How do scuba regulators deliver breathing gas?

1. A diver and her instructor swim slowly along a reef. Each carries a tank of air on their back. But how does the air get from the tank to the diver, one calm breath at a time?
2. A pump has squeezed a huge amount of air into the tank, about as much as fills a large wardrobe. It pushes on the tank about 200 times harder than the air around you. Nobody could breathe that directly.
3. The first stage is fixed to the top of the tank. Inside, a spring and a valve let out just a little air at a time. The air in the hose is now at a much lower, steady pressure.
4. The second stage sits in the diver's mouth. When she breathes in, a rubber sheet called a diaphragm bends inward and presses a lever. The lever opens a valve and air flows. When she stops, it closes.
5. The deeper the diver goes, the harder the water squeezes. The water also pushes on the diaphragm, so the regulator gives air at exactly the same pressure as the water. That keeps breathing easy, but each breath uses more air.
6. Divers learn all of this from trained instructors before they ever go in the sea. They watch their pressure gauge, stay close to a buddy, breathe calmly and come up slowly with plenty of air to spare.

Tap each part and follow the air from the tank to the diver's mouth.

• Tank. The tank is a thick metal bottle. A pump squeezes in far more air than the bottle could normally hold, so the diver can carry enough for a whole dive.
• First stage. The first stage screws onto the tank. A spring and a valve inside it turn the tank's huge pressure into a much smaller, steady pressure for the hose.
• Hose. A strong, bendy hose carries the air from the first stage on the tank around to the diver's mouth.
• Diaphragm. The diaphragm is a thin rubber sheet with water on one side and air on the other. When the diver breathes in, the water pushes it inward.
• Lever and valve. The diaphragm presses on a lever. The lever lifts a small valve off its seat, and air rushes in from the hose. When the diaphragm springs back, the valve closes.
• Mouthpiece. The diver bites gently on the soft mouthpiece and breathes in and out through it, slowly and calmly.
• Exhaust valve. When the diver breathes out, the used air pushes open a soft rubber flap and escapes as bubbles. The flap then closes so that no water gets in.
• Pressure gauge. The pressure gauge shows how much air is left in the tank. Divers check it often and start back up long before it gets low.

Press Breathe and follow the air through both stages. Then drag the diver deeper. What changes?

Experiment: The diver swims down to where the water pushes much harder. What will the regulator do?

1. Near the surface, press Breathe. Watch the diaphragm, the lever and the valve.
2. Drag the diver down deep and look at the pressure in the mouthpiece.
3. Take a few breaths there. Watch the tank gauge.

What we found: Breathing in bends the diaphragm, which opens the valve and lets air flow. Deeper down the water pushes harder on the diaphragm, so the regulator gives air at a higher pressure that matches the water. Each breath then holds more air, so the tank empties faster.

Turn on JavaScript to try it yourself.

Swim down and stay for 3 breaths beside each sea creature to take its photo. Then come back up with at least 50 bar of air left.

Air can be squeezed. A pump can push a whole room's worth of air into one scuba tank. Squeezed air pushes back very hard on the tank, about 200 times harder than the air around you. That push is called pressure, and it is much too high to breathe.

The regulator fixes this in two steps. The first stage, on top of the tank, lets the air out a little at a time so the hose holds a much smaller, steady pressure. The second stage, in the diver's mouth, is the clever part. It stays shut until the diver breathes in. Then a thin rubber diaphragm bends inward, presses a lever, and the lever opens a valve. Air flows for as long as the diver keeps breathing in.

Water is heavy, so the deeper you go, the harder it squeezes you. To breathe, a diver needs air that pushes back just as hard as the water. The regulator does this by itself, because the water also presses on its diaphragm. But air at a higher pressure is packed more tightly, so every breath takes more air out of the tank.

That is why divers keep checking their pressure gauge. Scuba diving is safe only for people who have been trained by a qualified instructor. They learn to breathe calmly without ever holding their breath, to stay with a buddy, and to swim up slowly while there is still plenty of air left.

Key words

Pressure

How hard a gas or a liquid pushes on things.

Regulator

The device that lowers the pressure of the gas from the tank and delivers it when the diver breathes in.

First stage

The valve on the tank that lowers the very high tank pressure to a steady medium pressure.

Second stage

The part in the diver's mouth that gives air only when the diver breathes in.

Diaphragm

A thin, flexible sheet that moves when the pressure on one side is different from the other.

Ambient pressure

The push of the water (and the air above it) all around the diver.

Check your thinking

1. What makes the second stage open and give air?

   Show the answer

   The diver breathing in, which bends the diaphragm and moves the lever. Breathing in bends the diaphragm inward. It presses the lever, and the lever opens the valve.

2. Why can't a diver breathe straight from the tank?

   Show the answer

   The air is squeezed far too hard and would rush out much too strongly. Tank air pushes about 200 times harder than normal air. The regulator brings it down to a gentle breath.

3. A diver swims deeper. What happens to the air the regulator gives?

   Show the answer

   It comes at a higher pressure, matching the water. The water pushes harder on the diaphragm, so the air is delivered with a matching push.

4. Why does a tank of air run out faster on a deep dive?

   Show the answer

   Each breath is packed with more air when the pressure is higher. Deep air is squeezed more tightly, so every breath takes more of it from the tank.

5. How do people learn to scuba dive safely?

   Show the answer

   They take lessons from a trained instructor. Diving needs training. Instructors teach how to breathe, check the gauge and come up slowly.