Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A BREATHING SYSTEM FOR SMORE DIVING AND THE LIKE
BACKGROUND OF THE lNv~ ION
The present invention relates to a closed or semi-
closed breathing system for smoke diving and the like.
There are a number of known embodiments of self-
contained breathing systems. Breathing equipment for smoke
diving is designed for firefighting operations in which a
firefighter dives into an environment containing smoke and
toxic gas. Some smoke diving breathing systems in the prior
art supply breathing gas through a breathing valve, and "dump"
exhaled gas directly to the surroundings through a one-way
valve t"open breathing system"). Alternative types of
breathing equipment are based on recovery of exhaled gas in
a "closed" or "semi-closed" circulatory system. Exhaled gas
is partly or completely purified of CO2 and supplied with
oxygen so that it is again suitable as a breathing gas. With
closed or semi-closed breathing systems, a long service life
is achieved with a moderate gas supply, but they are normally
difficult to breathe with because the gas is recirculated by
lung force. In comparison, good open breathing systems are
easy to breathe with, but have a considerably shorter service
life since the weight of the apparatus must be kept low. A
substantial advantage with open breathing systems is that one
is able to maintain a safety pressure (weak overpressure) in
the breathing mask, so that the ingress of gases which are
harmful to the user's health is prevented.
SUMMARY OF THE lNv~NlION
It is an object of the present invention to provide
a closed or semi-closed breathing system which, in a preferred
embodiment, has a safety overpressure in the breathing mask
and utilizes the available breathing gas reservoir optimally.
The invention is also reliable in service, simple to produce,
lightweight and has a long service life.
According to the present invention then, there is
provided a breathing system, especially for use in an
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atmosphere containing toxic gases, wherein exhaled gas is at
least partly recirculated, said system comprising a
circulation circuit, a breathing piece for application to the
face of a user, absorption means for absorbing exhaled C02,
a pneumatically controlled breathing bag communicating in said
circulation circuit with said breathing piece and said
absorption means, a pneumatic actuator arranged for
alternating expansion and contraction of said breathing bag
in accordance with the breathing pattern of the user, a
pressurized gas source coupled to said breathing bag to
supplement the breathing gas therein, a mode regulator
arranged to control the actuator's expansion and contraction
of the breathing bag, and to supply breathing gas to said
breathing bag, by selectively supplying breathing gas from
said pressurized gas source to said actuator, and by venting
breathing gas from said actuator to said breathing bag, and
dosing means for supplementing the breathing gas supplied to
the breathing bag by said mode regulator, by supplying a
metered gas quantity to said breathing bag in dependence on
the degree of filling of the bag after a user exhalation.
In the present breathing system, a small breathing
effort is required because the pressure of the supplied oxygen
is used to assist the recirculation of the breathing gas.
Oxygen is supplied through the pneumatic actuator which
alternatingly expands and contracts the breathing bag in
accordance with the breathing pattern of the user. This is
a technique which is already used in a semi-closed breathing
system for underwater diving, and reference is made to US
patent No. 4,793,340. The technique has not however been
previously used in a closed breathing system.
It is a important preferred feature of the invention
that this technique is utilized to establish a "safety
pressure" in the breathing mouthpiece or breathing mask of the
user, as this prevents the ingress of gases which are harmful
to the user's health. This is of great importance from a
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safety point of view, and is, as far as applicant knows, not
achieved in any other self-contained closed breathing system.
In the breathing system according to a preferred
aspect of the invention, the mode regulator supplies the
actuator with compressed oxygen, or alternatively "vents"
supplied oxygen to the breathing bag which thereby controls
the recirculation of breathing gas. At the same time it
ensures that a small safety overpressure is maintained in the
breathing mask during inhalation as well as during exhalation.
