Patent Description:
It is known for people to wear filtering face masks in environments wherein a risk of inhaling potentially hazardous airborne contaminants exists. Such face masks typically include a cup-shaped mask body for locating over the mouth and nose of a wearer and a valve assembly mounted in an aperture of the mask body proximal to the mouth of the wearer. The valve assembly typically includes a valve element configured to allow one-way or unidirectional flow of air into or out of the mask body in response to an inhalation or exhalation of air by the wearer which creates a pressure differential across the valve element to thereby urge the same towards an open position and allow air into or out of the mask body accordingly.

Conventional valve assemblies for face masks typically include a circular valve orifice defining a circular valve seat for a circular valve element to engage when in the closed position. The circular valve element is flexible and typically mounted at its centre such that the circumferential edge of the valve element is urged away from the valve seat when in an open position and back onto the valve seat when in a closed position. However, such a configuration requires a relatively high-pressure differential to be created across the valve to open the valve element, mainly because the distance from the central mounting point to the edge of the circular valve element is relatively small. Circular diaphragm valves also create a significant amount of air flow resistance through the valve assembly and in turn increased breathing resistance to a wearer which can become uncomfortable, particularly in a relatively hot environment.

Cantilever flap valves have been developed to address the abovementioned problems associated with circular diaphragm valves, such as described in <CIT> and <CIT>. Whilst a cantilevered flap valve presents less of an obstruction and in turn resistance to airflow through the valve assembly, conventional flap valves are substantially thin and flexible and can move away from the valve seat when the valve assembly is inverted for example which undesirably creates a leak path for potentially hazardous airborne contaminants to enter into the mask body. Furthermore, it is known to provide a crucifix arrangement of cross members extending across the valve orifice to prevent the flap valve flexing beyond the closed position and inverting. However, these cross members increase the resistance to airflow through the valve and do not sufficiently support the valve flap to prevent a leak path for potentially hazardous airborne contaminants to enter into the mask body.

It is an aim of certain embodiments of the present invention to provide a respirator valve for a filtering face mask wherein the valve is configured to minimise resistance to airflow through the valve in use, whilst also minimising a pressure differential required across the valve to open a valve flap thereof.

It is an aim of certain embodiments of the present invention to provide a respirator valve for a filtering face mask wherein a valve flap of the valve is biased in a closed position against a valve seat of the valve when a pressure differential across the valve is zero and the valve is in any orientation, such as inverted, whilst also minimising a pressure differential required across the valve to open the valve flap during inhalation or exhalation by a wearer of the face mask.

According to a first aspect of the present invention there is provided a unidirectional valve assembly for a face mask, comprising:.

Optionally, the valve orifice is substantially square.

Optionally, the cross members split the valve orifice into a pair of opposed first and second side ports extending from a proximal end of the orifice towards a distal end of the orifice with respect to the fixed end region of the valve flap, and a distal end port extending across the distal end of the orifice.

Optionally, the plurality of apertures of the valve cover member comprises a first side aperture substantially aligned with the first side port, a second side aperture substantially aligned with the second side port, and a distal end aperture substantially aligned with the distal end port.

Optionally, the valve cover member comprises a pair of opposed corner apertures each located between the distal end aperture and a respective one of the side apertures.

Optionally, the apertures are disposed in a wall region of the valve cover member and a closure region extends across the wall region to close the valve assembly distal and substantially opposed to the valve orifice.

Optionally, a plurality of spaced apart and parallel ribs extends inwardly towards the valve orifice from an inner surface of the closure region.

Optionally, the ribs are oriented substantially laterally with respect to the longitudinal axis of the valve flap.

Optionally, the valve seat surface comprises a pair of opposed side regions extending between proximal and distal end regions with respect to the fixed end region of the valve flap, and wherein the side regions of the valve seat surface are substantially concave.

Optionally, the distal end region of the valve seat surface is located further away from the valve orifice than the proximal end region of the valve seat surface in a direction parallel to an axis of the valve orifice.

Optionally, a flap support surface defined by the cross members is substantially concave and defines a curvature substantially corresponding to the curved side regions of the valve seat surface.

Optionally, a width of the flap support surface along each cross member is less than a width of an underlying main portion of each cross member.

Optionally, the flap support surface is spaced apart from the valve seat surface.

