Scuba set

A portable underwater breathing apparatus that supplies breathing gas from a compressed cylinder through a regulator. Its components support breathing and, in many configurations, buoyancy control and monitoring.

Demand regulator: A regulator that delivers breathing gas when a diver inhales, reducing cylinder pressure to approximately ambient pressure. It supplies gas only as the diver breathes, matching delivery pressure to surrounding water pressure.
Compressed air: Air stored at elevated pressure, commonly used as breathing gas in recreational scuba diving. It is the usual cylinder gas in basic scuba sets.
Recreational diving: Non-commercial underwater diving undertaken primarily for leisure, commonly within planned depth and time limits. Standard scuba sets are chiefly used for recreational underwater breathing.
Surface-supplied diving: A diving method in which breathing gas reaches the diver through a hose from the surface. It replaces the scuba set's carried cylinder with a surface-based gas supply.
First stage regulator: The regulator component that reduces high cylinder pressure to an intermediate pressure. It makes cylinder gas suitable for delivery through hoses to the second stage.
Scuba cylinder: A pressure vessel that stores breathing gas for a scuba diver. It is the set's gas reservoir and connects directly to the regulator first stage.
Technical diving: Scuba diving that exceeds recreational limits through greater depth, duration, decompression, or environmental complexity. Its additional risks often require redundant gas supplies and more elaborate set configurations.
Snorkeling: Swimming near the surface while breathing air through a tube whose opening remains above water. It provides no independent underwater gas supply, unlike a scuba set.
Second stage regulator: The regulator component that reduces intermediate-pressure gas to ambient pressure for breathing. It delivers breathable gas at the mouthpiece when inhalation activates its demand valve.
Ambient pressure: The pressure exerted by the surrounding environment at a given location. The regulator must deliver gas near the pressure of the surrounding water.

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Scuba divingBroader topic: It is the core equipment that makes independent underwater breathing possible.