halcyon pvr basc

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Good article describing the passive addition rebreather produced by Halcyon. These are respiratory minute volume keyed SCR Rebreathers.

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  • Halcyon PVR-BASC 1

    Halcyon PVR-BASC

    Schematic diagram of the breathing loop and gas supply pneumatics of the HalcyonPVR-BASC Rebreather.1 DSV/BOV with non-return valves 2 Exhalation hose 3 Primarywater trap 4 Manual drain pump 5 Overpressure relief valve 6 Main bellows counterlung

    7 Discharge bellows counterlung (variable volume) 8 Discharge valve 9 Axial flowscrubber with secondary water trap 10 Feed gas demand valves 11 Inhalation hose 12Feed gas supply cylinder 13 Cylinder valve 14 High pressure regulator (1st stage) 15

    Submersible pressure gauge 16 Intermediate pressure gas connectors 17 Drain port forcleaning and drying counterlung

    The Halcyon Passive, VariableRatio-Biased Addition Semi-Closedrebreather is a unique design ofsemi-closed rebreather using adepth-compensated passive gasaddition system.[1] Passive additionimplies that in steady state operation(at a constant depth) addition of freshfeed gas is a response to low volume ofgas in the loop - the gas is injectedwhen the top of the counterlungactivates a demand type addition valve,which provides feed gas as long as thediver continues to inhale. Themechanism discharges gas to theenvironment in proportion to breathingvolume to induce this gas feed.

    In the PVR-BASC the discharged gasvolume is a function of depth andbreath volume. The passive additionoccurs during each inhalation as theloop volume is deficient by the amountdisharged. The volumetric ratio ofdischarged gas to exhaled gas volumevaries with depth, and decreases as thepressure increases.

    At the surface one quarter of thevolume of an exhaled breath is discharged. As the ambient pressure increases with depth, the volume of the innercounterlumg 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. Italso means that the calculation of inhalation gas oxygen fraction must take this into account. This also reducesexposure of the scrubber absorbent medium to cold gas, and increases dwell time of exhaled gas in the scrubber, bothof which improve the efficiency of CO2 absorption.

    Gas discharge takes place before the remaining exhaled gas reaches the scrubber, so the discharged gas does notwaste 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 90m (10 bar) so thegas saving below this depth is not as great as for shallower dives. The slightly higher feed rates will push the partialpressure of oxygen in the loop closer to the feed gas value.[2]

  • Halcyon PVR-BASC 2

    CounterlungThe PVR-BASC has a hinged bellows counterlung, similar to that of the Interspiro DCSC, and like the DCSC the topcover of the counterlung is weighted to improve breathing effort. However unlike the DCSC, the PVR-BASC usesan internal secondary bellows to discharge a portion of the exhaled gas during the incalation part of the preathingcylcle, when the main counterlung closes and pumps out the contents of the inner bellows. The reduction in volumeof the inner counterlung with depth results in an approximation of a mass discharge proportional to breathingvolume.

    HarnessThe PVR-BASC is designed to be carried on a standard Hogarthian backplate and wing harness.

    Gas supplyThe frame is designed to carry a cylinder on each side. The only restrictions on size are what the diver can carry, andthe scrubber endurance. The cylinders are normally rigged with open circuit regulators in the standard DIRconfiguration for bailout, and a supply hose with quick connector on each for the rebreather supply.

    Loop oxygen fractionThe rebreather maintains a substantially constant breathing gas composition at any given depth regardless of thelevel of exertion, but gas consumption will vary with exertion.

    Gallery

    Halcyon PVR-BASC BOV/DSVand breathing hoses

    Halcyon PVR-BASC Bailoutvalve/Dive-surface valve

    Halcyon PVR-BASC BOV/DSVBailout valve/Dive-surface valve

    Halcyon PVR-BASC BOV/DSVBailout valve/Dive-surface valve

    Halcyon PVR-BASC breathinghose connector

    Halcyon PVR-BASC BOV/DSVbreathing hose connector

    Halcyon PVR-BASC BOV/DSVside view with cover

    Halcyon PVR-BASC BOV/DSVtop end view with cover

  • Halcyon PVR-BASC 3

    Halcyon PVR-BASC BOV/DSVwith cover

    Halcyon PVR-BASC BOV/DSVwith cover

    Halcyon PVR-BASC semi-closedcircuit rebreather - closed, from

    top/front

    Halcyon PVR-BASC semi-closedcircuit rebreather - open, from

    above

    Halcyon PVR-BASC semi-closedcircuit rebreather -open from

    above

    Halcyon PVR-BASC semi-closedcircuit rebreather - open, from

    left

    Halcyon PVR-BASC semi-closedcircuit rebreather - open, from

    right

    Halcyon PVR-BASC semi-closedcircuit rebreather - open, from

    top/front

    Halcyon PVR-BASC semi-closedcircuit rebreather - open, from

    top/front

    Halcyon PVR-BASC semi-closedcircuit rebreather - open from

    top/front

    Halcyon PVR-BASC semi-closedcircuit rebreather - open, from

    left

    Halcyon PVR-BASC semi-closedcircuit rebreather - open, from

    right

    Halcyon PVR-BASC semi-closedcircuit rebreather scrubber -

    assembled and mounted

    Halcyon PVR-BASC semi-closedcircuit rebreather - bellows

    counterlung

    Halcyon PVR-BASC semi-closedcircuit rebreather scrubber

    components

    Halcyon PVR-BASC semi-closedcircuit rebreather - Scrubber

    internal components

  • Halcyon PVR-BASC 4

    Halcyon PVR-BASC semi-closedcircuit rebreather absorbent

    canister

    Halcyon PVR-BASC semi-closedcircuit rebreather scrubber casinginterior and secondary water trap