The actuator is dimensioned so that the oxygen quantity
received and thereafter "vented" to the breathing bag, is
somewhat smaller than the quantity absorbed in the
respiration. It is therefore necessary to inject a certain
oxygen quantity directly into the circulation of the system,
to maintain the oxygen level in the breathing gas. The
invention achieves this because the dosing means is arranged
to discharge a metered quantity of gas into the breathing bag
each time when, during exhalation, there is insufficient
filling of the breathing bag. Thus, the system is not, like
many other closed oxygen apparatus, based on a fixed injection
of gas rich in oxygen so it utilizes the available gas
reservoir optimally. It has been found to be advantageous to
dimension the system so that the maximum driving pressure of
the actuator is approximately +/- 15 cm water column. In
practice this implies that the actuator is able to compensate
for the work which the lungs of the user otherwise would have
to carry out in order to overcome restrictions through one-way
valves, hoses C02 absorber, etc. in the system.
According to yet another aspect of the present
invention, there is also provided a breathing system,
especially for use in an atmosphere containing toxic gases,
wherein exhaled gas is at least partly recirculated, the
system comprising a circulation circuit, a breathing piece for
application to the face of a user, absorption means for
absorbing exhaled CO2, a pneumatically controlled breathing
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bag communicating in said circulation circuit with said
breathing piece and said absorption means, a pneumatic
actuator arranged for alternating expansion and contraction
of said breathing bag in accordance with the breathing pattern
of the user, a pressurized gas source coupled to said
breathing bag to supplement the breathing gas therein, a m~
regulator arranged to control the actuator's expansion and
contraction of the breathing bag while simultaneously
maintaining an overpressure in said breathing piece, relative
to the surroundings, and dosing means for supplying a metered
gas quantity to said breathing bag in dependence on the degree
of filling of the bag, wherein said mode regulator comprises
a valve arrangement and a sensing diaphragm cooperating
therewith, said sensing diaphragm having first and second
sides, said first side being influenced by the surrounding
atmospheric pressure and by a spring mechanism for maintaining
said overpressure in the breathing piece, said second side
being influenced by the gas pressure in said breathing piece;
and movement of said sensing diaphragm from a central position
is transferred to said valve arrangement which, in dependence
on the movement direction of the diaphragm, either opens to
supply pressurized gas to said actuator, or vents the
actuator.
An advantageous embodiment of the system according
to the invention is characterized in that the circulation
circuit of the system includes conduit stretches of which the
outer surfaces are covered by a relatively thick porous
material which, saturated with water, utilizes the evaporation
of the water for cooling down the breathing gas circulating
in the circulation circuit during operation.
The breathing system is constructed in such a manner
that surrounding gas flows past the surface and causes an
efficient evaporation. The evaporation heat is partly taken
from the wet surface of the conduit stretches which is cooled
down considerably. Further, the wet surfaces of the conduit
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stretches and other cooled-down surfaces in the system have
a good thermal conduction to internal surfaces of the
breathing system, so that an efficient cooling of the
breathing gas is achieved. Such an arrangement for cooling
of the breathing gas is advantageous as compared to
traditional breathing systems wherein the temperature of
inhaled gas may be well above body temperature. In addition,
this solution has the advantage that the evaporation increases
with the surrounding temperature, so that the system manages
to maintain an acceptable breathing gas temperature even in
rather warm surroundings. Another advantage of this solution
is that wetting with water is useful in a fire fighting
environment.
The system is easily made ready for operation by,
e.g. immersion in a container of water. A thick porous
material will be able to absorb a considerable quantity of
water, and the cooling therefore can take place over a
relatively long time without another wetting of the porous
material.
