Few pieces of dive gear are as hotly debated by divers as the choice of regulator.
Strangely enough, although frequently debated, few divers (or shop assistants for that
matter) can actually explain in detailed, logical & technical terms the reason they bought
what they use or what they recommend.
For many people new to diving, the choice of regulator is influenced by any number of
factors such as:
- Shop recommendations
- Instructor recommendations
- Club recommendations
“That’s what I used when I learned to dive”
While most sources can be well meaning, the advice given is not always good and there
may be ulterior motives, which you should be aware of. Dive shop assistants or owners
are often the worst people to get advice from as their recommendations are often
influenced by the margins that can be made on a particular product. Shop/Club
equipment is often at the lower end of the market in terms of performance and durability
due to cost constraints within the club. People will typically recommend what they use
without necessarily even knowing the type of valve they are using (e.g. balanced vs
unbalanced; piston vs diaphragm; upstream vs downstream). These three characteristics
have an important bearing on the performance, reliability and failure mode of the valve.
Some considerations when buying a regulator:
A) The regulator is the single most important piece of equipment you will buy, as it is
primary life support
B) They cost a fair bit of money, the wrong choice will be costly (it is because of this that
people are so adamant that what they bought is right, they don't want to admit that they
were wrong and don't want to splash out on a new one). The most expensive are not
always the best (in fact, the most expensive certainly isn’t the best).
C) An educated choice will mean that it will not need replacing for a long, long time.
Buy one that will "grow" with you and will still be useful if you ever get into more
adventurous/technical diving. It should be suitable for both single tank diving and, if you
ever wish to progress to it, twin set diving. Not all regulators are suitable for twin- sets as
the ports are not arranged suitably.
E) Avoid regulators with special fittings or non-standard parts. In the event of a problem,
non-standard hoses or parts can be difficult to get hold of – especially if diving abroad.
Some have unusual sized ports that make swapping things over difficult (e.g. a ½ inch LP
port rather than the standard 3/8ths inch), others have the ports arranged so closely that it
is very hard to get a spanner in to screw/unscrew them.
F) You should have logical reasons for what you buy – the regulator should meet certain
criteria - in short, you are looking at the following characteristics:
1) Reliability & "pedigree" from a proven track record
2) Performance (work of breathing & volume of as delivered at varying depths and
tank pressures)
3) Performance over time (some regulators perform well when brand new or just
after servicing, but quickly lose "tune")
4) Ease of hose routing (both for a single tank and for twin set)
5) Simplicity of design & failure modes (does it fail shut or open)
6) Servicing cost & ease of "in field" repairs or adjustments (e.g. being able to
unscrew the cover of the 2nd stage without tools to remove any debris)
7) Build quality
8) Price
Some Practical shopping Tips:
1) Know exactly what you want BEFORE you go into the shop.
2) Take little notice of the shop assistant’s advice (this may sound shocking at first
as we normally expect advice from shop assistants when buying things, after all,
isn’t that what they are paid for?) But consider that they may not have a broad
base of experience. They may not have much experience or knowledge of
regulators outside those they stock, they may not be a regulator technician, they
may not have read around the subject, and they make have little real diving
experience. What sort of diving have they done? Is their advice based on pooled
knowledge, or is it just based on their individual experiences?
3) You may be encouraged to buy the very latest model, but has this stood the test of
time?
4) Some models/brands have a higher profit margin and these may be “pushed” on
you.
5) You may be told that you should not mix different brands of 1st stage & 2nd stage.
There are some brands which should not be mixed (e.g. Poseidon), but others
actually work exceptionally well together (e.g. Apeks & Scubapro). If you wish
to understand why this is the case see the more technical section later.
7) Buy a 1st stage that has the DIN connection and buy the A-clamp adaptor
(between £20 and £35) for the DIN regulator if you regularly rent tanks (see
section on DIN vs A-clamp later). Remember that a DIN can be converted to be
used on a non-DIN tank in a few seconds by using the adapter, whereas, an AClamp
regulator needs to be taken apart by a technician and needs new parts to be
used with DIN.
