How it Works
Now for the fun
stuff, below is a diagram of how the unit works, things are not to scale but
the flow pattern is what were looking at. Follow the numbers from 1 to 15 and look
below for the descriptions.
1)
This
it the divers mouthpiece. It has two one way valves in it one in each end. These allow breathing gas to flow in only one
direction and must be assembled to the rebreather in the correct orientation. This also is called a DSV or Dive Surface
Valve and will close off the mouthpiece from water with a lever located in the
bottom of it.
2)
Exhale
side of the mouthpiece. This Is where the divers exhaled gasses go and pass through one
of the one way valves into the exhaust hose. These gases contain moisture and
Carbon Dioxide from the divers breath, there is also
residual oxygen from what the diver did not use and the diluent gas.
3)
This
is the exhale counterlung and water trap.
The bag is soft and flexible and due to the
positioning of the ports tend to trap any extra water that may enter the
loop. The capacity is limited
though. The gas then travels into the
scrubber canister.
4)
The
exhaust OPV (overpressure relief valve) is mounted through the top of the
rebreather housing and serves to vent the breathing loop whenever there is
built up pressure, usually due to expansion upon ascent. This valve is just like the exhaust valve in
your drysuit or lift bag. You can also
vent the loop through your nose, I prefer this method.
5)
Scrubber
canister. This is where you pack your
sodalime. The sodalime, via a chemical
reaction, converts the divers exhaled C02 into a chalk type substance, H20
(water) and heat. Consult your favorite
chemist for the exact formulas. This is
a bad place for a large quantity of water, which can form a nasty concoction
called the caustic cocktail. In the
Drager rebreather this has its own small water trap.
6)
Gas
now flows into the breathing bag or counterlung. This is where the gas comes from when you
inhale. The 02 monitoring device plugs
in here via a P connector as well as the dosage device and a cell holder that
connects to the Explorer dive computer to allow real time tracking of PPO2 for
decompression calculations.
7)
Oxygauge. This device has three components. The sensor, mounted in the breathing bag,
reads how many molecules of oxygen are present in the mix. It does this with a device called a fuel cell
that consumes a minute amount of oxygen and converts it to electricity, the
more oxygen molecules available, the higher the
voltage that can be measured on the output.
The second component is the cable that connects it to the readout
module. The third is the readout or
display. This takes the millivolt output of the sensor and does a bit of math
converting it to a format we can understand easily, PPO2. The partial pressure of oxygen. We can survive at a PP02 of between .10 where
we are barely conscious up to 1.6 where we are in danger of CNS oxygen toxicity. If these terms are unfamiliar to you,
consider taking a EANX or Nitrox course from your
local scuba instructor. This is a
minimum requirement to start a rebreather course.
8)
The
dosage device. This is where the gases
come from that fill the breathing bag.
There are two hoses connected to the dosage device and it is plugged
into the breathing bag or counterlung.
One hose comes from the diluent tank at a pressure of 150psi over
ambient. Inside the dosage device is a
demand valve similar to the one in your scuba second stage. Just like the scuba second stage, it provides
gas, at ambient pressure, whenever a slight vacuum is applied to the
output. This happens whenever the diver
inhales the entire contents of the counterlung and continues to inhale. This would happen upon descent in the water
column and serves to keep the breathing bag inflated. The dosage device also has another hose
attached to it coming from the KISS valve.
This is where the oxygen flow comes from. There is not a valve in the dosage device to
regulate oxygen, that is done in the KISS valve.
9)
Diluent
tank. This is where the supply of
diluent is stored. The tank beginning
pressure is 3000psi or 200bar. The
capacity of this tank on this unit is 19 cubic feet or 532 liters. The regulator on this is a standard scuba reg, made by Oceanic.
Coming from the regulator are 4 hoses. One high pressure hose going to
the divers console and a SPG to read diluent pressure. The console also contains a compass, and
bottom timer/depth gauge. One low
pressure hose connected to the BC. One
low pressure hose connected to a scuba second stage to allow Open Circuit
bailout on the diluent supply. One last LP hose that connects to the demand
port of the dosage device. The diluent
tank can be filled with air, for normal <130 foot diving, or a blend of
trimix for deeper excursions, usually 20/40 or 10/50 depending on the divers
needs. WARNING!!! Consult a qualified instructor to receive
training before conducting dives beyond your experience. YOU CAN BE KILLED!!
