Note: Descriptions are shown in the official language in which they were submitted.
1~29303
BACKGROUND OF THE INVENT ION
This invention relates to protective breathing
apparatus of the type in which a user wears a face mask,
sometimes referred to as a respiratory inlet covering,
communicating with a source of air or other breathing fluid
for use in toxic or oxygen deficient surroundings.
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In the use of such breathing equipment, it is mandatory
that pressure-demand apparatus be used where the atmosphere is
highly toxic. Pressure-demand apparatus provides air on demand
and in addition maintains a positive pressure within the face
mask in relation to the ambient environment, during both inhala-
tion and exhalation, thereby assuring that any leakage caused by
poor facepiece fit or component failure will be outward from
the mask to prevent inflow and possible inhalation of the atmos-
phere. However, a pressure demand regulator that will function
as above will open to full flow position at all times that the
users' face (or other means) does not close the man side of the
mask to stop the flow and permit the build-up of positive pressure.
If air is supplied to the regulator at such times it will deliver
; its maximum flow capacity, quickly depleting and wasting the air
supply.
The evolution of user and buyer requirements as well as
those of various regulatory agencies has seen an upward spiral
of flow requirements such that modern regulators, in fully open
position, can discharge enormous quantities of air as compared
to the normal breathing requirements of a man. Over 500 liters
per minute ~17.6 cfm) is not unusual as a free flow regulator
performance although the minimum approved quantity is 200
liters per minute. During donning and doffing or inadvertant
removal of the mask this high flow will occur unless the air
supply is
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of~. It is difficult to don or doff and simultaneously tl~rn
the air on or off, and if the mask is forced off the wearers'
face, for example during a fall~ he may not be in a condition to
immediately refit the mask or manually shut off the air supply.
It is therefore desirable, and the object of this invention~ to
provide an automatic shut-off of the air supply in such situations
where mask back pressure is lacking to prevent escape and rapid
wasteful depletion of the limited air supply.
Thus, the present invention provides pressure-demand
breathing apparatus including a face mask providing a mask
chamber and adapted for connection to an air supply through a
pressure demand regulator and an air supply line, the pressure-
demand regulator being adapted to maintain a predetermined
positiYe pressure in the mask chamber, and shut-off means
automatically operable to interrupt the supply of air to the
mask under abnormal flow conditions such as occur when the mask
is removed and open to ambient atmosphere.
The details, operation, and benefits of the present
invention will ~e described in detail with reference to the
accompanying drawings.
The Drawings
Fig. 1 is a somewhat schematic representation of a
breathing apparatus according to this invention, the supply line
being broken away to indicate indeterminate length.
Fig. 2 is a sectional view of the pressure-demand
regulator component of the apparatus, taken along line 2-2 of
Fig. 1.
Fig. 3 is a sectional view of the exhalation valve on
~,~ the face mask in Fig. 1.
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Fig. 4 is a longitudinal sectional ~iew of the automatic
: shut-off valve component of the apparatus.
Fig. 5 is a transverse sectional view of the shut-off
valve, taken along line 5-5 of Fig. 4.
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DESCRIPTION
Fig. 1 shows a tank 2 of air or other breathing fluid
under pressure, with a hand operable shut-off valve 4. A high
pressure air line 6 leads from the source 2 to a first stage
regulator 8 which reduces the high pressure air from the source
2 to an intermediate level, typically 100-150 psig. An
intermediate pressure air line 10 leads from regulator 8 to an
automatic shut-off device 12, which is mounted on and
communicates with the inlet side of a pressure-demand regulator
14. However, the shut-off device 12, sometimes known as a
pneumatic fuse or excess flow valve, also can be located at the
discharge side of regulator 8 or at any point in supply line 10
between regulators 8 and 14.
Regulator 14 is mounted on a face mask 16, which also
has an exhalation valve 18 mounted on it. Face mask 16 is
contoured to fit against the face of a wearer, not shown, and
provides a mask chamber defined by the mask and facial portion
, covered thereby, in a manner well known in the art.
Referring to Fig. 2, the mask chamber is at the desired
positive pressure and the pressure-demand regulator 14 is shown
in closed position. Regulator 14 communicates with the mask
chamber through inhalation aperture 20. Regulator 14 includes
a body or casing 22 enclosing a regulator chamber 24 which is
; partitioned by flexible diaphragm 26. Diaphragm 26 is biased
inwardly of chamber 24 by a spring 30 seated in an annular recess
28 in the cover of casing 22 and bearing against the diaphragm
which has a reinforcing member 27. A tilt valve stem 32 is
engaged by diaphragm 26 for movement thereby to open the demand
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valve 34 and admit air into chamber 24 from air passage A.
