Title: How Scuba Works | HowStuffWorks
Headings: How Scuba Works
How Scuba Works
Wet Suits, Dry Suits, and Buoyancy Control
Scuba Breathing Apparatus
Diving Physics, Physiology and Hazards
Effects of Scuba Diving on the Body
Scuba: Additional Equipment
Scuba Training
Amateur levels

Content: The process repeats when you inhale again. Operation of a regulator's first stage
The first stage usually has several ports with hoses that lead to the second stage as well as to other devices, such as an additional second stage, tank-pressure gauge and/or buoyancy control device (BCD -- more on this later). Inside a regulator's second stage
The regulator's second stage consists of: Plastic chamber with an outer rubber diaphragm that is in contact with ambient water pressure
Purge button
Inner valve that is connected to a movable lever
Exhaust valve
Mouthpiece
The second stage is connected by a hose to the intermediate-pressure chamber of the first stage. This is how the second stage operates: You inhale, thereby lowering the pressure within the second stage to below the ambient water pressure. The water pressure presses in on the diaphragm membrane and moves the lever. The lever's movement opens the inlet valve. This allows air to flow into the second stage from the first stage, and into your lungs through the mouthpiece. When you exhale, the pressure in the second stage exceeds the ambient water pressure and pushes out on the membrane.