NO314439B1 - One-way fluid valve - Google Patents

Abstract

A one-way fluid valve (14) comprises a flexible flap (24) having a first portion (28) and a second portion, the first portion being attached to a valve seat (26), and the valve seat having an opening and a sealing edge (30) which has a concave curvature when viewed in a profile projection. The flexible flap (24) contacts the concave curvature of the sealing edge (30) when a fluid does not pass through the opening, and the second portion of the flexible flap is free to be lifted from the sealing edge when a fluid passes through the opening. The one-way fluid valve (14) has a concave curvature corresponding to a deformation curve exhibited by the second portion of the flexible flap (24) when subjected to (i) a uniform force acting along the length of the deformation curve, normally thereon, (ii) a force acting in the direction of gravity with a magnitude equal to the mass of the second portion of the flexible flap multiplied by at least one unit of acceleration of gravity, or a combination of (i) and (ii).

Description

The present invention relates to a one-way fluid valve which comprises a

flexible valve with a first portion and a second portion, wherein the first portion is attached to a valve seat, wherein the valve seat has an opening and a sealing edge having a concave curvature when viewed in a profile projection, wherein the flexible flap contacts the sealing edge's concave curvature when a fluid does not pass through the opening, where the other part of the flexible flap is free to be lifted from the sealing edge when a fluid passes through the opening.

One-way fluid valves have been used in face filter masks for many years and are described in, e.g., US Patents 4,981,134, 4,974,586, 4,958,633, 4,934,362, 4,838,262, 4,630,604, 4,414,973 and 2,999,498. In particular, US patent 4,934,362 (the '362 patent), discloses a one-way exhalation valve with a flexible flap attached to a valve seat, the valve seat having a rounded sealing edge with a parabolic profile. The flexible flap is attached to the valve seat at the top of the parabolic curve, and rests on the rounded sealing edge when the valve is in the closed position. When a wearer of a face mask exhales, the exhaled air lifts the free end of the flexible flap away from the sealing edge, allowing the exhaled air to move from the interior of the face mask. The '362 patent states that an exhalation valve of this construction provides a substantially lower pressure drop in a face filter mask.

The purpose of the present invention is to provide a one-way fluid valve which opens more easily for blowing out in a flow direction than known one-way fluid valves, while at the same time it must be tight against blowing in in a blocking direction.

The purpose is achieved with a one-way fluid valve of the type mentioned at the outset, characterized by the features specified in the requirements.

The present invention provides a safe exhalation valve in that it has

a flexible flap having a substantially uniform seal against the valve seat under any orientation of the exhalation valve. Applied in a face filter mask, the present invention helps alleviate wearer discomfort by (1) minimizing exhalation pressure inside the face filter mask, (2) blowing out a greater percentage of exhaled air through the exhalation valve (as opposed to passing the exhaled air through the filter media). , and under certain conditions (3) produce a negative pressure inside a face filter mask during exhalation, so that a net flow of cool ambient air into the face mask is created.

With the invention, a one-way fluid valve is produced which makes it possible for a flexible flap to exert a substantially uniform force on a sealing edge in the valve seat.

The substantially uniform force is achieved by attaching a first portion of a flexible flap

to a surface, and hold up a second or free portion of the flexible flap as a cantilever beam. The second or free part of the flexible flap is then deformed using computer simulation, by applying a series of force vectors of the same

size of the flexible flap in directions normal to the curvature of the flexible flap. The other part of the flexible flap assumes a particular curvature, referred to as the deformation curve. The deformation curve is drawn, and the record is used to define the curvature of the sealing edge in the valve set. A valve seat with this curvature prevents the flexible flap from bulging, and from having little or no contact with the sealing edge in certain areas, and too much contact in other areas. This simple contact ratio makes the valve safe by preventing inflow in the blocking direction.

