Part I - DESIGN OVERVIEW
PRISM Topaz Underwater Breathing Apparatus
PRISM Topaz is a closed-circuit mixed gas underwater
breathing apparatus (frequently called a "rebreather") designed specifically for
the recreational diving marketplace. The PRISM Topaz model is the first of a new series of
"third generation" PRISM rebreathers. As such, PRISM Topaz also serves as the
development testbed for additional models based on third generation PRISM technology.
Models optimized for deep diving andfor military applications will be developed from the
PRISM Topaz foundation. This document presents the design goals and specifications of
PRISM Topaz Application Considerations
Serving as a final development testbed for the third
generation PRISM, the initial PRISM Topaz units will beoperated by Steam Machines at its
training center on Cayman Brac and elsewhere only under direct supervisionof Steam
Machines personnel. The units will be used by openwater certified divers in conjunction
with Steam Machines "Closed Circuit Diver certification courses. This will be
the first widespread use of such mixed gas closed circuit diving equipment by personnel
who have not had extensive military or commercial training.
It is Steam Machines intent to maintain tight control of the
operation of all PRISM Topaz units during this critical final "real world" test
phase. The units are fitted with onboard digital data loggers and will be maintained by
Steam Machines technicians. Regular performance and application suitability evaluations
will be performed throughout the operational test phase. This evaluation phase will
provide Steam Machines with invaluable data pertaining to actual use of closed-circuit
diving systems (and, more specifically the use of PRISM Topaz) in the real world by
civilian personnel. Final unit design review will incorporate changes that may result from
analysis of this operational evaluation.
Steam Machines will set operational limits on the PRISM Topaz units used
at the Steam Machines training centers. These limits will be targeted at operator, rather
than hardware, capability considerations. Such operational limitations will include an
operational depth limitation of 150fsw. Steam Machines test divers will perform manned
testing of all PRISM Topaz units outside the restricted recreational diver test envelope.
In addition, unmanned and manned testing beyond recreational limits is being undertaken in
conjunction with various military projects.
PRISM Topaz Flexible Platform Considerations
PRISM Topaz is designed specifically for the recreational marketplace.
An overwhelming design consideration for this market is unit size and ease of use. Extreme
dive duration was sacrificed in exchange for overall small form factor and light weight.
PRISM Topaz weighs about 38 pounds
about the same as an 80 cubic foot open circuit
The PRISM Topaz design, however, is very flexible, allowing
reconfiguration to more demanding applications with minimal component change. All
breathing loop components are designed for minimal work-of-breathing at extreme depths.
All major PRISM Topaz components are designed with an operational depth limitation goal of
500 fsw. Minor additional component changes could extend this depth. Since the PRISM Topaz
series platform is designed to physically perform well at 500 fsw, minimum performance
specifications of the PRISM Topaz version are determined primarily by gas cylinder and
The unique design of the PRISM Topaz series platform allows large
increases in operational range by simple increase of gas cylinder size and scrubber
length. A deep diving version of the PRISM Topaz will enter field testing by Steam
Machines concurrently with final PRISM Topaz operational trials.
PRISM Topaz Operational Design Specification
- Closed circuit constant PPO2
- Semi-closed circuit constant PPO2
- Closed circuit, PPO2 monitored, manually controlled
- Semi-closed circuit, constant mass flow, PPO2 monitored
- Open Circuit bailout with regulator on breathable diluent
Major physical components:
- Backpack mounted control/scrubber/cylinder assembly
- Integrated buoyancy compensator with detachable back
mounted wings, user-ditchable integrated weight and leg loops.
- Twin, over-shoulder counterlungs. Approximately seven
liter capacity, coated crushed neoprene. Water drain/dump valves fitted to both
counterlungs. Variable volume overpressurization valve on left counterlung.
Hydrostatic/manual diluent addition on lower right counterlung.
- Control housing/manifold. Houses main system electronics
and battery in sealed compartment fully isolated from breathing loop. Provides oxygen
injection plenum, water trap pathways, sensor plenum and scrubber basket manifold.
Positioned at top of backpack atop scrubber canister. Equipped with canister pressure
transducer, O2 sensors, CO2 sensor.
- Scrubber canister.
Insulating outer canister housing with quick replaceable radial flow scrubber
basket cartridge. Scrubber cartridge access through removable bottom plate. Accommodates
Steam Machines proprietary sensor calibration system.