Optionally, the intersection region of the cross members is offset with respect to a centre of the valve orifice.

Optionally, the valve seat surface surrounding the valve orifice is substantially square.

Optionally, the valve seat member comprises a mounting surface for mounting the fixed end region of the valve flap on, and the valve cover member comprises a clamping portion for clamping the fixed end region of the valve flap between the valve seat member and the valve cover member.

Optionally, the clamping portion comprises an elongate projection extending laterally across the valve flap.

Optionally, the mounting surface of the valve seat member and a clamping surface of the clamping portion are angled to urge the free end region of the valve flap towards the valve seat surface.

Optionally, the valve seat member comprises a pair of laterally spaced apart projections extending from the mounting surface each located in a corresponding notch disposed in a respective side edge of the fixed end region of the valve flap.

Optionally, the valve seat member comprises a central projection extending from the mounting surface located in a notch disposed in an end edge of the fixed end region of the valve flap.

Optionally, the valve cover member comprises a plurality of spaced apart projections for locating in corresponding apertures of the valve seat member during assembly, wherein the material of the projections is configured to melt on heating and fuse with the material of the apertures to provide a homogenous weld on cooling to securely attach the valve cover member to the valve seat member.

Optionally, each aperture comprises a countersunk region and each projection is configured to extend through the respective aperture before heating and to fill the countersunk region when molten to thereby create a tapered formation at the end of each projection.

Optionally, the valve flap is a monolithic polymeric element.

According to a second aspect of the present invention there is provided a face mask comprising a unidirectional valve assembly according to the first aspect of the present invention.

Optionally, the valve assembly is configured to allow a wearer of the mask to exhale through the valve assembly.

Certain embodiments of the present invention will now be described with reference to the accompanying drawings in which:.

As illustrated, a respirator valve assembly <NUM> for a filtering face mask includes two interconnecting housing members referred to herein as a valve cover member <NUM> and a valve seat member <NUM>. The housing members <NUM>,<NUM> are injection moulded from a plastics material, such as polypropylene or the like.

A polymeric valve flap <NUM> is clamped at a fixed end region <NUM> thereof between the valve cover member <NUM> and the valve seat member <NUM> when the two components are connected together by suitable means, such as bonding, adhering, welding, an interference fit, or a mechanical fixing or coupling, e.g. a snap-fit connection, or the like. The valve flap <NUM> is substantially flexible to allow a free end region <NUM> of the valve flap <NUM>, and at least partially a central region <NUM> of the valve flap, to move from a closed position towards an open position with respect to the valve seat member <NUM> in response to a pressure differential being created across the valve flap when a wearer of the face mask exhales. The valve flap <NUM> is substantially resilient to urge at least the free end region <NUM> back to the closed position when the pressure differential across the valve flap is zero. Furthermore, as described further below, the valve flap <NUM> is also mechanically biased towards the valve seat member <NUM> and in turn the closed position. The valve flap <NUM> is aptly a mono layer or monolith element and has a thickness of around <NUM> to <NUM>. Aptly, the valve flap <NUM> material has a density of around <NUM>/m^<NUM> to <NUM>/m^<NUM>, ideally around <NUM>/m^<NUM> which desirably provides a relatively lightweight valve flap for a given length and width which is aptly around <NUM> x <NUM> respectively. Desirably, a relatively lightweight valve flap requires less force to move a given distance, thereby reducing the required pressure differential across the valve and required breathing effort from a wearer of the face mask. Suitable polymeric materials for the valve flap <NUM> include polyethylene terephthalate (PET) or high-density polyethylene (HDPE) or the like.

The valve seat member <NUM> includes a substantially square base portion <NUM> defining a substantially square orifice <NUM>. The orifice may be a different non-circular shape such as rectangular or trapezoid for example but a substantially square orifice is preferred because such a shape maximises orifice area, and in turn airflow therethrough, whilst minimising resistance to the airflow and the size of the valve assembly. 'Substantially square' is intended to mean a shape having a maximum width dimension that is substantially similar if not identical to a maximum length dimension of the orifice, wherein opposed sides of the shape may be parallel or not and the four corner regions of the shape may be curved having the same or different radii of curvature. A continuous first wall portion <NUM> extends substantially perpendicularly from the base portion <NUM> to surround the orifice <NUM>. An outer surface <NUM> of the wall portion <NUM> is optionally tapered to engage by an interference fit with a correspondingly tapered inner surface <NUM> of the valve cover member <NUM> when the two components are connected together. The first wall portion <NUM> is located inboard of the outer edge of the base portion <NUM> such that a continuous flange surface <NUM> is provided around the valve seat member <NUM> for engagement with a corresponding flange surface <NUM> of the valve cover member <NUM> when the two components are connected together. The connected flange regions of the valve cover member and the valve seat member provide a flange portion for engagement with an outer surface of the body of the face mask.

