Hollis Prism 2 User manual

USER MANUAL
REV. 13

WARNING: INDICATES IMPORTANT INFORMATION THAT IF IGNORED MAY LEAD TO
INJURY OR DEATH.
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This is the User Manual for the Hollis PRISM 2 Rebreather.
Document #: 12-4072 Rev. 13
Release Date: 1/1/19
This manual, specifications and features of the PRISM 2 are proprietary and copyright Hollis Rebreather, LLC, 2019.
This document may not be copied or distributed without the prior agreement and authorization from Hollis
Rebreather, LLC. All information contained is subject to change. Contact the manufacturer for the latest information
or go to our website at: www.hollisrebreathers.com
The PRISM 2 is manufactured in the USA by Hollis Rebreather, LLC.
1540 North 2200 West, Salt Lake City, UT 84116. USA Ph [phone]
To ensure your user information is up to date. Please check www.hollisrebreathers.com for updates to this manual.
WARNINGS, CAUTIONS, AND NOTES
Pay attention to the following symbols when they appear throughout this document. They denote important information
and tips.
CAUTION: INDICATES INFORMATION THAT WILL HELP YOU AVOID PRODUCT
DAMAGE, FAULTY ASSEMBLY, OR UNSAFE CONDITIONS.
NOTE: indicates tips and advice.
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PRISM 2 DESIGN TEAM
Peter Readey
Bob Hollis
Robert Landreth
Art Ferguson
Chauncey Chapman
Matthew Addison
PRISM 2 MANUAL
WRITTEN BY
Matthew Addison
EDITORS
Jeffrey Bozanic
Chauncey Chapman
John Conway
Gerard Newman
CONTRIBUTORS
Jeffrey Bozanic
Gerard Newman
Dr. Richard Pyle
Sharon Readey
Kevin Watts
Hollis PRISM 2 eCCR
User Manual
Document Control Number:
12-4072 Rev. 13
Date: 1/1/19
NOTE:
Information on the operation of the Prism 2
electronics can be found in the Shearwater Petrel User
Manual which can be downloaded from https://www.
shearwater.com/support/petrel/

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GENERAL SAFETY
STATEMENTS + WARNINGS
WARNING: USE OF THE PRISM 2 MANUAL
This manual is to be used in conjunction with the Displays and Electronics User Manual for the version of
electronics your PRISM 2 is equipped with. The current copy can be found at www.hollisrebreathers.com.
This user manual does not, nor is it intended to contain any information needed to safely dive with any type of
SCUBA apparatus. It is designed as a guide for the proper setup, operation, maintenance, and eld service of the
Hollis PRISM 2 CCR only. It does NOT take the place of a recognized training agency instructor-led diver-training
course or its associated training manual(s) and materials. This user manual is intended to be used only as a type
specic addition to such training and materials, and as a user reference. This manual cannot be used as a substitute
guide for any other type of Self Contained Underwater Breathing Apparatus (SCUBA).
WARNING: GENERAL SAFETY
No person should breathe from, or attempt to operate in any way, a Hollis PRISM 2 rebreather, or
any component part thereof, without rst completing an appropriate Hollis Certied user-training
course.
Further, no PRISM 2 diver should use a Hollis PRISM 2 without direct Hollis instructor supervision until they have
mastered the proper set-up and operation of the Hollis PRISM 2 rebreather. This includes new PRISM 2 divers as
well as PRISM 2 certied divers who have been away from diving for an extended period of time and would benet
from an instructor-led refresher course to regain skills mastery of the Hollis PRISM 2. Failure to do so can lead to
serious injury or death.
Your safety while diving the PRISM 2 depends on you knowing your PPO2 (oxygen levels) at all times.
This is easily done by monitoring the Heads Up and wrist displays.
WARNING: CAUSTIC MATERIAL
The CO2 adsorbent used in the scrubber is caustic alkaline material. Take steps to protect yourself from direct lung
and skin contact. Furthermore, poor management of the breathing loop could lead to water contact with the CO2
adsorbent, causing a “caustic cocktail” (very caustic liquid). This could lead to severe chemical burns and if inhaled
- possible drowning. Proper handling procedures, pre-dive checks, dive techniques, and maintenance mitigates this
risk.
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WARNING: HIGH PRESSURE OXYGEN
The PRISM 2 uses cylinders, gas feed lines, pressure gauges and other devices which will contain pure oxygen at
high pressure when in operation. Oxygen by itself is non-ammable, however it supports combustion. It is highly
oxidizing and will react vigorously with combustible materials. Oxygen at elevated pressure will enhance a re or
explosion and generate a large amount of energy in a short time.