According to yet another aspect of the present
invention, there is also provided a breathing system,
especially for use in an atmosphere containing toxic gases,
wherein exhaled gas is at least partly recirculated, said
system comprising a circulation circuit, a breathing piece for
application to the face of a user, absorption means for
absorbing exhaled C02, a pneumatically controlled breathing
bag communicating in said circulation circuit with said
breathing piece and said absorption means, a pneumatic
actuator arranged for alternating expansion and contraction
of said breathing bag in accordance with the breathing pattern
of the user, a pressurized gas source coupled to said
breathing bag to supplement the breathing gas therein, a m~
regulator arranged to control the actuator's expansion and
contraction of the breathing bag while simultaneously
maintaining an overpressure in said breathing piece, relative
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to the surroundings, and dosing means for supplying a metered
gas quantity to said breathing bag in dependence on the degree
of filling of the bag, said actuator comprising a
cylinder/piston unit coupled to said pressurized gas source
through said mode regulator, said mode regulator including a
valve arrangement comprising a first valve which is opened for
venting said actuator, and a second valve which is opened to
supply pressurized gas to the actuator.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be further described below in
connection with an exemplary embodiment with reference to the
drawings, wherein:
Fig. 1 shows a schematic view, partly in section,
of a preferred embodiment of a breathing system according to
the invention;
Fig. 2 shows a sectional view of the mode regulator
in Fig. 1 on an enlarged scale, and
Fig. 3 shows an enlarged sectional view of the
breathing bag in Fig. 1, the Figure showing more detailed
sectional views of the elements and units arranged within the
breathing bag.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The embodiment shown in Fig. 1 constitutes a closed
breathing system wherein a breathing bag 1, a breathing mask
2 and a CO2 absorbing means are connected in series in a
closed circulation circuit, said units being interconnected
through conduit lengths or tubes 4, 5 and 6. The breathing
gas is inhaled from breathing bag 1 through breathing mask 2
which is provided with one-way valves 7 and 8 ensuring that
inhaled and exhaled gases are not mixed. Exhaled gas passes
via means 3 which consists of a container containing a CO2
absorbing material, into breathing bag 1.
Within breathing bag 1 there is arranged a pneumatic
actuator 9 consisting of a cylinder/piston unit (see Fig. 3)
which, as shown, is articulated to the side walls of the
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breathing bag in the central region thereof. The actuator
causes alternating expansion and contraction of the breathing
bag in accordance with the breathing pattern of the user, as
further described below. For control of actuator 9, a mode
regulator 10 supplies the actuator with compressed oxygen, or
alternatively vents supplied oxygen to the breathing bag, as
also further described below. Pressurized oxygen is supplied
from a source 11 through a pressure reducing valve 12.
In the illustrated embodiment, actuator 9 is
dimensioned such that the oxygen quantity which is received
and thereafter vented to the breathing bag is somewhat smaller
than the quantity absorbed in the user's respiration. In
order to maintain the oxygen level in the breathing gas, it
is therefore necessary to inject a certain oxygen quantity
directly into the circulation circuit. For this purpose there
is a dosing means 13 which discharges a metered oxygen
quantity into breathing bag 1 each time when, during
exhalation, there is insufficient filling of the breathing
bag.
In order to determine the filling degree of the
breathing bag in each exhalation (expansion of the breathing
bag), there is provided a sensing means 14 in combination with
a pair of arms 15, 16 following the movement of the breathing
bag, the arms at one of their ends being pivotally connected
to each other, and at their other ends being articulated to
the side walls of the breathing bag at the same places where
actuator 9 is coupled to the breathing bag. The sensing means
comprises a holding member 17 fixed to one arm 15 and
extending in the direction of and past the other arm 16, a
lever 18 pivotally connected to the free end of the holding
member, a transverse pin 19 fixed to the arm 16 and
cooperating with lever 18, and a valve 20 (see Fig. 3)
provided in the holding member and arranged to be actuated by
lever 18. This valve is opened when lever 18 is lifted by
transverse pin 19 when breathing bag 1 is filled beyond a
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certain degree. A "blocking signal" is then delivered to
dosing means 13, as further described below.
As appears from Fig. 1, the outer surfaces of
conduit lengths 4, 5, 6 are covered by a relatively thick
layer of a material 21 which is porous and water-absorbing,
and which, in operation, is intended to be saturated with
water. The water evaporates and cools-down the breathing gas
in the circulation circuit. Container 3 is also covered by
the water-absorbing material, and those parts of the
circulation circuit located downstream of container 3, may be
extended in a suitable manner to achieve a large, efficient
evaporation surface to the surrounding atmosphere.
