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This invention relates to a closed circuit re-breathing apparatus intended
primarily for the use of a diver, and has for an object the conservation
of gases.
A further object of the invention is to provide apparatus which will
incorporate valuable safety features.
Although a device according to this invention is intended primarily for the
use of a diver, it will be apparent that the invention is also of use in
other applications wherein a breathable mixture is required, for example
under-water living quarters, decompression chambers, space capsules,
incubators, oxygen tents, work in smoke or polluted atmosphere, underwater
fire-fighting work, or the like.
BACKGROUND OF THE INVENTION
When deep lung dives are to be undertaken, decompression requirements make
it necessary for the diver to remain under the surface of the water for
some considerable time. Open circuit breathing is therefore no longer
feasible because of cost, and it is necessary for a diver to rebreath
atmosphere which has already been breathed, scrubbing the carbon dioxide
exhaled by the river with a suitable material (for example barium
hydroxide) and replenishing the oxygen as it is required. It is believed
that the safest inert gas to be mixed with oxygen is helium, and for deep
dives it is necessary that the percentage of oxygen be very much less than
under atmospheric conditions. Thus typically it is necessary for the
oxygen content of the breathable gas to be about 10% if the depth of the
dive is between 250 feet and 600 feet. (The standard procedure is to use
air 0-100 feet; from 100-250 feet either 50% helium, 50% air or 20%
O.sub.2 in helium; from 600 feet to a greater depth the oxygen content is
varied in accordance with calculations, but will be less than 10%). If
oxygen is used to excess, oxygen poisoning can result, this being a most
serious hazard to a diver.
In the U.S. Pat. No. 3,556,098 issued to John W. Kanwisher and Walter A.
Starck there was described and claimed an apparatus for use by divers
wherein the partial pressure of the oxygen in the breathing gases was
sensed and when the partial pressure dropped below a lower limit which was
not predetermined for a specific dive, but calculated as a percentage per
atmosphere, an electrical circuit was energised to drive a solenoid and to
add further oxygen. Equipment produced in accordance with the said Patent
Specification has been used with some degree of success, but certain
difficulties have been encountered. Owing to the lethal nature of
difficulties encountered with diving apparatus it is not clear what the
basic problems have been, but it is believed that one of the difficulties
encountered is the inability of partial pressure sensing to provide a very
smooth transition from one mixture strength to another, (for example, when
surface supplied emergency gas needs to be used). Furthermore, the
percentage of oxygen in the breathing gases varies widely with differences
of pressure encountered under normal diving procedures. It is recognised
that there are some circumstances under which the human body can tolerate
only gradual changes (not more than 3% per minute), and one of the objects
of this invention is to provide means whereby the oxygen is maintained,
not to pre-determined partial pressure, but to a pre-determined percentage
of the total breathable gas.
Further, to meet the difficulty of a diver transferring from automatic to
manually controlled fixed percentage breathable gases, another object of
this invention is to provide simple means whereby a diver can control the
atmosphere which he breathes, over-riding the automatic control device.
Other prior art includes the United States Specification accompanying the
U.S. Pat. No. 3,695,261 issued to Donald R. Emmons, wherein a re-breathing
apparatus was described which was useful for scuba diving, and the
apparatus incorporated means for breathing into and out of a CO.sub.2
scrubber for the removal of CO.sub.2, and an oxygen sensor for sensing the
partial pressure of oxygen in the atmosphere of the re-breather. It is
stated to be not useful for very deep dives, (say exceeding 200 feet)
except for very short periods of time, partly because the device described
therein does not provide means for breathing inert gases other than
nitrogen, and partly because it does not provide means for reducing the
percentage of oxygen (by volume) as the diver depth is increased, and
oxygen poisoning or nitrogen narcosis can result.
Further prior art known to the applicant includes the specification
accompanying U.S. Pat. No. 3,252,458 issued to A. R. Krasberg. In that
apparatus however the sensing of oxygen was again the sensing of partial
pressure rather than the sensng of percentage.