The user must maintain all parts of the PRISM 2 that can come into contact with high-pressure oxygen as oxygen-
clean components. This includes scheduled servicing by a Hollis service professional, and using approved oxygen-
compatible lubricants on any part of the gas delivery systems that will come into contact with high-pressure
oxygen.
If any part of the oxygen-clean system comes into contact with contaminants or is accidentally ooded with
any substance (including fresh water), you MUST have the entire high-pressure oxygen system serviced by an
authorized PRISM 2 service professional prior to use. Failure to do so can cause re or explosion and lead to
serious injury or death.
WARNING: DESIGN AND TESTING
The Hollis PRISM 2 has been designed and tested, both in materials and function to operate safely and consistently
under a wide range of diving environments. You must not alter, add, remove, or re-shape any functional item of the
Hollis PRISM 2. Additionally, NEVER substitute any part of the Hollis PRISM 2 with third-party items which
have not been tested and approved by Hollis for use with the PRISM 2.
This includes, but is not limited to, hoses, breathing assemblies, electronics, breathing gas delivery assemblies
and their constituent parts, sealing rings, valves and their constituent parts and sealing surfaces, latches, buoyancy
devices, ination and deation mechanisms and on-board alternate breathing devices.
Altering, adding, removing, re-shaping or substituting any part of the Hollis PRISM 2 with non-approved parts can
adversely alter the breathing, gas delivery or CO2 absorption characteristics of the Hollis PRISM 2 and may create
a very unpredictable and dangerous breathing device, possibly leading to serious injury or death.
Non-approved alterations to functional parts of the PRISM 2 will automatically void all factory warranties, and
no repairs or service work will be performed by any Hollis service professional until the altered PRISM 2 unit is
brought back into factory specications by a Hollis service professional at the owner’s expense.
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WARNING: COMPUTER / CONTROLLER-SPECIFIC WARNINGS
This computer is capable of calculating deco stop requirements. These calculations are predictions of physiological
decompression requirements. Dives requiring staged decompression are substantially more risky than dives that stay
well within no-stop limits.
Diving with rebreathers and/or diving mixed gases and/or performing staged decompression dives
and/or diving in overhead environments greatly increases the risks associated with scuba diving.
WARNING: COMPUTER SOFTWARE
Never risk your life on only one source of information. Use a second computer or tables.
If you choose to make riskier dives, obtain the proper training and work up to them slowly to gain experience.
Always have a plan on how to handle failures. Automatic systems are no substitute for knowledge and training. No
technology will keep you alive. Knowledge, skill, and practiced procedures are your best defense.
WARNING: WEIGHTING OF THE HOLLIS PRISM 2
Unlike open circuit scuba gear, it is possible for the Hollis PRISM 2 breathing loop to ood, causing the rebreather
to quickly become 17 pounds negatively buoyant (not including any user-added weight or offsetting buoyancy
ination). It is the responsibility of the diver to insure that the Hollis PRISM 2 is never weighted in such a way that
it is not possible for the installed buoyancy device to overcome the ooded weight of the unit plus any diver-added
non-detachable weights, and still provide enough positive buoyancy at the surface to keep the divers head well
above water.
Consult your instructor, dealer, or call the Hollis factory directly with any questions or concerns. Failure to maintain
positive buoyancy at the surface with the Hollis PRISM 2 in a fully ooded state can lead to serious injury or death.
WARNING: BAILOUT GAS
The diver must always carry bailout gas, that provides an adequate volume and safe breathing mix, to deliver the
diver safely to the surface from all points during the dive. Divers can and do die from underestimating their bailout
needs. The diver shall receive details, training, and materials on selecting appropriate gases, volumes, and bailout
equipment from their selected Hollis approved training agency and instructor.
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WARNING: USER-PACKED RADIAL SCRUBBER
As of this writing, the Hollis PRISM 2 design does not include any technology or other device which can detect
or warn of potentially dangerous levels of carbon dioxide (CO2) within the breathing loop.
The Hollis PRISM 2 utilizes a user-packed, radial design CO2 scrubber. Only Hollis tested and approved CO2
adsorbents should be used, and factory-stated maximum scrubber durations must NEVER be exceeded.
Exceeding factory stated scrubber durations for a tested material will eventually lead to serious injury or death.
