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When divers talk about regulators they are usually talking about a complete set of regulators which is typically made up of a first stage, hoses, a second stage, a redundant second stage (normally referred to as an Octopus) and an instrument console (which can include pressure gauge, depth gauge, compass or possibly a dive computer)

All of these components can be bought individually but manufacturers match suitable elements together to create pre-assembled packs to meet a number of uses and environments that both recreational and technical divers typically find themselves in.

When it comes to choosing your regulators it is very important to bear in mind what sort of diving you intend to do and environments in which you’ll be diving. For example, if you intend to only dive to normal recreational limits whilst on holiday in tropical location your choice of regulator is not going to be any where near as demanding as a diver descending to 50m plus in water temperatures below 10°C (below this temperature is considered to be coldwater).

To view our full range of regulators please see our Scuba Diving Regulators department.


The first stage is the work horse of the regulator, converting the cylinder pressure (up to 300 Bar) down to approximately 10 Bar as quickly and stably as possible to supply the diver with a constant flow of air. It also provides either one or two bypass ports which supply cylinder pressure to the pressure gauge or possibly a dive computer transmitter to allow the diver to keep track of available air remaining.


Piston first stages offer the simplest design and usually the highest performance due to their low number of moving parts and efficiency which means that piston design first stages are usually found on both entry level models (few parts make them cheap to manufacture) and flagship models (extreme high performance due to increased flow rate). Although not generally considered for coldwater use advances in material coatings, insulation and environmental sealing (see below) on higher specification models has seen the piston first stage become more popular in low temperature waters.

Diaphragm first stages are more complex than piston designs and have, in the past, been lower performing. With advances in design, materials and manufacturing the diaphragm first stage is typically the more popular than piston designs with the majority of mid to high specification regulators featuring a diaphragm first stage. The biggest advantage of this type of first stage is that the design allows for it to be easily fitted with an environment seal (see below) for coldwater use.



First stage fitting type

There two basic types of cylinder to regulator fitting, DIN (up to 200 or up to 300 Bar) or A-Clamp (also referred to as Yoke) which is up to 232 Bar only. DIN is a much newer fitting which has been gaining popularity over the  last few years, particularly within the technical sector. Where once DIN was confined to Europe and A-Clamp the rest of the world, DIN cylinders are becoming much more readily available especially thanks to convertible valves that are fitted to the majority of new 232 Bar cylinders these days.

The DIN fitting provides a safer coupling to the cylinder, successfully trapping the o-ring between the cylinder valve the the first stage. Permanent converters can be fitted by a qualified technician at a later date if a diver needs to change from A-Clamp to DIN but the added benefit of a DIN fitting is that screw on adapters are available to conveniently convert the fitting if the diver travels to an area where only A-Clamp cylinders are available

Unbalanced V Balanced

Both Piston and Diaphragm first stages can be split further into unbalanced or balanced types. Unbalanced systems are affected by cylinder pressure and depth changes, becoming marginally more difficult to breathe from as depth increases and the cylinder becomes depleted. Modern designs have helped to noticeably reduce this but Balanced regulators still offer consistent performance at any depth regardless of cylinder pressure.

There is also a third system referred to as Over-balanced which provides similar affects to a standard balanced system but increases the flow even further as the depth increases. The main disadvantage of this system is that the diver needs to be more aware of potential freeflows due to the overal regulator sensitivity. A diver using this system will usually start the dive off with the second stage slightly detuned using the ‘inhalation adjuster’ (see below) and gradually  lower the resistance as the depth increases to provide the best performance at the desired depth.


The intended diving environment (warm or cold water) will affect the number of first stage ports the diver will need. In warm waters a typical regulator set will include the primary regulator, an Octopus, a BCD inflator hose and a gauge / console – 3 low pressure ports and 1 high pressure port are required for this configuration.

