[0001] The present invention refers to an air demand-valve device of a compressed-air breathing
apparatus (for open circuit compressed-air), that is apt for supplying air, at a prefixed
pressure - slightly higher than atmospheric pressure, into an ambient (normally comprising
an inner cavity with an anti-gas mask) of said breathing apparatus, which must result
as being structurally very simple, reliable, and which must allow for a very high
delivery-flow of air into the above-said ambient, and with moreover, maintaining substantially
constant the ambiental-pressure itself.
[0002] A demand-valve device of the type to which the device of the invention belongs, usually
comprises a chamber that communicates with a source-of-air having a mean pressure
- i.e. comprised between 2 and 10 Bar., through a first-entry- gate, and with the
above-said ambient, through a second- exit-gate. The passage-opening, through the
first-entry-gate is controlled by intercepting-means comprising a blocking-element
mechanically connected to a deformable membrane apt for defining a surface of said
chamber, in such a way that - following the shifting of the membrane, the blocking-element
is also shifted, for thus controlling the passage-opening. With said constructive
disposition, whenever - following a pressure decrease that is verified in said ambient
due to the effects of inhalation on the part of the user of the breathing apparatus,
the above-said deformable membrane shifts - and the opening is effectuated of the
above-mentioned blocking-element, in such a way as to allow a sufficient admission
of the air-flow into said chamber for restoring the original pressure conditions once
again.
[0003] The complex - comprised by the above-said membrane and by the kinematic chain that
connects it to the above-mentioned blocking-element, substantially constitutes a transducer
which is apt for measuring the pressure existing inside the chamber, and for controlling
- as a function of said pressure, the shifting of the blocking-element, for feeding
appropriate quantities of air into the chamber.
[0004] Under the conditions described till now, the pressure existing downstream of the
blocking-element is, in static terms, equal to atmospheric-pressure, and it decreases
slightly during the act of inhalation - with putting the interior of the mask under
vacuum. The addition of a spring - having suitable mechanical characteristics, that
presses against the membrane from the outside, or else, some other device that performs
the same task - allows for obtaining, in static terms, a slight overpressure, with
respect to the surrounding atmosphere, downstream of the blocking-element - which,
during any actual inhalation, decreases and can also change signs.
[0005] However, the air demand-valve devices of the type described, present certain drawbacks.
[0006] First and foremost, when particularly high air delivery-flows are required - as a
consequence of increased and repeated inhalation on the part of the user, the air
pressure existing inside said chamber - and hence, also in the ambient that communicates
with the chamber itself, decreases sensibly with respect to the initial pressure.
In such a situation, the respiratory efforts of the user himself, also increase -
owing to the greater difficulty had in inhaling air. Moreover, the pressure inside
the mask decreases sensibly, with assuming - even in instances of the apparatus also
being endowed with an overpressure spring, lower values as compared to those of atmospheric-pressure.
[0007] As a consequence of this, with the air demand-valve devices of the type described,
the user is required to make non- negligible breathing efforts - and particularly,
whenever greater air delivery-flows are necessary. Therefore the specified conditions
of safety cannot be realized - because, in the proximity of the sealing-surface, inside
the mask, the pressure can notably decrease to below that of the outside atmosphere,
with thus involving risks of gases and/or vapours entering-in from the polluted surrounding
ambient where the user happens to be.
[0008] The above-mentioned drawbacks depend substantially upon the fact that - apart from
the atmospheric-pressure and the pressure existing inside the above-mentioned chamber,
there also act, on the above-said membrane, the fluodynamic effects of the air-jet
that enters into said chamber, and which - - owing to the repeated surface-reflections
taking place, can affect the membrane itself.
[0009] Said fluodynamic actions can have either a positive or a negative sign - and can
vary considerably, besides irregularly, as a function of the air-flow delivered by
the device, with also changing signs, and with resulting as being strongly resistent
to static action in instances of any greater air-flows. Therefore, for obtaining these
actions, a vacuum is often required - and hence, an effort on user's part, that proves
to be much greater than what is foreseen by a calculation of static-balance. It results
from this that, to-date, there are many constructors who have conceived various, more
or less complex, devices for eliminating any direct contact of the dynamic air-flow
upon the surface of the membrane itself - for suppressing in this way, the above-
described fluodynamic effect.