It is entirely possible that, for any number of reasons including but not limited to: channeling, ambient
temperature, exhausted, damaged, inappropriately stored, or (for whatever reason), inert scrubber material, the
chemical and thermodynamic reaction required to sequester gaseous CO2 will not occur as expected, and a toxic,
and possibly fatal level of gaseous CO2within the breathing loop can result.
You must carefully follow all instructor and manufacturer recommendations for use and handling of CO2
adsorbent, never use a CO2 adsorbent if you cannot verify that it is able to sustain CO2 absorption and carefully
pack the radial scrubber and complete a system pre-breathe prior to each immersion, as you were taught in your
training course.
Further, you must carefully monitor yourself for any symptoms of possible CO2 poisoning whenever you are
breathing from the Hollis PRISM 2, and bail-out to open circuit should any physical or mental symptom lead
you to suspect elevated CO2 levels in your breathing loop. Failure to bailout at the rst sign of trouble can lead to
serious injury or death.
WARNING: NAUSEA AND THE BREATHING LOOP
The introduction of biological solids into the DSV/BOV can lead to obstruction of the critical mushroom valves
causing a situation whereby fresh gas is not being circulated to the diver and consequently, a buildup of CO2
in the diver. Additionally, nausea is a known symptom of improper gas mixture and/or contamination. During
operation of the Prism 2, should you begin to feel the onset of nausea, immediately switch to an appropriate open
circuit bailout as soon as you can perform the task safely, and abort the dive. Consult your PRISM 2 instructor for
further details/training.
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WARNING: PROPER BATTERIES
ONLY name-brand batteries (such as “Duracell” or “Eveready”) may be used to power the PRISM 2. Off-brand
or Discount batteries have been found to vary greatly in quality of materials from batch to batch (and even piece to
piece!) Therefore they may not perform as expected, or be capable of consistently delivering the power required to
drive the Prism 2 components, despite battery voltage levels reported by a battery voltage meter.
While off-brand / discount batteries are perfectly acceptable for use in toys and ashlights, they
have no place in life support gear and must never be used to power any component of your PRISM
2.
Because of the potential rapid drop-off of charge from rechargeable batteries, rechargeable
batteries are not recommended for use with your PRISM 2 rebreather and must not be used.
Diagram showing rapid discharge of non-branded batteries that in life support
gear can result in unnecessary hazards.
The full article, “Are Expensive Batteries Worth The Extra Cost?” is available
at Wired.com
Image courtesy of Rhett Allain, Wired
WARNING: OPERATIONAL RANGE
The PRISM 2 has been tested and qualied for use in water depths of up to 328 ft (100 m) and water temperatures
between 39° - 93° F (4° - 34° C).
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WARNING: COLD WATER
Diving rebreathers in frigid water requires special equipment, training, and preparation to prevent possible injury
or death. Closed Circuit Rebreathers present unique variables to cold water diving that are not a factor in open
circuit diving in the same temperatures. Cold water diving is beyond the scope of this manual. There are many
variables not listed here. It is essential and the responsibility of the diver to be aware of all issues. The diver must
know how to best prepare their equipment, and how to best prepare themselves for the cold water environment.
The diver must obtain further training beyond standard CCR training or Open Circuit Ice Diver certication alone.
Cold Water Issues Include The Following:
- Alkaline battery performance degrades as the temperatures decrease. If diving consistently in waters approaching
freezing, it is recommended to use lithium batteries.
- If using a BOV with a PRISM 2 in water colder than 50°F/10°C, you must use an approved Hollis PRISM 2
Environmentally Sealed Regulator First Stage for the diluent supply gas.
- Changes in temperature may lead to expansion and contraction of CO2 adsorbent material possibly leading to
channeling or damage to the adsorbent itself. Further, allowing the moisture in the adsorbent to freeze will mean
that CO2 adsorption may not occur.
- Decreases in temperature effect the efciency of the scrubber considerably.
-Sensors are sensitive to extreme temperatures. Storage of Oxygen Sensors below 32° F (0°) or above
100° F (37.8° C) can damage or greatly shorten the life of the sensor.
- Mushroom valves may freeze open or closed if condensation is allowed to cool. Always perform mushroom
valve (stereo valve) checks and pre-breathe the unit before entering the water and before any subsequent dives.
The diver should warm and visually inspect the mushroom valves between dives.
- Use of the manual addition valves should be limited to short bursts of less than 1 or 2 seconds at a time.
