An Introduction to Diving Regulators

Regulator first- and second-stage resting on top of a dive cylinder

In diving, the regulator (the devices that provides the diver with air, ready-for-breathing, from the cylinder) is not just a mouthpiece. It is actually a system that converts air at high pressure (the air stored in your cylinder) to a pressure suitable for breathing. The regulator also supplies air to other various components of your dive set.

Generally, recreational divers use a system in which air pressure is controlled at two specific points: parts of a regulator that we call stages. Each stage has a specific function in the system. Understanding these functions (along with structure of the system) is important to understanding both how your scuba set works and how to take care of your regulator.

Many explanations of how dive regulators work start with the cylinder--in this article, we will explain starting with the diver, working backwards to the source.

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Demand Valve (Second-Stage)

Regulator Second-Stage (Demand Valve)

Regulator Second-Stage

At the end of the system, the diver breathes the air. In recreational diving this is done through a demand valve (also called a regulator second-stage). The demand valve receives air supplied to it through the air lines and, when the diver inhales ('demands' air), makes air available to him or her. When the diver stops breathing, the demand valve stops air flow, to keep the air from escaping from the system unnecessarily.

Any quality second-stage will also include a purge button (the button opposite the side the diver breathes from), which allows air from the air lines to vent (expel water) the second-stage.

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First-Stage - The Connection between the Cylinder and the Second Stage

Regulator First-Stage

Regulator First-Stage,
Attached to Dive Cylinder

The air in a full diving cylinder is stored at 3,000-4,000 psi. If your demand valve is set to allow you to draw breath with minimal effort, you will naturally want something to deliver air to the demand valve at lower pressure than what it is stored at in the cylinder. You will also want to reduce the pressure on your air lines, since they cannot handle the same amount of air pressure your cylinder can. These needs define the primary role played by the regulator first-stage. The fist-stage connects directly to the cylinder and provides air to the second-stage, through the air lines. The first-stage manages what is called intermediate air pressure--that is, the pressure in the lines between the cylinder and what the diver ultimately breathes.

TThe first-stage also distributes air from the cylinder to any of a number of different components in your diving set (such as pressure gauges, BCD inflator, octopus regulator, and drysuit inflator).

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Working forward, then, from the cylinder to the diver:

  • The cylinder holds pressurized air.
  • The first-stage takes high-pressure air from the cylinder, regulates the pressure of the air (intermediate air pressure) to be supplied to the air lines.
  • The first-stage distributes air at intermediate pressure to the second-stage (and, potentially, a number of other devices).
  • The second-stage takes air supplied to it by the first-stage and stops the flow of air until the diver inhales from it. When the diver exhales, the air passes back through the demand valve and (in most cases) out of the system.

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Additional Components

With an understanding of how the system works, it should also be easy to understand the roles different components of a dive set play:

Second-Stage Features

Regulator second-stages also offer the option of being pneumatically balanced. This option (first offered by ScubaPro's Balanced Adjustable model second-stage in 1995) lessens the effort required to draw breath from the demand valve.

Sometimes issues with the balancing can cause free-flow. This can often be repaired; however, with balanced second-stages repair can be difficult; as a result some second-stages (like the ScubaPro G250) offer a predive button, which stops free-flow due to balancing when not using breathing through the demand valve.

Alternate Air Source ("Octopus Regulator")

Also referred to as a 'safe secondary' or 'safe-second'), the octopus regulator is an alternate (spare) demand valve, which, in addition to your primary second-stage, you carry (attached to your first-stage) when you dive. A spare demand valve can be a valuable second-option, if either your buddy needs to breathe from your cylinder or if you have issues with your primary second-stage.

It is recommended that your octopus and your primary demand valve be made by the same manufacturer, to ensure common parts.

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Scubapro-Uwatec's Alternate Inflator Regulator (AIR 2)

Scubapro AIR2

The AIR 2 is a combination BCD-inflator and alternate second-stage. It has buttons that can be used to inflate (or deflate) the BCD to control buoyancy and a mouthpiece that can be used to breathe from. Like the octopus, AIR 2 is a useful addition to any dive set, as an alternate air source for situations where either you or your buddy need a spare. Because it is attached to your first-stage, the air AIR2 provides is fresh from your cylinder.

AIR 2 is a technology that has been around for some time, over which it has continued to answer, simply, the question of how to.

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Underwater Scene