The construction of mode regulator 10 is shown in
more detail in Fig. 2. It consists of a housing 22
containing a sensing diaphragm 23 dividing the housing into
a pair of chambers 24, 25. Chamber 24 communicates with the
outer atmosphere through a pair of apertures 26, 27. Chamber
25 communicates with breathing mask 2 through conduit 4 and
is supplied with breathing gas from breathing bag 1 through
a one-way valve 28. In chamber 24 there is a spring 29 which
acts upon sensing diaphragm 23, so that it is affected by a
spring force in addition to the atmosphere pressure in chamber
24. In this manner there is an overpressure or safety
pressure achieved in the system when the spring is activated.
Spring 29 is arranged in a cap 30 which is screwed into
housing 22 and can be screwed in to a greater or lesser
extent, for setting of a desired spring prestressing force and
thereby a desired overpressure. It is obvious that the
diaphragm-influencing means may be carried out in many other
ways than the illustrated spring and cap, but it is essential
that the means is easily accessible to the user.
Sensing diaphragm 23 is mechanically coupled to a
lever 31 for alternative actuation of a first and a second
valve 32 and 33. First valve 32 communicates with actuator
9 through a conduit 34, and second valve 33 is coupled to a
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conduit 35 communicating with pressurized gas source 11
(through reducing valve 12) as well as with actuator 9, as
shown in Fig. 3.
! The construction of actuator 9 and dosing means 13
is shown in more detail in Fig. 3.
As shown, actuator 9 consists of a cylinder 36 and
a piston 37 having, as viewed in Fig. 3, an upper pressure
surface 37a which is substantially smaller than the lower
pressure surface 37b of the piston. The upper cylinder
compartment 36a is connected to pressurized gas source 11
through a conduit 38, and the lower cylinder compartment 36b
is connected to valves 32, 33 of the mode regulator through
a conduit 39 (passing through dosing means 13) and conduit 34.
Thus, the smallest pressure surface 37a of the piston stands
under a constant pressure influence from pressurized gas
source 11, so that the pressure direction of actuator 9
changes as its lower cylinder compartment 36b is supplied with
gas from the pressurized gas source (through mode regulator
valve 33) or is vented (through valve 32). As an alternative
to connecting the pressurized gas source to the upper cylinder
compartment, the upper side of the piston instead might be
acted upon by a continuous spring force.
Dosing means 13 includes a small gas reservoir 40
which is filled with oxygen through a first valve or inlet
valve 41 which is connected to pressurized gas source 11
through conduit 42 and conduit 38. Dosing means 13 discharges
into the breathing bag through a second valve or outlet valve
43. Valves 41 and 43 are arranged to be opened and closed
alternatively by an operating means in the form of a spring-
loaded lever 44 which, in its initial position, keeps valve41 open. There is a unit connected in the conduit 39 between
valves 32, 33 of mode regulator 10 and the lower cylinder
compartment of actuator 9. This unit consists of a pair of
spring-loaded and oppositely directed one-way valves 45, 46
connected in parallel, and a chamber 47 connected in parallel
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to the valves and which is divided in two parts by a control
diaphragm 48 as shown in Fig. 3.
When gas is flowing through one of one-way valves
45, 46 in the conduit 39, the pressure drop across the one-way
valve concerned causes diaphragm 48 to be pressed in the flow
direction of the gas. This is utilized to control dosing
means 13, so that it discharges the gas in the reservoir 40
into breathing bag 1 (through the valve 43) each time when,
during exhalation, there is insufficient filling of the
breathing bag.