CHOICE OF 1ST STAGE
Many 1st stages can be discounted simply because they do not allow for clean hose
routing – whether you are going to using it on a single tank or a twin set. The 1st stage
may not have enough ports for use with a dry suit, or they be arranged in such a way that
hoses come out at all sorts of angles (usually radially). You need a minimum of 4 low
pressure (LP) and 1 high pressure (HP) port.
You want one that allows the hoses to be neatly arranged so that large loops of hose are
not in your face or tempting entanglement. A large loop of hose can easily get hooked on
a piece of wreckage and either damage the hose or pull the regulator from your mouth.
Large loops of hose also create more drag in the water and can lead to jaw fatigue if
swimming against the current or when scootering. Ideally, all hoses should point down
thus minimising the risk of loops that will cause entanglements.
Various manufacturers have introduced ultra-light first stages that should be avoided.
These are made from aluminium and are prone to breaking and internal corrosion over
time.
The design of the 1st stage should be simple yet reliable. Experience has repeated shown
that over-complicated deigns fail more frequently and go out of tune more readily. You
are looking for quality of materials, workmanship & design.
Which 1st stage should I go for then?
There are few 1st stages that meet all the above requirements and the shortlist boils down
to just two:
The Apeks DS4 (with DIN fitting)
This is a “balanced” diaphragm 1st stage with four 3/8th inch LP ports and 1 HP port (see
Background section below for differences between diaphragm & piston 1st stages).
The “DS” stands for “Dry Sealed” as the 1st stage is completely environmentally sealed.
There is no turret and so the LP ports do not swivel. This still allows proper hose routing
and has one important advantage – it removes a failure point (the O-ring that is in the joint
between the swivel section and the rest of the first stage). If the turret fails on any
regulator the result is a catastrophic loss of gas.
The Apeks 1st stages are some of the very highest performing on the market.
Apeks also make the DST first stage. The “DST” stands for “Dry Sealed Turret”. This is
the one that normally comes with a TX50 or TX40 second stage. They both have the
same performance and internals except that the DS4 has no turret and so is safer &
cheaper too. The DST also has a single stupid ½ inch LP port that causes compatibility
problems with hoses (the others are the standard 3/8th inch).
Note that the DS4 is NOT the one that normally comes with an Apeks TX50 or TX40.
You have to ask for it specially. The Apeks DS4 currently can be bought for between
£90 and £100. This is cheaper than the DST, which sells for around £110.
Stay clear of the Apeks DS1 as it only has one LP port and 1 HP port and so is only good
as an argon suit inflator regulator. The new Apeks first stage that comes with the TX100
may be all right but it has yet to pass the test of time.
The Scubapro Mark 20 (with DIN fitting)
Unlike the Apeks, the Scubapro is a piston 1st stage (see Background section for more
detail). The Mark 20 has 5 LP ports and 2 HP ports. The big advantage that the Mk20
has here is that there is a port at the end of the regulator thus facilitating a wide variety of
hose routings. The Mark 20 is also very high performing and the design is very robust.
They do have a swivel turret and so they do have an extra failure point than the DS4.
That said, their record is good and they are the preferred choice for stage and
decompression bottles. This is because a piston design can better withstand any water
accidentally getting into the HP chamber than a diaphragm design. Water may get into
the HP side either if you left the cylinder for a long time under water and the regulator
got depressurised (e.g. left in a cave for a “set-up stage dive”), or if you had to unscrew
and swap the 1st stages over underwater.
Avoid the Ultra-Light Version (Scubapro Mk20 UL) as this is made of aluminium and is
more brittle than the normal brass ones and some have been known to corrode internally.
I, and many other people in my diving groups, have opted for the Apeks DS4 for
cylinders that are back-mounted (benefit of no turret & sealed) but retain the Scubapro
Mark 20’s for cylinders that are side-mounted (simple robust piston design).