As illustrated in <FIG> and <FIG>, a continuous projection <NUM>,<NUM> is provided around each of the flanges of the valve seat member and the valve cover member such that the projections are adjacent to each other and spaced apart when the two components are connected together to thereby define an outer one <NUM> and an inner one <NUM> of the continuous projections. The projections <NUM>,<NUM> taper to an apex and engage into/on the outer surface of the mask body when the valve assembly is located thereon during assembly of the mask. A lower wall portion <NUM> of the valve seat member <NUM> extends around the orifice <NUM> for engagement in a correspondingly shaped aperture provided in the mask body to thereby ensure the valve assembly is correctly located and securely mounted on the mask body. Heat is applied proximal to the projections <NUM>,<NUM> to cause the plastics material to melt and homogenously fuse or weld the valve cover member <NUM> and the valve seat member <NUM> locally together, whilst also securing the valve assembly <NUM> to the mask body when the molten plastics material solidifies. This allows the valve assembly to be secured to the face mask in a relatively quick and efficient manner whilst, at the same time and by the same operation, securely connecting the two main components of the valve assembly together.

A proximal end region of the first wall portion <NUM> with respect to the fixed end of the valve flap <NUM> is wider than the distal end region and side regions of the first wall portion <NUM>. The proximal end region of the first wall portion <NUM> provides a substantially curved mounting surface <NUM> for engagement with an inner surface of the valve flap <NUM> at the fixed end region <NUM> thereof. A pair of laterally spaced apart projections <NUM> extend upwardly from each side of the mounting surface <NUM> for engagement in a corresponding notch <NUM> provided in each side of the fixed end region <NUM> of the valve flap <NUM>. The notch and projection arrangement constrains the valve flap <NUM> in both lateral and longitudinal directions with respect to the valve seat member <NUM>. A further projection <NUM> is provided on the mounting surface <NUM> and substantially centrally and proximal to an outer edge thereof. A further notch <NUM> is provided in the fixed end edge of the valve flap <NUM> for the central projection <NUM> to engage in when the valve flap <NUM> is mounted on the mounting surface <NUM>. The central notch and recess arrangement acts as a further locator for mounting the valve flap on the valve seat member in a correct orientation and location, whilst also providing additional security and constraint to the valve flap in both longitudinal and lateral directions. The inner surfaces of the projections are convex to engage with corresponding concave surfaces of the respective notches. The curves engagement surfaces ensure any stress concentrations and potential fatigue locations on the valve flap are minimised, whilst providing maximum contact area between the fixed end region of the valve flap and the projections for optimum security and constraint.

As illustrated in <FIG>, a clamping portion <NUM> in the form of a laterally oriented and elongate projection extends inwardly from a closure region <NUM> of the valve cover member <NUM> towards the valve seat member <NUM> and engages the outer surface of the valve flap <NUM> to clamp the same between the valve cover member <NUM> and the valve seat member <NUM>. The clamping portion <NUM> has an angled surface at its free end which engages the valve flap and corresponds to the angle of the mounting surface <NUM> at that location to efficiently clamp the valve flap <NUM> therebetween. The angle of the mounting surface <NUM> at the clamp location is around <NUM>-<NUM> degrees with respect to the horizontal, and aptly around <NUM> degrees. An inner surface of the clamping projection <NUM> vertically aligns with the inner surface of the proximal end region of the first wall portion <NUM> to thereby define a continuous hinge line laterally across the valve flap <NUM> about which the valve flap flexes when moving between the open and closed positions with respect to the valve seat in use. The clamping projection <NUM> is longitudinally spaced from the locating projections <NUM>,<NUM> towards the free end region <NUM> of the valve flap <NUM> to thereby, in combination with the angled/curved mounting surface <NUM>, urges or biases the valve flap <NUM> towards the closed position and against a valve seat of the valve seat member <NUM>, as described further below.