[0010] The aim of the present invention is to realize an air demand-valve device for a compressed-air
breathing apparatus of the previously indicated type, but which will be in a condition
to eliminate the above-mentioned drawbacks, and which, in particular, will be apt
for supplying air - that is sensibly constant and of a better quality than the air
of the surrounding atmosphere, into the ambient of the breathing apparatus, and even
in those instances when the air-delivery flows may be considerably increased.
[0011] On the basis of the present invention, there has been realized an air demand-valve
device for a compressed-air breathing apparatus, that is apt for supplying air, at
a pre- fixed pressure, into an ambient of said breathing apparatus, said device comprising
a chamber that is substantially cylindrical and a first air-entry-gate into the chamber,
which substantially opens out onto the lateral surface of said chamber, and which
communicates with a source of compressed-air, and which presents a passage-opening
that is controlled by intercepting-means - comprising a blocking-element mechanically
connected to a deformable membrance which is apt for defining a base-surface of said
chamber, in such a way that - following the shifting of said membrane, the said blocking-element
is also shifted for controlling said opening, the said device comprising moreover,
a second exit-gate disposed on the other base-surface of said chamber, and predisposed
for feeding said air into said ambient, and being characterized by the fact that the
axis of said first-entry-gate forms a second angle with the axis of said lateral surface,
said two axes lying substantially on the same diametrical plane of said chamber.
[0012] Said first angle is opportunely comprised between 15° and 25°, and said second angle
is comprised between 5° and 15°. Moreover, for convenience sake, the distance between
said axis of said lateral surface, and the point-of-intersection of said axis of the
second gate with the plane that frontally delimits the gate itself, is comprised between
20% and 35% of the diameter of said chamber.
[0013] For having a better comprehension of the device of the present invention, there will
now be given, solely by way of example, the description of one particular form of
realization with making reference to the attached drawings, whereby:
- FIGURE 1 represents a vertical section of the air demand-valve device of the invention;
- FIGURE 2 represents a plane view, partially in section, of the device of FIG. 1;
FIGURES 3 and 4 represent sections - of a part of the air demand-valve device of Fig.
1, in two different operative positions;
- FIGURE 5 represents certain diagrams apt for illustrating the curve of the air-pressure
delivered, as a function of the air-flow capacity itself, that is encountered in the
device of the invention, as well as in the devices of the prior art of the same type.
[0014] First and foremost, referring to FIG. 1, the air demand-valve device of the invention
- indicated in its complex whole with the reference numeral 1, is apt for being interposed
between a compressed-air feeding breathing-tube 2 and an ambient (not shown) comprised,
for example, by the space inside an anti-gas mask, into which breathable air has to
be fed.
[0015] The device comprises a substantially cylindrical chamber 3, delimited by a lateral-wall
4 and a pair of substantially flat base-walls 5 and 6. Inside the chamber 3, there
is disposed a membrane 7 which comprises a substantially flat base-wall 8 and a lateral-wall
9, that presents a plurality of corrugations apt for rendering said membrane substantially
deformable in the direction of the axis of the chamber 3. With the wall 5, said membrane
defines another chamber 10, which communicates with the atmosphere through one or
several holes 11, made in the wall 5. For convenience sake, the device can comprise
a spring 7a, disposed inside the membrane 7 and predisposed for exercising a prefixed
axial-force on the flat wall 8. The device comprises moreover, a first entry-gate
14 - that is apt for putting the tube 2 into communication with the chamber 3, and
which is made substantially in the lateral-wall 4 which delimits said chamber, and
a second exit-gate 15 - for putting the latter into communication with the internal
ambient of the mask, and which is made in the base-wall 6 that also delimits the chamber
itself.
[0016] Inside the entry-gate 14, there is disposed a bush 16, provided with a pair of axial
holes 17 and 18 - of which the first is cylindrical and the second conical, as well
as with a seat 19 having a substantially annular form, apt for housing the blocking-element
20 that is normally held against said seat by means of a spring 21 - interposed in-between
the latter and another bush 22 that is screwed into a threaded- hole made inside the
entry-gate 14 - as is clearly visible in FIG. 1.
[0017] The blocking-element 20 is made solidal with a rod 23 that goes through the holes
17 and 18, and whose extremity is provided with a stylus 24 apt for collaborating
with the surface of the wall 8 of the membrane 9.
