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The
Salvus Oxygen Rebreather made by Siebe Gorman
General description of the
apparatus:
Two versions of the Salvus
where offered:
Salvus apparatus for use on Land
Salvus apparatus for use underwater
Written by Anthony Appleyard
1998
In the 1970's I got hold of two
Siebe Gorman Salvus ANS industrial and shallow diving oxygen
rebreathers, which I here call 'Salvus :A' and 'Salvus B'. It is a light
short-duration set notable for the unusual arrangement of its parts
compared with modern backpack rebreathers and most bag-on-chest
frogmen's rebreathers.
ANS' is 'Admiralty Neck Salvus';
there was an industrial-only type of Salvus with the same
cylinder-and-canister pack but the bag hanging down the left hip. A
member of HDS told me that despite the name my sets were made for sale
to civilians, not for naval use, else they would have a small anchor
mark on them somewhere. They are officially 30-40 minutes duration,
compared with frogman sets which are bigger and can last 4 hours or
more. They were made in the late 1940's but their rubber is as good as
new 50 years later: Siebe Gorman made good kit in the old days. This can
be compared with an Italian Cressi-Sub 2-hour-duration sport diving
oxygen rebreather which Captain Hampton of the British Underwater Centre
(Dartmouth, Devon, UK) bought in summer 1968: within a year its
all-rubber breathing bag was badly perished and he had to replace it
with a Siebe Gorman naval set bag, which is still as good as new; in
1970 I bought that set from him.
Salvus A
reached me as new, with all its spares in a red metal carrying case. It
is made of metal and rubber with straps of strong light brown Army-type
webbing, with no plastic anywhere except perspex mask and goggle plates,
but weighs only 21 pounds empty. Much of the metal seems to be brass, to
avoid rust or in case the diver has to work near magnetic mines. Here,
direction words refer to a wearer standing on land. A metal plate
carrying valvework is strapped to the left waist by a diagonal shoulder
strap and a waist strap, which each fastens with a small karabiner. It
has an adjustable steady-flow valve, and a bypass that can be cracked to
let more oxygen into circuit. Connected to it is a pressure gauge which
reads up to 150 bar. The waist strap carries a pouch for the pressure
gauge, and a small pouch containing blankers for the holes left by
removing the pressure gauge and the drain valve. A bunch of spare
gaskets was tied to the bypass. A canister for absorbent, and behind it
a small oxygen cylinder with valve upwards, are strapped to this plate,
and can be detached for refilling. On the bottom of the canister is a
drain plug operated by pressing its end in. The cylinder's connection
thread is like on blowtorch oxygen cylinders (5/8" BSP) but right-angled
and the opposite gender, for direct decanting. The black rubber
collar-shaped breathing bag is worn round the neck, mostly behind, and
has wide rubber straps which hang down the back and chest. The back
strap is brought up the crotch and buckled to the front strap. The bag
has a long tube which screws onto a connection on the canister. This
leaves most of the diver's chest and back free for other kit. The bag
material feels like old-type frogman's drysuiting and is probably
reinforced with cloth; I have no intention of cutting into it to find
out.
Its single breathing tube runs
from the canister to a mouthpiece, which as often in industrial
breathing sets has an extra flap outside the lips running into straps
fastened behind the neck. It has a manual shutoff valve to stop water
entering. A noseclip is tethered to it, and a separate pair of black
rubber and perspex goggles is with it. The breathing tube and the bag
tube are corrugated with brown cloth on the outside like on some gas
masks. This tube can be exchanged for a breathing tube ending in a
gasmask-like fullface mask with an inner mouth-and-nose mask. This also
has cloth on the outside. It has no shutoff valve, only a wooden plug
tethered to it by string. A spare gasket was tethered to each of the
corrugated tubes. This is the condition of a new set (but I have now
detached all loose spares and put them in a polythene bag so they cannot
be lost during a dive).
Salvus B
clearly has seen action underwater in the old days, perhaps with `Clyde
Diving' whose name is on the back of its maker's label that I found in
with it. It is sound and came in its red metal case, but:- The spare
gaskets are missing. I found a tin of mask demister in with it. The
pressure gauge and the canister's blowoff valve are missing and the
resulting holes are blanked off. The fullface mask and its tube are
missing. Its mouthpiece tube had lost its mouthpiece in an unrecorded
mishap but has its shutoff valve. In with it as an old replacement is a
shorter mouthpiece tube without shutoff valve which a member of HDS
identified as being off a very short duration set used to escape from
submerged Army tanks; a noseclip is fastened to it by two metal links.