Prolonged valve activation may cause freezing of the mechanism in frigid waters due to adiabatic cooling.
Training Standards:
Hollis Rebreathers recommends rebreather training from a recognized training agency that meets or exceeds the
minimum standards set by the Rebreather Education Safety Association (RESA).

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TABLE OF CONTENTS
General Safety Statements & Warnings
PART 1
SYSTEM OVERVIEW
SECTION 1
DESIGN PHILOSOPHY
SECTION 2
SCHEMATICS + DESIGN
ARTICLE: TAKING CARE OF YOUR
OXYGEN SENSORS
ARTICLE: THE SOLENOID AND
THE PID CONTROLLER
SECTION 3
FITTING YOUR PRISM 2
ARTICLE: STABILITY
PART 2
SETUP
SECTION 1
AN O-RING CLEANING PRIMER
SECTION 2
PACKING THE PRISM 2 CO2 SCRUBBER
SECTION 3
USING CHECKLISTS
SECTION 4
COMPONENT INSPECTION CHECKLIST
SECTION 5
ASSEMBLY ORDER CHECKLIST
SECTION 6
PRISM 2 OPERATIONAL CHECKLIST
SECTION 7
POST DIVE CHECKLIST
SECTION 8
MAINTENANCE + REPAIR LOG
iii-viii PART 3
ARTICLE: MINIMUM, MAXIMUM AND
OPTIMAL LOOP VOLUMES AND WORK OF
BREATHING
PART 4
MAINTENANCE +
CLEANING
SECTION 1
SERVICE FACILITY & YOU
SECTION 2
ROUTINE CLEANING
PART 5
APPROVED PRODUCTS,
CAPACITIES, & SPECS
SECTION 1
LIST OF APPROVED PRODUCTS
FOR USE IN YOUR PRISM 2
SECTION 2
COMPONENT CAPACITIES + SPECS
SECTION 3
GLOSSARY
SECTION 4
NOTES

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REBREATHERS CAN KILL YOU!
PROPER TRAINING, FOLLOWING YOUR TRAINING, NOT EXCEEDING THE LIMITS
OF YOUR TRAINING, AND STAYING CURRENT WITH YOUR TRAINING ARE ALL
PREREQUISITES FOR A SAFE REBREATHER DIVING CAREER, NO MATTER WHICH
REBREATHER YOU ARE USING.
READ THE MANUAL.
STAYING CURRENT ON REBREATHER X DOES NOT MEAN YOU ARE CURRENT ON
REBREATHER Y. THAT IS WHY WE WRITE THESE MANUALS. TAKE A PAUSE AND RE-
READ THE MANUAL IF IT HAS BEEN A WHILE SINCE YOU HAVE BEEN DIVING YOUR
PRISM 2. IT CAN MAKE ALL THE DIFFERENCE BETWEEN A GREAT OR TERRIFYING
DIVE.
DONT BE CHEAP.
LASTLY, REMEMBER DON’T BE CHEAP! DON’T BE CHEAP WITH YOUR
CONSUMABLES SUCH AS ADSORBENT, O2 SENSORS, ANNUAL SERVICES, AFTER-
DIVE SANITIZING REGIMIN AND MOSTLY, DONT BE CHEAP WITH YOUR TIME IN
CAREFUL SETUP, PRE-DIVE AND IN-WATER CHECKS.

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PART 1 . SECTION 1
SYSTEM OVERVIEW DESIGN
PHILOSOPHY
The PRISM family of rebreathers has a long and illustrious history, and it is
considered one of the foundation platforms of the modern day electronically
controlled “sport” rebreather.
The PRISM 2, like its predecessor the PRISM Topaz, is a digitally controlled
electronic closed circuit rebreather with split front-mounted over the
shoulder counterlungs (OTS-CL) or Back Mounted Counterlungs (BMCL). It
incorporates a radial design scrubber for the best possible duration and work-
of-breathing. All gas delivery systems on the PRISM 2 have both automatic and
manual function.
MANUAL CONTROL OR COMPUTER CONTROL?
One of the ongoing debates when discussing rebreather safety is whether manually controlled or
electronically controlled rebreathers are safer. From the day in 1995 when PRISM Topaz class
#1 was held in Hermosa Beach, CA, students were taught to “y” their rebreathers manually by
watching their secondary analog displays and manually injecting oxygen and diluent as needed.
From day one, PRISM students were taught that the primary control system was always the
divers brain. It wasn’t until the last dive of the last day of class that students were told, “OK, you
can turn on your electronics and experience a computer controlled dive”.
