Note: Descriptions are shown in the official language in which they were submitted.
CA 02404509 2002-10-21
26783-6D
1
TITLE OF THE INVENTION
Uni-Directional Fluid Valve
BACKGROUND OF THE INVENTION
This is a division of our copending Canadian Patent
Application No. 2,181,878 filed on July 23, 1996.
The present invention relates to a uni-directional fluid
valve which may in particular be used as an exhalation
valve for a filter mask. By a "filter mask" we mean a
device adapted to be worm over the nose and mouth of a
user and made from or incorporating a filter material to
remove one or more unwanted components from the inspired
air. To improve the comfort and efficiency of such
devices it is common to provide a uni-directional
exhalation valve on the mask which opens under the
pressure differential consequent upon exhalation of the
user to allow for a relatively unrestricted flow of
exhalate out of the mask, but which closes under other
conditions. Examples of valued filter masks are shown
in GB-2072516, DE-4029939, US-4414973, US-4630604, US-
4838262, US-4873972, US-4934362, US-4958633, US-4974586,
US-4981134 and US-5325892.
A common type of exhalation valve comprises a circular
diaphragm of e.g. silicone rubber and a cooperating
circular valve seat surrounding the orifice which passes
the user's exhalate. The diaphragm is clamped at its
centre and marginal portions flex away from the seat when
the user exhales. In another known type the diaphragm
is in the form of a flexible flap which is attached to a
CA 02404509 2002-10-21
2
cooperating seat structure at one end, that is to say in
cantilever fashion, and flexes away from the rest of the seat
when the user exhales. In the design of an exhalation valve it
is important to maximise the cross-sectional area of the open
orifice to allow free flow of exhalate through the valve, and
also to minimise the differential air pressure required to open
the valve (i.e. the valve "cracking" pressure). Centrally
clamped diaphragm valves require a greater force to open them
than cantilevered flap type valves of equivalent size because
their available "lever arm" :is less. Furthermore, the
structure of a cantilevered :flap type valve, when open,
generally presents less of an obstruction to flow than the
centrally clamped circular diaphragm type valve, or in other
words imposes a smaller pressure drop for a given orifice size.
A potential problem which must be addressed in the design of a
cantilevered flap valve, however, lies in ensuring that the
flap will remain closed in all orientations of the structure
while it is not subject to an exhalatory pressure differential.
That is to say, while in order to minimise the opening pressure
differential of the valve it. is desirable to employ a highly
flexible flap of minimal thickness, the very flexibility of the
flap may mean that if the valve is inverted in use (i.e.
orientated with the seat lying above the flap), the flap may
droop down from the seat when the user is not exhaling. This
is clearly undesirable as it may open a leakage path into the
mask for the contaminants which it is intended to exclude.
US-5325892 discloses an exhalation valve with a
cantilevered flap in which the valve seat has a seal ridge
which is curved in the longitudinal direction of the flap, the
curvature corresponding to ,a deformation curve exhibited by the
flap when it bends under its own weight (with no pressure
CA 02404509 2002-10-21
2a
differential). In other words the design of that valve
recognises that the flap is unable to stay flat when the
structure is inverted and
CA 02404509 2005-04-15
26783-6D(S)
3
matches the configuration of the :;eat to the curvature of
the flap under that condition.
SUMMARY OF THE INVENTION
According to an aspect of the invention, there is
provided a filter face mask comer=Lsing: (a) a mask body
adapted to fit over a nose and month of a wearer; and (b) a
unidirectional fluid valve mounte<~ to the mask body, the
unidirectional fluid valve compri:~ing: a valve seat having
an orifice, a seal surface having an inner peripheral edge
surrounding said orifice, said seal surface having opposed
first and second portions spaced apart by said orifice and
opposed third and fourth portions between said first and
second portions and spaced apart by said orifice, a flexible
flap positioned over said orifice for engaging said seal
surface and having a free portion, said free portion
including a portion above said first portion of said seal
surface and which makes contact therewith to close said
orifice and which lifts from the ~>eal surface to open said
orifice, and a retainer from which said free portion extends
and for resisting movement of a second portion of said
flexible flap in a direction in which the free portion lifts
from said seal surface, and for rE~taining in said flexible
flap a curvature transverse to an axis extending between
said opposed first and second portions of said seal surface,
wherein said retainer is positioned relative to said first
and second portions of said seal surface such that the
position from which said free portion extends from said
retainer to the inner edge of the first portion of said seal
surface is closer to the inner edge of said second portion
of said seal surface than to the inner edge of the first
portion of said seal surface.