[0018] On the basis of the invention, the axis of the first entry- gate 14 - indicated with
a
1 in FIG. 1, forms a first angle α with the base-surfaces that delimit the chamber
23 and, in particular, with the surface of the flat wall 8 of the deformable membrane
9. Moreover, the axis of the second exit-gate 15, indicated with a
2 in Fig. 1, forms a second angle β , with the axis a of the chamber itself; the two
axes, a and a
2, lie substantially in the same diametrical plane of the chamber 3 - which coincides
with that in the drawing of FIG. 1.
[0019] For the purpose of achieving the aims that shall be indicated further on in the text,
the angles α and β are comprised respectively between 15° and 25° and between 5° and
15°. Moreover, the distance - between the axis a
0 of the chamber 13 and the intersection point C of the axis a
2 of the exit-gate 15 with the plane that frontally delimits the gate itself (and which
has been indicated with 6 in FIG. 1), is comprised between 20% and 35 % of the diameter
of said chamber. In this manner, the opening of the outlet 25 of the exit-gate 15,
results as being substantially eccentric with respect to the axis a
0 of the chamber 3 - as clearly results in FIG. 1.
[0020] Inside the chamber 3, and in the vicinity of the lead-in of the second gate 15, there
is disposed a substantially flat wall 29. The plane of said wall is substantially
parallel to that of the axis a
0 and perpendicular to the plane that contains the axes a and a
2 respectively, of the gates 14 and 15. Moreover, the said wall comprises, for convenience
sake, a rib 30, having the function of conveying the air-flow, as well as that of
acting as a stiffening.
[0021] Next, the half-opening of the conical surface - that delimits the second hole 18,
downstream of the blocking-element 20, is comprised between 16° and 18°. The ratio,
between the axial length of the first and second hole 17 and 18, is comprised between
0.85 and 0.45; whereas, for convenience sake, the axial lengths of the holes themselves,
are comprised between 4 and 6 mm and between 7 and 9 millimeters respectively.
[0022] To end with, the ratio between the diameter of the first hole 17 and its axial length,
is comprised between 0.85 and 1.32, and - for convenience sake, the diameter of the
hole itself, is comprised between 5.1 and 5.3 mm.
[0023] In practical usage tests, the air demand-valve device described, has - quite surprisingly,
proved to function in a very satisfactory way. It has been endeavoured to give a rational
explanation, with the following considerations, which must be taken as being qualitative
- since the complexity of the forms, and of the surface reflections in particular,
that are for the most part curved, impede obtaining, with any precise mathematical
calculus, an exact prevision of the behaviour of the device itself.
[0024] When it is inserted into the circuit of the self-breathing apparatus, there exists
inside of chamber 3 - between the compressed-air feeding tube 2 and the mask of the
compressed-air breathing apparatus itself, and under normal functioning conditions
of the device, a pressure that is slightly higher than atmospheric-pressure - for
example: a pressure that has from 30-40 mm of water-column-height above said pressure.
As is already known, such a pressure inside the chamber 3 - and hence, in the ambient
of the compressed-air breathing- apparatus into which breathable air must be introduced,
offers a greater guarantee of safety for the user - since, under such conditions,
there is impeded any infiltration of gases or vapours from the polluted surrounding
atmosphere wherein the user happens to be.
[0025] If it is supposed that the spring 7a is absent (a functioning condition that can
be defined as "negative pressure") the membrane 9 becomes disposed in a balanced position,
depending upon the pressure value that exists inside the chamber 10 - which acts on
one of the surfaces of the wall 8, and the above-said pressure that exists in the
chamber 3 - which acts upon the other surface of the wall itself. When the pressure
inside the chamber 3 is reduced, even to a modest extent - following an inhalation,
said 'balanced condition' becomes changed and the wall 8 of said membrane, shifts
towards the stylus 24, determining the rotation of the rod 23 substantially in the
plane of the drawing of FIG. 1, for controlling the opening of the blocking-element
20 - which substantially assumes the configuration illustrated in FIG. 3, whereby
it leans just on a very restricted zone of the housing 19, with leaving free a part
having prefixed dimensions, through which there is established an air-flow entry into
the chamber 3.
[0026] The addition of a spring such as 7a - having suitable mechanical characteristics,
which presses against the wall 8 of the membrane 7 (or some other such device for
carrying out the same task), allows for obtaining - under static conditions, a slight
overpressure, with respect to the surrounding atmosphere, downstream of the blocking-element
- and hence, inside of the mask; which said overpressure becomes reduced during the
act of inhalation and can also change its sign. This functioning condition can also
be defined as being "positive pressures".