Diving with the computer monitoring the oxygen and the user keeping an eye on everything
with (at that time) a Heads Up Display primary and a wrist-mounted analog secondary sure kept
us busy, but we quickly realized that the computer was a LOT better at closely maintaining a
setpoint! We also realized that our instructor had trained us to be manually controlled rebreather
divers with the safety of “computer over-watch”.
Why two independent monitoring systems in one rebreather? Simply put, electronics, batteries
and wiring combined with salt water (or even fresh water) do not get along well together. While
we can seal circuit boards and wiring interfaces against water intrusion, rebreathers should have
a diver accessible compartment to change batteries, and because of this need for accessibility,
ooding can occur.
This is the Achilles heel of rebreathers with on-board electronics. Any time an O-ring
sealed Compartment is unsealed, the potential for debris to get on the O-ring and cause the
compartment to ood during the next dive is increased.
So, with two separate systems onboard with separate battery compartments, if one battery
compartment oods and destroys the battery, we simply switch to the other monitoring system
to safely end the dive. When our dive is over, we dispose of the wiring harness and battery, clean
the compartment and put in a fresh battery and new O-ring(s).

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Fig. 1.1
SCHEMATICS + DESIGN THE GAS PATH
The PRISM 2 incorporates an over-the-shoulder split counterlung design or a back
mounted counterlung. The gas ows through the loop from left to right shoulder
in both the Front-Mounted Counterlungs and the Back-Mounted Counterlungs, as
has become a standard in the recreational rebreather market. Figure 1.1a shows the
Front-Mounted Counterlung design.

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PART 1 . SECTION 2
OXYGEN & THE EXHALATION SIDE OF THE LOOP
Pure oxygen injection into the system, whether manually or electronically, via the
solenoid, is injected into the exhalation side of the breathing loop. This design
insures that a diver can never inadvertently get a high partial pressure dose of
oxygen while diving, and that oxygen which is injected into the loop has plenty of
time to properly mix with the loop gas, thereby avoiding potentially dangerous O2
spikes.
HEAD PLATE + RED CO2SEAL
Once the diver-exhaled gas enters the head, it travels into the head plate, which is
also where O2 injected by the solenoid enters the breathing loop. The red CO2seal
(Fig. 1.2) which seals the scrubber basket to the head plate sits in a groove at the
end of the head plate facing the scrubber basket. The Red CO2seal must be in place
at all times during diving operations!
WARNING: BREATHING FROM THE PRISM 2 WITHOUT
THE RED CO2 SEAL IN PLACE WILL RESULT IN 100% GAS
BYPASS OF THE SCRUBBER. FAILURE TO INSURE THAT
THE RED CO2SEAL IS PROPERLY INSTALLED MAY LEAD TO
INJURY OR DEATH.
THE SCRUBBER BASKET
The gas leaves the head plate and enters the radial scrubber basket through its center
tube (Fig. 1.3). As the gas radiates outwards through the CO2 adsorbent and towards
the bucket walls, exhaled CO2 is chemically sequestered (adsorbed) by the CO2
adsorbent, and any added oxygen is mixed with the loop gas as it travels through the
scrubber granules. Upon exiting the scrubber, the heated gas enters the thermal air
jacket area between the basket and bucket.
The air jacket serves two purposes: First and most important, it insulates the scrub-
ber material from colder external temperatures, which helps increase the efciency
of the absorption process. Secondly, the moisture in the heated gas exiting the
scrubber has an opportunity to condense along the cooler bucket wall, dropping the
overall humidity of the gas entering the oxygen sensor housing.
From the thermal jacket, the gas ows up through the scrubber basket ow
vanes (Fig. 1.4). This restriction creates higher gas velocities in the sensor area
without increasing work of breathing, further dropping the dew point of the gas as it
reaches the oxygen sensors. By using natural condensation along the surface of the
bucket wall and manipulating gas velocities in the area around the O2 sensors, we
are able to keep the sensors as dry as possible without adding complexities such as
sponges or other moisture blocking devices.
Fig. 1.2
Fig. 1.3
Fig. 1.4
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Fig. 1.6
THE COUNTERLUNGS: FRONT MOUNTED (FMCL)
THE INHALATION COUNTERLUNG
The inhalation counterlung is a 3.5 L or optional 2.5 L (currently available in the
USA market only) front-mounted split counterlung design (Fig. 1.5) made of
rugged nylon with a food-grade urethane interior. It houses the automatic diluent ad-
dition valve (ADV), counterlung drain, hose mounting hardware and BCD ination
hose wrap at its front.