Which 2nd stages should I go for then?
Whether you are single tank diving or twin set diving, you will need two 2nd stages, one
as a primary (the one you breathe) and one as a backup (the one you don’t normally
breathe).
The requirements of the backup and primary are quite different and so the characteristics
you want are also different.
The Primary second stage
For the primary you want a reliable but high performance regulator. The Work of
Breathing (WOB) should be low (inhalation & exhalation effort) so as to prevent
respiratory stress and prevent CO2 retention. It should ideally be adjustable such that the
cracking pressure can be adjusted to be harder or easier to suit conditions. For example,
in a head down position whilst static in a flow, there is a tendency for the 2nd stage to leak
a small stream of bubbles. In this situation you might increase the cracking pressure. On
the other hand, when swimming hard against the flow/current, you want the breathing
resistance & cracking pressure low.
Poor performance can lead to Co2 build up in your lungs and body. Co2 worsens nitrogen
narcosis, heightens oxygen toxicity, is contributory to DCI and gives a headache, just to
mention a few. High work of breathing actually increases gas consumption.
In order to get a high performing 2nd stage, it ideally needs to be “balanced” (I
recommend reading the section later on balancing of 2nd stages). 2nd stages, such as the
Scubapro G250 or Apeks TX50, where the cracking pressure is adjustable are of the “airtube”
design and are “balanced”. These two 2nd stages have an extremely low WOB and
have been extensively field tested over he last 8 or so years. The more recent Scubapro
G500 and G600’s may have slightly better WOB but they have both been subject to
product recalls (as do many other brands) and the fronts do not unscrew easily. They also
have fewer metal parts, which might reduce their cold water suitability.
Poseidon 2nd stages are “upstream” (see later section) and if the LP seat or spring fails
they fail closed – this is shear stupidity when it comes to 2nd stages. There popularity
among die-hards harks back to the days when they were a relatively good performer, alas,
the rest of the world has overtaken them with higher performing & more reliable
regulators.
It is also important that you are able to unscrew the front of the 2nd stage off, should
debris get trapped in either the diaphragm or exhaust valve (mushroom valve). 2nd stages
such as the Mares do not allow one to do this, nor is their breathing resistance adjustable.
The back-up second stage
You do not want a very high performance, sensitive regulator that is not in your mouth
because it will be more likely to freeflow.
You therefore want a simple “unbalanced” 2nd stage for the back up. Because it is
unbalanced you won't get into that positive feedback loop whereby the air gushing out
assists in opening the valve, and so the freeflow continues. When descending a shot line
in a current (or diving in any current for that matter), the water flowing over the 2nd stage
can trigger a reduction in pressure in the 2nd stage thus opening the valve causing a
freeflow. The cracking pressure for the back-up should therefore be higher than your
primary.
When considering all the contenders in the market, there aren’t actually that many that
are unbalanced, have the simple so-called “classic downstream” design, are compact and
have a front which you can unscrew.
The Scubapro R380 does meet these criteria and being compact goes under the chin well
without getting in the way. It has been extensively field-tested. It sells for around £80.
The R380, G250, TX50 and TX40 all run off the same Intermediate Pressure (between
9.0 to 9.6 Bar). The Mark 20 and Apeks 1st stages also operate in this range (but can be
detuned – see later). They are therefore interchangeable and so you can have an R380 off
of an Apeks 1st stage for example.
Summary Recommendation
The two systems that seem to fulfil all the above are therefore as follows:
1) Apeks DS4 1st stage with TX50 primary 2nd stage and Scubapro R380 back-up,
or;
2) Scubapro Mark 20 1st stage with G250 primary 2nd stage and Scubapro R380
back-up
Preventing Freeflows
Freeflows are the most likely regulator problem an inexperienced diver will encounter.
They result from a combination of bad technique, regulator set-up and regulator choice.
