Mailing List Archive Mailing List Archive
On Jan 8th Ian Horsfall & Steve Millard went on a 1-day 'tryout' course to have
a look at the Mk 4 Cis-Lunar rebreather & to find out more about the Mk 5 model
soon to be put onto the techdiver market. Although 1 day is *much* too short a
time to gain a full appreciation of a pretty spectacular piece of equipment,
the
following report gives some of our first impressions & may be of interest to
others on the techdiver listserver.
The course was held by Kevin Gurr & Jim Booth of Cis-Lunar Developments
Ltd., at Poole in Dorset, England. Cis Lunar have set up a techdiver training
centre with a large 5m deep test pool and a fairly extensive stock of techdiver
equimpent not normally available in the 'normal' dive shop.
En route from Liverpool to Poole we stopped off at two other diveshops
specialising in technical diver needs, one in South London & the other in the
south of England. We were suprised to hear very opinionated views lodged
against other commercial interests within the English technical diving
community, and of Cis Lunar in particular. Stories I have heard on this
occasion and in talking to other "experts" at other times have included :
"The Cis-Lunar will never reach the market, there is too much litigation
in the USA that will never be resolved"
"Various customers in the USA have had their deposits returned
already"
"The Oceanic rebreather will never work because the counter-lung is too
small"
"The Prism will never be sold because the English Health & Safety
Executive won't let it"
"The liability insurance on any rebreather will price it out of the
market"
"One techdiver centre specialising in Nitrox only has one bottle of O2
to work with when you go behind the counter...you call this a specialist ?"
....and so on, & so on....
The only way to *REALLY* find out what the truth is behind the fiction
is to go and see for yourself, to listen to what is said by the people involved
themselves (rather than about them by others...) & where statements are made
that are regarding future products/performance etc..to wait and see what
eventually materialises. What we saw at Cis-Lunar was impressive !
********************************************************************************
Editorial Note
--------------
I can see us being *seriously* flamed for airing some of the above
statements. I expect that none of the suggestions are in fact true or even
remotely approaching the truth...but this is the information we have been given
at one time or another. The best way to refute a rumour is to bring it out
into
the open & then to give the *real* story.
********************************************************************************
So it was with some misgivings that we arrived at Cis-Lunar to see the
Mk 4. I am pleased to say that the course given by Kevin & Jim was one of the
most professional diving courses I have had the pleasure to be on & can
thoroughly recommend it to anyone able to take it. The cost of the full 1-day
course was 85 pounds each. This has gone up to 95 pounds for new courses in
1995 (Hmmm ! That's inflation for you...). To data about 50 divers in England
have been on a Cis-Lunar course. The course commenced with a
historical overview of rebreather development, from the 1700's to WW 1, WW 2 &
to the present. (Much of this I had seen on a previous "Prism" rebreather
course given by Peter Ready, but was mostly new to Ian). Advantages and
disadvantages of oxygen rebreathers, semi-closed rebreathers and fully-closed
rebreathers were then reviewed. A 3rd lecture was concerned with the physics &
physiology of rebreathers.
At this point the course became *especially* interesting as the
component parts of a closed circuit rebreather were discussed, with particular
reference to the Cis-Lunar Mk 4. This was what we had come to see & hear
about.
We also heard a lot of preview details of what to expect on the Mk 5 when it
becomes available. This is expected "around May '95".
Details of the Mk 4 we were interested to find out were as follows :
The mouthpiece is connected to corrugated rubber inlet & outlet hoses,
protected with a "ballistic" nylon outer cover to protect against accidental
damage. Within the mouthpiece is a second stage regulator. A simple rotating
switch on the front of the mouthpiece converts the rebreather immediately into
open circuit mode. In the event of a *dire* problem, it was recommended that
this should be the first action to take & gives 'thinking time' to work out
what
to do next. As we saw later, there was almost no plausible scenario that the
Cis-Lunar couldn't deal with & still function. Although open circuit use of
the
on-board gases isn't going to last very long at depth, it was nice to see this
option there. (I later found this facility to my benefit during the practical
dives using the Cis-Lunar Mk 4. I managed to push away from the side & briefly
go underwater before Jim had fully turned all systems on...my fault ! As I
went
down, the counter-lung collapsed with pressure and breathing became tight. A
simple rotation on the mouthpiece to open circuit enabled me to return to the
surface & rectify my mistake effortlessly)
Also attached to the mouthpiece was the 'head up display' (HUD),
comprising a small metal box containing 4 led's. Each led can display green,
orange or red & indicated "OK", "a small problem" or "a serious problem".
