In the PVR-BASC the discharged gas volume is a function of depth and breath volume. The passive addition occurs during each inhalation as the loop volume is deficient by the amount discharged. The volumetric ratio of discharged gas to exhaled gas volume varies with depth, and decreases as the pressure increases.[2]
At the surface one quarter of the volume of an exhaled breath is discharged. As the ambient pressure increases with depth, the volume of the inner counterlumg is reduced and the reduced discharge both provides an oxygen addition more closely matched to usage, and saves a considerable amount of gas.
Gas is added to the loop after the scrubber, and this means that the fresh gas is immediately available for breathing. It also means that the calculation of inhalation gas oxygen fraction must take this into account. This also reduces exposure of the scrubber absorbent medium to cold gas, and increases dwell time of exhaled gas in the scrubber, both of which improve the efficiency of CO2 absorption.
Gas discharge takes place before the remaining exhaled gas reaches the scrubber, so the discharged gas does not waste scrubber capacity. The fresh gas is added when the counterlung cover bottoms out towards the end of a breath, so the fresh gas is largely inhaled into respiratory dead space, and most of the mixing occurs after exhalation.
Excess gas due to expansion during ascent is vented through the overpressure relief valve.
The proportionality of the discharge counterlung volume to depth is lost below a depth of around 90 m (10 bar) so the gas saving below this depth is not as great as for shallower dives. The slightly higher feed rates will push the partial pressure of oxygen in the loop closer to the feed gas value.[3]
The PVR-BASC has a hinged bellows counterlung, similar to that of the Interspiro DCSC, and like the DCSC the top cover of the counterlung is weighted to improve breathing effort. However unlike the DCSC, the PVR-BASC uses an internal secondary bellows to discharge a portion of the exhaled gas during the inhalation part of the breathing cycle, when the main counterlung closes and pumps out the contents of the inner bellows. The reduction in volume of the inner counterlung with depth results in an approximation of a mass discharge proportional to breathing volume.
The PVR-BASC is designed to be carried on a standard Hogarthian backplate and wing harness.
The frame is designed to carry a cylinder on each side. The only restrictions on size are what the diver can carry, and the scrubber endurance. The cylinders are normally rigged with open circuit regulators in the standard DIR configuration for bailout, and a supply hose with quick connector on each for the rebreather supply.
The rebreather maintains a substantially constant breathing gas composition at any given depth regardless of the level of exertion, but gas consumption will vary with exertion.
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Halcyon PVR-BASC BOV/DSV and breathing hoses
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Halcyon PVR-BASC Bailout valve/Dive-surface valve
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Halcyon PVR-BASC BOV/DSV Bailout valve/Dive-surface valve
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Halcyon PVR-BASC BOV/DSV Bailout valve/Dive-surface valve
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Halcyon PVR-BASC breathing hose connector
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Halcyon PVR-BASC BOV/DSV breathing hose connector
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Halcyon PVR-BASC BOV/DSV side view with cover
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Halcyon PVR-BASC BOV/DSV top end view with cover
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Halcyon PVR-BASC BOV/DSV with cover
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Halcyon PVR-BASC BOV/DSV with cover
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Halcyon PVR-BASC semi-closed circuit rebreather - closed, from top/front
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Halcyon PVR-BASC semi-closed circuit rebreather - open, from above
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Halcyon PVR-BASC semi-closed circuit rebreather -open from above
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Halcyon PVR-BASC semi-closed circuit rebreather - open, from left
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Halcyon PVR-BASC semi-closed circuit rebreather - open, from right
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Halcyon PVR-BASC semi-closed circuit rebreather - open, from top/front
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Halcyon PVR-BASC semi-closed circuit rebreather - open, from top/front
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Halcyon PVR-BASC semi-closed circuit rebreather - open from top/front
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Halcyon PVR-BASC semi-closed circuit rebreather - open, from left
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Halcyon PVR-BASC semi-closed circuit rebreather - open, from right
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Halcyon PVR-BASC semi-closed circuit rebreather scrubber - assembled and mounted
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Halcyon PVR-BASC semi-closed circuit rebreather - bellows counterlung
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Halcyon PVR-BASC semi-closed circuit rebreather scrubber components
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Halcyon PVR-BASC semi-closed circuit rebreather - Scrubber internal components
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Halcyon PVR-BASC semi-closed circuit rebreather absorbent canister
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Halcyon PVR-BASC semi-closed circuit rebreather scrubber casing interior and secondary water trap
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Halcyon PVR-BASC semi-closed circuit rebreather - scrubber medium retaining screen and spring
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Halcyon PVR-BASC semi-closed circuit rebreather - overpressure dump valve
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Halcyon PVR-BASC semi-closed circuit rebreather - bellows counterlung detail
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Halcyon PVR-BASC semi-closed circuit rebreather
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Halcyon PVR-BASC semi-closed rebreather. breathing hose connector
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Halcyon PVR-BASC semi-closed rebreather Manual gas supply valves and loop drain pump
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Halcyon PVR-BASC semi-closed rebreather - underside
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Halcyon PVR-BASC semi-closed rebreather - underside, showing gas supply connectors, hoses and manual valves, and loop drain pump
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Halcyon PVR-BASC semi-closed rebreather underside, showing bolts for connection to backplate
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Halcyon PVR-BASC semi-closed rebreather breathing hose connector
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Halcyon PVR-BASC semi-closed rebreather. breathing hose connector cover
Underwater diving
- Diving activities
- Diving modes
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Basic equipment | |
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Breathing gas | |
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Buoyancy and trim equipment | |
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Decompression equipment | |
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Diving suit | |
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Helmets and masks | |
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Instrumentation | |
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Mobility equipment | |
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Safety equipment | |
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Underwater breathing apparatus | |
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Diving equipment manufacturers | |
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Access equipment | |
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Breathing gas handling | |
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Decompression equipment | |
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Platforms | |