- Scrubber basket. Interchangeable cartridge style, radial
flow, accommodating 8-12 mesh size, 797 grade Sofnolime. Injection molded A3K nylon with
integrated high flow screen. Screw top with foam compression pads.
- Alternate scrubber: Steam Machines proprietary
"solid state" scrubber. Fully water tolerant solid scrubber cartridge will
directly exchange with loose fill basket.
- Cylinders. 15 cubic foot steel oxygen and 15 cubic foot
steel diluent. 3000 PSIg provided with crossflow DIN valves and "fill-in-place"
- O2 sensors. Three Steam Machines proprietary galvanic
designed for extended operation at elevated absolute pressures and elevated PPO2.
- CO2 sensor. Proprietary Steam Machines bio-optical with
low-cost disposable sensor element.
- Primary instrumentation display. Wrist mounted
human-factors engineered status display with shape and color keyed system status elements.
Digital LCD display of current PPO2, oxygen cylinder pressure and diluent cylinder
pressure. Connected by heavy duty cable to control unit.
- Secondary instrumentation display. Jeweled movement
analog PPO2 meter driven directly by the galvanic O2 sensors. Switch selectable to read
sensors 1, 2, 3 or battery voltage. Used to verify primary display and control system and
during manual operation with electronics offline. Connected by heavy duty cable to control
unit. Normally stored in special pocket on buoyancy compensator.
- Tertiary in-water training display. (optional) Duplicate
of primary display status element section. Mounted at top of control unit. Allows easy
viewing of system operational status by in-water training personnel.
- Diluent addition valve. Mounted on the lower right
counterlung. Adds diluent to maintain nominal ambient counterlung pressure. Diaphragm face
button serves as manual diluent addition valve.
- Oxygen injection valve. Low current, long life, pulse
width modulated solenoid valve. Pulse duration proportional to PPO2 deviation from
setpoint, providing proportional control with minimal complexity and maximum reliability.
- Oxygen mode/manual bypass valve. Mounted at lower
righthand corner of unit, protected by backplate and case. Provides three position
switching of oxygen delivery mode: Automatic/OFF/Inject. Inject position is spring return
to OFF mode providing intuitive quarter-turn lever for manual O2 injection.
- Mass flow control valve. (optional) Mounted at lower
righthand corner of unit, protected by backplate and case. Allows user/technician
adjustable control of injected gas flow rates.
- High volume mouthpiece/hose assembly. Large diameter,
high compliance mushroom valves in removable large-area seats. Lever actuated,
quarter-turn dive/surface valve with water purge in surface mode. 35mm minimum bore
diameter hoses. Mouthpiece weighted for neutral buoyancy.
- Back unit overall dimensions: 14" X 17" X 9"
- Overall system weight: Approx 38 pounds
- Standard counterlungs approximately 7 liters capacity with user
adjustable working volume. Counterlungs quickly changeable to accommodate larger capacity.
- Scrubber Basket Size, radial flow, Topaz:
6" diameter X approx 6.5" overall
Minimum cross sectional area of approx 14.8".
Charge: 1.7 kg 8-12 grade Sofnolime
- Scrubber duration, radial flow, Topaz:
2 hours minimum at 62LPM RMV, 32°F, 300fsw, 1.35LPM CO2
- Maximum scrubber basket size, PRISM Topaz series platform:
6" diameter X approx 13" overall
Minimum cross sectional area approx 37.1"
Charge: 4.2 kg 8-12 grade Sofnolime
- Maximum possible scrubber duration, PRISM Topaz series platform:
6.5 hours minimum (est.), 62LPM RMV, 32°F, 300fsw, 1.35LPM CO2
- Solid State Scrubber duration,
Topaz series platform:
1.3 to times Sofnolime duration, minimum. Preliminary testing indicates possible
performance of up to 3X Sofnolime at extreme work rates and temperatures.
- Cylinder capacity, Topaz: 15 cu ft oxygen + 15 cu ft diluent @ 3000 PSIg
- Nominal depth limitation, PRISM Topaz series platform: 500fsw
- Stated depth limitation, PRISM Topaz: 150fsw
Steam Machines solid state scrubber technology
is currently under development. All performance figures are preliminary.
[ Topaz Main
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Revised: December 01, 2002.
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