Scuba Dive Regulators Explained for Beginners

A scuba regulator is the gear that lets you breathe from a cylinder. A recreational cylinder is filled to about 200 bar, far too much pressure to breathe directly, so the regulator lowers it in two steps and hands you each breath at the same pressure as the water around you, only when you breathe in. The part of the regulator that connects to your scuba cylinder is the first stage; the part in your mouth is the second stage.

If a course knowledge review asks for the most important feature of a scuba regulator, think about what it is for. It has to give you air easily every time you inhale, at any depth and however much is left in the cylinder, and stop the flow when you stop. Everything else on a spec sheet, from balanced stages to environmental sealing and adjustment knobs, exists to protect that. Engineers call the effort it takes "work of breathing": a regulator that breathes hard limits how hard you can work underwater, and it matters most in an emergency, when you are breathing fastest.

This guide is part of the Beginner Gear Guide in our Learn to Dive hub. Day-to-day care has its own page, our regulator maintenance guide.

How a Regulator Works

Almost every modern regulator is a single-hose, two-stage design. The single-hose regulator was invented by an Australian, Ted Eldred, in the early 1950s, for his Porpoise regulator.

The first stage bolts onto the cylinder valve and drops cylinder pressure to an intermediate pressure, usually about 8 to 11 bar above the surrounding water. A low-pressure hose carries that air to the second stage.

The second stage is a demand valve. Inside it is a flexible diaphragm with air on one side and water on the other. When you breathe in, the pressure inside drops, the water pushes the diaphragm inwards, and the diaphragm presses a lever that opens a small valve. Air flows until you stop inhaling; then the pressure balances, a spring closes the valve and the flow stops. Your exhaled breath leaves through a one-way rubber exhaust valve, and a cover called the exhaust tee steers the bubbles to the sides of your face.

Both stages sense the surrounding water pressure, so the regulator keeps delivering air at the right pressure as you go deeper. Breathing does get a little harder with depth, because the air you breathe is denser, which is one more reason breathing performance matters.

The Parts of a Regulator Set

A full regulator set has five pieces.

First stage

The metal body that attaches to the cylinder valve, either with a yoke clamp or a DIN screw fitting (more on that below). It has several low-pressure ports for second stages and inflator hoses, and one or two high-pressure ports for a pressure gauge or a computer's transmitter. The two kinds of port use different thread sizes, so you cannot screw a hose into the wrong one.

Second stage

The part you breathe from: mouthpiece, diaphragm, valve, exhaust and a purge button that blows water out when you press it. Almost all second stages are built for the hose to come in from your right-hand side. Mouthpieces are now hypoallergenic silicone and come in different shapes, and comfort is personal, so try a few if you get jaw ache.

Many second stages have a dive/pre-dive switch (a venturi control) and some add a breathing resistance knob. Apeks's manual, for example, tells you to set both to the minimum on the surface so the regulator does not free-flow, and open them up once you are underwater for easier breathing.

Octopus

A spare second stage for your buddy, or for you, if someone runs out of air. It normally sits on a longer hose (about 100 cm, against 76 cm for the primary) and is often yellow so it is easy to find. Clip it where you and your buddy can both see and reach it. Some divers use an octopus built into the BCD inflator instead; then you give your buddy the regulator from your mouth and breathe from the inflator unit yourself.

Pressure gauge and console

The submersible pressure gauge (SPG) sits on a high-pressure hose and shows how much air is left in the cylinder. It often sits in a console with a depth gauge, compass or computer. Air-integrated computers read cylinder pressure through a hose or a wireless transmitter, and most divers who use one still carry an ordinary gauge as a backup. Our guide to choosing a dive computer covers the options.

Inflator hose

A low-pressure hose that feeds your BCD inflator, plus a second one for a drysuit if you wear one. Most BCDs use the same standard low-flow quick-connector, so inflator hoses work across most brands.

Balanced or Unbalanced?

In an unbalanced first stage, the cylinder pressure itself helps hold the valve shut. As the cylinder empties, the intermediate pressure drifts, and to keep that drift small the designer has to use a small valve opening, which limits how much air the regulator can deliver at once. Unbalanced regulators are simpler and cheaper.

A balanced first stage cancels out the effect of cylinder pressure, so it delivers the same intermediate pressure and much the same breathing effort from a full cylinder to a nearly empty one, at any depth. Second stages can be balanced too, but balancing the first stage makes the bigger difference. Most top-range regulators have at least one balanced stage, and for a regulator you will own for years, a balanced first stage is worth paying for.

Piston or Diaphragm First Stage?

The valve inside a first stage is moved either by a piston or by a diaphragm.

- Piston first stages have fewer parts and a simpler design. Some of their moving parts can be exposed to the water, so they may need more careful maintenance against corrosion and grit. - Diaphragm first stages are more complex, but the only parts touching the water are the main spring and the diaphragm; everything else is sealed off. That makes them particularly suited to cold water and to salty, silty or dirty water.

Both types can be balanced or unbalanced, and both can be excellent. You may read that pistons are the cold-water choice because they have fewer parts. In cold water it is the sealing that matters, not the mechanism, and an unsealed piston first stage is the type that needs extra protection.

Environmental Sealing and Cold Water

Air gets very cold as it expands through a regulator. In cold water, ice can jam a stage open, causing a free-flow that can empty a cylinder in minutes. Purging hard, filling a surface marker buoy from your primary regulator and sharing air through one first stage all raise the risk, because they push a lot of air through quickly.

The European standard behind regulator testing defines cold water as 10°C or lower. Regulators certified under that standard (EN 250) that are not designed for cold water are marked ">10°C".