    Halcyon PVR-BASC semi-closedcircuit rebreather - scrubbermedium retaining screen and

    spring

    Halcyon PVR-BASC semi-closedcircuit rebreather - overpressure

    dump valve

    Halcyon PVR-BASC semi-closedcircuit rebreather - bellows

    counterlung detail

    Halcyon PVR-BASC semi-closedcircuit rebreather

    Halcyon PVR-BASC semi-closedrebreather. breathing hose

    connector

    Halcyon PVR-BASC semi-closedrebreather Manual gas supplyvalves and loop drain pump

    Halcyon PVR-BASC semi-closedrebreather - underside

    Halcyon PVR-BASC semi-closedrebreather - underside, showing

    gas supply connectors, hoses andmanual valves, and loop drain

    pump

    Halcyon PVR-BASC semi-closedrebreather underside, showing

    bolts for connection to backplate

    Halcyon PVR-BASC semi-closedrebreather breathing hose

    connector

    Halcyon PVR-BASC semi-closedrebreather. breathing hose

    connector cover

  • Halcyon PVR-BASC 5

    References[1][1] DUI Halcyon PVR-BASC Manual[2] Kellon, J. (1996), Passive Semi-Closed Circuit Rebreather Diver Manual, International Association of Nitrox Technical Divers. (IANTD)

  • Article Sources and Contributors 6

    Article Sources and ContributorsHalcyon PVR-BASC Source: http://en.wikipedia.org/w/index.php?oldid=571773102 Contributors: Gene Hobbs, Pbsouthwood

    Image Sources, Licenses and ContributorsFile:Halcyon PVR-BASC loop schematic.png Source: http://en.wikipedia.org/w/index.php?title=File:Halcyon_PVR-BASC_loop_schematic.png License: Creative CommonsAttribution-Sharealike 3.0 Contributors: User:PbsouthwoodFile:PVR-BASC BOV and breathing hoses P5167681.JPG Source: http://en.wikipedia.org/w/index.php?title=File:PVR-BASC_BOV_and_breathing_hoses_P5167681.JPG License: CreativeCommons Attribution-Sharealike 3.0 Contributors: User:PbsouthwoodFile:PVR-BASC Bailout valve P5167687.JPG Source: http://en.wikipedia.org/w/index.php?title=File:PVR-BASC_Bailout_valve_P5167687.JPG License: Creative CommonsAttribution-Sharealike 3.0 Contributors: User:PbsouthwoodFile:PVR-BASC Bailout valve P5167688.JPG Source: http://en.wikipedia.org/w/index.php?title=File:PVR-BASC_Bailout_valve_P5167688.JPG License: Creative CommonsAttribution-Sharealike 3.0 Contributors: User:PbsouthwoodFile:PVR-BASC Bailout valve P5167689.JPG Source: http://en.wikipedia.org/w/index.php?title=File:PVR-BASC_Bailout_valve_P5167689.JPG License: Creative CommonsAttribution-Sharealike 3.0 Contributors: User:PbsouthwoodFile:PVR-BASC breathing hose connector P5167690.JPG Source: http://en.wikipedia.org/w/index.php?title=File:PVR-BASC_breathing_hose_connector_P5167690.JPG License: CreativeCommons Attribution-Sharealike 3.0 Contributors: User:PbsouthwoodFile:PVR-BASC breathing hose connector P5167692.JPG Source: http://en.wikipedia.org/w/index.php?title=File:PVR-BASC_breathing_hose_connector_P5167692.JPG License: CreativeCommons Attribution-Sharealike 3.0 Contributors: User:PbsouthwoodFile:Halcyon PVR-BASC side view P5167697.JPG Source: http://en.wikipedia.org/w/index.php?title=File:Halcyon_PVR-BASC_side_view_P5167697.JPG License: Creative CommonsAttribution-Sharealike 3.0 Contributors: User:PbsouthwoodFile:Halcyon PVR-BASC top end view P5167699.JPG Source: http://en.wikipedia.org/w/index.php?title=File:Halcyon_PVR-BASC_top_end_view_P5167699.JPG License: CreativeCommons Attribution-Sharealike 3.0 Contributors: User:PbsouthwoodFile:PVR-BASC P5167701.JPG Source: http://en.wikipedia.org/w/index.php?title=File:PVR-BASC_P5167701.JPG License: Creative Commons Attribution-Sharealike 3.0 Contributors:User:PbsouthwoodFile:PVR-BASC P5167703.JPG Source: http://en.wikipedia.org/w/index.php?title=File:PVR-BASC_P5167703.JPG License: Creative Commons Attribution-Sharealike 3.0 Contributors:User