The invention also provides a one-way fluid valve that minimizes the pressure required to open the valve in the direction of flow. This advantage has been achieved by finding the minimum force necessary to hold the flexible flap in the closed position in any orientation. The minimum closing force for the flap is obtained by equipping the valve with a valve seat that has a sealing edge with a concave curvature that corresponds to a deformation curve exhibited by the flexible flap when it is fixed as a cantilever at one end, and bends under its own weight. A sealing edge corresponding to this deformation curve allows the valve to remain closed when fully inverted, but also allows it to be opened with a minimum of force in the direction of flow.

The invention provides a one-way fluid valve that can exhibit lower resistance in the direction of flow, making the valve easier to open. This advantage is achieved in the present invention by attaching the flexible flap to the valve seat outside the area covered by the valve opening. A valve of this construction allows the flexible flap to be more easily lifted from the curved sealing edge, because a larger moment arm is produced when. the flexible flaps fitted to the valve seat outside the area covered by the opening. A further advantage of a valve of this construction is that it allows the entire orifice to be open during flow in the direction of flow.

In addition to the advantages mentioned above, when the valve according to the invention is used as an exhalation valve in a face filter mask, this invention allows a greater percentage of exhaled air to be blown out through the exhalation valve, and after an initial positive pressure has opened the valve, the pressure inside the face filter mask is allowed to decrease and in some cases become negative during exhalation. These two essential properties are achieved by (i) placing the valve according to the invention in a face filter mask mainly opposite where the user's mouth will be when the face mask is used, and (ii) determining a preferred cross-sectional area for the exhalation valve opening. When a valve according to the invention has an opening with a cross-sectional area larger than approx. 2 square centimeters (cm<2>) when viewed from a plane perpendicular to the direction of a fluid flow, and the valve is located in the face filter mask, mainly directly in front of the wearer's mouth, lower and negative pressures can develop inside the face filter mask during normal exhalation.

With the invention, at least 40 percent of the exhaled air can leave the face mask through the exhalation valve at a positive pressure drop of less than 24.5 pascal at low exhalation air velocities and volume air flows greater than 40 liters per minute (l/min). At higher exhalation air velocities (such as when the wearer's lips are pursed), a negative pressure can develop inside the face filter mask. In a preferred embodiment of the invention, a face filter mask is produced which exhibits a negative pressure. The negative pressure allows an air volume greater than 100 percent of the exhaled air to pass out through the exhalation valve, and further allows ambient air to pass in through the filter media when a person exhales. This creates a situation where, on the next inhalation, the user breathes in cooler, fresher ambient air with lower humidity than the user's breath, and with a higher oxygen content. The inflow of ambient air is called aspiration, and it gives the user of the face mask increased well-being. The aspiration effect also reduces fogging on the eye protection because less exhaled air leaves the face mask through the filter media. The discovery of the aspiration effect was very surprising.

The above-mentioned new features and advantages of the present invention are shown and described more fully in the drawings and in the following detailed description, where identical reference numbers are used to refer to like parts. However, it should be understood that the drawings and detailed description are intended as an illustration only, and must not be read in a manner that unduly limits the scope of the invention.

Brief description of the drawings:

Fig. 1 is a front view of a face filter mask 10 with a one-way fluid valve according to the present invention.

Fig. 2 shows a cross-section of the face filter mask body 12 in fig. 1.

Fig. 3 shows a cross-section of an exhalation valve 14, laid along the lines 3-3 in fig. 1.

Fig. 4 is a front view of a valve seat 18 according to the present invention.

Fig. 5 is a side view of a flexible flap 24, the cantilevers attached and subjected to a uniform force. Fig. 6 is a side view of a flexible flap 24, the cantilevers attached and exposed to the acceleration of gravity, g. Fig. 7 is a perspective view of a valve cover 50 for the one-way fluid valve according to the present invention.

When describing preferred embodiments of the present invention, specific terminology will be used for reasons of clarity. However, the invention is not intended to be limited by the specific terms so chosen, and it is to be understood that each term so chosen includes all technically equivalent terms which function similarly.

