Easy Breathing By Steve Warren and Andrew Bell.
Apeks Marine is a British-based manufacturer whose product range enjoys success worldwide. Its breakthrough came nearly 20 years ago with the launch of the Manta side-exhaust regulator line. This was followed with the Octo Plus combined regulator and BCD inflator and a set of drysuit inflation and dump valves that are used by many leading drysuit manufacturers. Ten years ago the company launched a more conventionally-styled regulator (the T series) that has proved very popular. Apeks found other major players abroad who wanted to buy its equipment and market it under their own label. Last year the company was acquired by the Aqualung group which also owns US Divers, Fenzy, Technisub, SeaQuest, Nihon and Spirotechnique, but still operates as a totally independent manufacturer.

The TX100 is the flagship regulator in the Apeks line-up. The first stage is a balanced diaphragm design with two high-pressure outlets and four medium-pressure ports constructed from brass and finished in satin chrome. It feels substantial. It is available with A-clamp or DIN connections and can handle pressures of 300 bar/5,500 psi. The unit is completely dry-sealed against the outside environment, which stops freezing and corrosion.

The second stage is a venturi design, with a control for the flow assist and another for the spring tension which governs the cracking effort. (see How A Regulator Works box) These controls are designed to allow the user to customise breathing resistance to the needs of the moment. The second stage is pneumatically balanced which allows a less powerful spring to be used to help close the valve when the diver stops inhaling. The diver must work against this spring to initially open the valve to begin inhalation, so reducing its strength and help reduce cracking effort. A heat exchanger helps to prevent icing in the second-stage mechanism.

The regulator is sold ready for use with Nitrox up to a 40 per cent oxygen content.

The Testing

Formal testing took place off Gibraltar under often much less than ideal conditions. A five-strong team each dived the TX100 a minimum of five times to become familiar with the regulator, and scored it for comfort and performance against a standard Dive International questionnaire.


Each team member set up their hose layout to suit themselves. One of the medium pressure ports is a half-inch, high-flow fitting and is dedicated to the primary second stage. The others are 3/8ths. Apeks supplied the units with octopus rigs. Each diver used a direct feed (some used two) and a pressure gauge. This can be fed from a 7/16ths port on either side of the first stage. One drysuit diver would have preferred an additional port to accommodate his particular lay-out. The TX100 scored one adequate, two goods and two excellents for hose routing. 64 per cent.

Second Stage

The second stage is lightweight plastic. Normally we score mouthpieces for comfort but the units on loan were not equipped with the US Divers Comfo Bite mouthpiece that will be standard on consumer models.The Comfo Bite has a reputation as a ‘love it or loathe it’ product. For those who dislike it, a normal mouthpiece is easy to fit.

Two of the five divers felt that the rim of the exhaust tee was uncomfortable where it butted up against their lower lip. This can be a result of hose length, hose inflexibility and the height of the tank or routing of hoses (one tester used twinned singles that placed the Apeks to the far right, for example) influencing the set of the second stage.

Our team evaluated the TX100 second stage for ease of clearing both by exhaling and by using the large centrally-mounted purge button.

A unanimous five excellents. 80 per cent

We asked our team to try and get the TX100 to breathe wet by lying on their backs and swimming face-down.The TX100 gained strong scores across the team for dry breathing.

Again, all excellents. 80 per cent

Two of the team were using underwater camera housings and needed to get their masks as close to the viewfinders as possible. Regulators can get in the way, but the Apeks created no such problems.


Our in-water breathing tests are necessarily subjective. This is why we also include a machine bench test to recognised industry standards. Each diver set up the regulator to breathe as they wanted it to. Early on we ran into a problem, not with the regulators, but with the environment. An easy-going beach dive turned into a fight for survival against a very strong down current, with the sea-bed churned to near mud. At 25m half the team aborted and crawled hand over hand to shore while the balance were kindly rescued by the Gibraltar police boat. Such events are not planned but certainly placed the TX100s under extreme demand, which it met with flying colours. The regulators were, of course, dived deeper to assess performance, but nothing matched the demands placed upon them by that dive!