CA 02404509 2005-04-15
26783-6D(S)
3a
The invention provides, in a further aspect, a
filter face mask comprising: (a) a mask body adapted to fit
over a nose and mouth of a wearer; and (b) a unidirectional
fluid valve mounted to the mask body, the unidirectional
fluid valve comprising: a valve Neat having an orifice, a
seal surface having an inner peripheral edge surrounding
said orifice, said seal surface having opposed first and
second portions spaced apart by said orifice and opposed
third and fourth portions between said first and second
portions and spaced apart by said orifice, a flexible flap
positioned over said orifice for Engaging said seal surface
and having a free portion, said free portion including a
portion above said first portion of said seal surface and
which makes contact therewith to close said orifice and
which lifts from the seal surface to open said orifice, and
a retainer from which said free portion extends and for
resisting movement of a second portion of said flexible flap
in a direction in which the free portion lifts from the seal
surface, and for retaining in said flexible flap a curvature
transverse to an axis extending between said opposed first
and second portions of said seal ;>urface, wherein said
retainer is positioned between said first and second
portions of said seal surface, anc~ is closer to the second
portion than to the first portion, the flap having a
longitudinal curvature between the retainer and the inner
peripheral edge of the first portion of the seal surface
along said axis when the free portion of the flap is in
contact with the seal surface, and wherein the tightness of
the transverse curvature of the flexible flap between the
inner peripheral edges of said op~~osed third and fourth
portions of the seal surface is greater than the tightness
of said longitudinal curvature, wren the free portion of the
flap is in contact with said seal surface.
CA 02404509 2005-04-15
26783-6D(S)
3b
The invention also provides a filter face mask
comprising: (a) a mask body adap-~ed to fit over a nose and
mouth of a wearer; and (b) a unidirectional fluid valve
mounted to the mask body, the unidirectional fluid valve
comprising: a valve seat having an orifice, a seal surface
having an inner peripheral edge surrounding said orifice,
said seal surface having opposed ==first and second portions
spaced apart by said orifice, and opposed third and fourth
portions between said first and second portions and spaced
apart by said orifice, a flexible flap positioned over said
orifice for engaging said seal surface and having a free
portion, said free portion includ=_ng a first portion above
said first portion of said seal surface and which makes
contact therewith to close said orifice and which lifts from
the seal surface to open said orij=ice, and a retainer
engaging a second portion of said flap and for preventing
movement of said second portion of: said flap in a direction
in which the free portion of the f-lap lifts from said seal
surface to open said orifice, said retainer being positioned
such that the position from which said free portion extends
from said retainer to the inner edge of the first portion of
the seal surface is closer to the inner edge of said second
portion of said seal surface than to the inner edge of the
first portion of said seal surface, and wherein said
flexible flap has a curvature transverse to an axis
extending between said opposed first and second portions of
said seal surface to bias the fla~> to the seal surface in
the absence of a pressure differential across the flap,
under any orientation of the valve.
In accordance with a still further aspect of the
invention, there is provided a filter face mask comprising:
(a) a mask body adapted to fit over a nose and mouth of a
wearer; and (b) a unidirectional fluid valve mounted to the
CA 02404509 2005-04-15
26783-6D(S)
3c
mask body, the unidirectional fluid valve comprising: a
valve seat having an orifice, a seal surface having an inner
peripheral edge surrounding said orifice, said seal surface
having opposed first and second portions spaced apart by
said orifice, and opposed third and fourth portions between
said first and second portions anti spaced apart by said
orifice, a flexible flap positionE~d over said orifice for
contacting said seal surface and having a free portion, said
free portion including a portion above said first portion of
said seal surface and which makes contact therewith to close
said orifice and which lifts from the seal surface to open
said orifice, said free portion oi= said flexible flap
extending from said first portion of said seal surface at
least to a position proximate said second portion of said
seal surface and continuously across said orifice
transversely of a direction between said first and second
portions, and wherein said flexib~_e flap has a curvature
transverse to an axis extending between said opposed first
and second portions of said seal ~>urface when the free
portion of said flexible flap is raised from said seal
surface to bias said free portion towards said seal surface.
