|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.
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
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.
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
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
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
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,
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
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.
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
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.