The shoulder strap clip is strained out by the set's weight over use.
Its waist strap is missing (likely cut off by a plump civilian whose
waist it failed to meet round) and replaced by a diver's weight belt cut
from what looks like reinforced rubber conveyor belting.
In 1970 a man who I knew in a
diving club sold Salvus A to me, and Salvus B to a friend of mine who
(unknown to me at the time) used it for much lone sea diving on a
holiday touring Scotland, getting oxygen from garage blowtorches and
using Protosorb from a big batch of tins of it that he got from a
fireman whose fire station was changing from Proto rebreathers to
compressed-air sets; later I bought his set and the rest of the
Protosorb from him. I am angry that, after surviving intact all hazards
of much lone oxygen rebreather diving (including a reprimandable case of
diving to 60 feet with air deliberately kept in circuit, an action to be
totally avoided except in sets designed for mixture use), he became a
respiratory cripple due to routine work diving by that supposedly safe
method, surface-supplied open-circuit air, for that air was oily from
bad filters which his employers persistently refused to put right and
his lungs finally collapsed into severe emphysema; he later died of it.
He told me that he still would dive if his emphysema could be cured.
I had some rebreather training
with Captain Hampton at Dartmouth in Devon. He disliked fullface masks
and strapped-in mouthpieces, but I found with his Mark IV Amphibian in
1966 and his Cressi-Sub set in 1968 that the aqualung habit of not
bothering to keep the lips tight as any water shipped is easily blown
out, is inappropriate where brief laxness can get water in circuit and
wet the absorbent and end the dive. A naval UBA frogman set which I used
in 1973 in a short commercial diving course run by an ex-naval diving
instructor called Ginger Snell at Eye near Peterborough, had a naval
fullface mask with mouthpiece inside and such risks did not occur. I do
not use Salvus A's fullface mask in water, as it cannot be sealed
against entry of water when not being worn, so I use Salvus B's
mouthpiece tube fitted with a rubber Spirotechnique fullface mask that I
bought in the 1970's and was intended to fit onto an aqualung
regulator's mouthpiece stub instead of a mouthpiece. A Nemrod new but
old-style twin-hose aqualung regulator which I bought in 1991 has a
strapped-on mouthpiece with outside flap like on some old rebreathers;
in 1997 at Trearddur Bay I found that even if I go completely limp as if
unconscious that mouthpiece stays in and airtight.
Captain Hampton kept his
rebreathers covered when in the dive boat to keep sun off them so the
rubber breathing bags would not perish. A rebreather diver who is
correctly weighted in swimming, sinks when he runs out of oxygen and his
bag empties. Naval divers are trained to schedule their dives not to run
out of air, and in emergency can easily drop their weights and have them
replaced off the taxpayer; but most civilians are not as lucky. When
Salvus diving I feel much happier wearing also my Buddy Pacific diver's
lifejacket. I put the Salvus's body on, with fullface mask, then the
lifejacket (passing its belt under the Salvus's cylinder), then the
breathing bag (passing its front strap under the lifejacket). For when I
run out of oxygen I put a snorkel and halfmask in the Buddy Pacific's
big front pocket. For once and thankfully I do not have to `split my
weights' either side of a backpack cylinder as I put my weight belt on.
Post-1991 sport diving mixture rebreathers are designed to be worn in a
stab jacket.
The Salvus's bag is even further
forward than a frogman's set's bag and with a weight belt makes the
diver very stern-heavy. Some UK naval frogman's sets have on the back
well above the waist a pouch full of lead balls, which can released by
pulling a cord. With a Salvus and a lifejacket, with a belt weighted for
my single-cylinder modern aqualung, plus a 6lb pair of lead-shot anklets
inside my wetsuit chest, I am correctly weighted and have no
fore-and-aft buoyancy imbalance. With a light rebreather a diver is much
more agile than with an aqualung, as the set is lighter and better
streamlined in forward swimming and in rotating, and closer to the body
causing much less rotation-inertia. With a fullface mask I can talk
underwater without the noisy bubbles caused by talking into an aqualung.