Spring 30 biases diaphragm 2~ to open valve 34 whenever
the relative pressure within chamber 24 drops below the positive
pressure desired to be maintained, the spring bias being overcome
when chamber 24 is at the desired pressure to permit spring 29
to tilt stem 32 to its centered position with valve body 34
closed against seat 31. The force of spring 30 therefore deter-
mines the positive pressure maintained in chamber 24, which of
course is the same as the pressure in the mask chamber, and
spring 30 is selected accordingly. If desired, means can be
provided to adjust the biasing force of spring 30. Such means
are known in the pressure-demand regulator art and, being no
part of this invention, are not shown.
In normal operation, upon inhalation diaphragm 26 moves
inwardly because of the resulting drop in pressure within
chamber 24 and the mask chamber. As it moves inwardly,
diaphragm 26 tilts stem 32 against the bias of its centering
spring 29 to open valve 34 and admit air under pressure into -
the regulator chamber 24 and through passage 20 to the mask
chamber and the user. Valve 34 will remain open between
inhalation and exhalation and during exhalation until the
; pressure within the regulator chamber 24 and the mask chamber
; reaches the positive pressure level determined by the biasing
action of spring 30, at which level diaphragm 26 will have
moved to a position permitting spring 29 to close the tilt
valve. Continued exhalation will raise the pressure above the
predetermined positive pressure to be maintained in the mask,
~ opening the exhalation valve 18 and permitting exhalation to
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the ambient atmosphere.
Exhalation valve 18 is a check valve, opening for
outward air flow or exhalation, and closing to prevent inflow
or inhalation through the valve. As shown in Fig. 3, a floating
disc 36 is lightly biased against a valve seat 38 by a valve
spring 40, sufficient to hold valve disc 36 seated against the
positive pressure for which the regulator is pre-set by spring
30. Disc 36, when seated, blocks the valve passage P during
inhalation by the wearer. During exhalation, the additional
pressure within the mask caused by the exhalation moves disc 36
against spring 40 to open passage P for exhalation to atmosphere.
An apertured cover 42 threads onto the body of valve 18 to hold
spring 40 and disc 36 in place, and also to adjust the closing
bias force on the valve by varying the compression of spring 40.
This permits adjustment of the pressure required to open the
exhalation valve to a level greater than the positive pressure
being maintained within the mask chamber.
Whenever the pressure in the mask chamber, as
reflected in the regulator chamber 24 drops below the predetermined
positive pressure desired to be maintained, diaphragm 26 will
move inwardly, causing valve 34 to open. This creates a serious
problem if the mask is removed from the face, because the
pressure-demand regulator will move to a wide-open, full-flow
position with the result that a substantial quantity of air
will be lost and, if permitted to continue, the air supply will
be quickly depleted. This can occur, for example if the mask
` is knocked from the face of a fireman during a fall and he is
, unconscious and unable to manually turn off the air supply.
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However, it is a particular feature of this invention that
under such abnormal flow conditions the supply of air will shut-
off automatically.
Fig. 4 shows in sectional detail the automatic shut-off
device 12 which is located in the supply line 10 upstream of
the pressure demand regulator 14. A suitable hose fitting 44
connects air line 10 to shut-off valve 12 and continues the
air passage A from line la into valve 12. Passage A at the top
portion of Fig. 4 leads directly into the regulator 14 as shown
in Fig. 2.
Valve 12 includes a body 46 in which a generally
cylindrical passage or bore 48 is formed. Passage 48, open to
the source end of valve 12, leads into a second passage 50
which is open to the regulator end of valve 12. Passages 48
and 50 are part of the total air passage A through the system.
Body 46 is configured to form a valve seat 52 near the interior
end of passage 48 through which it leads into passage 50.
A valve poppet 54 is axially movable in passage 48
between a seated closed position against valve seat 52 and a
wide open position abutting the hose fitting 44. Fig. 4 shows
the poppet 54 in its unseated, wide-open position, the
position it takes during normal operation of the system,
permitting free air flow through passage A. A compression
spring 56 is disposed between poppet 54 and the valve body 46
around the valve seat 54 to bias the poppet 54 away from the
valve seat to the normally open position shown. A plurality
of grooves 58 extend axially along the exterior of poppet 54
and form a part of air passage A. A small bleed orifice 60
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is formed through the poppet 54 to permit a restricted flow
of air through the valve even when poppet 54 is seated.
A pair of parallel reset ports 62 and 54 extend
raclially outward from passage 48, one upstream and the other
downstream of the valve seat 52. A reset spool valve 66 is
associated with the shut-off 12 and is shown in its inoperative
or standby position during normal system operation. Spool
valve 66 includes a body 68 defining a longitudinal passage 70
which communicates with reset ports 62 and 64. The reset valve
66 may be formed of the same body 46 as the associated shut-off
valve 12 as shown, but this is not essential. Reset valve
stem 72, including a hand actuator 74 at its outer end, is axially
movable within the passage 70, against the bias of a
compression spring 76, between an inoperative position as
shown and an operative position. Valve stem 72 includes
suitable air seals such as O rings 78 located along passage
70 outward in each direction from the reset ports 62 and 64.