An environmentally sealed first stage keeps water out of its spring chamber, either with an extra outer diaphragm (Apeks calls its version the "DRY" system) or by filling the chamber with silicone oil or grease. That helps stop ice forming inside the first stage and keeps salt and silt away from the internal parts. Sealing does not stop the second stage icing, though; some second stages add metal heat-exchange fins for that, while plastic parts insulate a cold regulator from the warmer water around it.

What this means in Australia:

- Port Phillip Bay at St Kilda averages about 11°C in July and August, right on the cold-water line, and Hobart's sea bottoms out at about 12.5 to 13°C in late winter. - Sydney's monthly average never drops below about 18.5°C, and Queensland is warmer still.

So if you will dive Port Phillip through winter, buy a regulator rated for cold water with a sealed first stage; in Tasmania it is a sensible margin. If you dive mostly in NSW or Queensland, sealing matters less, though it still keeps silt and salt out. Our wetsuit thickness guide has typical water temperatures by state.

DIN or Yoke: Which Is Common in Australia?

- Yoke (also called A-clamp or INT) fits over the valve and is tightened by hand, sealing on an O-ring that sits on the valve face. Divers Alert Network (DAN) lists Australia among the places where yoke valves are the most common in recreational diving, alongside the US and Southeast Asia. Yoke fittings are quick to set up, and yoke valves stand up well to the dents and knocks of charter use, but the exposed O-ring can crack or blow out, so dive operators carry spares. Yoke fittings are rated to a maximum of about 240 bar. - DIN screws into the valve and traps its O-ring inside the fitting. It comes in 200 bar and 300 bar versions, is standard in much of Europe, and is preferred by many technical divers because it is more compact and less likely to blow an O-ring if knocked.

Some cylinder valves take a screw-in insert, so the same valve can accept either type, and DIN regulators can be fitted with a yoke adapter. DAN notes that DIN-to-yoke inserts only fit 200 bar DIN valves. Some first stages, Apeks's among them, can be converted between DIN and yoke with the right parts.

For most Australian beginners who hire cylinders from shops and boats, a yoke regulator is the simple choice; if you are heading towards technical diving, a DIN regulator with a yoke adapter works too. Either way, ask the shops and boats you use what their cylinders take.

How to Choose Your First Regulator

First, decide whether to buy one yet: our guides to what scuba gear to buy first and the gear you'll use in your course cover what to hire and what to own. When you are ready, check these points:

1. Ease of breathing. Look for a balanced first stage, and for EN 250 certification, the European minimum performance standard tested to 50 metres. A mark of "EN250A" means the regulator was also tested to supply two second stages at once, as when your buddy breathes from your octopus. 2. Cold-water rating, if you will dive Victoria or Tasmania in winter (see above). 3. The right connection for where you dive: yoke or DIN. 4. Local servicing. Manufacturers expect servicing by a trained technician at an authorised dealer, and warranties can depend on it, so buy a brand that a shop near you is authorised to service. 5. Comfort. Mouthpiece shape, hose length and the weight of the second stage all affect jaw fatigue on a long dive. Ask to breathe from one in the shop or the pool. 6. Nitrox. Standard regulators are generally treated as suitable for nitrox up to 40% oxygen if kept clean (Apeks builds its regulators to that). Check your manual and do a nitrox course first; our guide to diving gases explains the basics. 7. A complete set. Make sure the price covers first stage, primary second stage, octopus, pressure gauge and inflator hose.

If you are offered a second-hand regulator, only buy one with a service history, and have it serviced before you breathe from it. Our gear reviews compare current regulator sets at Australian prices, such as the Apeks XTX200.

Servicing Basics

Before every dive, run a quick check, the same one Apeks lists in its manual: look over the hoses and both stages for damage, open the cylinder valve slowly, press the purge and listen to make sure the flow stops when you let go, take several slow, deep breaths (it should breathe easily with no noticeable resistance), and check the gauge reads what you expect.

After every dive, rinse it in fresh water with the dust cap firmly on. Our regulator maintenance guide walks through the full routine and what you should never do at home.

Professional servicing intervals are set by each manufacturer and change over time, so your manual is the final word. When Undercurrent asked the big brands in 2018, Scubapro said every two years or 100 dives, Aqua Lung at least every two years with a yearly inspection, Apeks every two years for first stages with yearly second-stage inspections, and Mares every two years or 200 dives with an inspection after one year or 100 dives. Older Apeks manuals, like the XTX manual below, say once a year. Aqua Lung adds that a regulator needs a service before reuse after a hard knock, water getting inside or a leak under pressure, and every six months if used in pools or for hire.

Between services, have it checked if you notice a free-flow, a hiss or regular popping from the second stage, water coming in with your breath, or breathing that feels harder than it used to. If a regulator free-flows during a dive, end the dive with your buddy as you were trained, and do not use it again until a technician has looked at it.

Sources

- Wikipedia: Diving regulator - Wikipedia: Mechanism of diving regulators - Wikipedia: Breathing performance of regulators - Divers Alert Network: DIN Connectors Are No Yoke - Apeks: XTX Regulator Owner's Manual (copy hosted by Scuba Doctor) - Scuba School: EN 250, what is it and why is it stamped on my regulator? - Undercurrent: Regulator Servicing, Do It Every Two Years (January 2018) - Wikipedia: Climate of Melbourne (St Kilda sea temperatures) - Wikipedia: Hobart (sea temperatures) - Wikipedia: Climate of Sydney (sea temperatures)

Header photo: A regulator set with a diaphragm DIN first stage, second stage, pressure gauge and drysuit inflator hose, by Mark.murphy at English Wikipedia, Public domain, via Wikimedia Commons.