According to another as~~ect of the invention,
there is provided a filter face mask comprising: (a) a mask
body adapted to fit over a nose and mouth of a wearer; and
(b) a unidirectional fluid valve mounted to the mask body,
the unidirectional fluid valve co~iprising: a valve seat
having an orifice, a seal surface having an inner peripheral
edge surrounding said orifice, said seal having opposed
first and second end portions spaced apart by said orifice,
and opposed third and fourth portions between said first and
second portions and spaced apart ~~y said orifice, a flexible
flap positioned over said orifice for engaging said seal
surface and having a free portion, said free portion
CA 02404509 2005-04-15
26783-6D(S)
3d
including a portion above said first portion of said seal
surface and which makes contact t:zerewith to close said
orifice and which lifts from the ;peal surface to open said
orifice, wherein the free portion of said flexible flap
extends from said first portion o:E said seal surface at
least to a position proximate sai<~ second portion of said
seal surface and continuously across said orifice
transversely of a direction betweE~n said first and second
portions, and said flexible flap has a curvature transverse
to an axis extending between said opposed first and second
portions of said seal surface to. bias the flap to the seal
surface in the absence of a pressure differential across the
flap, under any orientation of the valve.
According to another aspect of the invention,
there is provided a filtering face mask that comprises:
(a) a mask body that is adapted to fit over the nose and
mouth of a person; and (b) an exhalation valve that is
attached to the mask body, which Exhalation valve comprises:
(i) a valve seat that comprises an orifice and a seal
surface; and (ii) a single flexib~_e flap that has a
stationary portion and only one free portion and a
peripheral edge that includes stat:ionary and free segments,
the stationary segment of the peripheral edge being
associated with the stationary portion of the flexible flap
so as to remain in substantially t:he same position during an
exhalation, and the free segment c>f the peripheral edge
being associated with the one freE~ portion of the flexible
flap so as to be movable during an exhalation, the free
segment of the peripheral edge being disposed beneath the
stationary segment when the valve is viewed from the front
in an upright position, the single flexible flap also having
a longitudinal dimension that is c.efined by a line extending
from the stationary segment of the flap to the free segment;
i ~ i
CA 02404509 2005-04-15
26783-6D (S)
3e
the flexible flap being secured t~~ the valve seat non-
centrally relative to the orifice, there being a force
exerted upon the flap in the upstream direction relative to
fluid flow through the valve to impart a curvature to the
flap when in a closed position, which curvature extends at
least transversely to the longitudinal dimension, the free
portion of the flexible flap being in contact with the seal
surface when a wearer of the mask is neither inhaling nor
exhaling and being free to be lifi:ed from the seal surface
during an exhalation.
CA 02404509 2002-10-21
- 4 -
The effect of the transverse curvature of the flap in a valve according to the
invention is therefore to stiffen the flap sufficiently to resist any drooping
away
from the seat when there is no applied pressure differential, even in the
inverted
orientation of the structure. As soon as the flap is "cracked" by an
appropriate
pressure differential, however, the free end of the flap will rapidly flex
away from
the seat and this flexure will progress along the length of the flap to a
position
determined by the instantaneous rate of fluid flow. At least the root end of
the
flap, at its position of attachment to the seat, will retain its transverse
curvature
however, and this will apply a restorative force to the flexed flap, assisting
to
to reseat the flap when the permitted flow of fluid ceases. The stiffening
effect of this
transverse curvature is therefore to be distinguished from the longitudinal
curvature of the flap in US-5325892.
The flap for a valve according to the invention may be manufactured to exhibit
the
requisite transverse curvature in its natural state, e.g. by means of
injection
moulding or thermoforming. In the preferred embodiment to be described
hereinafter, however, the flap as manufactured is flat and its curvature is
imparted
in use by means of the shaping of the valve structure in which it is mounted.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be more particularly described, by way of example, with
2 o reference to the accompanying schE:matic drawings, in which:-
26783-6
CA 02404509 2002-10-21
Figure 1 is a perspective view of a filter mask incorporating a uni-
directional valve
in accordance with the invention as an exhalation valve;
Figure 2 is an "exploded" isometric viE:w of the components of a preferred
embodiment of the exhalation valve for the mask of Figure 1;
Figure 3 is an isometric view showing the interior of the upper housing member
of
Figure 2;
Figure 4 is a longitudinal section through the valve assembled from the
components of Figure 2, on the line I'V-IV of Figure 5, in the closed
condition; and
Figure 5 is a section on the line V-V of Figure 4.
to DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Figure 1, the illustrated mask body 1 is made from one or more
layers
of flexible sheet filter material cut from a blank, folded and welded to form
a cup-
shaped structure to be worn over the nose and mouth of the user. It is in
particular shaped in accordance with the invention in GB-2046102, to which
reference is directed for a fuller description of the method of forming the
mask
from a flat blank. In use the peripheral edge of the mask body forms a seal
against the wearer's face and it is held in place by elastic headbands 2 and a
deformable wire nose clip 3 as well known in the art.
