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Breathing Loop
The Sentinel has a single 4.8 liter back-mounted counterlung (BCL) attached via a quick-disconnect
system to the canister head. Each end of the breathing hose attaches at the head of the canister holder with a
bayonet-type connector and are attached at the mouthpiece by u-clips which allow the hoses to be rotated for
adjustment. The Sentinel comes with a bail-out valve (BOV), which is fed by the on-board diluent.
The BOV is designed to provide sanity breaths, not primary bailout, and is removable.
The Sentinel uses a combined water release and over-pressure release valve
(OPV) - when the unit vents it also removes any water from the system, which can also be performed manually by
overinflating the loop. The design of the loop allows for easy water removal from the loop hoses by closing the
mouthpiece, raising the hoses to evacuate water, then slightly overpressurizing the loop until it vents. The
balanced valve ensures the release pressure is near constant in any orientation.
The canister holder consists of three compartments: the electronics head, the middle tube that holds the
filter canister, and the canister base that includes the filter carrier, spring system, temperature profile
monitor (TPM), and the over-pressure valve (OPV)/water dump. The Sentinel TPM displays a thermistor based bar chart
of the temperature profile through the filter to give the diver information on the activity of absorbent.
The Sentinel employs a highly efficient self-packing axial
canister design which gives extended durations and is less affected by loss of efficiency associated with
increasing depth.
VR Electronics Package
For the first time in a rebreather, the electronics system has been developed by a leading dive computer
company. Control, setup, decompression and alarm systems evolved from the VRx dive computer and includes proven
features and design based on a considerable knowledgeable base, research, development and design for underwater
computer systems. The Sentinel has the most richly featured, integrated software for a rebreather on the
market, with electronics designed for intelligent monitoring. No single electronics failure will cause failure
of the complete system. Any problems are clearly described on the main and summary screens.
Calibration in ambient air ensures calibration in a known gas, that no over pressurization has occurred, and
reduces the risk from improper flushing of the loop. An on-screen checklist guides the user through the
pre-dive sequence. The auto set point selects the appropriate setting for current depth and dive duration.
Options allow the user to set preferences for: last stop depth, HUD brightness, deco set point,
safety factor, CNS alarm level, auto set point max, auto or manual mode, HP alarms on/off, cell
configuration (on/off), gas configuration options for Dil and bailout. Main screen dive data includes: PO2,
depth and max depth, dive time, decompression obligation, temperature, CNS, and battery level.
The electronics head holds the 3 oxygen sensors and the battery compartment. The ADV and oxygen solenoid
housings are mounted on either side of the head. The Sentinel uses 3 rechargeable lithium polymer batteries,
which can be recharged at any time without a significant memory effect. Two of the batteries act as main
batteries, and when they become low the third will activate as will the battery reserve alarm. The battery pack
lasts for approximately 60 hours in light on mode. The Sentinel has a backup display independent from the
main electronics and with an independent power source that allows the user to stay on the loop in the event of
a main electronics failure. The backup is not software driven and consists of 3 separate digital voltmeter LCD
displays with potentiometers for calibration. The backup display's independent battery is recharged as the main
battery charges. Highlights of other Sentinel electronics features include:
- Auto turn-on with the detection of a PO2 drop (detection of breathing) or at greater than 1.6 atm
absolute pressure (detection of depth).
- Diver and back mounted Heads Up Displays (HUDs) configured for color blind and highly stressed divers by
positioning and flashing or solid state. Vibrating alarm on diver HUD.
- Digital pressure sensors for monitoring of HP Dil and O2 cylinders for low levels and high rate of use;
will alarm when Dil reaches the amount needed for exit.
- Maintains 0.4 set point in OC mode to keep loop breathable.
- Pre-breathe screen in the Pre-dive checklist sequence includes a bar graph showing the temperature
difference across the filter.
- Auto calibration immediately triggered when sensor is replaced, ensuring calibration is in ambient
air.
- Scrubber duration analysis from an oxygen injection meter and a temperature profile monitor.
- Valve over inject and no inject sensors to help detect sensor failure or leak.
- Sensor percentage remaining analysis and a dynamic algorithm for automatically removing a sensor from the
PO2 averaging.
- PCLink option allows reprogramming and upgrades via downloads through the Internet as well as downloading
of dive profile data with ProLink software.
- Full decompression dive computer incorporating a derivative of the Bühlmann ZH-L16 algorithm with
modifications to support deep stops, adjustable shallow stop depth, and dynamic decompression ceilings. An
optional upgrade allows switching between the Bühlmann ZH-L16 and Varying Permeability Model B/E
algorithms
Regulators, SPGs and Hoses
The Sentinel uses the highly reliable and easily serviceable Poseidon Xtreme first stage regulators. The
regulators each have an Over Pressure Valve installed in a low pressure port. The oxygen regulator supplies the
oxygen injection solenoid and a multi-port gas manifold block with manual addition valve.
The diluent regulator supplies the ADV and BC inflator hose and a multi-port gas manifold block
manual addition valve. Both manual addition valves offer optional kit to allow
plug-in off-board gas supplies, and a Solenoid and ADV cutoff slide valves.
The low pressure piping consists of stainless steel plumbing and high impact resistant, flexible Miflex
hoses. A 20 micron O2 filter protects the solenoid from debris.
Harness and Wing
The Sentinel uses a custom lightweight stainless steel backplate designed to fit the contours of the outer
case. Included in our price and shipped with the unit are a wing style aircell and a 4-point quick-release harness.
The harness is fully adjustable, even for smaller women, and includes D-rings for attaching bail-out bottles
and accessories.
Cylinders
Our price includes steel gas supply cylinders and valves. Sentinels ship with a 15 cubic foot diluent and oxygen cylinders, and
we recommend carrying an external bailout with these units.
 Physical Characteristics
The Sentinel is shipped in a fully assembled state with the exception of the hose and mouthpiece assembly,
which will be in a separate bag. Our standard package includes the sturdy and low weight carry case. The outer
case is constructed of high impact plastic and serves as a strong yet lightweight shell to protect the internal
components. It's held in place by four quick-release fasteners, allowing for easy access to scrubber, hoses and
cylinders. For traveling, the cylinders may be removed and the extendable base foot adjusted to shorten the
length. The canister assembly can also be removed completely and carried as hand luggage on many airlines.
Consumables
The recommended consumables are: Molecular Products Sofnolime 8-12 mesh (797 grade, 1-2.5 mm granules) CO2
absorbent, DuPont RelyOn MDC (formerly Virkon) 1% solution for breathing loop disinfection, McNett 100% Pure
Food-Grade Silicone Grease for lubricating seals, and Caig Labs DeoxIT GOLD for cleaning gold electrical
contacts.
Training
The Sentinel rebreather requires formal training for safe use. The pricing does not include training, and
training is solely the responsibility of the purchaser. Training is available worldwide from Closed Circuit
Research approved instructors. The training time is five to seven days consisting of a classroom lecture,
confined water session and at least seven OW dives. Fill Express also offers Sentinel instruction at our
International Training Center in SE Florida.
When you order your Sentinel rebreather, we suggest you immediately complete the required Liability Release and mail it to VR Technology Ltd at
the address declared in the release. When you begin training, because the liability release is already on file,
your instructor will only need contact VR Technology and provide the serial number of your unit. They will
register the serial number of the unit in your name and issue, only to your instructor, the codes
required to enable the electronics.
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