ASME/FCI 70-2 Class of maximum permissible seat leakage
Class IV 0.01% of rated valve capacity [3-4 bar air or water], g/min = 3.785412 l/min
Class V 5x10¯¹² m³ per second of water per mm of seat diameter per bar differential
( =3x10¯⁴ x bar differential x mm of seat diameter <cc/min> )
4.7 standard ml per minute of air per inch of orifice diameter
Class VI Specified [3.5 bar air or nitrogen gas]