BRIEF SUMMARY OF THE INVENTION
This invention relates to re-breathing apparatus of a closed circuit type
which is useful for underwater use, and which comprises a first gas
storage bottle containing air, or helium and oxygen, a second cylinder
containing oxygen alone, a gas circuit, and an electrical circuit. The gas
circuit is provided with gas flow control valves coupled to the respective
cylinders, a breathing bag, a mouth piece, a carbon dioxide scrubber, and
a solenoid valve coupled to the oxygen cylinder and arranged to be
energised to introduce oxygen into the breathable atmosphere when the
oxygen content therein drops below a certain limit. The solenoid is
arranged to terminate addition of oxygen when the oxygen content increases
above a further limit.
The electrical circuit comprises a pair of transducers in the gas circuit,
one of which is sensitive to oxygen partial pressure and the other
sensitive to total pressure, the outputs of the two transducers being
amplified and fed into an analogue divider, the output of the divider
being responsive to percentage of oxygen in the breathable atmosphere and
the output of the divider being effective to energise the solenoid through
solenoid driving means (which may itself be constituted by amplifiers).
The device thereby maintains the oxygen content of the breathable
atmosphere within limits of percentage, rather than within limits of
partial pressure. These limits are maintained notwithstanding variation of
depth of operation by the diver.
BRIEF DESCRIPTION OF THE DRAWINGS
An embodiment of the invention is described hereunder in some detail with
reference to and as illustrated in the accompanying drawings in which:
FIG. 1 is a block diagram illustrating the gas circuit,
FIG. 2 is a wiring diagram illustrating the electrical circuit, and
FIG. 3 shows the physical arrangement of the elements of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the preferred embodiment a mouth piece 10 opens into a small manifold
11, the manifold 11 having a main inlet conduit 12 formed with flexible
bellows section rubber hosing, and a similar main outlet conduit 13. The
inlet conduit 12 is provided with a one way flap valve 15 and the outlet
conduit 13 is provided with a flap valve 16, in this regard the device
being in accordance with standard mouth piece design.
However the manifold 11 is further provided with a flexible hose 19 which
couples through a regulating valve 20 and a shut off valve 21 to a gas
cylinder 22 containing helium, or air and oxygen mixtures under pressure.
The hose 19 does not pass directly into the manifold 11, but leads into a
push button valve 24, the push button valve 24 constituting one of two
over-riding valves enabling a diver to immediately provide himself with a
breathable atmosphere (for example of helium and oxygen) in the event that
there is malfunction of the equipment, or to manually inflate the
breathing bag. This constitutes a very important safety feature in this
invention.
A second cylinder designated 26 contains oxygen alone (of sufficient purity
for breathing purposes), and this oxygen is coupled to a mixing chamber 32
through a flexible hose 27, the second cylinder 26 like the first cylinder
22, being provided with a shut-off valve also designated 21 and a
regulator valve which is also designated 20 as in the first cylinder 22. A
second over-ride push button valve 28 is provided, this being the line 27.
The push button valve 28 is provided with a spring loaded safety cover
(not shown) to prevent accidental oxygen injection, to make it a little
less obvious for the diver to operate, although the valve will be readily
operable by the diver. The diving procedure is discussed below.
The flexible hose 27 is essentially a branch line, since the breathable
atmosphere is continuously monitored and oxygen is added automatically as
it is required through a main oxygen line designated 30 by means of a
solenoid valve 31. The main oxygen line 30 passes into a mixing chamber
designated 32 which contains three sensors. The first sensor is designated
34 and is a total pressure transducer, and the second sensor is an oxygen
partial pressure transducer and is sensitive to the partial pressure of
oxygen within the breathable atmosphere, while the third self-biasing
transducer designated 36 is a separate transducer also being an oxygen
partial pressure transducer, and feeds an independent meter 37 which
functions as a double check, as discussed below.
