This very high quality reversible shutoff valve by OmniSwivel International fits in-line between your low-pressure hose and first stage regulator. The shutoff valve opens and closes very quickly by sliding (ON is toward the First Stage), and provides positive tactile feedback when operated. Used to prevent gas loss from dribbling or free flowing from a second stage or rebreather ADV, or whenever the ability to very rapidly stop gas flow is required. The regulator first stage should also have an OPV if the shutoff is used to disable the only pressure relief path.