EIGHT years ago, when Diver first tested all the regulators on the market using the scientific methods of the ANSTI breathing machine, it was a great surprise to find that many regulators failed to meet the criteria for breathing resistance at 30m. Many manufacturers went away with their tails between their legs.
A year later, we were reassured to find that nearly every model still on the market was capable of reaching the recommended limit of 50m for air-breathing diving.
Today no one in their right mind would buy a regulator without the important and recently introduced CE mark, which indicates that it meets the breathing requirements laid down in European Union law.
These tests are undertaken using machines not dissimilar to the machine we used for our earliest tests. There are additional conditions for regulators that meet the criteria for the CE cold water tests.
Diver now compares regulators in sterile laboratory conditions and at depth in the sea. Unfortunately, some manufacturers and distributors have been less than happy with our findings. So what does a regulator do? Air is stored in the TPR (scuba cylinder) at very high pressures, and the first stage of the regulator allows some of that air to pass at a reduced pressure equal to about 8-10 bars greater than that of the surrounding water. This air passes down the medium pressure hose to the second stage where it is supplied on demand, matched to the pressure of the surrounding water.
To achieve this, the designer has to work with the physical properties of compressed air and water plus complex engineering constraints. Consequently, regulators have differing performances and different feels.
First stages tend to be either piston-type or diaphragm-type designs. Diaphragm types, such as the Spiro Supra, keep the water away from the working parts of the regulator first stage and so are the best choice for use in dirty or cold water. Apeks completely dry-seals the first stage of its top products. By and large, piston regulators sacrifice performance for simplicity. This means they are a better choice for those going to remote locations and who might need to do their own servicing. Scubapro regulators are favourites in such places, as are the piston-type designs from Oceanic.
Some top-of-the-line - and top-price - diaphragm regulators are now coming onto the market, such as the Mares MR22 Abyss Ruby, and promise to do away with servicing altogether.
The performance of an unbalanced piston design drops as the main cylinder pressure falls during the dive, but it is cheaper to manufacture and this is revealed in the price. Unbalanced piston designs are more suitable for use by those who do undemanding dives, and for schools that want an inexpensive item for use by trainees in safe, confined water. The Mares Nikos and Spiro Ranger are both popular.
The Poseidon Jetstream and Cyklon 5000 have been favourites with deep-divers for many years. With a side-mounted exhaust port, they can be used either right- or left-handed. These are diaphragm-design regulators that use a small servo piston to help reduce the initial effort to inhale, but their inter-stage pressures need careful setting-up during servicing, so they may not be suitable in remote areas.
As regulator designs have taken advantage of lightweight thermoplastics, they have become less appropriate for cold-water diving. This is because there are fewer metal parts, which act as a heat sink to conduct heat from the water to the much colder air. The air, already cooled in the submerged scuba cylinder, is liable to drop in temperature within the regulator, and this goes hand-in-hand with a drop in pressure. It can cause water within the regulator mechanism to freeze and interfere with the operation, with potentially disastrous consequences.
Regulators specifically designed for coldwater use include extra metal parts to act as heat exchangers, and Teflon-coated moving parts that are less likely to stick. The Spiro Supra Arctic, Oceanic Delta II Sub Zero, Apeks TX series, and Mares MR12 Akros are examples of this genre. However, no regulator can be guaranteed against the effects of freezing.
When you get a design that breathes easily, with the minimum "cracking pressure" needed to get the air flowing, you may find you want to tune down the performance. This can be particularly important if you want to fit a regulator to a full-face mask or underwater communications device. Many regulators come with a breathing resistance adjustment control to allow de-tuning. Because most regulators are extremely sensitive to ambient pressure changes, they can have a tendency to free-flow at the cusp between air and water.
The rush of air within the body of the second stage causes a suction effect which allows the pressure-sensitive diaphragm to be pulled in and the valve lever to be depressed.
Many second stage designs have an adjustable flap of material within them to redirect the flow of air back onto the inner side of the diaphragm, thus countering the effect. This flap is moved out of the air-flow by the diver once submerged.
Some regulators have a Venturi +/- switch, while others offer an alternative design solution to this problem. Mares regulators incorporate a by-pass tube which takes air directly from the second-stage valve to the uthpiece, avoiding the main body of the second stage and neatly side-stepping the problem.
A solution to the problem of bringing air efficiently from the first to second stages of the regulator is to use a wide-bore hose. This requires a special over-sized medium-pressure port. Other mp ports are used to supply BC, drysuit and the alternate air source.
The high-pressure port supplies air directly from the TPR to a submersible pressure gauge. Some regulators have more than one hp port, which is useful if a diver wishes to use an air-integrated computer alongside a mechanical instrument.
Many regulators can be oxygen-cleaned for use with nitrox, but we are now beginning to see oxygen-dedicated regulators. These are O2-cleaned at the factory and come equipped with O2-compatible O-rings and lubricants. They are colour-coded, normally in yellow and green, although some manufacturers use blue as their colour for nitrox.
Technical divers using a number of different gas mixes during the same dive must have their regulators clearly marked if they are to avoid fatal mistakes.
Regulators like the Apeks TX Nitrox are suitable for use with nitrox mixes of up to 100 per cent O2. However, if an O2-clean regulator is used with an ordinary compressed air supply, it immediately loses its O2-clean status.
Most regulators are fitted to the diver's TPR using the international A-clamp or yoke system. Some prefer to use the DIN screw-in system with its captive O-ring.