page_title: Rebreather
section_title: Dive/Surface valve
hierarchical_section_title: Rebreather / Architecture of a rebreather / Breathing gas passage configuration / Dive/Surface valve
caption_attribution_description: English: Dive-surface valve and breathing hoses of a Draeger Ray semi closed rebreather
context_page_description: A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's exhaled breath to permit the rebreathing of the substantially unused oxygen content, and unused inert content when present, of each breath. Oxygen is added to replenish the amount metabolised by the user. This differs from open-circuit breathing apparatus, where the exhaled gas is discharged directly into the environment. The purpose is to extend the breathing endurance of a limited gas supply, and, for covert military use by frogmen or observation of underwater life, eliminating the bubbles produced by an open circuit system. A rebreather is generally understood to be a portable unit carried by the user. The same technology on a vehicle or non-mobile installation is more likely to be referred to as a life-support system.
  Rebreather technology may be used where breathing gas supply is limited, such as underwater or in space, where the environment is toxic or hypoxic, as in firefighting, mine rescue and high-altitude operations, or where the breathing gas is specially enriched or contains expensive components, such as helium diluent or anaesthetic gases.
context_section_description: The Dive/Surface valve (DSV) is a valve on the mouthpiece which can switch between the loop and ambient surroundings. It is used to close the loop at the surface to allow the diver to breathe atmospheric air, and may also be used underwater to isolate the loop so that it will not flood if the mouthpiece is taken out of the mouth.
caption: Dive-surface valve and breathing hoses of a Draeger Ray semi closed rebreather
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