The scores were consistent regardless of depth (maximum depth was 45m, though most team members didn’t dive much over 30m).

Scores for ease of breathing were five excellents. 80 per cent

The octopus rig remains the most popular choice of alternate air source for recreational buddy pairs, so we also tested the TX100 on a moderate speed swim at 45m, with a diver breathing off each second stage and attempting to breathe simultaneously. This is designed to place the regulator under a realistic workload. We did not detect any difference in breathing effort.

Score was two excellents (this test performed by Warren and Olivero only). 80 per cent

The Test Team scores indicate that the TX100 provides consistent ease of breathing pretty much regardless of the demand a recreational diver might place on it. Even under the duress of working hard at depth or supplying an octopus user, the 100 provided all of the air demanded with minimum effort.

Total score 76.8 per cent


The high scores from our test team and the ANSTI performance figures should put the TX100 on your regulator short list.

•RRP £329 includes a bag worth £18

•We would like to thank the Gibraltar Tourist Office, Cadogan Travel and Monarch Airlines.


Assessing a regulator’s breathing performance objectively must be done on a machine. Few such machines exist worldwide and within the UK the best-known company carrying out such tests is ANSTI of Fareham, Hampshire.

During machine testing, a regulator’s breathing effort is measured. This is the work involved, firstly, to open the valve to admit air against the opposing force of the spring (cracking effort), and then to sustain an adequate volume of air and, finally, to exhale.

The following is one of the very basic tests in assessing whether a regulator meets European (CE) standards – if a regulator fails this test you don’t bother to carry out any further ones.

At a ventilation of 62.5 litres of gas per minute (representing a heavy workload, such as fast swimming) at 50m, the maximum limit allowed for the energy it would take for a diver to breathe is 3 joules per litre. The TX100 scored 0.75 joules per litre – an exceptionally good score

How a regulator works

Regulators are simply mechanical devices that reduce higher than normal pressure to a pressure identical to that surrounding the diver. The first stage must commonly handle tank pressure starting as high as 300 bar/4,500 psi at the start of the dive and reducing to perhaps as little as 30 bar/450 psi by the end. It has to consistently supply air to the second stage at around 9 bar/132 psi above the surrounding pressure. The second stage must then reduce this to ambient – anything from less than one bar/14.7 psi to 20 bar/294 psi involving a range of depths from a few metres to possibly several hundred The diver’s lungs are the switch that turns the air supply from the tank, via the regulator, on and off. Breathing through mechanically elongated airways, and using gases that become denser or thicker to breathe with increasing depth, while increasing the volume of air required for each breath, is not easy. Modern regulator designs aim to make breathing as easy as possible. Cylinder valves and regulator first and second stages are built to provide high flow rates and large volumes of air on demand. They are engineered so that cracking effort – the energy required to open the second stage valve against the closing force of the spring which stops the valve free-flowing – is minimised. Once the air starts to flow, it is routed so as to form a venturi effect. The air-flow keeps the diaphragm depressed and the valve open. This keeps the air flowing to the diver with almost no additional lung power required. Exhaust valves are designed to reduce exhalation effort to a minimum. Contrary to myth, high-performance regulators do not waste air, they save it. By minimising breathing effort, they reduce how hard the body must work in order to breathe, and its demand for oxygen.

The Team

Geoff and Alexandra Logan Vetrans of Dive International's 1997 Red Sea tests, who have dived in the Maldives, Malta, Red Sea and British waters and hold cavern diving qualifications in addition to being PADI Rescue Divers.

Andrew Bell Canadian underwater cameraman. Currently filming a pilot for a new diving series in the Red Sea.

Darren Olivero BSAC Instructor with a string of other qualifications and chairman of the Gibraltar Sub Aqua Club. Served as test team co-ordinator.

Steve Warren BSAC and PADI Instrutor, Steve has worked as a professional instrutor as well as being at one time training officer of the Gibraltar Sub Aqua Club.

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