The first wall portion <NUM> of the valve seat member <NUM> is located inboard of the inner edge of the base portion <NUM> which defines the orifice <NUM>. A second wall portion <NUM> is provided between the orifice <NUM> and the first wall portion <NUM> and extends substantially perpendicularly from the base portion <NUM> and surrounds the orifice. An inner surface of the second wall portion <NUM> is vertically aligned with an inner surface of the lower wall portion <NUM> to provide a continuous orifice inner surface. The first and second wall portions <NUM>,<NUM> are spaced apart to define a gap therebetween. An upper surface of the second wall portion <NUM> provides a continuous valve seat surface <NUM> for the valve flap <NUM> to sealingly engage with when in the closed position. As illustrated in <FIG>, the valve seat surface <NUM> is substantially convex, and aptly semi-circular in cross section, to minimise the contact area between the seat surface and the valve flap whilst efficiently sealing the valve flap against the seat surface when in the closed position. The substantially rounded seat surface minimises the effects of any forces acting between the seal surface and the valve flap which could prevent the same from efficiently opening from the closed position, such as if moisture accumulated on a substantially flat seat surface which could undesirably cause the valve flap to stick to the seat surface in use.

The substantially square valve seat surface <NUM> comprises opposed end surfaces and opposed side surfaces with respect to a longitudinal axis of the valve flap <NUM> in a direction from the fixed end region <NUM> to the free end region <NUM> thereof. The valve seat surface <NUM> has a material hardness of around at least around <NUM> GPa, and aptly around <NUM> GPa, to provide a substantially rigid seal surface against which the valve flap engages in use to create an effective seal. Hardness testing was conducted using a Hysitron Ti950 nano-indenter and a standard diamond Berkovich probe. The second wall portion <NUM> defining the seat surface is around <NUM> wide.

As illustrated in <FIG>, the side surfaces of the valve seat <NUM> are substantially concave, whilst the end surfaces of the valve seat <NUM> are substantially flat and parallel. This configuration allows the valve flap <NUM> to flex longitudinally only, i.e. not laterally, and engage with the longitudinally curved side surfaces of the valve seat <NUM> in a relatively natural and low strained manner to ensure an efficient and consistent seal is created between the valve flap and the valve seat in use. A proximal end surface <NUM> of the valve seat <NUM> with respect to the fixed end of the valve flap <NUM> is lower than a distal end surface <NUM> of the valve seat when viewed in cross section as illustrated in <FIG>. In combination with the valve flap <NUM> being biased towards the closed position by the arrangement of the curved mounting surface <NUM> and the clamping projection <NUM>, the higher distal end surface <NUM> increases the seal force, particularly at the free end region of the valve flap, to provide an efficient and effective seal between the valve seat member and the valve flap and particularly in any orientation of the valve assembly, such as when inverted, to prevent the valve flap undesirably opening when a zero pressure differentiation is across the valve.

Three elongate cross members <NUM> extend across the orifice <NUM> to add strength and stiffness to the valve seat member <NUM>. The cross members <NUM> are arranged in a Y-shape configuration such that two of the cross members extend inwardly from a respective one of the distal corner regions of the orifice towards the longitudinal axis (proximal-distal direction) of the orifice, and a third cross member extends along the longitudinal axis to the proximal end of the orifice. The cross members <NUM> extend inwardly from the second wall portion <NUM> which provides the valve seat surface <NUM>. Aptly, the cross members <NUM> meet at an intersection region which, as illustrated in <FIG>, is offset, i.e. not coaxial, with respect to a central axis of the valve orifice <NUM>. This defines two relatively large proximal or side ports <NUM> of equal size and one smaller distal or end port <NUM>. Furthermore, the area of the smaller port decreases in the proximal direction, i.e. away from the free end of the valve flap, whereas the area of the larger ports increases in the proximal direction. When the valve flap is open, the free end region thereof will flex further away from the valve seat surface than the central region of the valve flap and yet further away than a proximal region of the valve flap near the fixed end region thereof, so this arrangement aims to promote substantially equal and balanced air flow through the valve assembly when the valve flap <NUM> is open. Alternatively, the intersection region of the cross members may be substantially coaxial, i.e. aligned, with a centre of the orifice. Providing three cross members <NUM> in the Y-shape arrangement also sufficiently strengthens and stiffens the valve seat member <NUM> whilst minimising the resistance to air flowing through the valve assembly in use compared to, for example, a cruciform arrangement.

