, its leakage class is ''air bubble tight class A(EN 12266-1).ANSI leakage rating is ''1 to 6''. more want to know about it from valve specialist. thanks