[0027] The above-said air-flow that, given the pressure conditions inside chamber 3 and
inside tube 2, realizes a true and proper supersonic expansion - enters into said
chamnber through a plurality of axial deviations that are comparable, for simplicity
sake, to reflections on the walls of the holes 17 and 14 - for example: according
to the succession of reflections indicated with the broken-line of FIG. 3. As can
clearly be seen from said broken-line, the above-said flow follows a trajectory comprised
by a succession of rectilineal tracts, as a consequence of these said reflections,
which do not interfere with the flat wall 8 of the membrane 9. In particular, the
trajectory tract indicated with t
0' by which the above-said flow passes through chamber 3 - substantially in the transversal
direction, has a slightly inclined direction with respect to the plane of the wall,
in such a sense as to draw away from it, so as to strike further surfaces inside of
the chamber 3 and to come out from the exit-opening 15, through the means of a series
of further reflections.
[0028] A trajectory of this type, i.e. comprising a succession trajectory-tracts - none
of which strike the wall 8 of the membrane 9, is the result of the form of the disposition
of the various parts of the device and, in particular, of the relative position of
the axes a and a
2 of the gates 14 and 15, defined by the angles α and ? , of the presence of the eccentricity
presented by the exit-gate 25 of the gate 15 with respect to the axis a
0 (eccentricity E ), as well as by the form and the dimensions, defined previously,
for the holes 14 and 17, downstream of the blocking-element 20.
[0029] It has been verified that, whenever the previously mentioned geometrical parameters
are selected from the indicated ranges of values, the favourable condition - for realizing
trajectories of air-flows from the entry-gate 14 to the exit-gate 15, with trajectories
that never interfere with the wall 8 of the membrane 9 - is obtained not only for
a particular opening angle of the blocking-element 20, but substantially for opening
angles which go from zero to a maximum angle - to which correspond considerably high
air-flow entries into the chamber 3, that are necessary for feeding breathable air
for the user, with continuity, even under the most unfavourable operative conditions.
In FIGS. 3 and 4, there have been indicated two different configurations of the membrane
9, to which correspond two diverse opening-angles of the blocking-element 20. There
are also shown herein, the trajectories of the air-flows which are obtained presumably,
in these two instances. As can be clearly seen, none of these comprise flow-tracts
that strike the membrane 8.
[0030] It has also been verified that the first wall 29, inserted into the first position
indicated inside of the chamber 3, also contributes for conveying the air-flow towards
the exit-gate 15. Moreover, said wall can constitute the end-stop limiter, for the
shifting-movement of the wall 8 of the membrane 9.
[0031] Therefore, it is evident that, with the air demand-valve device of the invention,
any negative fluodynamic actions on the membrane 8 generated by the air-jet entering
chamber 3, is prevented, i.e. those actions which tend to take membrane towards the
at-rest conditions corresponding to the null flow - and without even needing to have
recourse to any costly and complex mechanisms for removing the membrane from the effects
of said air-flow; but instead, it is had that, through the effects of the air-flow
divergence from the membrane, as can be seen in FIGS. 3 and 4, the action of said
membrane on the blocking-element 20 is amplified in such a way as to achieve a minimum
lowering of the pressure (or of the overpressures) existing inside the mask for the
entire field of instantaneous respiratory intensity, as necessited by human physiology
(upper limit about 300 1/min). Under these conditions, an air-flow having a very high
capacity can be controlled, without any particular respiratory effors on the user's
part. It has been found that, under particular functioning conditions of the device,
involving trajectory tracts that tend to draw away from the membrane 8 (as was shown
in the instance of FIGS. 3 and 4), there is even had a suction action upon the membrane,
which can favour the opening of the blocking-element whenever very high air-flows
must be supplied.
[0032] In FIG. 5 there is indicated, with the curve A, the development of the pressure inside
the chamber 3 as a function of the air-flows supplied. As can be seen from said curve,
inside of the chamber 3 there exists a substantially constant pressure (no matter
what the flow of air supplied may be) comprised within the range that concerns those
applications to which the air demand-valve device of the invention is intended. Moreover,
the above-said pressure tends to become lower, only in correspondence of the upper
value limit of the above-said range of values - without however, creating a depression
inside the mask to which the air-breathing device itself is connected.
