ANSI/FCI 70-2-2021确定了控制阀的六类阀座泄漏。还定义了确定适当等级的具体试验程序。包括通常与带有活塞环密封或金属对金属阀座的双端口、双座或平衡单端口控制阀相关的类别；商用不平衡单端口、单座和平衡单端口阀门，带有超紧活塞环或其他密封方式以及金属对金属阀座；用于关键应用的阀门，其中可能需要长时间关闭控制阀，而无需关闭截止阀； 以及带有O形环或类似无间隙密封件的弹性阀座控制阀等。

ANSI/FCI 70-2-2021 establishes six classes of seat leakage for control valves. Also defined are specific test procedures to determine the appropriate class. Included are classes commonly associated with double-port, double-seat or balanced single-port control valves with a piston ring seal or metal-to-metal seats; commercial unbalanced single-port, single-seat and balanced single-port valves with extra tight piston rings or other sealing means and metal-to-metal seats; valves for critical applications where the control valve may be required to be closed, without a blocking valve, for long period of time; and resilient seating control valves with "O" rings or similar gapless seals, among others.