The hose attaching hardware for both the head and DSV/BOV assembly attaching
points (Fig. 1.6) are welded into place, so they cannot become loose and cause an
unintended loop ood. The DSV/BOV hose attaching hardware is “keyed” (Fig.
1.7) and will only accept the corresponding hose assembly elbow, thereby avoid-
ing incorrect assembly of the loop which would result in potential reversal of gas
ow within the loop. The Inhalation Counterlung has a 6-sided key, the Exhalation
Counterlung has a 4-sided key.
Behind each counterlung, under the Fastex Buckle panel are weight pockets (Fig.
1.8) which will accept up to 5 lbs/2.3 kg of hard or soft weight. The weight pouch
ap is held in place with Velcro. There are 2 D-rings on the counterlung, one on the
side and one at the bottom. Each counterlung has a water drain at its bottom (Fig.
1.9) to drain uids as they accumulate during a dive. The Fastex clip panel on the
back of the counterlung contains 2 Fastex clips for clipping the counterlungs to the
harness, backplate, and one chest strap with Fastex clips.
ADV (AUTOMATIC/MANUAL DILUENT ADDITION VALVE)
Having the ADV (Fig. 1.10) on the inhalation side of the loop makes sense for sev-
eral reasons. Should the oxygen content ever become dangerously low, dangerously
high, or the diver begins feeling “abnormal”, a known normoxic gas is immediately
available while still breathing from the loop prior to switching to bailout*. There-
fore, having the diluent as close to the mouthpiece as possible is the best way to
insure that fresh breathing gas of known and safe oxygen content is only a breath
away. *(Not applicable if the diluent is a hypoxic mix)
The ADV is held in place by a threaded tting welded to the counterlung. To remove
the valve for servicing, unscrew the outside retaining nut by turning it count-
er-clockwise until the valve comes loose. There is a rubber gasket under the valve
which seals the valve body to the counterlung tting. The removable plunger acti-
vates a Schrader valve which allows the gas to ow into the loop. The counterlung
tting is keyed so the valve will not rotate while in use. While the valve is shipped
from the factory with the QD tting facing up, the valve will work in any rotation.
Fig. 1.5
Fig. 1.7
Fig. 1.8
Fig. 1.9
Fig. 1.10

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PART 1 . SECTION 2
THE EXHALATION SIDE COUNTERLUNG
The Exhalation side counterlung is of similar build and size to the Inhalation side
counterlung in all respects excepting it houses the manual oxygen addition valve and
the automatic, adjustable loop over-pressure valve (OPV). (Fig. 1.11)
BREATHING HOSES + HARDWARE
The Breathing hoses (Fig. 1.12) are 15” X 11/2” xed-length rubber breathing hoses.
They can not be cut to a different length. The Inhalation hose hardware which
connects the hose to the DSV/BOV and counterlungs, also houses the inhalation
mushroom valve on the DSV side of the hose. The BOV inhalation hose does not
house the inhalation mushroom valve. All mounting hardware is held in place by
two Oetiker clamps on each side of each hose.
Fig. 1.11
Fig. 1.12
DSV or BOV hose? - The CRITICAL differences!
WARNING: DO NOT ATTEMPT TO ATTACH A BOV TO A SYSTEM
PLUMBED FOR A DSV OR A DSV TO A SYSTEM PLUMBED FOR A BOV.
DOING SO WILL CAUSE TOTAL OBSTRUCTION OF THE GAS PATH OR A
COMPLETE STALL OF THE GAS FLOW, EITHER CONDITION LEADING TO
POSSIBLE INJURY OR DEATH.
DSV Inhalation side tting BOV Inhalation side tting
You will notice that the mounting hardware for the DSV also holds the inhalation
mushroom valve while the mounting hardware for the BOV does not. In the BOV,
the mushroom valve is contained inside the BOV in a separate mushroom valne
holder. It is imperative that you DO NOT try to mate a DSV tted hose wioth a
BOV, or visa-versa.
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OPV (OVER PRESSURE VALVE)
The OPV (Fig. 1.13) is an automatic or manual adjustable pressure relief valve which
is screwed into a tting welded onto the front of the exhalation counter-lung. To
adjust the release pressure of the ADV, simply turn the body of the valve clockwise to
increase the cracking pressure and counter-clockwise to decrease cracking pressure.