As illustrated in <FIG> and <FIG>, each cross member <NUM> includes a main portion <NUM> extending from a respective region of the valve orifice <NUM> and a flap support portion <NUM> each defining a support surface <NUM> for engagement with the valve flap <NUM> when in an 'over-closed' position. An 'over-closed' position refers to the valve flap being urged by a pressure differentiation created across the flap during inhalation by a wearer which causes the central region of the flap to bend beyond the closed position ('neutral/normal' engagement with the valve seat). The cross members <NUM> act to the support and limit this movement of the flap beyond the closed position and prevents the same collapsing or buckling during inhalation by the wearer. As illustrated in <FIG>, the support surfaces <NUM> of each cross member <NUM> are substantially curved in a longitudinal direction of the valve flap to provide a combined concave surface which substantially follows the curvature of the mounting surface <NUM>. A radius of curvature of the valve seat surface <NUM> and the Y-shaped support surface <NUM> may be substantially the same as the mounting surface <NUM> on which the fixed end region of the valve flap <NUM> is mounted. Alternatively, the curvature of the valve seat surface and the Y-shaped support surface may tend towards the horizontal (as viewed in <FIG>) whilst optionally not reaching the horizontal.

The support surfaces <NUM> are aptly distanced slightly below, i.e. inwardly, from the valve seat surface <NUM> such that they are offset from the valve flap when the same is in the 'neutral/normal' closed position. The offset is aptly less than or equal to <NUM>. This arrangement provides support to the valve flap if/when it is urged beyond the closed position by a negative pressure created across the valve flap in use, to prevent the same from collapsing/buckling, whilst also limits the contact area on the valve flap in the 'normal closed position to only the seat surface to thereby minimise the risk of the valve flap sticking in the closed position in use.

The support surfaces <NUM> aptly have a width which is less than a width of the main portion <NUM> of the respective cross member <NUM>. The support surfaces <NUM> may be rounded. This arrangement minimises the contact area of the support surfaces <NUM> and thereby the risk of the flap valve sticking to the support surfaces in use and in turn requiring an increased pressure to move the flap valve back towards the open position. The Y-arrangement of cross members <NUM> desirably supports the flap valve <NUM> at the free end corner regions thereof which are furthest away from the fixed end region of the valve flap and therefore at greater risk of inversion by a negative pressure than, for example, a central or proximal region of the flap valve with respect to the fixed end thereof. The central region of the flap valve is supported in the over-closed position by the central portion of the Y-arrangement of cross members and the proximal region of the valve flap is supported centrally along the longitudinal axis by the proximal cross member with respect to the fixed end of the valve flap. This arrangement provides sufficient support to the flap valve in the over-closed position, whilst maximising air flow through the valve assembly and minimising resistance to the airflow through the valve assembly.

As illustrated in <FIG> and <FIG>, each flap support portion <NUM> is spaced away from the second wall portion <NUM> defining the orifice to provide a gap <NUM> therebetween and isolate the support surface <NUM> provided by each cross member <NUM> from the valve seat <NUM>. The gaps <NUM> allow air to flow through and help to prevent an adhesion force being created between the flap valve and the support surfaces <NUM>.

The valve cover member <NUM> is a one-piece moulded component and includes a peripheral flange region <NUM> defining the flange surface <NUM> for engagement with the corresponding flange surface <NUM> of the valve seat member <NUM> when the two components are assembled together. An inwardly tapered and peripheral cover wall region <NUM> extends from the flange region <NUM> to define the tapered inner surface <NUM> for engagement with the corresponding inner surface <NUM> of the valve seat member <NUM> when the two components are assembled together. A cover closure region <NUM> extends across the cover wall region <NUM> to close an end region thereof which is distal to and opposite the valve orifice. As illustrated in <FIG>, the cover closure region <NUM> defines a plurality of spaced apart and parallel ribs <NUM> disposed on an inner surface thereof. The ribs <NUM> extend laterally with respect to the valve flap <NUM> and each have a length which is less than a width of the valve flap. The ribs <NUM> present a smaller combined contact area compared to if they were not present for the flap valve <NUM> to engage when in the fully open position or even if urged beyond a normal open position. Presenting a relatively small contact area to the flap valve when in the open, or over-open, position, the risk of the valve flap undesirably sticking to the underside of the cover closure region <NUM> is minimised if not eliminated. The ribs <NUM> space the valve flap <NUM> away from the underside of the cover closure region <NUM> and air is allowed to flow between the valve flap and the cover member, and between the ribs, if the valve flap is forced against the ribs to thereby ensure the flap does not stick to the same, particularly if moisture is present on the ribs in use. In view of the length of each rib <NUM> being less than a width of the valve flap <NUM>, the side regions and free end region of the valve flap <NUM> is not engaged with any other component when in the open or an over-open position which desirably further reduces the risk of the valve flap sticking to a surface of the valve cover member <NUM> in use.

