ANSI/FCI 70-2-2006 standard establishes a series of seat leakage classes for control valves and defines the test procedures.

Leakage Classes	Maximum Seat leakage	Test Procedure
Class I	-	None
Class II	0.5% of rated valve capacity	Type A
Class III	0.1% of rated valve capacity	Type A
Class IV	0.01% of rated valve capacity	Type A
Class V	5 x 10-4 ml per minute of water per inch of seat diameter per psi differential	Type B
	5 x 10-12 m3 per second of water per mm of seat diameter per bar	Type B
	4.7 standard ml per minute of air per inch of orifice diameter	Type B1
	11.1 x 10-6 standard m3 per hour of air per mm of orifice diameter	Type B1
Class VI	See table 2	Type C

Table 2

Nominal Seat Diameter mm (inches)	ml per minute	bubbles per minute *
< 25 (< 1)**	0.15	1**
38 (1.5)	0.30	2
51 (2)	0.45	3
64 (2.5)	0.60	4
76 (3)	0.90	6
102 (4)	1.70	11
152 (6)	4.00	27
203 (8)	6.75	45
250 (10)	11.1	-
300 (12)	16.0	-
350 (14)	21.6	-
400 (16)	28.4	-

*Bubbles per minute as tabulated are a suggested alternative based on a suitable calibrated measuring device, in this case, a 6 mm (0.25 inch) O.D. x 1 mm (0.032 inch) wall tube submerged in water to a depth of from 3 to 6 mm (0.125 to 0.25 inch). The tube end shall be cut square and smooth with no chamfers or burrs and the tube axis shall be perpendicular to the surface of the water. Other apparatus may be constructed and the number of bubbles per minute may differ from those shown as long as they correctly indicate the flow in ml per minute.

**If the valve seat diameter differs by more than 2 mm (0.08 inch) from one of the values listed, the leakage rate may be obtained by interpolation assuming that the leakage rate varies as the square of the seat diameter.