10)Oxygen tank. This cylinder is filled with 100% oxygen,
usually to a pressure of 2000psi or higher if you have special filling
equipment such as a booster. The rated
capacity of this cylinder
is 13 cubic feet at 3000 psi. 364 liters.
11)Fitted to the cylinder is an oxygen cleaned regulator modified to keep the intermediate
pressure at about 150 psi. The reason for this is that as a diver makes
a descent, the intermediate pressure of a normal regulator would begin to
climb, increasing the flow of oxygen into the breathing bag. We want the oxygen flow to remain at the same
mass/minute, not volume/minute. The
difference is in the number of molecules of gas passed through the orifice in
the KISS valve. At a higher pressure the
volume would remain the same but the gas is compressed to ambient pressure and
contains more molecules
for the same volume. With
the IP held constant, the volume actually slows down but the mass remains the
same, to a point. The math involved is
beyond the scope of this article, consult your local
CCR instructor. The SS ball valve is the
next item in line, it allows the user to shut off the
flow of 02 to the KISS valve. This
serves two purposes, one to allow the diver to stop flow in the instance of a
stuck add button on the KISS valve, or to turn off the rig upon return from the
dive. This can also be accomplished via
the tank valve but is faster and closer to access.
12) This is the final path of the gas, we have
now trapped any water, scrubbed out our waste C02, added necessary amounts of
diluent and oxygen, checked our PP02 and now we are back at the divers
mouthpiece ready to be inhaled again and start the cycle over.
13) The KISS valve was designed by Gordon
Smith of KISS manufacturing. He wanted a simpler way to inject oxygen into
a rebreather without all the electronics, solenoids and complication of current
automatic computer driven rebreathers such as AP valves Inspiration, Cis Lunar’s MK5p and others.
It flows a predetermined amount of oxygen,
adjustable by changing the IP of the supply regulator, into the dosage
device. It also has a bypass valve
allowing the diver to inject a larger quantity of oxygen by pushing a button on
the end of the unit. See pictures in Photos and Construction. The controlling software is the divers brain, using the information available to them in the
form of PP02 from the Oxygauge. The second hose connected to the regulator is a
HP hose leading to the SPG allowing the diver to monitor the contents pressure
of the 02 supply. I have considered
adding another scuba second stage to this regulator allowing OC access to 100%
02 in the event of a bailout and needed decompression and as I begin to dive
this rig deeper I may in fact do that.
It would require a method of preventing accidental access at depth,
maybe by a nylon bag around the reg with 100%O2 in
big letters. The dangers of high PP02
are well documented and have contributed to several divers
deaths.
14) HS Explorer Dive Computer. This is an actual screen shot of the Explorer,
model M, trimix and CCR capable. This
model has a port on the side allowing an oxygen sensor to be plugged in, thereby the computer gets to see the PP02 of the
breathing mix. Go to www.hs-eng.com
for more information on this unit. The
computer can be purchased from www.oxycheq.com.
15) Oxygen sensors. The HS Explorer uses a Teledyne R 22 D sensor, mounted into a connector available through Oxycheq,
plugged into a P-Port, that was added to the inhale counterlung, the P-Port was
purchased from my local Draeger dealer.
The oxygen sensor for the Oxygauge comes mounted into a P-connector and
is in the spot provided for it in the inhale Counterlung, another P-Port.
There is a lot more to
rebreather diving that what is described here.
If this piques your interest, I suggest that you read all you can about
the subject, check my More Stuff and
Links page to find some more reading material and enroll in a course for
beginning rebreathers. The Drager
Dolphin is an excellent beginning rebreather even though it is
semi-closed. The things you learn by
starting there will stay with you for your entire diving career. The modifications on this unit are my own and
this page is submitted for information only.
Any modifications you make to your own equipment are on your own nickel,
meaning only you are responsible for your safety. Don’t come crying to me if what you have done
doesn’t work, or worse yet, kills you.
Gordon Smith says it best, engraved on every rebreather he sells is the
statement, THIS
DEVICE IS CAPABLE OF KILLING YOU WITHOUT WARNING! I couldn’t agree more.