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 ascent is made.
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 occur 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.
Two toroidal low profile bags, one encircling each arm at the shoulder.
Breathing dynamics are virtually unchanged by varying 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.
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.
Approximately 48 lbs. dry, depending on size and type of harness.
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.
A revolutionary new semi-closed diver rebreather system is now available
to the scientific, military, and public safety diving communities.
Originally developed to provide additional safety within the commercial
diving industry, the SCR-4 offers a dive duration of up to 4 hours in the
air diving range, allowing for greatly extended operations not possible with
conventional open circuit scuba systems. Breathing function is linked to
diver activity level using a special proportional valve, making electronic
control unnecessary. The elegantly simple design incorporates a highly
efficient, low resistance scrubber unit and hybrid face mask and helmet.
The standard production unit uses compressed air as the single supply gas
and can maintain safe oxygen partial pressures even at the surface.
Utilizing automatic and redundant breathing loop inlet gas flows, including
two linked to diver work level, the SCR-4 design prevents the development of
the classical low oxygen conditions inherent to other designs. More stable
inhaled oxygen levels also allow decompression to be predicted more
accurately than is possible with traditional semi-closed rebreathers. The
SCR-4 comes equipped with a specially programmed ORCA Phoenix dive computer
built for the system.
The Minihat 1600-R Hybrid Hat, supplied with the unit, provides corrected
panoramic vision, high-impact head protection, is extremely light weight,
and incorporates a new concept speaker/microphone compatible with most
through-water communication systems. The unique "hard hat like" enclosure
system allows for easy donning and doffing while preventing inadvertent
Keeping Advanced Technology Simple...
The SCR-4 system was developed in order to resolve the historical
problems and limitations found in conventional rebreather designs. As an
example, its unique approach utilizes toroïdal,
pressure-balanced counterlungs that ensure minimal breathing resistance in
all positions. A totally new "interactive" breathing circuit permits the
safe use of air as the single supply gas. A proportional valve recirculates
most of each breath and exhausts the remainder overboard through a diffuser,
producing very small bubbles that are unubtrusive to marine life. This
exhaust rate is linked to the diver's inhalation volume which is delivered
using up to 4 independant gas addition systems. This feature permits the
SCR-4 to maintain a stable oxygen level over a wide range of diver
workloads. A special ORCA Phoenix dive computer takes advantage of the
stable oxygen levels, making decompression efficient and easily managed. The
scrubber is designed for up to four hours of use and is protected from
flooding and insulated from cold. The BMD "hat" is not only light weight and
low volume, but combines the airway protection of a full face mask with the
protection and communications of a helmet. A special panoramic lens is
perfect for close work in low visibility and ideal for photographers. This
rounds out the most advanced personal diving system available today.
* The unit weighs less than 45 pounds and sits comfortably close to the
diver's back utilizing a soft harness
* The SCR-4 has no electronic control systems requiring batteries, but
included an oxygen partial pressure monitor for added safety
* The SCR-4 contains 73 cubic feet of gas in 4 composite cylinders at
4500psig. This is comparable to 292 cubic feet in an open circuit unit. (the
cylinders contain 48 cubic feet of gas at 3000 psig, which is comparable to
192 cubic feet with an open circuit system)
* An interactive relationship of the components in the breathing circuit
provides for a safe partial pressure of oxygen, even when utilizing air at
or near the surface where PO2 is lowest.
* Standard SCR-4 units are charged with air, but special units can be
factory modified for oxygen enriched air or pure oxygen missions.
* The unit has the same depth restrictions as open circuit equipment
utilizing the same gas mixture and equivilent supply volume.
* The unit is designed to maintain function despite substantial flooding and
is (less? more??) likely than open circuit scuba to fail to supply breathing
* The SCR-4 system takes advantage of hydrodynamic differentials between the
counterlungs and diver lung centroid to maximize breathing performance.
Breathing resistance is lower that U.S. Navy requirements in all diver
* A partially or totally occluded breathing circuit will simply force the
system to shift to proportionately greater open circuit operation in order
to maintain breathing gas supply as long as primary pressure is available.
* Four in dependant gas addition devices are included in the circuit, three
of which operate independantly of diver control.
* Two in dependant and redundant addition systems are keyed to diver RMV
(breathing rate) with individual selection and activation depending on diver
position within the water column, or use of manual overrides.
* An adjustable base flow addition system, similar to other semi-closed
addition systems, provides up to 10 scf/h of gas flow independent pf diver
* The fourth addition system is a diver actuated high pressure bypass which
is in dependant of the regulation system. This eliminates the classic
concern of first stage regulator failure.
* Buddy breathing can be safely effected utilizing the mouthpiece attached
to the counterlung manual addition control.
* The SCR-4's unique circuit dynamics prevent debilitating CO2
concentrations regardless of scrubber absorbent condition.
* Scrubber design provides extremely low breathing resistance with
efficiency uneffected by loose CO2 absorbent packing.
* CO2 scrubber performance is optimized by thermally insulating the unit in
order to maintain the reaction in cold water environments and by dumping a
portion of the diver's exhalation gas prior to passage through the scrubber.