Water conducts heat significantly better than air though so a diver will rapidly start to become cold. This can be overcome easily in warm waters using a wetsuit of a suitable thickness but in colder waters a dry suit is typically used to provide better thermal protection. The dry suit requires its own inflator hose so an additional low pressure port is generally required for cold water diving, giving a total of 4 low pressure ports and 1 high pressure port required for low temperatures.

Environmentally Sealed

This is a feature found on the vast majority of cold water rated first stages. An environmental seal prevents the surrounding water from interacting with the internal mechanisms of the first stage, helping to prevent any issues related to cold water diving such as ice crystals forming resulting in a first stage freeflow.



The second stage converts the intermediate pressure (approximately 10 Bar) provided by the first stage and reduces it further to ambient pressure for the diver to breathe. Again, there are features to look for depending on the intended use

Unbalanced V Balanced

As with first stage, second stages are available in either unbalanced or balanced variants with very similar advantages and disadvantages of those for first stages. Basically balanced second stages will provide consistent performance and flow rates at any depth whilst unbalanced second stages will not be able to maintain the same performance as the depth increases.

Venturi Control

Regardless of whether the second stage is balanced or not it is likely to have some means of controlling the flow of air inside the second stage housing. The flow of air is usually designed to create a low pressure or vacuum behind the second stage diaphragm, helping to keep or open the valve further without any increased inhalation effort required by the diver. The control usually consists of a vane moved with a lever, the vane will direct the air flow based on its set location. Under normal diving conditions the lever will be set to ‘+’ or ‘dive’ to provide the best performance. The ‘-‘ or ‘pre-dive’ setting is typically used for water entry or on a redundant second stage (Octopus) where the vane will direct the flow forwards towards the diaphragm, increasing the pressure and helping to shut the valve.

Inhalation Adjustment

Typically seen on balanced second stages, the inhalation adjustment control can be used to alter the effort required to open the valve. This is particularly useful for deeper dives where a comfortable resistance at depth may result in a freeflow at the surface.



All of the points covered under ‘second stage’ apply here with an additional choice to bear in mind. When it comes to choosing an octopus there are a couple of options. A standard octopus is fitted with a high visibility yellow front cover and yellow hose for easy location and the hose is longer to allow for its donation to the diving buddy or victim. In most circumstances an equal or lower performing model to that of the primary second stage is the best/preferred option.

There are ‘Alternative Air Sources’ (AAS) available which combine a redundant second stage and BCD buoyancy control into one unit. The advantages are that it reduces the required number of low pressure ports by one and it is always readily available and easy to find, the disadvantages are that the diver has to donate their primary second stage (ie swap their supply for the AAS) and that the shorter length of the primary second stage hose means that the movements of two divers are much more restricted.

To view our octopus range, please see our octopus regulators department.



Modern materials have allowed manufactures to experiment and make use of much more advanced lightweight materials. There are advantages and disadvantages to their use though. The latest travel regulators utilise a range of composite materials to produce the lightest models yet with compact designs specially tailored for travelling divers, the new materials drastically reduce the overall weight of the regulator set and new braided hoses help to reduce this even further. The disadvantage is that the majority of these regulators can be only be used in waters above 10°C due to the much lower thermal transfer properties of the composite materials which limits their use to warmer climates.

There are, however, high specification hybrid regulators that use materials such as carbon technologies to mimic the benefits of more traditional metal housings but significantly reduce the weight of the second stage whilst still meeting the strict requirements for coldwater use.



The majority of regulators are manufactured to be compatible with increased oxygen content up to 40% Enriched Air Nitrox (EAN) but this depends entirely of the manufacturer so it always recommended to check the owners manual before using a regulator for Nitrox. Most manufacturers offer a Nitrox version which is compatible with 100% Oxygen straight out of the box whilst service centres offer Oxygen Cleaning for the vast majority of other regulators.

Some materials, such as Titanium, cannot be used with enriched gas mixes over certain percentages so it important to bear this in mind if there is any possibility of higher levels of oxygen use (such as a 100% oxygen stage cylinder for reduced decompression as used by technical divers).

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