The flexible hose 19 may also be regarded as a by-pass line to a main
helium and oxygen line designated 40, the line 40 passing to the mixing
chamber 32 through a check valve 41. The check valve 41 is of known type,
either a balanced spool valve or a balanced diaphragm valve, wherein the
pressure in the mixing chamber 32 is referenced to the pressure
surrounding the apparatus as the diver descends, and when the pressure
surrounding the apparatus due to the depth of water increases above the
pressure within the mixing chamber 32, the check valve 41 opens to allow
the passage of a further quantity of helium and oxygen to pass into the
mixing chamber. It should be pointed out that in some instances the check
valve 41 can be dispensed with entirely, and the valve 24 only be employed
to replenish helium and oxygen to the breathable atmosphere.
As will be seen from FIG. 1 the outlet conduit 13 from the manifold 11 has
a branch line 43 extending into a breathing bag 44 formed from flexible
material (for example rubber sheet) the breathing bag 44 being provided
with a pressure relief valve 45 which opens if the pressure within the
breathing bag 44 exceeds that of the surrounding water, that is it opens
automatically upon the diver's ascent.
The outlet conduit 13 extends to a carbon dioxide scrubber designated 48,
the carbon dioxide scrubber 48 being a container containing granules of
barium hydroxide through which the gas passes before re-entering the
mixing chamber. (About four pounds of barium hydroxide is useful for a 6
hour dive at 70.degree.F.) It will thus be seen that the gas generally
circulates from the mixing chamber, through the mouth piece, and then
outwardly from the mouth piece through the carbon dioxide scrubber and
back to the mixing chamber, after the carbon dioxide has been depleted.
Referring now to FIG. 2, an electronic control, generally designated 51
comprises the two transducers 34 and 35. It will be appreciated by those
skilled in the art that a problem exists in converting the partial
pressure of oxygen which is essentially that pressure sensed by the
transducer 35 to become a percentage or proportion of oxygen in the
breathable mixture so as to avoid the variations of oxygen concentration
as a diver varies his depth of dive during a normal working period. This
is achieved in this invention by amplifying the output of the partial
pressure transducer 35 through an amplifier 52 and amplifying the output
of the total pressure transducer 34 through an amplifier 53, and feeding
the amplified signals to an analogue divider designated 54. The output of
the analogue divider 54 is in turn fed into further amplifiers designated
56 (for the addition of oxygen) and 57 (to effect de-energising of the
solenoid 31). The amplifiers 56 and 57 in turn drive a solenoid valve
control transistor network which is designated generally 58, and which
controls the solenoid 31 in accordance with known art. The solenoid draws
its energy from a battery designated 59. The transistors of the network 58
are designated 60, 61, 62 and 63.
In order to provide additional safety to the diver, use is made of an
illuminated alarm designated 65. Conveniently this alarm is carried on the
diver's facepiece, but is illustrated only in FIG. 2. The alarm 65 draws
its power (as do the transducers 34 and 35) from electronics power battery
designated 66, it being noted that the batteries 59 and 66 are separated
from one another to reduce the risk of battery power failure. The alarm is
excited from the analogue divider 54 when the oxygen percentage drops
below a safe level or when it rises above its safe level, the alarm being
controlled by a network of transistors designated 67. It should be noted
that the transistors 67 and the transistors of the network 68 are well
known and used in accordance with their normal functions, but the actual
selection of elements for the invention is discussed below.
In order to provide the diver with an indication of the breathable mixture
which he is using, there is provided an oxygen meter 69 carried on a wrist
strap 70 (see also FIG. 3) the meter 69 reading the output of the two
amplifiers 52 and 53. The outputs of these amplifiers can also be
transmitted by lines 71 to a separate controller who is above the surface
of the water.
It is also desirable that the diver should be able to immediately read the
depth at which he is operating, and this is achieved by a depth meter
designated 72, the depth meter 72 merely being a pressure gauge but
calibrated in feet (or meters) instead of in pressure. The depth meter 72
is also carried on the wrist strap 70.
The oxygen partial pressure transducer 35 is of the electrolytic type.