To operate the valve manually, simply depress the body of the valve. The OPV is not
a serviceable part so should it ever fail, it must be replaced.
MANUAL OXYGEN ADDITION VALVE
The manual oxygen addition valve (Fig. 1.14) is located on the inside of the ex-
halation counterlung. It is a push button valve operated by a schrader valve. Under
the quick disconnect tting is a 0.0020 inch ow restrictor, to meter the injection of
oxygen into the Loop. The manual oxygen valve is held in place by a threaded tting
welded to the counterlung. To remove the valve for servicing, unscrew the outside
retaining nut by turning it counter-clockwise until the valve comes loose. There is a
rubber gasket under the valve which seals the valve body to the counterlung tting.
The counterlung tting is keyed so the valve will not rotate while in use. While the
valve is shipped from the factory with the QD tting facing up, the valve will work in
any rotation.
DSV (DIVE SURFACE VALVE)
The Dive Surface Valve (Fig. 1.15) is a neutrally buoyant one-way loop “shut down”
valve with a water purge. The rotating barrel is made of stainless steel. The exhalation
mushroom valve is seated on the right side of the valve housing. The DSV can be
used with the Front-Mounted or Back-Mounted Counterlungs.
BOV (BAIL-OUT VALVE)
BOV (Bail Out Valve) (Fig. 1.16) is a unique 2-position neutrally buoyant loop
shutdown valve with an in-line second stage for single action bail out to open circuit.
When the lever is in the top position, the valve in closed circuit mode. The lower
position is open circuit bail-out. The BOV can be used with the Front-Mounted or
Back-Mounted Counterlungs. The Bail Out Valve operation manual can be found on
the Hollis Rebreather website.
Fig. 1.13
Fig. 1.14
Fig. 1.15
Fig. 1.16

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THE COUNTERLUNGS: BACK MOUNTED (BMCL)
THE INHALATION COUNTERLUNG
The Back-Mounted Counterlungs comprise 2 3.5 L back -mounted split counterlungs
consisting of a food-grade urethane interior counterlung encased in a rugged nylon
exterior (Fig. 1.17). The T-Piece at the top of the Inhalation counterlung houses the
automatic diluent addition valve (ADV) and a manual diluent addition is plumbed
in line with the ADV supply hose. The ADV is a “Tilt Valve” design to reduce the
unwanted addition of diluent as gas shifts around the system during normal diver
movement. There is no drain valve on the inhalation counterlung.
The hose attaching hardware for both the head and DSV/BOV assembly attaching
points (Fig. 1.18) are attached to the T-Piece. The T-Piece is screwed into the
Inhalation Counterlung tting. The Urethane Counterlung threaded tting is screwed
into the urethane counterlung opening at the top of the counterlung.
Attaching a DSV
The inhalation side DSV attaching hardware houses the inhalation mushroom valve
and DSV counterweight in the plastic holder (Fig. 1.19) . The exhalation side
attaching hardware is an open plastic tting which also holds the DSV counterweight
in place. The Inhalation side of the DSV contains a channel cut across the threads of
the DSV housing. If a user were to accidentally install the DSV reversed, this channel
creates a bypass that will insure the assembled unit would not pass a positive or
negative test. Also, with both the inhalation and exhalation mushroom valves butted
up against each other in such a conguration, would insure that a user could neither i
inhale OR exhale into the assembled rebreather through the incorrectly placed DSV.
Attaching a BOV
Unlike the DSV, both inhalation and exhalation mushroom valves are secured in
the BOV itself, so there are no mushroom valves on the hose attaching hardware.
The plastic ttings do hold the counterweight attaching hardware for the BOV (Fig
1.20). The counterweight for the inhalation side of the BOV is thinner in order to
clear the gas supply hose attachment point, and will t onto the inhalation side of the
BOV once the BOV supply hose is attached. The exhalation side Counterweight is
thicker. Should a user attempt to install the BOV in reverse, the larger Counterweight
on the exhalation hose will prevent the ability to attach the gas supply hose. This
arrangement prevents incorrect assembly of the loop, which would result in potential
reversal of gas ow within the loop.
Behind the inhalation counterlung are Velcro straps to hold the BMCL snugly onto the
backplate harness (Fig. 1.21).