26783-6
CA 02404509 2002-10-21
-5a-
At a suitable location in the side wall of the mask 1 an aperture is formed in
which
an exhalation valve 4 is fitted, the structure of which is more clearly
illustrated in
Figures 2 to 5.
The illustrated valve 4 comprises two interfitting moulded plastics housing
members 5 and 6, also referred to as a valve seat and a valve cover
respectively,
and an elastomeric flap 7 which in the assembled valve is trapped at one end
between the housing members (i.e. between the seat 5 and the cover 6). The
upper housing member 5 as viewed in Figure 2 is also seen from its opposite
face
in Figure 3. It has inlet ports 8 passing through it which on the downstream
side
to are surrounded by a seal ridge 9A/9B/9C of generally trapezial plan-form.
The
lower housing member 6 as viewed in Figure 2 is of dished form with a series
of
outlet ports 10, and snaps onto the member 5 by means of a pair of integral
lateral lugs 11 engaging in slots 12 'formed in member 5. The flap 7 is of
generally trapezial plan-form sized to fit over the seal ridge and is formed
from a
thin and highly flexible piece of elastomer, e.g. 0.5mm thick latex natural
rubber
having a Shore micro hardness of about 30.
The flap 7 is positioned in the valve by a notch 13 at one end embracing a
block
14 on housing member 5, and when the housing members are snapped together
that end of the flap becomes trappE:d between the adjacent portion 9A of the
seal
2 o ridge and a profiled block 15 upstanding from housing member 6. That is to
say it
is mounted in the valve in cantilever fashion. In its natural state, if the
flap 7 is
26783-6
CA 02404509 2002-10-21
-5b-
held horizontally at one end it will tend to bow longitudinally under the
force of
gravity, i.e. so that its opposite end droops down considerably from the plane
of its
fixed end. Both the block 15 and the facing portion 9A of seal ridge are,
however,
curved so
26783-6
CA 02404509 2002-10-21
6
as to impart to the flap a transversely arched
configuration in the assembled valve, as seen
particularly in Figures 4 and 5. In the illustrated
embodiment this arching is accentuated for the central
part of the flap by means of a second profiled block 16
upstanding from the housing member 6 in front of and to a
slightly greater height than the block 15, although this
is not essential in all embodiments of the invention.
The arching of the flap stiffens it sufficiently to
prevent it drooping away from any part of the seal ridge
under zero pressure differential conditions, whatever the
orientation of the valve. The preferred orientation of
the valve is in fact with. the outlet ports 10 directed
with a downward component, as indicated in Figure 1, so
that the user's exhalate will not mist any associated
eyewear, and if the user lowers his head the valve may
become oriented with the flap 7 lying wholly below the
housing member 5.
In use, therefore, the flap 7 seats upon the seal ridge
to prevent the passage of any air into the mask through
the valve 4 while the user is not exhaling. At the
commencement of exhalation, as soon as a minimum
"crackingn pressure differential is applied to the flap 7
from the interior of the mask the free end of the flap
will lift away from the ~;eal ridge in the sense of the
arrow X in Figure 4, and flexure of the flap will
progress rapidly along its length towards the fixed
(root) end, to a position determined by the instantaneous
rate of flow of exhalate out through ports 8 and 10.
When exhalation ceases, the restorative effect of the
arched mounting of the flap will cause the flap as a
whole rapidly to reseat upon the seal ridge, to minimise
the risk of any inward leakage of contaminant through the
valve in the period between the end of exhalation and the
commencement of inhalation. In particular, the flap 7
does not depend for its closure upon the subsequent
application of an inhalat.ory pressure differential.
CA 02404509 2002-10-21
7
From Figure 3 it will be seen that while the portion 9A
of the seal ridge at the root end of the flap has a
concave curvature the remainder 9B/9C of the ridge has a
flat surface. From Figures 3 and 4 it will also be seen
that the portion 9C of the seal ridge at the free end of
the flap rises further from the plane of the member 5
than does the root end portion 9A, and the two side
portions 9B are straight but inclined as viewed in
elevation. The combined effect of this configuration is
that the transverse curvature of the flap 7 decreases
towards its free end, which lies flat against seal ridge
portion 9C, while a degree of longitudinal curvature is
also imparted to the central section of the flap (but not
to its side edges which lie flat against the ridge
portions 9B). This has been found to enhance the
stability of the flap in its closed condition while
minimising the opening pressure differential for the
particular embodiment illustrated. In other
embodiments, however, there may be no longitudinal
curvature of the flap and/or its transverse curvature may
extend throughout its whole length, in the latter case
the seal ridge portion 9C being modified to a concave
form as indicated in broken line in Figure 3.