The 4 led's indicated
- PO2
- Battery life
- CO2 (I'm not sure if the CO2 led is to be available on the Mk 5)
- Decompression
For example, if the actual PO2 varied by more than 0.2 bar from the 'set
point', one led would turn from green to orange & eventually to red. This red
led would be flashing for a hypoxic PO2 & constant for a hyperoxic PO2.
A nice touch was that every 5 minutes or so all led's flashed from green
to red 3 times. This was a "wake up" call, just to get your attention and
check
you were still monitoring the HUD. It certainly woke me up when it flashed !!!
The 'all-flashing' led indication is the same as the 'shit has hit the fan'
indication. It stops after a couple of seconds...but it certainly get your
attention !!
Where each corrugated hose from the mouthpiece meets the shoulder blades
of the diver are two efficient water traps. In the event that the mouthpiece
is
removed underwater without switching to open circuit, the water entering the
exhaust hose will be diverted into the counterlung before it reaches the CO2
scrubber stack. Once here, it can be easily routed back out to rejoin the
water
outside via an automatic dump valve at the base of the counterlung. Water will
not enter the inlet side of the breathing loop due to a simple mushroom valve
provided to ensure a circular flow of breathed gases.
The CO2 scrubber stack normally uses sodium hydroxide, which give about
6 hours of diving, at any depth. Lithium hydroxide can be used to extend this
time to 8 hours, but has cost and handling penalties. The cost of a pre-packed
scrubber canister was estimated at about 8 pounds (English currency), giving a
dive cost of 2 pounds/hour, including helium/oxygen gas costs.
In the event that water got into the breathing loop and got past the
water trap, a water-repellant/gas-permeable membrane around the stack prevents
a
"caustic cocktail" from occurring. Unlike other membranes, the one used in the
Cis-Lunar can tolerate a substantial hyperbaric pressure and still keep out
water. The special hydrophobic membrane was developed by NASA &
means that you could flood the set by throwing away your mouthpiece, you could
decend "several metres" and you could *still* put the mouthpiece back in, &
vent
gas into the counterlung & stack to blow out the ingressed water. The
Cis-Lunar
would then carry on working as though nothing had happened. Hmmm....*that's*
impressive !
The counterlung itself is split into two halves & is located wrapping
over both shoulders. This (patented) counterlung location meant that there was
absolutely no 'hydrostatic effect' in almost any diver orientation. Inhalation
and exhalation was effortless...just like breathing in fresh air (apart from
the
mild taste of "Dettox" dissinfectant....!).
On the right hand side of the counterlung was a diluent inlet valve
located inside the counterlung. If the counterlung starts to collapse then gas
is automatically fed in. A manual over-ride can also vent diluent into the
counterlung by pressing onto the switch located on the outside right hand side
of the counterlung.
Three oxygen cells are used to monitor the PO2 within the counterlung
and to keep it close to the 'set point'. If any one of the three disagrees
with
the other two by more than a small tolerance it is rejected & the system works
with the remaining two cells. An error warning is indicated to the diver.
However, if the errant cell comes back into line then the Cis-Lunar will accept
it again.
There has been a recent thread on techdiver regarding the cost of
replacing O2 cells. We were informed on the course that all three cells would
have to be replaced every 2 years at a cost of about 40 pounds each. That
doesn't sound too bad to me. That works out at 5 pounds a month.
The Cis-Lunar must be returned every 2 years for a mandatory service.
This is expected to work out at about 300 pounds (I think), *including* the
cost
of replacing all 3 O2 cells.
