33 C.F.R. § 157.228
Isolating Valves: Closed during a voyage
(a) The master of each U.S. tank vessel under § 157.10a(b), § 157.10a(c)(2), § 157.10b(a)(2), or § 157.10c(c)(2) shall ensure that the valves under § 157.222(d) remain closed during each voyage.
(b) The master of each foreign tank vessel meeting § 157.10a(b), § 157.10a(c)(2), § 157.10b(a)(2), or § 157.10c(c)(2) shall ensure that the valves under § 157.222(d) remain closed when the vessel is on a voyage in the navigable waters of the United States.