The BMD/SCR-4 specifications

Method of Operation

Semi-closed circuit recirculation using an all new Oxygen addition method that is keyed to both respiratory minute volume and depth, thus making decompression calculation similar to open circuit and just as accurate. Existing tables for various standard mixes can be used with very minor calculation adjustments. A custom Orca Phoenix decompression computer is provided with each unit for either air or EAN-32, customer's choice. Gas consumption is approximately 1/5 of open circuit at any depth due to the addition method, lower work of breathing and conservation of body heat. Additions are accomplished through a single first stage supplying a base flow metering valve and redundant (2) second stages. The manual bypass is high pressure in case of a first stage stoppage (highly unlikely). One second stage is adjustable by the diver and can be used as a bailout in case of a catastrophic counterlung breach (also highly unlikely). The same second stage can be buddy breathed by a second diver while the primary diver is still breathing off the recirculating loop. Most gas venting to ambient is done through a sizable diffuser, allowing very silent operation. A counterlung overpressure relief will expel gasses independently if too rapid an acsent is made.

Safety features

It is impossible to become unconscious as a result of hypercapnia with this unit, although a considerable degree of discomfort will occur if the scrubber is completely expended.

Gas flow obstruction due to scrubber flooding is automatically compensated for by the addition mechanism only to the degree necessary for normal breathing until the scrubber can be cleared of water. The scrubber has a power water purge that can be operated by the diver during the dive Scrubber floods are instantly detectable.

Automatic gas addition failure is detectable within 2 breaths. Manually operating the high pressure bypass does not shorten the gas duration because the control mechanism is on the exhalation side of the breathing loop. As long as the diver is able to get a breath, all is well.

Hyperoxia cannot occcur as long as the supply mix is not breathed deeper than would be acceptable on open circuit equipment.

Hypoxia cannot occur as long as the supply mix is not breathed shallower than would be acceptable on open circuit equipment, even on rapid ascents. Provision is made at the valving in the full face mask (provided with the unit) to dump "caustic cocktails" overboard.

Counterlung

Two toroidal low profile bags, one encircling each arm at the shoulder. Breathing dynamics are virtually unchanged by varrying positions. Each bag can be drained both after maintenance rinses and during the dive after inadvertent flooding. The pressure relief is adjustable by the diver during the dive. Total volume is 6.5 liters.

Gas Supply

Four composite cylinders of 18.3 cubic feet each at 300 bar for a total of 73.2 cubic feet (48.8 cubic feet at 200 bar). The cylinders are manifolded to asingle valve and must be both hydrostatically and ultrasonically tested every three years by BMD. The cylinder life is 10,000 cycles over 15 years. Filling is accomplished through an exteriorwhip without removing the case cover.Regulated (140 PSI over ambient) alternate gas sources can be plugged into an exterior quick disconnect fitting and breathed through the recirculating system for efficiency. Disconnection of the alternate supply automatically restores the use of the internal gas supply.

Carbon dioxide removal

Twenty-five percent of all carbon dioxide production is dumped overboard before reaching the scrubber. The remaining 75% is passed transversely through a 4 lb. bed of 8-12 mesh Sofnolyme. The scrubber is constructed of heat formed and welded ABS and is double wall insulated on the exterior. It is also extensively baffled to be highly tolerant of loose packs. The scrubber is not removable. All filling and removal is accomplished from the outside of the rebreather without removing the case cover.

Buoyancy Compensation

Integrated into the system using a completely separate bag. Can be used as an optional bailout.

Exterior Case

Molded flat finish black UHMW polyethylene in 2 pieces. All components are mounted on one piece and the other serves as a removable cover for access. Dimensions are 28.8 inches long by16.5 inches wide by 4.75 inches deep.

Unit Weight

Approximately 48 lbs. dry, depending on size and type of harness.

Maintenance

Approximately 20 minutes per dive, including scrubber repack and rinse. Add gas refill times.

Approximately 30 minutes per week to disinfect breathing loop.

One day (24 hr. turnaround) plus shipping time every 18 months for BMD factory rehab. The first 2, included in the purchase price, are covered exclusive of shipping charges by the BMD 3 year product warranty.
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