Also inside the back of the Cis-Lunar Mk 4 were 2 two litre cylinders
containing O2 and diluent respectively. Using a metabolic oxygen use rate of
0.5 litre/minute...a 232 bar 2 litre cylinder will last about 15 hours, at
*any*
depth. In principle the diluent cylinder only has to fill the counterlung once
at depth (& some of the inert gas will be absorbed into your tissues). Hence
depending upon the dive depths, I suppose this would last about 5 to 10 dives
or
so. If you lose gas from the system by excessive mask clearing, breathing out
through the nose or "saw-tooth" diving then the two litre diluent cylinder will
be quickly emptied.
Also part of the Cis Lunar was a 'gas block' located on the LHS. A
master switch enabled the oxygen to be manually turned off (in the event of a
oxygen feed solenoid failure). This was made deliberately difficult to do by
recessing the switch into the block. Turning the oxygen off isn't as drastic
as
it sounds and is *nothing like* someone turning your open circuit gas off. As
part of the practical drills in the later part of the course we practised
'driving' the Cis-Lunar manually after an O2 switch off. Using a set point of
0.6 bar...after about 2 or 3 minutes this had *crawled* down to 0.5 bar.
Getting bored, I then started trying to swim fast around the tank in an effort
to use up oxygen (!). After what seemed like ages later it crpt down to 0.4
bar. On the side of the gas block were two manual injection switches..one for
O2 and one for diluent. A short depression of the O2 switch brought the PO2
quickly back to the desired set point of 0.6. It's *that* easy !
On the end of the gas block are two input connections allowing up to two
side mount external cylinders to be switched into the rebreather system. These
might be used if the 15 hour capacity of the inboard gases isn't enough (!) or
if you wish to switch to another gas cocktail. For example, a heliox dive can
take advantage of significant decompression reduction (typically 30% less) if a
switch is made to nitrox for decompression. This is in addition to the
reduction from open circuit decompression times gained by breathing a constant
PO2 mix & hence decompressing on less & less diluent % as the depths reduces...
ending up on 100% O2 at a depth of 6 metres.
The use of external gas cylinders can also provide a 'sensible' open
circuit bailout facility & provide additional redundancy for example if an
O-ring failed on the in-board gas cylinder or 1st stage.
Leaving the best until last, brings us to the Cis-Lunar computers &
control system. The Mk 4 has *three* independant computer control systems &
three independant display systems. If they all go wrong...then it really isn't
your day !!! When were you last struck by lightening...twice !!
The main display block has many more features than we had time (or were
allowed ?) to see. The O2 set point can be input at the beginning of the dive,
and varied at any point during the dive..with appropriate locking safeguards to
prevent an accidental change. The computers will take account of this in
calculating decompression times. Both nitrox or heliox diluent can be used.
The diluent normally is a breathable mix at depth to allow open circuit
operation. A gas switch possibility, via the gas block, to an alternative
diluent (and back again if you wish !) is incorporated into the decompression
model. With over 25000 (I think) hours spent by various divers to
date on tne Cis-Lunar, they must have gotten the deco model right by now.
On the main display during diving is shown :
- Dive time
- Depth
- All 3 PO2 cell values + a large text indication of the average
- Total time to surface, including decompression
- Contents of both on board cylinders
- Battery life indication
_ plus some more I'm too dazed to remember (!)....it's a lot to
take in @ one go !! Many different menus we didn't get time to study can also
be accessed by the main display, by pressing watertight buttons on the end of
the block.
The HUD display has been described above & could be used alone to drive
the rebreather.
In addition is a 'passive display' of the 3 PO2 cells. In the event of
a complete computer system failure of all the control systems...on a wrist
mounted display using a bank of led's and a sliding switch it is still possible
to independently interrogate each O2 cell to find the present PO2 in the
counterlung.
Well...having looked at many of the functions of the Mk 4, we finally
got to try it out in Cis-Lunar's 5m tank. Although it looked pretty bulky, the
weight on my back felt pretty similar to my normal twin 10's. Underwater,
using
my normal weightbelt I found myself to be slightly negatively bouyant. This
was
easily rectified by manually feeding more gas into the counterlung...but if I
had had a compatible direct feed fitted to the rig, could also have been done
by
putting gas into my drysuit. nb .. if breathing heliox, a separate air or
argon
suit feed would be needed to conserve heat.
