Full Description

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This standard 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 valveswith "O" rings or similar gapless seals, among others.