| Scuba regulators reduce the air pressure from the | | | | compensate for changes in cylinder pressure and |
| tank to ambient pressure to allow us to breathe | | | | therefore have a larger opening with which to deliver |
| underwater. The regulator is in two stages; the first | | | | more air. |
| reduces the tank pressure to an intermediate | | | | Finally, some first stage regulators are |
| pressure; the second stage, which is usually | | | | environmentally sealed; that is to say, rather then the |
| incorporated into the mouthpiece in modern | | | | water acting on the mechanism directly, it acts upon |
| recreational scuba equipment, reduces it further so | | | | a fluid that transmits the pressure to the piston or |
| that we can breathe at ambient pressure. | | | | diaphragm. The advantages of this are that it |
| Scuba regulators provide air on demand; that is to | | | | reduces the risk of internal corrosion or sediment |
| say that when the diver breathes in the demand | | | | build up inside the first stage as well as providing |
| valve is opened to provide air and when the diver | | | | thermal insulation to the mechanism; this is important |
| exhales the air demand valve is closed and the stale | | | | in low temperatures to prevent the regulator from |
| air is vented into the water. | | | | freezing up. |
| First stage regulator | | | | The second stage |
| The first stage regulator attaches directly to the | | | | The second stage regulator is attached to the first |
| scuba tank. The standard connector is an A-clamp, | | | | stage by a hose that is usually worn over the right |
| which fits over the valve at the top of the tank and | | | | shoulder. It consists of a diaphragm and purge valve |
| is fastened by tightening a yoke screw, although | | | | at the front, the mouthpiece top rear and exhaust |
| some European divers use a DIN connector. DIN | | | | bottom rear. |
| provides a more secure fastening by screwing | | | | As with the first stage there are different types of |
| directly into the tank valve and can be used with | | | | second stage scuba regulators - the most common is |
| higher cylinder pressures than the A-clamp, but divers | | | | the downstream valve, where a diaphragm |
| with DIN regulators can use a converter to attach | | | | connected to a lever opens or closes a one-way |
| their equipment to a US style scuba tank. | | | | valve. In the other option the lever opens a pilot |
| It is not only the connector type that can vary | | | | valve, which in turn opens the main valve, a more |
| though; the mechanism to detect pressure changes | | | | complicated design that provides greater airflow for |
| can either use a piston, upon which external water | | | | less effort. The greater complexity of the latter |
| pressure acts, or a flexible diaphragm attached to a | | | | makes them both more expensive and harder to |
| push rod. Both types of regulator can be either | | | | maintain. |
| balanced or unbalanced, with the former able to | | | | |