Over a hundred years ago, the ability to breath underwater was made possible by long tubes, sacks of air carried with the scuba diver and many other ingenious methods. Today’s modern demand valve regulators and pressurized thanks have solved many of the problems associated with these methods.
The pressure on your body increases as you dive deeper; it increases about 1 atm (one atmosphere) for every thirty-three feet.
Because air is easily compressed, to overcome the pressure your lungs and chest muscles have to exert a force. But breathing free air from the surface makes it more difficult. That air remains at 1 atm, so to counteract the increasing pressure, you need to use pressurized air.
Not only do you have to deal with increase air pressure and you dive deeper, but the gases inside your body also gets compressed a small amount. Air near sea level is about 78% nitrogen, and 21% oxygen with small amounts of other gases. This mixture of nitrogen and oxygen isn’t the ideal underwater mixture as the pressure changes. The mixture has to be regulated to deliver the proper concentration of oxygen.
Overtime, air delivery systems have improved and today’s systems compensates for those changing circumstances. They are able to provide the right mixture and pressure as divers descend.
Most recreational scuba dives are done with a mask that fits around the eyes and nose. This causes another problem since the mouth is wrapped around the regulator’s mouthpiece.
As you take in air when you inhale, the body will use the air, then it will exhale part oxygen and part carbon dioxide.
You don’t want to confuse carbon dioxide and carbon monoxide. Carbon dioxide isn’t as toxic as carbon monoxide, but the relative amount oxygen you intake can be decreased by breathing too high a concentration of carbon dioxide. This may eventually lead to oxygen starvation.
The lack of oxygen can lead to light-headedness, disorientation, and could even cause death. This problem is solved by the scuba regulator/tank system by simple expedient of venting the exhaled gas to the surroundings.
Today’s scuba regulator designs are mostly the open circuit 2-stage diving regulators. The original Aqua-Lung design was only one stage. Both the one stage and the 2-stage diving regulator deliver the air at a pressure that matches the ambient pressure of the scuba diver.
Air is pressurized in the tank to around 200 atm. The first stage regulator reduces the air pressure to 10 atm in the 2-stage-design.