The purpose of your regulator makes it possible to use the air inside the dive cylinder. Regulators reduce the tank's high-pressure air to match the surrounding water pressure - ambient - and then deliver air on demand, when you inhale it. It regulates the air flow, hence the name 'regulator'. Technically, it is a highly sophisticated demand valve, so in some areas they are referred to as 'demand valves'.

Styles and Features
The modern scuba regulator is a simple and reliable device with only a few moving parts. It has two stages.

• The 1st Stage attaches to the scuba cylinder valve

• The 2nd Stage contains the mouthpiece

The two stages reduce high-pressure air in sequence from the tank. The first stage reduces the pressure to an intermediate pressure of 7 - 10 bar (100 - 150psi) above the surrounding water pressure. Next, the second stage reduces this intermediate pressure to the same pressure as the water surrounding you. This is what diver's need for comfortable breathing. Easy breathing is the most important feature of a scuba regulator.

Regardless if the make, all modern regulators share a relatively similar basic structure and function. The second stage is a cup or air space covered with a flexible diaphragm, (usually made of silicone rubber), a lever-operated inlet valve, a mouthpiece, and an exhaust valve. When the diver inhales, it pulls the diaphragm inwards, which pushes on the inlet valve lever to release air. When he stops inhaling, air pressure rises inside the second stage and the diaphragm returns to its relaxed position. This releases the lever and allows the valve to close. The purge valve button also allows the diver to control the flow of air manually, by depressing the diaphragm and the lever.

When the diver exhales, the exhaust valve opens and the air vents out through the one-way exhaust valves. These remain closed when you are not exhaling, which keeps water out of the regulator.

Your regulator will also have an extra second stage called an alternate air source. However, in some configurations, the alternate air source may also be part of the BCD inflation/deflation hose assembly. The alternate air source - commonly called an octopus - simplifies sharing air with another diver, should the need arise. The octopus usually has a longer, brightly colored hose and mouthpiece so that you can easily identify it.