Once I had resurfaced to get the Cis-Lunar swiched on (!), the whole
experience became very pleasant. With a HUD, a main display block and the
passive display block to look at, it was easy to get absorbed with the
technology and forget how easy it was to breath & how quiet it was with no
bubbles. Some tricks we learn on open circuit don't always carry over... eg as
I breath in & out my overall bouyancy no longer varies (useful for
photography).
Hence when I decided to swim a summersault, breathing in as usual did *not*
lift me off the bottom as it normally does & prevent my head hitting the floor
(!) More care is needed...!
As the breathing rate makes no difference to the amount of gas used up,
only an increased metabolic rate will use up more O2, you can breath as fast
and
as deep as you like. It makes no difference. CO2 buid-up & headaches from
slooooow breathing are no longer a consideration.
The 40 minutes we were allowed on the Mk 4 passed very quickly & turning
the O2 off to force a manual 'driving' of the rebreather presented no real
difficulties...depending on your boredom tolerance....!
What of the Mk 5 ?? We were told that there were 10 versions of the
"explorer" Mk 4's made & none were for sale. The Mk 5 will be for sale at a
price of 8000 pounds, including all necessary training & will be available in
May '95. It will be cosmetically much slimmer & will be significantly lighter
and smaller than open circuit twin 10's (that's about twin 80 cu ft in USA).
The Mk 4 was built to house 2 complete rebreather systems...ie 2 counterlungs,
2
sets of hoses, mouthpieces & water traps, 2 independant stacks etc. Hence its
bulky appearance. The Mk 5 will have all the redundancy described, but will
not
have 2 independant counterlungs, hoses & stacks. It should weigh in at under
60
pounds & will have the main display block about half the size & the passive
block mounted on the reverse side. The mouthpiece is to be 'streamlined' & all
the hoses tidied up. There was a 'wings' style BC attached to the MK 4. It
wasn't clear whether this would be part of the Mk 5 or would be an extra needed
to be purchased.
The 8000 pound price quoted is for the full heliox version, you can get
itnitrox only (price less, but not told what) and you can convert up to heliox
at any time. Any new bits can also be added at a later date, so you don't
have to go out and buy a new one when they bring out the Mk6, just update your
Mk 5.
Divers wishing to buy a Cis-Lunar have to have prior experience of
nitrox and heliox (if you have the full version), but both things can be added
to the course. You can also take the full 5 day (8 day ?) Cis-Lunar rebreather
course even if you are not about to buy a Mk 5. Training included a hypoxia
test. OC mixed gas experience would be needed especially for management of
bailout OC supplies if deep decompression (ie most deep dives) diving.
Sounds good to me....now where can I get hold of 8000 pounds ???
Seriously though, it is a lot of money for one impressive product, but I
will have a close look at the Oceanic unit (I'm *sure* the counterlung will
turn
out to be big enough...!) before I decide to spend any hard earned cash. Then
I will weigh up what else I could spend the money on. I can get a lot of
exotic
holidays for 8000 pounds...! Then again, I may end up coming back to Cis-Lunar
after all. It was certainly an impressive piece of kit.
Many thanks to Kevin & Jim for looking after just 2 divers on a Sunday.
Fot those techdivers who have heard all this before...my apologies for the
band
width.
We have posted this report on the Cis-Lunar with an OK, but without
prior editing from Kevin or Jim. One or two commercially sensitive details
(but
not much) have been left out for obvious reasons. Our apologies for anything
we
got wrong ...or forgot.
Regards, Steve M. (ec96@li*.ac*.uk*) & Ian H (imh@li*.ac*.uk*).
**************************************************************************
* * *
* Dr. S. G. Millard, * E-Mail : ec96@li*.ac*.uk* *
* Senior Lecturer, * *
* Department of Civil Engineering * Tel : 051 794 5224 (UK) *
* University of Liverpool, * 44 51 794 5224 *
* PO Box 147, * (International) *
* Liverpool L69 3BX, * *
* UK. * Fax : 051 794 5218 (UK) *
* * 44 51 794 5218 *
* * (International) *
* * *
**************************************************************************
Navigate by Author:
[Previous]
[Next]
[Author Search Index]
Navigate by Subject:
[Previous]
[Next]
[Subject Search Index]
[Send Reply] [Send Message with New Topic]
[Search Selection] [Mailing List Home] [Home]