Fortunately there are some easy steps to avoid them:
1) ALWAYS pass a regulator to someone else with the mouth-piece facing DOWN.
2) Avoid repeated purging and breathing from regulator whilst either the 1st stage or
2nd stage is in the air (air temperature is usually lower than water).
3) Test the regulator once early on in the kitting up process and then leave it until
you are submerged.
4) Lower the Intermediate Pressure (IP) to 8 Bar (120 psi). This makes the 2nd stage
slightly less sensitive but will ensure that the force that the spring in the 2nd stage
is working against is less and so the valve is closed more easily. This is certainly
recommended for the backup regulator on the left post if using a twin-set.
5) Buy a regulator that is cold water protected. This might be the Thermal Insulation
System (TIS) that Scubapro uses (cover parts with Teflon to prevent ice crystals
forming), or better still, totally sealing the 1st stage off from the water. Note that
if the 1st stage is fully sealed but the 2nd stage is set to be too sensitive, or the user
keeps purging the 2nd stage before use, the regulator can still freeflow from the 2nd
stage.
6) Keep your regulator serviced but check it out in the pool before using it in cold
water.
7) Avoid taking a breath at the same time as either inflating your suit or stab
jacket/wing (this causes less gas to rush from the 1st stage - as this gas expands it
cools).
Explanation for 1) above: the difference in the water pressure from the diaphragm to the
top of the mouthpiece (despite only being about 2cm to 3cm apart) is sufficient to open
the valve.
So, if you pass a regulator with the mouth piece up, the pressure will be greater at the
diaphragm than at the mouth piece and the valve will easily open as it is being assisted by
the water pressure - possibly leading to a free-flow.
Whereas, if you pass a regulator with the mouth piece down, the pressure will be less at
the diaphragm than the mouth piece and the valve will not open so easily because it is
working against this pressure and thus less likely to free-flow.
Submersible Pressure Gauge (SPG) vs Console
When buying the regulator you will need to buy a contents gauge (Submersible Pressure
Gauge - SPG). Most divers around the world use one of those large consoles that contain
the SPG, a compass & perhaps a computer or depth gauge as well. Whilst this seems a
good idea superficially (keep all those handy things in one place), it does have some
serious drawbacks:
1) They are necessarily large and get in the way and drag along the bottom or catch
on wrecks. How often have you seen a console get dragged along or clonk
things? Diving in silty overhead environments with such consoles stirs up silt.
2) The computer is better suited to being on the wrist where it can easily be read
whilst reeling in a DSMB on the ascent for example. The face & contacts of a
computer are reasonable delicate and could do without being regularly clonked!
3) The rubber boot of the console covers the connection between the HP hose and
the actual SPG. This has three distinct disadvantages :–
· Firstly, the rubber prevents grit, dirt and saltwater being properly washed off
when the console is cleaned. Even a good soak in warm water fails to get rid of
all this salt and grit as an inspection under the boot will bear testament. The little
swivel pin that sits in the joint between the HP hose and SPG, has two small Orings
at either end, this will wear down faster if not cleaned properly as grit acts
as grinding surface. With no rubber console it is easy to thoroughly clean.
· Secondly, should a small leak occur in this area, it would not be immediately
obvious from exactly where it is coming. It takes time for the small bubbles to
find their way out of the console and during this time you are descending deeper.
With no rubber console any leaks are immediately visible and it is clear to see
where they are coming from.
· Thirdly, should there be a more dramatic leak from the HP hose whilst on the
boat/shore it is very easy to get access to the joint with a spanner when there is no
rubber console and so the problem can very often be fixed there & then without
missing the dive. With the rubber console in place this job takes much longer and
may be impossible with cold hands.
What sort of SPG do I need then?
All you need is the SPG itself, the compass is better on the wrist or stowed in a pocket
until needed. The depth gauge is part of your computer and should also be wrist-mounted.