Various types of oxygen transducers are available, and for example a
suitable transducer may be purchased from Bio Marine Industries, 303 West
Lancaster Avenue, Devon, Pennsylvania, U.S.A.. Another type is an
electrolytic cell containing an electrolyte of potassium hydroxide and
electrodes of silver and tin, the total cell reaction being 2Ag +
1/2O.sub.2 = Ag.sub.2 O. However there is a transient species which
releases two electrons as the tin reacts with the hydroxide radical, and
it is the release of these electrons which provides the electrical impulse
for driving the amplifier 52. The total pressure transducer 34 may be an
LX1440 AO (1000 psi) (National Semi-conductor) transducer, although
alternatives may be used. The amplifiers may be selected from any suitable
types, one suitable type being the Fairchild .mu.A7141. The divider may be
any one of a number of readily available types or alternatively may be
made up by simply joining end to end a series of resistors. However one
suitable type is designated LM310 and is also available from National
Semi-conductor Corporation, Santa Clara, California U.S.A..
The transistors designated 60, 61 and 67 may be standard transistors,
purchased under the designation BC108. The transistors 62 may be BC178,
and the transistor 63 may be a 2N3054. However those skilled in the art
may have personal preferances for other selections of electronic elements.
It is desirable for a diver to be able to double check the atmosphere which
he breathes, and the independent oxygen transducer 36 may be of the same
type as the transducer 35, but is coupled to the independent oxygen meter
37 which may be a self-biasing oxygen analyser, for example as that
produced by Bio Marine Industries and under Model OA202. The advantage of
having a self-biasing oxygen analyser is that the diver is still able to
ascertain his oxygen content even though there is a serious malfunction in
the electronic circuit. If the lines 71 which extend to the surface are
coupled to a Bio Marine oxygen analiser recorder Model 602, there will be
provided a continuous record of diving conditions.
The following is the diving procedure with this equipment:
It is assumed that the dive will be a deep dive and therefore that the
final oxygen percentage (by volume) to be breathed by the diver is only
10%. The oxygen percentage may be adjusted, for example, for some
extremely deep dives the oxygen percent used may be as low as 5%. The
helium and oxygen mixture are stored in the breathable ratio of 9 to 1 in
the bottle 22, and the diver prepares for immersion by affixing the mouth
piece and the face-piece. However the diver must avoid sudden change of
atmosphere for reasons described above, and the push button valve 24 is
operated to increase the oxygen content from 10% to 20%. The diver is able
to ascertain when 20 percent oxygen has been reached by reading the
independent oxygen meter 37.
The diver then descends into the water, his descent rate being adjusted so
that by the time he has reached a depth of about 100 feet, he will have
used up the additional oxygen which has been introduced by the push button
operation. He may of course slightly increase his oxygen at any time
during descent if the usage of oxygen is faster than the corresponding
descent rate. The depth meter 72 will be monitored periodically by the
diver alongside the independent oxygen meter 37 to ensure that he is
within the allowable range of oxygen and pressure. This range is a wide
range, the main requirement being to avoid sudden changes of percentages
of gas. After the diver has reached a depth of about 100 feet he is then
reliant upon the operation of the two transducers 34 and 35 to maintain
his percentage oxygen constant. In the event of a malfunction of the
electronics, the diver can separately and independently add oxygen by
operation of the oxygen push button valve 28. In the more likely event of
sudden failure of gas (for example due to puncturing the breathing bag 44)
the diver can have breathable mixture by merely depressing the push button
valve 24. Thus it will be seen that the diver can separately over-ride the
automatic system at any time.
Various modifications of the illustrated embodiments of the disclosed
invention are within the skill of the art. This invention is therefore not
limited to the description and drawings and all such modifications are
intended to be included within the scope of the appended claims.
The above description has been limited to a single electronics and power
unit. However in practice it is desirable that this should be duplicated,
and the diver should have freedom to transfer from one system to another
so that if there is failure of one system he can still rely upon the
automatic monitoring by the other system.
The equipment will be seen to operate without discharge of bubbles, and
therefore has certain military advantages.
The equipment is compatible with standard decompression tables which are
calculated from constant gas composition, not oxygen partial pressure.
By simple adjustment, the equipment is suitable for maintaining a constant
breathable mixture at any depth which man is capable of physiologically
sustaining.
Since the equipment already incorporates a total pressure transducer, a
signal therefrom, may, if desired be used to energise the depth meter so
as to give the diver an accurate reading of depth.
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