Valve 72 also includes a valve spool 80. In the illustrated
inoperative position of reset valve 66, valve spool 80 covers
port 62 to block communication of port 62, which is on the
upstream of valve seat 52, with port 64 which is on the downstream
side of seat 52. A stop 82, in the form of a pin engagable
with the opposite ends of an elongated groove in stem 72, limits
the axial travel of valve stem 72. The extreme outward
position of the stem is shown; the inward or reset position
is that position where valve spool 8a uncovers reset port 62
connecting it with port 64 through passage 70.
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OPERATION
In normal operation, shut-off device 12 is open and
air is pressure-demand regulated to the face mask and wearer.
In the event that the mask is forced from the wearer, the mask
internal pressure is lost and it appears to the regulator as
a continuing unlimited demand situation. Diaphragm 27 moves
inwardly, tilting valve 34 to its full wide open position to
provide full flow of air in a fucile attempt to restore the
predetermined positive pressure to the mask chamber. Normally
this would result in rapid depletion of the air supply. For
example what normally would be a thirty minute supply can be
exhausted in two minutes under such wide open, free flowing
conditions. However, such wasteful loss is prevented by the
action of the automatic shut-off 12. As soon as this
extraordinary, abnormal flow occurs, the normal pressure
differential across the valve 12 becomes a significantly
greater pressure drop. The large drop in pressure on its
downstream side causes poppet 54 to move quickly to its seated
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closed position, i.e. to slam shut, thereby preventing further
loss and conserving the air supply. Once poppet 54 closes,
the only loss of air is a small bleed flow through orifice
60. The upstream air pressure acting against the complete
end face area holds poppet 54 closed.
When the mask is refitted on the wearer, the shut-
off 12 can be reset by momentarily depressing the actuator 74.
This puts port 62, which is on the pressure side of valve
, seat 52, in communication with port 64 and passage A on the
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downstream side. The pressure on the downstream side quickly
builds up to a level permitting valve poppet 54 to spring back
to its open position permitting normal air flow to the mask.
Resetting also would occur automatically, upon refitting the
mask in place because of accumulating downstream pressure by
alr flowing through the bleed orifice 60 without any operator
action. While the manual reset is part of the preferred
embodiment of this invention shut-off and reset will occur
automatically without it. When a manual reset is provided,
the automatic reset is not essential and bleed 60 can be omitted
whereby the air supply to the mask will be completely shut-
off when device 12 closes.
SUMMARY
To prevent a run away of air supply when for some
reason the mask is separated from the wearer, a pneumatic
fuse automatic shut-off is interposed in the system to sense
the attendant extraordinary pressure conditions and to react
by closing the air system. The shut-off device resets or
can be manually reset to its normally open condition when
;~ 20 the mask is refitted on the wearer.
j The pressure drop occurs across both the shut-off
12 and the fully open pressure demand regulatox 14. Therefore,
it is most important that the pressure drop at the demand
regulator be a small percentage of the total pressure drop
when it is fully open (i.e. facemask removed), but that it
represents a significant part of the total pressure drop when
the breathing apparatus is in use. A pressure demand
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regulator with a flow capacity considerably greater than
that normally used by the wearer is necessary for the shut-
off device to differentiate between a deep breath or gasp
by the wearer or removal of the facepiece. For example, if
a maximum flow capacity of 500 liters per minute is required
for normal operation, a regulator having a capacity of
up to 700 liters per minute will be used with the shut-off 12
adjusted or selected to close at a flow rate between 500
and 700 liters per minute. The "fuse" would be set to flow
enough to supply the peak flow of a predetermined breathing
requirement but would be designed to close at a flow under
the maximum free flow discharge.
Fuse closing characteristics are flexible and optimum
performance can be obtained by varying the poppet cylinder
bore, effective orifice size around poppet, spring force
and rate, poppet travel and the diameter of the closing seat.
The reopening characteristics are a function of
the spring, closing seat size, orifice bleed flow, volume
downstream of the fuse and the flow demand placed on the
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pressure demand regulator. For optimum reopening performance,
the pressure demand requirements should approach zero flow
during opening cycle.
The term "air'l has been used thxoughout for
simplicity of description. It will be appreciated that there
may be appropriate circumstances where the breathing fluid
is not, strictly speaking, "air" but oxygen, or a mixture
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of oxygen and other gases. The term "air" in this specification
and the following claims is therefore intended to include all
such fluids as are used in respiratory systems. The term
"mask" is intended to include any appropriate respiratory
inlet covering.
The foregoing description and summary of this
invention are given only by way of illustration and not of
limitation. The concept and scope of the invention are
intended to be limited only by the purview of the following
claims.
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