For this purpose control diaphragm 48 is coupled to
an operating rod 49 which is moved to the right and affects
lever 44 when diaphragm 48 is pressed to the right and opens
valve 43. This will occur provided that the movement of
lS operating rod 49 is not prevented by a 'blocking signal"
delivered from sensing means 14. As mentioned above, this
blocking signal is provided from valve 20. This is connected
to pressurized gas source 11 through a conduit 50, upper
cylinder compartment 36a of actuator cylinder 36 and conduit
38. It is further connected through a conduit S1 to a
cylinder/piston unit 52 arranged in dosing means 13 and having
a spring-loaded blocking piston 53 and an associated venting
valve 54. The blocking signal occurs when blocking piston 53
is pressure-actuated by opening of valve 20 so that the piston
is moved to the left and actuates a blocking lever 55
preventing said movement of operating rod 49 even if control
diaphragm 48 is pressed to the right. The blocking signal is
nullified and reset when control diaphragm 48 is pressed to
the left, so that blocking lever 55 is pivoted by actuation
from operating rod 49 and opens venting valve 54, so that
blocking piston 53 is returned to its initial position by
spring influence.
The operation of the breathing system will be
further described below.
As soon as the user of the system starts inhalation,
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the pressure in chamber 25 of mode regulator 10 falls so that
sensing diaphragm 23 is pressed towards the chamber and opens
valve 32. Venting of gas from lower cylinder compartment 36b
of the actuator 9 starts, so that the actuator contracts the
side faces of breathing bag 1 and maintains a safety
overpressure in breathing mask 2. With exhalation the
pressure in the breathing mask rises, and this pressure
increase is transferred through a passage 56 to chamber 25 of
the mode regulator, so that sensing diaphragm 23 is pressed
outwards towards chamber 24. Thereby valve 33 is opened, so
that the lower cylinder compartment of actuator 9 is supplied
with compressed gas (oxygen) from the pressurized gas source.
The main supply of oxygen to the breathing bag takes
place through venting valve 32 of the mode regulator. Since
the actuator is dimensioned to supply only part of the
necessary oxygen, dosing means 13 injects the metered oxygen
quantity from reservoir 40 to breathing bag 1 after each
exhalation when the breathing bag is insufficiently filled
with breathing gas. The injection of oxygen takes place at
the same time as oxygen is vented from the actuator. Control
diaphragm 48 is pressed to the right and opens valve 43 by way
of operating rod 49 and lever 44 ~ust after the inhalation
phase has started. Valve 43 will only open if sensing means
14 has not delivered a "blocking signal", which signal is
delivered from valve 20 when lever 18 is lifted by transverse
pin 19 on arm 16. As mentioned above, the blocking signal
disables control diaphragm 48 from moving the lever 44 to the
right and opening valve 43. The blocking signal is nullified
and reset automatically when the breathing bag again gets into
the exhalation mode and diaphragm 48 is pressed to the left
and opens venting valve 54.
In the embodiment described above it has been
emphasized that the equipment is to be completely "closed",
since this gives advantages with respect to safety in
inflammable surroundings. In principle, there is nothing to
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prevent the equipment from being made "semi-closed", for
example with a view to sports diving. In that case the oxygen
supply through the pneumatic actuator is larger than the
consumption, and an automatic means may be constructed which
dumps gas each time the breathing bag in exhalation is filled
beyond a given level. Further, it is conceivable that the
pneumatic assistance could be based on gas supply from one gas
reservoir, and that the compensation of oxygen could take
place from another one, without changing the structure to a
substantial degree.
In cases where the system according to the invention
is to be used in a gas filled atmosphere, it is natural,
because of weight, size, etc., to build the mode regulator
into the breathing bag, as shown and described. In connection
with e.g. diving, hydrostatic conditions will make it natural
to build the mode regulator into the breathing mouthpiece or
breathing mask. The breathing system will be operative as
soon as the reducing valve supplies gas to the pneumatics of
the system.
It is clear that the arrangement for cooling-down
of the breathing gas may be applied for virtually all types
of breathing systems used in gas-filled surroundings.
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