Your regulator makes it possible to breathe underwater by allowing you to use the air in your cylinder. It reduces the scuba cylinder's high pressure to match the surrounding water pressure, and it delivers air only on demand, when you inhale, or push the purge button. You can read more about the components of a regulator here. It regulates your air flow, hence the name, and is technically a highly sophisticated demand valve so some divers prefer the term 'demand valve' but we shall call it a regulator as most recreational divers like to refer to it.
Regardless of the make, all modern regulators share a relatively similar basic structure. The modern scuba regulator is a simple and reliable device with only a few moving parts. It reduces the air from a high pressure to a breathable pressure in two separate stages; the first stage, which you attach to the scuba cylinder valve and a second stage which is connected to the mouthpiece.
The stages reduce high-pressure air from the scuba cylinder sequentially because they would not be able to convert pressure that much in just one step. The first stage reduces the high cylinder pressure to an intermediate pressure of 7-10 bar above the surrounding water pressure. The second stage then reduces this intermediate pressure to the surrounding water pressure, which is what is breathed in by you. This reduction in pressure is vital for comfortable breathing; easy breathing is the most important feature when it comes to selecting a regulator.
Selecting a regulator for purchase can be a rather daunting task especially if you are a new diver. As with fins and BCDs there are a wide range of manufacturers and models with vastly different prices, but they all essentially do the same job.
1st Stage Value
Piston or Diaphragm
It is the job of the 1st stage to take the cylinder contents – typically anything up to 300 bar and convert it for use by the 2nd stage (approx. 10 bar depending on manufacturer). It also provides ports for the octopus, BCD/drysuit, and console. The diaphragm 1st stage is the most popular choice nowadays because it is generally more compact, environmentally sealed (or easy to fit an environmental kit) for cold water use (below 10 deg). In terms of performance for example the Scubapro Mk17 can deliver 6500 litres of air per minute. The piston 2nd stage was traditionally the simpler design and higher performer but susceptible to free flow in cold water. This problem has been addressed using modern materials and piston stages have become more popular for cold water applications. In terms of performance for example the Scubapro Mk25 can deliver 8500 litres of air per minute. In use it is highly unlikely that the diver will be able to discern between a piston or diaphragm 1st stage.
Balanced / Unbalanced
Originally, all regulators were unbalanced, meaning that as depth increased and cylinder pressure decreased the reg became more difficult to breathe from i.e. the work of breathing went up. Balanced regulators on the other hand are designed to offer the same work of breathing irrespective of depth or cylinder pressure.
There are two types of fitting for 1st stages, Din and A Clamp. Din fittings can be used up to 300bar and are generally thought of as more secure and robust. Starting out in Europe, you can now use Din regs around the world, although in some obscure places they may only have A clamp compatible tanks which means you may need an adaptor. A clamp, or yoke fittings, are used around the world, they are sometimes called international fitting which gives the clue. They can only be used up to 232 bar and are potentially more susceptible to O ring failure than Din. A clamp regs can be permanently converted to Din by using a converter kit fitted by a technician.
Din or 'A' Clamp
There are two types of fitting for 1st stages, Din and A Clamp. Din fittings can be used up to 300bar and are generally thought of as more secure and robust. Starting out in Europe, you can now use Din regs around the world, although in some obscure places they may only have A clamp compatible tanks which means you may need an adaptor. A clamp, or yoke fittings, are used around the world, they are sometimes called international fitting which gives the clue. They can
only be used up to 232 bar and are potentially more susceptible to O ring failure than Din. A clamp regs can be permanently converted to Din by using a converter kit fitted by a technician.
Probably the final thing to consider is whether or not the 1st stage can provide for all the equipment you are likely to use. In general you are only likely to require 1 HP port for your contents gauge. Having more than 1 just means you have some choice with how you want to have your gauge, but as we know most people have them to the left.LP ports are more significant. In warm water you will probably need 3, one each for reg, octopus and BCD. In cold water 4 may be required, the additional one being for a drysuit. 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 cold water).
2nd Stage Regulator
Balanced / Unbalanced
The second stage receives the air at intermediate pressure provided by the first stage and reduces it further to ambient pressure for the diver to breathe. As with 1st stages there are a number of factors to consider when selecting your 2nd stage. 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.
Modern 2nd stages are likely to have some form of air flow control. A typical control is a moveable vane operated by a lever which directs the airflow to create a low pressure or vacuum behind the diaphragm. This helps to open the valve further without requiring extra diver effort i.e. keeping the work of breathing low. Think of it in terms of controlling the flow performance once the valve has been cracked.
Some 2nd stages have a control allowing you to adjust the 'cracking pressure'. This is how hard you have to draw breath before the regulator delivers gas to you.
•Although it is often nice to have 'bells & whistles' they are often seen as encouraging people to play and tweak them without any real understanding of their operation. Many top performing regs have no user adjustment facility at all so bear this in mind.
•Most people will have a 2nd stage matched with a 1st stage from the same manufacturer. Although this is not strictly necessary, unless you have some knowledge of this area it's probably better to stick with matched products.
•Remember that the 2nd stage is the part of the reg system that you put in your mouth so it must be comfortable for you.
Octopus or Alternate Air Source
The Octopus is another 2nd stage so the points highlighted above apply here also. The octopus traditionally has a bright yellow faceplate or purge button to be easily recognizable. The octopus may or may not have a venture control depending on its specification but it may be slightly 'detuned' to avoid inadvertent free flows. Some brands, Scubapro & AP Valves for example, offer an alternate air source that combines the 2nd stage with the BCD inflator. This means that in an out of air situation, the buddy would get your main reg and you would breathe from the AAS.
In recent years there have been great advances in the use of technopolymers and other lightweight composite materials, which have found their way into regulator construction. Some manufacturers use titanium in their efforts to reduce weight. These materials offer some advantage to the travelling diver, but may carry a prohibitive extra cost and are not always suitable for use in cold water or with mixed gases.
Most regulators are compatible with Nitrox up to a max of 40% 'out of the box' but this is at the manufacturers recommendation so please check the instruction manual. The use of Nitrox above 40% is moving into a more specialised area and further advice should be sought before making any purchase