The SPG to try & get is the UWATEC "Master Diver Pressure Gauge" shown in website
below.
http://www.uwatec.com/english/framem04.htm
To quote website:
"The Master Diver is also anti-magnetic with a chrome-plated, solid brass case, highly
luminous dial face and a scratch resistant, chemically hardened, mineral glass lens. The
spiral bourdon tube measurement system is accurate within +/-5 bar from 0 - 300 bar.
Also available in 5000 psi."
Note that the "Uwatec Submersible Pressure Gauge" (one below on the website) has a
plastic face. Plastic is not as good as on deep dives as they flex & make the needle stick.
Now you won't be diving to a 100m for a while but the glass face doesn't scratch like
plastic and it is clearer to read. Furthermore, a brass case resists the water pressure at all
depths better and so the gauge tends to be more accurate than the plastic cased SPG’s.
Unfortunately, the above SPG is now very hard to get so you must look for alternatives.
Try to find one with clear numbering, a brass case and, if possible, a mineral glass face.
The HP that you normally see in shops is in the region of 36 inches long. This is
excessive as can be seen from all those holiday brochure photos, where it dangles down
too far. Ideally the HP hose should be 24 inches long and clipped off to the left near the
left hip using a large stainless steel piston clip. Here the SPG & HP hose is streamlined,
it won’t dangle and it is protected. Practice is needed so that you can quickly unclip it
when needed. The piston clip should be held by a cable-tie and O-ring which provides a
quick break-away if needed or should the HP hose accidentally get caught (will prevent
excessive strain on HP hose).
BACKGROUND
The task of the regulator 1st stage is to deliver a constant Intermediate Pressure (IP) above
ambient pressure regardless of depth and regardless of tank pressure (in the case a
balanced 1st stage). In a non-balanced 1st stage the IP will either drop (as with
“downstream” designs) or increase (as with “upstream” designs) as tank pressure drops.
In an “upstream” valve the seat (rubber/plastic surface that forms the seal) mechanism is
upstream of the orifice that it is closing (can apply to both HP seat in 1st stage and LP seat
in “2nd stage). If the valve fails it will generally fail closed.
In a “downstream” valve the seat (rubber/plastic surface that forms the seal) mechanism
is downstream of the orifice that it is closing. If the valve fails it will generally fail open.
There are broadly two types of 1st stage mechanism:
Piston first stages
Here the water pressure and air pressure act on a piston that transmits the pressure to
open & close the valve. If the piston is orientated perpendicular to the incoming airflow
of the tank, then the tank pressure has little bearing on the force on the piston – this is
how a piston 1st stage is “balanced”. Pistons allow a large volume of air to be delivered
and are simple and robust in design.
Because the piston has to be exposed directly to the water, you will always find little
holes in the 1st stage allowing the water to act on the piston. These holes are the telltale
sign that the 1st stage is of the piston type. Because this chamber is exposed to water, for
diving in very cold water, the 1st stage has to be cold water protected in some way. For
pistons this is achieved by either filling this space with silicone grease or by covering the
moving parts with a non-stick compound to prevent ice crystals building up. Scubapro
call this latter system TIS and use Teflon to coat the parts (as in the Mark 20).
Scubapro have specialised in the design of piston 1st stages since the early 1960’s and
piston regulators have struggled to achieve the same performance with the piston design.
It will therefore come as no surprise to learn that the pinnacle of piston 1st stage design is
the Scubapro Mark 20. It definitely has a long pedigree.
Piston regulators are almost without exception “downstream” in design and so, unless
they are “balanced”, the IP drops as tank pressure drops (when the tank pressure is high it
has a tendency to assist opening the valve and so it takes a higher pressure in the LP
chamber to close the valve to overcome this. When the tank pressure is low the spring
closing the valve has an easier job as the pressure of the gas it is opposing has dropped
and so the valve closes at a lower IP – easier to understand with a diagram!).
