Halcyon PVR-BASC

Last updated
Schematic diagram of the breathing loop and gas supply pneumatics of the Halcyon PVR-BASC Rebreather.
.mw-parser-output .plainlist ol,.mw-parser-output .plainlist ul{line-height:inherit;list-style:none;margin:0;padding:0}.mw-parser-output .plainlist ol li,.mw-parser-output .plainlist ul li{margin-bottom:0}
1 DSV/BOV with non-return valves
2 Exhalation hose
3 Primary water trap
4 Manual drain pump
5 Overpressure relief valve
6 Main bellows counterlung
7 Discharge bellows counterlung (variable volume)
8 Discharge valve
9 Axial flow scrubber with secondary water trap
10 Feed gas demand valves
11 Inhalation hose
12 Feed gas supply cylinder
13 Cylinder valve
14 High pressure regulator (1st stage)
15 Submersible pressure gauge
16 Intermediate pressure gas connectors
17 Drain port for cleaning and drying counterlung Halcyon PVR-BASC loop schematic.png
Schematic diagram of the breathing loop and gas supply pneumatics of the Halcyon PVR-BASC Rebreather.
  • 1 DSV/BOV with non-return valves
  • 2 Exhalation hose
  • 3 Primary water trap
  • 4 Manual drain pump
  • 5 Overpressure relief valve
  • 6 Main bellows counterlung
  • 7 Discharge bellows counterlung (variable volume)
  • 8 Discharge valve
  • 9 Axial flow scrubber with secondary water trap
  • 10 Feed gas demand valves
  • 11 Inhalation hose
  • 12 Feed gas supply cylinder
  • 13 Cylinder valve
  • 14 High pressure regulator (1st stage)
  • 15 Submersible pressure gauge
  • 16 Intermediate pressure gas connectors
  • 17 Drain port for cleaning and drying counterlung

The Halcyon Passive, Variable Ratio-Biased Addition Semi-Closed rebreather is a unique design of semi-closed rebreather using a depth-compensated passive gas addition system. [1] Passive addition implies that in steady state operation (at a constant depth) addition of fresh feed gas is a response to low volume of gas in the loop - the gas is injected when the top of the counterlung activates a demand type addition valve, which provides feed gas as long as the diver continues to inhale. The mechanism discharges gas to the environment in proportion to breathing volume to induce this gas feed.

Contents

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]

Counterlung

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.

Harness

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

Gas supply

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.

Loop oxygen fraction

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.

Related Research Articles

<span class="mw-page-title-main">Scuba set</span> Self-contained underwater breathing apparatus

A scuba set, originally just scuba, is any breathing apparatus that is entirely carried by an underwater diver and provides the diver with breathing gas at the ambient pressure. Scuba is an anacronym for self-contained underwater breathing apparatus. Although strictly speaking the scuba set is only the diving equipment that is required for providing breathing gas to the diver, general usage includes the harness or rigging by which it is carried and those accessories which are integral parts of the harness and breathing apparatus assembly, such as a jacket or wing style buoyancy compensator and instruments mounted in a combined housing with the pressure gauge. In the looser sense, scuba set has been used to refer to all the diving equipment used by the scuba diver, though this would more commonly and accurately be termed scuba equipment or scuba gear. Scuba is overwhelmingly the most common underwater breathing system used by recreational divers and is also used in professional diving when it provides advantages, usually of mobility and range, over surface-supplied diving systems and is allowed by the relevant legislation and code of practice.

<span class="mw-page-title-main">Aqua-Lung</span> Original name for open-circuit scuba equipment

Aqua-Lung was the first open-circuit, self-contained underwater breathing apparatus to achieve worldwide popularity and commercial success. This class of equipment is now commonly referred to as a twin-hose diving regulator, or demand valve. The Aqua-Lung was invented in France during the winter of 1942–1943 by two Frenchmen: engineer Émile Gagnan and Jacques Cousteau, who was a Naval Lieutenant. It allowed Cousteau and Gagnan to film and explore underwater more easily.

<span class="mw-page-title-main">Rebreather</span> Portable apparatus to recycle breathing gas

A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. Oxygen is added to replenish the amount metabolised by the user. This differs from open-circuit breathing apparatus, where the exhaled gas is discharged directly into the environment. The purpose is to extend the breathing endurance of a limited gas supply, while also eliminating the bubbles otherwise produced by an open circuit system. The latter advantage over other systems is useful for covert military operations by frogmen, as well as for undisturbed observation of underwater wildlife. A rebreather is generally understood to be a portable apparatus carried by the user. The same technology on a vehicle or non-mobile installation is more likely to be referred to as a life-support system.