[0033] In the same FIG. 5, there are represented, with the curves B and C, the pressure-flow
characteristics, for other known air breathing-devices of the type described. As can
be seen, not only is a sensible reduction of pressure had - as soon as the air-flow
introduced by the device tends to increase, but said pressure can become already negative
because of the flow- values comprised within the range that concerns the viewpoint
of practical applications.
[0034] In said FIGURE, the scales given on the left-hand side, relate to a functioning-configuration
with "positive pressures" (obtained through the presence of the spring 7a); whereas
those given on the right-hand side, relate to a functioning-configuration with "negative
pressures" (obtained without the spring 7a).
[0035] The air demand-valve device of the invention - apart from its presenting the favourable
properties described previously, results as also being constructively very simple
- because of its being constituted of a only a few elements that can easily be constructed
and which do not require any restricted working tolerances. Hence, this device results
as also being very reliable - seeing that it maintains, during the course of its usage,
the favourable characteristics that have been previously described.
[0036] What results as being obvious, is that to the forms of realization described in the
present invention, there can be brought about modifications and other alternative
variations - both, in the form as well as in the disposition of the various parts,
without this exiting in any way from the ambit of the inventive idea itself.
1. Air demand-valve device (1) for a compressed-air breathing apparatus, apt for distributing
air at a pre-fixed pressure into an ambient of said compressed-air breathing apparatus,
said device - that comprises a substantially cylindrical chamber (3) and a first air
entry-gate (14) into the chamber, which opens out substantially upon the lateral surface
of said chamber, is in communication with a source of compressed-air and presents
a passage-opening controlled by intercepting-means, comprising a blocking-element
(20) fixed mechanically to a deformable membrane (7) apt for defining a substantially
flat base-surface (8) in said chamber, in such a way that, following the shifting
of said membrane, said blocking-element is also moved for controlling said opening,
the said device comprising moreover, a second gate (15) disposed on the other base-surface
of said chamber and predisposed for feeding said air into said ambient, characterized
by the fact that the axis (a 1) of said first- gate forms a first angle (α) with said base-surfaces (8) of said
chamber and the axis (a 2) of said second-gate (15) forms a second angle ( β) with the axis' (a 0) of said lateral surface, said two axes lying substantially on the same diametrical
plane of said chamber (3).
2. Air demand-valve device, according to CLAIM 1, characterized by the fact that said
first angle is comprised between 15° and 25° and said second angle is comprised between
5° and 15°.
3. Air demand-valve device, according to CLAIMS 1 or 2, characterized by the fact
that the distance (ε), between said axis (a 0) of said lateral surface and the point-of-intersection (C) of said second-gate's
axis with the plane that frontally delimits the gate itself, is comprised between
20% and 35% of the diameter of said chamber.
4. Air demand-valve device, according to one of the previous Claims, characterized
by the fact that it comprises a diaphragm, disposed inside said chamber, comprising
at least a flat wall (29) disposed in the vicinity of the mouth of said second-gate
and on a plane that is substantially parallel to said axis (a 0) of said lateral surface and perpendicular to said plane that contains the axes of
the gates (a , a 2).
5. Air demand-valve device, according to one of the previous Claims, wherein, downstream
of said blocking-element (20), said gate comprises a first, substantially cylindrical
hole (17) and a second hole (18) delimited by a conical surface, characterized by
the fact that the half-opening of said conical surface is comprised between 16° and
18°.
6. Air demand-valve device, according to CLAIM 5, characterized by the fact that the
ratio between the axial length of said first and second holes, is comprised between
0.85 and 0.45.
7. Air demand-valve device, according to CLAIM 4 or 5, characterized by the fact that
the axial lengths, of said first and said second hole, are comprised respectively,
between 4 and 6 mm. and between 7 and 9 mm.
8. Air demand-valve device, according to one of the CLAIMS from 5 to 7, characterized
by the fact that the ratio - between the diameter of said first hole and its axial
length, is comprised between 0.85 and 1.32.
9. Air demand-valve device, according to CLAIM 8, characterized by the fact that the
diameter of said first hole, is comprised between 5.1 and 5.3 mm.
10. Device, according to CLAIM 1, characterized by the fact that said membrane (7)
comprises a substantially flat and indeformable base-surface (8), apt for defining
said base-surface of said chamber, and a deformable lateral surface (9) provided with
a plurality of corrugations.