As illustrated in <FIG>, a plurality of apertures is defined in the cover wall region <NUM> of the valve cover member <NUM> which include a pair of opposed elongate side apertures <NUM>, an elongate distal aperture <NUM>, and a pair of corner apertures <NUM>. The side apertures <NUM> and distal aperture <NUM> are substantially rectangular in shape and the corner apertures <NUM> are substantially square in shape. The side apertures <NUM> are substantially aligned with the elongate proximal/side ports <NUM> of the valve seat member <NUM> and have a length substantially corresponding to a length of the proximal/side ports <NUM>. The distal aperture <NUM> is substantially aligned with the distal port <NUM> of the valve seat member <NUM> and has a length substantially corresponding to a length of the distal port <NUM>. Each corner aperture <NUM> communicates with the distal port <NUM> and a respective one of the proximal/side ports <NUM>. This arrangement, i.e. location and size and shape, of the apertures <NUM>,<NUM>,<NUM> in the valve cover member <NUM> ensures optimum air flow through the valve assembly in use, whilst minimising resistance to said air flow and in turn the breathing of a person wearing the face mask. In use, the distal aperture <NUM> in the valve cover member <NUM> faces substantially downwardly such that air being expelled from the valve assembly (when configured as an exhale valve assembly) is directed substantially away from a wearer's eyes so that the risk of steaming up a visor or eyewear also being worn by the person is minimised if not eliminated.

A respirator valve assembly <NUM> for a filtering face mask according to an alternative embodiment of the present invention is illustrated in <FIG>.

As illustrated in <FIG>, the proximal end region of the first wall portion <NUM> of the valve seat member <NUM> includes a plurality of scalloped regions/recesses <NUM> extending downwardly therein from the mounting surface <NUM> to thereby define a plurality of ribs <NUM>,<NUM> for engaging and supporting the underside of the fixed end region <NUM> of the valve flap <NUM>. The ribs include a central rib <NUM> located between a pair of side ribs <NUM>, wherein the ribs extend substantially longitudinally between a rear laterally oriented rib <NUM> and a front laterally oriented rib <NUM>. The ribs collectively define the mounting surface <NUM> for engaging and supporting the underside of the fixed end region <NUM> of the valve flap <NUM>. Reversing the moulding direction compared to the embodiment illustrated in <FIG> which includes a single recess (<NUM> in <FIG> and <FIG>) extending inwardly from the under surface of the valve seat member <NUM>, desirably maximises the flat surface area of the underside of the valve seat member <NUM> to increase security if the valve assembly <NUM> is adhered to a corresponding surface of a filtering face mask.

As illustrated in <FIG>, the valve cover member <NUM> of the valve assembly <NUM> includes a plurality of longitudinally oriented and laterally spaced apart ribs <NUM>, <NUM> which are respectively in alignment with the central rib <NUM> and the side ribs <NUM> of the valve seat member <NUM> for engagement with the upper surface of the valve flap <NUM> to securely clamp the fixed end region <NUM> of the valve flap <NUM> therebetween. The longitudinally oriented ribs <NUM>,<NUM> extend rearwardly from a laterally oriented wall/projection <NUM> extending across the inside of the valve cover member <NUM> which corresponds with the front laterally oriented rib <NUM> of the valve seat member <NUM> to thereby clamp the fixed end region <NUM> of the valve flap <NUM> therebetween.