As most of the bag is above the lungs in horizontal swimming, I have to
breathe in against a slight negative pressure, like with some old-style
twin-hose aqualung regulators. (A hint re finding what weights you need.
My friend above needed several Salvus dives to weight himself correctly
for it. I did it in one dive: I picked up stones until I was correct,
then after the dive took the stones home and weighed them.)
On my first Salvus dive its
steady-flow supplied oxygen much too fast and the dive was soon over,
and setting its flow regulator would have needed a flow-meter which I
have no access to. Now I keep the cylinder switched off and crack its
bypass at intervals as my bag gets low. My friend above found the same
with his Salvus. With a single-tube rebreather the diver must breathe
deeply to get his breath all the way to the canister. He should breathe
continuously so the absorbent gets as much chance as possible to work;
that won't waste air like with an aqualung! Avoid hard exertion and fast
swimming, so you don't build up carbon dioxide in circuit; too much
carbon dioxide can cause `shallow-water blackout'. The diver's breathing
tends to get fast when he has gone back from oxygen to air after the
dive, independent of any out of breath condition; this may disconcert
him until he gets used to it. A light rebreather is a easily-carried
handy friend in water where what you want to see or do is within the top
30 feet, particularly to get into small holes; but rebreathers are less
fail-safe than aqualungs.
This article is not a
training manual; get training from a qualified person.
UK naval work divers after 1945
sometimes used a Salvus with a heavy drysuit and weighted boots. I once
read a 1950's UK naval diving manual that said that the aqualung also
was to be used with weighted boots, mentioning fins only with
rebreathers, and Cousteau and sport diving not at all, as if fins and
aqualung contradict each other because fins were only for reaching a
target without being seen while aqualungs make bubbles.
The Salvus ANS is a good
well-designed well-made light short-dive set, and it is a pity that due
to chances of policy and commercial dislike of the unattractively
functional it is no longer made. At least my two are still ready for use
and have not been crushed and tipped or swallowed in batches by a naval
security incinerator as `unused or still fit for use but obsolete'. The
design could have been developed and seen descendants. With modern
strong polymers in suitable places the set could be even lighter. With a
modern high-pressure cylinder and a larger canister, duration could have
been increased to say an hour and a half. Within the Salvus layout of a
short-dive set with a kit pack on the left waist and a bag round the
neck, an automatic mixture variant with a separate diluent cylinder and
a ppO2 meter might even have been possible. If only a short dive is
needed, there would be no need to use as much absorbent as in a heavy
long-dive set and have to throw it all away afterwards. The user's back
(diving or industrial) is left free for say a tool powerpack or small
blowtorch cylinders or an underwater motor-and-propeller backpack.
British aqualung divers
unconcerned with other kit or old kit should remember that rebreathers
including Salvuses were a mainstay of British sport diving in its early
struggles to survive while Siebe Gorman kept its aqualungs expensive
beyond hope of most sport divers and cheaper foreign aqualungs were out
of reach beyond Treasury restrictions on taking or sending money abroad,
until from about 1956 sport divers' backstreet workshops making crude
but usable aqualungs from Calor gas regulators and RAF pilots' oxygen
cylinders brought sport aqualunging within reach of many more people
until Submarine Products Ltd in Hexham in Northumberland designed round
Siebe Gorman's patent and fully broke the blockade at last.
For 40 years British sport
diving organizations said `here be dragons' and pushed rebreather diving
so far from thought and club legality that sport diving books often say
`oxygen' and once even `rebreather' and expect readers to know that it
means resuscitators. A 1960's BSAC rule even forbad hardhat diving! But
civilian rebreathers are coming back - after world Communism fell in
1991, as if before that the defence labs requisitioned and made secret
every diving mixture rebreather patent that came for at least 20 years
when people could have been using and developing them instead of having
to tow bulky open-circuit cylinders on long dives such as for caving.
That is no fantasy: Captain Hampton invented a circular aqualung
fullface mask whose whole front window was a very big and thus very
sensitive second-stage regulator diaphragm, but when he patented it the
Navy requisitioned the patent and ordered him to secrecy; the UK navy
developed nitrox from the 1940's (but called it `mixture'), but kept it
secret while civilian deep divers struggled with air and its bends and
narcosis, until 20 years later civilians laboriously retrod the same
ground and we heard of nitrox. But civilian rebreathers are back at last
- but not the Salvus so far. |