Fig. 1.17
Fig. 1.18
Fig. 1.19
Fig. 1.20
Fig. 1.21
WARNING: IT IS IMPERATIVE THAT YOU USE THE CORRECT
ATTACHING HARDWARE FOR THE MOUTHPIECE YOU INTEND ON
USING. THE DSV ATTACHING HARDWARE AND BOV ATTACHING
HARDWARE ARE NOT INTERCHANGEABLE. HOLLIS HAS TAKEN
EVERY REASONABLE DESIGN PRECAUTION TO INSURE THAT
INCORRECT HARDWARE COMBINATIONS ARE OBVIOUS AND NOT
DIVABLE, HOWEVER A DILIGENT, TRAINED DIVER MUST BE PART
OF THE SAFETY EQUATION. ATTEMPTING TO DIVE USING THE
INCORRECT COMBINATION WILL LEAD TO INJURY OR DEATH.
!

19 |
THE EXHALATION SIDE COUNTERLUNG
The exhalation counterlung (Fig. 1.22) is similar in most respects to the inhalation
counterlung. It too is a 3.5 L back -mounted split counterlung design consisting of
a food-grade urethane interior counterlung encased in a rugged nylon exterior. The
T-Piece at the top of the exhalation counterlung houses the manual oxygen addition
port There is a manually activated drain valve on the bottom rear of the exhalation
counterlung.
The hose attaching hardware for both the head and DSV/BOV assembly attaching
points are attached to the T-Piece. The T-Piece is screwed into the exhalation
counterlung tting (Fig.1.23). The Urethane Counterlung threaded tting is screwed
into the urethane counterlung opening at the top of the counterlung.
The exhalation side DSV attaching hardware is an open port and holds the DSV
counterweight in the plastic holder (Fig. 1.24).
Unlike the DSV, the counterweight attaching hardware for the BOV is dissimilar
from side to side (Fig. 1.25). The counterweight for the inhalation side of the BOV is
thinner and will t onto the inhalation side of the BOV once the BOV supply hose is
attached.
Should a user attempt to install the BOV in reverse, the larger Counterweight on
the exhalation hose will prevent the ability to attach the gas supply hose. This
arrangement prevents incorrect assembly of the loop, which would result in potential
reversal of gas ow within the loop.
Fig. 1.22
Fig. 1.23
WARNING: IT IS IMPERATIVE THAT YOU USE THE CORRECT
ATTACHING HARDWARE FOR THE MOUTHPIECE YOU INTEND ON
USING. THE DSV ATTACHING HARDWARE AND BOV ATTACHING
HARDWARE ARE NOT INTERCHANGEABLE. HOLLIS HAS TAKEN
EVERY REASONABLE DESIGN PRECAUTION TO INSURE THAT
INCORRECT HARDWARE COMBINATIONS ARE OBVIOUS AND NOT
DIVABLE, HOWEVER A DILIGENT, TRAINED DIVER MUST BE PART
OF THE SAFETY EQUATION. ATTEMPTING TO DIVE USING THE
INCORRECT COMBINATION WILL LEAD TO INJURY OR DEATH.
WARNING: DO NOT ATTEMPT TO ATTACH A BOV TO A SYSTEM
PLUMBED FOR A DSV OR A DSV TO A SYSTEM PLUMBED FOR A BOV.
DOING SO WILL CAUSE TOTAL OBSTRUCTION OF THE GAS PATH
OR A COMPLETE STALL OF THE GAS FLOW, EITHER LEADING TO
POSSIBLE INJURY OR DEATH.
!
!
Fig. 1.24
Fig. 1.25

| 20
Manual Gas Addition Blocks
Diluent Addition Block
The top of the manual Diluent Addition Block gas supply houses a standard threaded inlet
supply hose and returns to the Inhalation T-Piece just below the ADV swivel through a QD
connected hose (Fig. 1.26). On one side of the block is a blue, un-shrouded gas injection
button and on the other side a pronounced relief with a hole for mounting the block as the
diver prefers. On the bottom of the block is a secondary in-port for attaching off-board
diluent supplies should the diver wish to add such a system.
Oxygen Addition Block
The Oxygen Addition Block is similar to the Diluent block with a few important tactile
differences. The Oxygen addition button is shrouded to prevent accidental injections of
Oxygen and so a diver can tell the difference between the two blocks just by feel (Fig.
1.27). The gas supply comes from a standard threaded inlet supply hose and returns to the
Exhalation T-Piece through a QD connected hose. On the bottom of the block is a secondary
in-port for attaching off-board Oxygen supplies should the diver wish to add such a system.
Fig. 1.27
Fig. 1.26