As illustrated in <FIG>, the side regions of the valve seat <NUM> curve gradually into the front laterally oriented rib <NUM> such that the mounting surface <NUM> extends onto the valve seat <NUM> without a gap therebetween. The curved proximal corner regions of the valve seat <NUM> have in profile a radius of curvature of around <NUM>. This arrangement uses a distal portion (front laterally oriented rib <NUM>) of the mounting/clamping surface <NUM> as a proximal end surface of the valve seat <NUM> which in turn increases sealing efficiency and responsiveness of the valve flap and reduces the risk of leakage past the valve flap in use. The larger radii of the curved proximal corner regions of the valve seat <NUM> also help to reduce the risk of leakage past the valve flap in use.

As illustrated in <FIG>, the valve cover member <NUM> includes a plurality of projections <NUM>,<NUM> extending downwardly therefrom for locating in corresponding through apertures <NUM> provided in the valve seat member <NUM>. As illustrated, a distal projection <NUM> extends from the underside of each of the front/distal corners of the cover wall region <NUM> of the valve cover member <NUM>, and a pair of side proximal projections <NUM> and a central proximal projection <NUM> located therebetween extend from respective truss regions <NUM> extending inwardly from the inner surface of the valve cover member <NUM>. The side projections <NUM> are oriented laterally and the central projection <NUM> is oriented longitudinally. The truss regions <NUM> are slidably received in correspondingly shaped and sized bores <NUM> which extend axially through each locating projection <NUM>,<NUM> and terminate at a respective one of the proximal apertures <NUM>. As described above for the embodiment illustrated in <FIG>, the locating projections <NUM>,<NUM> locate and constrain the valve flap <NUM> on the mounting surface <NUM> in both the longitudinal and lateral directions. Engagement of the valve cover projections <NUM>,<NUM>,<NUM> into the corresponding bores <NUM> and through the corresponding apertures <NUM> of the valve seat member <NUM> positively locates and couples the valve cover member <NUM> with respect to the valve seat member <NUM> prior to welding the two components together.

As illustrated in <FIG>, the valve cover projections <NUM>,<NUM>,<NUM> extend through the apertures <NUM> when the valve cover member <NUM> is mounted on the valve seat member <NUM> during assembly. Each aperture <NUM> includes a countersunk region <NUM>, i.e. an inwardly tapering surface, extending into the under surface <NUM> of the valve seat member <NUM>. The ends of the projections <NUM>,<NUM> extending through the apertures <NUM> are then subjected to localised energy, such as high frequency ultrasonic acoustic vibrations, or localised heating by, for example, heat staking or the like, to cause the plastics material at the ends of each projection to deform and fill the countersunk regions <NUM> of each respective aperture <NUM> such that, as illustrated in <FIG>, a substantially flat under surface is provided. The surface material of the countersunk regions <NUM> may aptly also be caused to soften/deform such that, once cooled and hardened, a solid homogenous weld between the two components is created. The countersunk regions <NUM> also create a tapered formation at the end of each projection <NUM>,<NUM>,<NUM> which securely anchors the valve cover member <NUM> to the valve cover seat <NUM> and prevents separation in use.

Claim 1:
A unidirectional valve assembly (<NUM>) for a face mask, comprising:
a valve seat member (<NUM>) providing a continuous valve seat surface (<NUM>) surrounding a non-circular valve orifice (<NUM>), and a plurality of cross members (<NUM>) each extending partially across the valve orifice to meet at an intersection region;
a substantially flexible and cantilevered valve flap (<NUM>) mounted at a fixed end region <NUM>) to the valve seat member (<NUM>) and configured to engage the valve seat surface (<NUM>) when in a closed position to prevent air flow through the valve assembly; and
a valve cover member (<NUM>) attached to the valve seat member (<NUM>) and defining a plurality of apertures (<NUM>,<NUM>,<NUM>) in fluid communication with the valve orifice (<NUM>) when at least a free end region (<NUM>) of the valve flap is in an open position with respect to the valve seat surface (<NUM>) to allow air flow through the valve assembly,
characterized in that
the cross members (<NUM>) are arranged in a Y-shape configuration and consist of a first cross member extending from a first corner region of the valve orifice, a second cross member extending from a second corner region of the valve orifice, and a third cross member extending substantially longitudinally with respect to an axis of the valve flap and away from the first and second corner regions of the valve orifice.