More importantly, because they are “downstream” in design, if the high pressure O-ring
fails, the valve will be forced open and so HP air is allowed into the LP chamber and into
your hoses and 2nd stage. This can cause a LP hose to rupture (they are designed for 10
bar not 200 bar!).
The disadvantage of the piston design is that for very cold water, or polluted water, it is
nice to completely “environmentally seal” the 1st stage thereby allowing no water to the
internals. A diaphragm design 1st stage can do this, a piston cannot.
Diaphragm 1st stage
Here the HP valve seat is pushed forwards or backwards to close or open the valve via a
small rod connected to a flexible diaphragm. This means that there is no need to have
holes in the 1st stage and so these valves can be completely sealed making them ideal for
polluted water or very cold water. All diaphragm 1st stages are “upstream” in design and
so they fail closed.
Like the piston they can be “unbalanced” or “balanced”. Unlike the piston 1st stage, the
diaphragm 1st stage is balanced by allowing air to both sides of the HP seat. The IP of an
unbalanced diaphragm will gradually increase as tank pressure drops (at high tank
pressures the air assists in closing the valve, as the tank pressure drops the valve is held
open longer and the IP creeps up). Note that this is opposite to piston 1st stages.
With diaphragm 1st stages you are looking for simplicity and regulators like the Apeks
range, tend to have a static orifice and a moving seat (in theory you can have a moving
orifice and a static seat and both types are common). The Apeks is robust in design and
has some neat but simple solutions, such as the way in which they are balanced. They are
also very easy to dismantle and adjusting the IP is a piece of cake. Apeks service kits are
also cheaper than many other brands, yet their reliability & performance is probably the
best of the diaphragms.
The above diagram shows an Apeks DST 1st stage (with swivel turret & A-clamp
unfortunately!)
Note that the air is allowed on both sides of the HP valve in the above diagram, so tank
pressure has no bearing on Intermediate Pressure.
Common 1st stage Problems
Most 1st stage problems relate to a “creeping” IP that causes the 2nd stage to eventually
start dribbling bubbles. This is caused by the HP seat not quite seating properly and so
HP air can leak into the LP chamber. The IP thus creeps up until it is too much for the 2nd
stage LP seat to hold back and so a stream of bubbles results.
Apeks have a “forgiving” seat, that I, or any member of the email list, have never heard
of leaking, other brands such as Poseidon have notoriously poor HP seats and commonly
suffer from creep. The Poseidons I had from 1993 to 1995 crept on 3 separate occasions
even with annual servicing.
“Balanced” vs “Unbalanced”
To get high performance out of a regulator, the 2nd stage has to be sensitive. That means
the spring pressure that closes the valve (pushes low pressure seat onto a crown/orifice)
has to be weak or assisted.
Balancing in the 2nd stage is whereby the pressure of air coming from the 1st stage
(around 9.0 to 9.4 Bar) is used to assist in opening the 2nd stage valve. Air BOTH sides
of the actual LP seat (where the seal is formed) is at this intermediate pressure and so the
spring only has to be strong enough to reliable close the valve (because the gas on the
downstream side of the LP seat is assisting with closing the valve). The spring can be
therefore be weak. Because the spring is weak the inhalation effort is small, thus high
performance. The diagram below of a TX50 2ns stage will aid explanation; Apeks call it
“pneumatically balanced”.
With an unbalanced 2nd stage, the spring has to be stronger as it does not have the
assistance of the 9 Bar of air behind it. The spring has to be strong enough to close the
valve against the interstage/intermediate pressure without the assistance of this gas
pressure behind it. This stronger spring means that performance is poorer.
Balanced is therefore desirable for your primary regulator (the one in your mouth) as it is
higher performance due to the sensitivity of a weaker spring. This is the case with the
G250 or TX50. The TX40 is also balanced but you cannot adjust the spring pressure as
you can with the TX50 or G250.