<span class="mw-page-title-main">Diving regulator</span> Mechanism that controls the pressure of a breathing gas supply for diving

A diving regulator or underwater diving regulator is a pressure regulator that controls the pressure of breathing gas for underwater diving. The most commonly recognised application is to reduce pressurized breathing gas to ambient pressure and deliver it to the diver, but there are also other types of gas pressure regulator used for diving applications. The gas may be air or one of a variety of specially blended breathing gases. The gas may be supplied from a scuba cylinder carried by the diver, in which case it is called a scuba regulator, or via a hose from a compressor or high-pressure storage cylinders at the surface in surface-supplied diving. A gas pressure regulator has one or more valves in series which reduce pressure from the source, and use the downstream pressure as feedback to control the delivered pressure, or the upstream pressure as feedback to prevent excessive flow rates, lowering the pressure at each stage.

<span class="mw-page-title-main">IDA71</span> Russian military rebreather for underwater and high altitude use

The Soviet, later Russian IDA71 military and naval rebreather is an oxygen rebreather intended for use by naval and military divers including Russian commando frogmen. As supplied it is in a plain backpack harness with no buoyancy aid. The casing is pressed aluminium with a hinged cover. It has a small optional nitrox cylinder which can be clipped on its outside to convert it to nitrox mode. It contains one oxygen cylinder and two absorbent canisters. In the bottom of its casing is an empty space which is intended for an underwater communications set.

<span class="mw-page-title-main">Breathing apparatus</span> Equipment allowing or assisting the user to breath in a hostile environment

A breathing apparatus or breathing set is equipment which allows a person to breathe in a hostile environment where breathing would otherwise be impossible, difficult, harmful, or hazardous, or assists a person to breathe. A respirator, medical ventilator, or resuscitator may also be considered to be breathing apparatus. Equipment that supplies or recycles breathing gas other than ambient air in a space used by several people is usually referred to as being part of a life-support system, and a life-support system for one person may include breathing apparatus, when the breathing gas is specifically supplied to the user rather than to the enclosure in which the user is the occupant.

<span class="mw-page-title-main">Dräger (company)</span> German manufacturer of breathing equipment

Dräger is a German company based in Lübeck which makes breathing and protection equipment, gas detection and analysis systems, and noninvasive patient monitoring technologies. Customers include hospitals, fire departments and diving companies.

CUMA is a make of rebreather underwater breathing set designed and made in Canada for the Canadian Armed Forces by Fullerton Sherwood Engineering Ltd to replace the Royal Navy CDBA.

<span class="mw-page-title-main">Bailout bottle</span> Emergency gas supply cylinder carried by a diver

A bailout bottle (BoB) or, more formally, bailout cylinder is a scuba cylinder carried by an underwater diver for use as an emergency supply of breathing gas in the event of a primary gas supply failure. A bailout cylinder may be carried by a scuba diver in addition to the primary scuba set, or by a surface supplied diver using either free-flow or demand systems. The bailout gas is not intended for use during the dive except in an emergency, and would be considered a fully redundant breathing gas supply if used correctly. The term may refer to just the cylinder, or the bailout set or emergency gas supply (EGS), which is the cylinder with the gas delivery system attached. The bailout set or bailout system is the combination of the emergency gas cylinder with the gas delivery system to the diver, which includes a diving regulator with either a demand valve, a bailout block, or a bailout valve (BOV).

<span class="mw-page-title-main">Underwater breathing apparatus</span> Equipment which provides breathing gas to an underwater diver

Underwater breathing apparatus is equipment which allows the user to breathe underwater. The three major categories of ambient pressure underwater breathing apparatus are:

<span class="mw-page-title-main">Scuba gas management</span> Logistical aspects of scuba breathing gas

Scuba gas management is the aspect of scuba diving which includes the gas planning, blending, filling, analysing, marking, storage, and transportation of gas cylinders for a dive, the monitoring and switching of breathing gases during a dive, efficient and correct use of the gas, and the provision of emergency gas to another member of the dive team. The primary aim is to ensure that everyone has enough to breathe of a gas suitable for the current depth at all times, and is aware of the gas mixture in use and its effect on decompression obligations, nitrogen narcosis, and oxygen toxicity risk. Some of these functions may be delegated to others, such as the filling of cylinders, or transportation to the dive site, but others are the direct responsibility of the diver using the gas.