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Remotely operated underwater vehicles | |
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Safety equipment | |
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General | |
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Activities | |
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Competitions | |
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Equipment | |
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Freedivers | |
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Hazards | |
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Historical | |
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Organisations | |
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Occupations | |
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Underwater work | Salvage diving | - SS Egypt
- Kronan
- La Belle
- SS Laurentic
- RMS Lusitania
- Mars
- Mary Rose
- USS Monitor
- HMS Royal George
- Vasa
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Diving contractors | |
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Tools and equipment | |
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Underwater weapons | |
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Specialties | |
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Diver organisations | |
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Diving tourism industry | |
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Diving events and festivals | |
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Diving hazards | |
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Diving procedures | |
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Risk management | |
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Diving disorders | Pressure related | Oxygen | |
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Inert gases | |
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Carbon dioxide | |
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Breathing gas contaminants | |
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Immersion related | |
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Treatment | |
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Personnel | |
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Screening | |
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Research | Researchers in diving physiology and medicine | |
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Diving medical research organisations | |
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Archeological sites | |
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Underwater art and artists | |
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Engineers and inventors | |
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Historical equipment | |
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Military and covert operations | - Raid on Alexandria (1941)
- Sinking of the Rainbow Warrior
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Scientific projects | |
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Awards and events | |
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Incidents | Dive boat incidents | |
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Diver rescues | |
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Early diving | |
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Freediving fatalities | |
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Offshore diving incidents | - Byford Dolphin diving bell accident
- Drill Master diving accident
- Star Canopus diving accident
- Stena Seaspread diving accident
- Venture One diving accident
- Waage Drill II diving accident
- Wildrake diving accident
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Professional diving fatalities | |
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Scuba diving fatalities | |
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Publications |
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Manuals | - NOAA Diving Manual
- U.S. Navy Diving Manual
- Basic Cave Diving: A Blueprint for Survival
- Underwater Handbook
- Bennett and Elliott's physiology and medicine of diving
- Encyclopedia of Recreational Diving
- The new science of skin and scuba diving
- Professional Diver's Handbook
- Basic Scuba
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Standards and Codes of Practice | |
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General non-fiction | |
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Research | |
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Dive guides | |
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Training and registration |
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Diver training | |
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Recreational scuba certification levels | Core diving skills | |
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Leadership skills | |
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Specialist skills | |
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Diver training certification and registration organisations | Commercial diver certification authorities | |
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Commercial diving schools | |
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Free-diving certification agencies | |
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Recreational scuba certification agencies | |
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Scientific diver certification authorities | |
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Technical diver certification agencies | |
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Military diver training centres | |
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Military diver training courses | |
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Surface snorkeling | |
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Snorkeling/breath-hold | |
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Breath-hold | |
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Open Circuit Scuba | |
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Rebreather | |
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Sports governing organisations and federations | |
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Competitions | |
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Pioneers of diving | |
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Underwater scientists archaeologists and environmentalists | |
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Scuba record holders | |
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Underwater filmmakers and presenters | |
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Underwater photographers | |
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Underwater explorers | |
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Aquanauts | |
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Writers and journalists | |
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Rescuers | |
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Frogmen | |
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Commercial salvors | |
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Diving physics | |
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Diving physiology | |
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Diving environments | |
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Other |
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Deep-submergence vehicle | - Aluminaut
- DSV Alvin
- American submarine NR-1
- Bathyscaphe
- Archimède
- FNRS-2
- FNRS-3
- Harmony class bathyscaphe
- Sea Pole-class bathyscaphe
- Trieste II
- Deepsea Challenger
- Ictineu 3
- JAGO
- Jiaolong
- Konsul-class submersible
- Limiting Factor
- Russian submarine Losharik
- Mir
- Nautile
- Pisces-class deep submergence vehicle
- DSV Sea Cliff
- DSV Shinkai
- DSV Shinkai 2000
- DSV Shinkai 6500
- DSV Turtle
- DSV-5 Nemo
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Submarine rescue | Deep-submergence rescue vehicle | |
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Submarine escape | |
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Special interest groups | |
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Neutral buoyancy facilities for Astronaut training | |
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Other | |
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