The balanced type will more likely stay in free-flow should one occur. This is because the
spring will be stronger on an unbalanced 2nd stage (unless you swap out the normal
spring on a balanced 2nd stage for a stronger one) than a balanced 2nd stage.
Advice on DIN fittings and A-Clamps.
Before outlining all the benefits of DIN fittings, I would like to dispel some myths:
Myth number 1: “If you buy DIN fitting regulators you won’t be able to use them
abroad”.
I have dived using DIN fitted regulators since 1989 in the following Countries without
EVER being unable to use my regulators (UK, Bahamas, Barbados, Australia, Egypt,
Jordan, Maldives, Spain and the USA). People I know have had no problems in many
others.
The reason is that the vast majority of cylinders manufactured since the mid 1980’s have
an insert in the pillar valve that can easily be unscrewed using a hexagonal alum key so
that the DIN fitting can be screwed in. This takes about 5 seconds. In the couple of
instances where this has not been possible (e.g. Maldives), I have simply used a yoke
adapter (A-Clamp) that simply screws onto my DIN fitting. Also a 5-second job. The
point is that, DIN is very quickly adapted to an A-Clamp but an A-Clamp not so easily
adapted to a DIN (but can be done for about £30 – 40 by a dive shop).
In the UK (where I do most of my diving) I have my cylinders set up permanently for
DIN.
Myth number 2: “DIN fittings are hard to undo”.
This was the case with some Poseidon regulators (until you learnt the knack) but is not
the case with other brands of regulator (Scubapro, Spiro, Apeks, Oceanic, Sherwood,
Mares etc).
Myth number 3: “DIN fittings are more expensive”.
This is simply not the case. The price of a DIN and A-Clamp regulator are the same
bought from new.
Myth number 4: “DIN fittings are only for “tekkies” and they offer no advantages to
the recreational sports diver”.
After reading the various benefits that follow ask yourself this again:
1) The first advantage that a DIN fitting has over an A-Clamp is that it is a more
secure and positive connection. If the first stage or pillar valve is knocked
(against wreck/cave/on boat) the connection is much less likely to fail. If an AClamp
is knocked with reasonable force the seal can be broken between the
regulator 1st stage and the cylinder pillar valve.
Most experienced divers would have seen at least one occasion where, on
pressurising the regulator, a hiss was heard as gas escaped out of the tank between
the O-ring and regulator 1st stage when using an A-Clamp.
This is usually put right on the boat/shore, but how much confidence does this
give you about the strength/integrity of the seal? About the A-Clamp - “It might
simply take a few goes to get it to seal right”. What sort of confidence does this
give you!!
2) The O-ring on a DIN fitting is trapped and cannot burst out. Similar comments
as 1) above apply. Again, many an experienced diver has seen the O-ring burst
out the side of an A-Clamp.
3) For the above reasons DIN fittings can be rated to 300 Bar, A-Clamps can only
rated to 232 Bar. What does this tell you?
4) The O-ring on a DIN fitting is part of the regulator not part of the tank. It
therefore gets looked after better and is kept out of the sun and salt water. Sun &
salt water cause O-rings to harden, crack and thus form a less good seal. Whilst
on your Red Sea live-aboard, you may check the O-ring on the tank each time you
select a new tank, but what is the betting that you will still use an O-ring that
“looks OK” but is actually past its best. Is your buddy as thorough? This is a
major failure point and not fun with a single tank!
5) The DIN fitting is more compact and does not have a knob at the back. The
knob at the back of an A-Clamp is a great place for line to entangle. The worst
place to be entangled is behind you. With a single tank configuration the pillar
valve is hard to reach, never mind untangle line from.
When you consider the above points together you have to ask the question: “What are the
benefits of an A-Clamp?” because there are certainly some very serious disadvantages.
So much so that some training agencies ban A-Clamps on back mounted cylinders whilst
in any overhead environment (i.e. wreck, cavern or cave). Frankly, I can’t think of any
advantages to using an A-Clamp and would be interested in hearing any from other
people.