<span class="mw-page-title-main">Rebreather diving</span> Underwater diving using self contained breathing gas recycling apparatus

Rebreather diving is underwater diving using diving rebreathers, a class of underwater breathing apparatus which recirculate the breathing gas exhaled by the diver after replacing the oxygen used and removing the carbon dioxide metabolic product. Rebreather diving is practiced by recreational, military and scientific divers in applications where it has advantages over open circuit scuba, and surface supply of breathing gas is impracticable. The main advantages of rebreather diving are extended gas endurance, low noise levels, and lack of bubbles.

<span class="mw-page-title-main">Interspiro DCSC</span> Military semi-closed circuit passive addition diving rebreather

The Interspiro DCSC is a semi-closed circuit nitrox rebreather manufactured by Interspiro of Sweden for military applications. Interspiro was formerly a division of AGA and has been manufacturing self-contained breathing apparatus for diving, firefighting and rescue applications since the 1950s.

The Halcyon RB80 is a non-depth-compensated passive addition semi-closed circuit rebreather of similar external dimensions to a standard AL80 scuba cylinder. It was originally developed by Reinhard Buchaly (RB) in 1996 for the cave exploration dives conducted by the European Karst Plain Project (EKPP).

Work of breathing (WOB) is the energy expended to inhale and exhale a breathing gas. It is usually expressed as work per unit volume, for example, joules/litre, or as a work rate (power), such as joules/min or equivalent units, as it is not particularly useful without a reference to volume or time. It can be calculated in terms of the pulmonary pressure multiplied by the change in pulmonary volume, or in terms of the oxygen consumption attributable to breathing.

<span class="mw-page-title-main">Diving rebreather</span> Closed or semi-closed circuit scuba

A Diving rebreather is an underwater breathing apparatus that absorbs the carbon dioxide of a diver's exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. Oxygen is added to replenish the amount metabolised by the diver. This differs from open-circuit breathing apparatus, where the exhaled gas is discharged directly into the environment. The purpose is to extend the breathing endurance of a limited gas supply, and, for covert military use by frogmen or observation of underwater life, to eliminate the bubbles produced by an open circuit system. A diving rebreather is generally understood to be a portable unit carried by the user, and is therefore a type of self-contained underwater breathing apparatus (scuba). A semi-closed rebreather carried by the diver may also be known as a gas extender. The same technology on a submersible or surface installation is more likely to be referred to as a life-support system.

<span class="mw-page-title-main">Mechanism of diving regulators</span> Arrangement and function of the components of regulators for underwater diving

The mechanism of diving regulators is the arrangement of components and function of gas pressure regulators used in the systems which supply breathing gases for underwater diving. Both free-flow and demand regulators use mechanical feedback of the downstream pressure to control the opening of a valve which controls gas flow from the upstream, high-pressure side, to the downstream, low-pressure side of each stage. Flow capacity must be sufficient to allow the downstream pressure to be maintained at maximum demand, and sensitivity must be appropriate to deliver maximum required flow rate with a small variation in downstream pressure, and for a large variation in supply pressure, without instability of flow. Open circuit scuba regulators must also deliver against a variable ambient pressure. They must be robust and reliable, as they are life-support equipment which must function in the relatively hostile seawater environment, and the human interface must be comfortable over periods of several hours.

<span class="mw-page-title-main">Glossary of breathing apparatus terminology</span> Definitions of technical terms used in connection with breathing apparatus

A breathing apparatus or breathing set is equipment which allows a person to breathe in a hostile environment where breathing would otherwise be impossible, difficult, harmful, or hazardous, or assists a person to breathe. A respirator, medical ventilator, or resuscitator may also be considered to be breathing apparatus. Equipment that supplies or recycles breathing gas other than ambient air in a space used by several people is usually referred to as being part of a life-support system, and a life-support system for one person may include breathing apparatus, when the breathing gas is specifically supplied to the user rather than to the enclosure in which the user is the occupant.

<span class="mw-page-title-main">Index of underwater diving: A–M</span> Alphabetical listing of underwater diving related topics

The following index is provided as an overview of and topical guide to underwater diving:

References

  1. DUI Halcyon PVR-BASC Manual
  2. Nuckols, ML; Finlayson, WS; Newville, B; Gavin, WA Jr (2001). "Comparison of predicted and measured oxygen levels in a semi-closed underwater breathing apparatus". Oceans 2001. Vol. 3. pp. 1725–1730. doi:10.1109/OCEANS.2001.968093. ISBN   978-0-933957-28-2. Archived from the original on 2014-04-07. Retrieved 2013-05-16.
  3. Kellon, J. (1996), Passive Semi-Closed Circuit Rebreather Diver Manual, International Association of Nitrox Technical Divers. (IANTD)