Fig. 1 illustrates a face filter mask 10 with a one-way fluid valve according to the present invention. The face filter mask 10 has a cup-shaped mask body 12 to which an exhalation valve 14 in the form of a one-way fluid valve according to the invention is attached. The mask body 12 is provided with an opening (not shown)

through which exhaled air can escape without having to pass through the filtration layer. The preferred location of the opening in the mask body 12 is directly in front of where the user's mouth will be when the mask is in use. Exhalation valve 14

is attached to the mesh body 12 at the location of this opening. With the exception of the location of the exhalation valve 14, essentially the entire exposed surface of the mask body 12 is fluid permeable to the inhaled air.

The mask body 12 may have a curved, hemispherical shape, or may assume others

forms if this is desired. E.g. the mask body can be a cup-shaped mask with a structure like the face mask described by Japuntich in US patent 4,827

924. The mask body 12 can comprise an inner shaping layer 16 and an outer filtering layer 18 (fig. 2). Shaping layer 16 provides the structure of the mask 10, and supports the filtering layer 18. Shaping layer 16 can be placed on

the inside and/or the outside of the filtering layer 18, and can e.g. be made of a non-woven mat of thermally jointable fibers formed into a cup-shaped shape. The shaping layer can be shaped according to known procedures. Although a shaping layer 16 is designed with the primary purpose of providing a structure of the mask and support for a filtering layer, the shaping layer 16 can also provide filtration, typically filtering of larger particles. In order to keep the face mask close to the wearer's face, the mask body may have straps 20, cords, fastening straps, etc., attached thereto. A flexible soft band 22 of dead metal, such as aluminum, can be provided on the mask body 12, so that this is allowed to be shaped so that the face mask is held with the desired fit on the wearer's nose.

When a user of the face filter mask 10 exhales, the exhaled air passes through the mask body 12 and the exhalation valve 14. The greatest comfort is achieved when a high percentage of the exhaled air passes through the exhalation valve 14, as opposed to through the filter media in the mask body 12. The exhaled air is expelled through the valve 14 by the fact that the exhaled air lifts the flexible flap 24 from the valve seat 26. The flexible flap 24 is attached to the valve seat 26 in a first portion 28 of the flap 24, and the remaining surrounding edge of the flexible flap 24 is free to be lifted from the valve seat 26 during exhalation. As the term is used here, "flexible" means that the flap can be deformed or bent into a self-supporting arch when it is fixed at one end as a cantilever, and considered in a profile projection (see e.g. fig. 5.)

A flap that is not self-supporting will tend to fall towards the ground in approx. 90°

relative to the horizontal.

As shown in fig. 3 and 4, the valve seat 26 has a sealing edge 30, which has a sealing surface 31 against which the flexible flap 24 has contact when a fluid does not pass through the valve 14. An opening 32 is placed radially within the sealing edge 30, and is circumscribed by this. The opening 32 may have transverse members 34 which support the sealing edge 30, and ultimately the valve 14. The transverse members 34 may also prevent the flexible flap 24 from entering the opening 32 during reversing airflow, e.g. during inhalation. Viewed in a side view, the surface of the cross members 34 is slightly recessed below (but not in line with) the sealing surface 31, so as to ensure that the cross members do not lift the flexible flap 24 from the r sealing surface 31 (see Fig. 3).

The sealing edge 30 and the opening 32 can assume any shape viewed from

a plane perpendicular to the flow direction of the fluid (fig. 4). E.g. can the sealing edge 30

and the opening 32 be square, rectangular, circular, elliptical, etc. The shape of the sealing edge 30 need not correspond to the shape of the opening 32. Eg. the opening 32 can be circular and the sealing edge rectangular. It is only necessary that the sealing edge 30 circumscribes the opening 32 to prevent unwanted inflow of contaminants in the blocking direction of the valve, through the opening 32. However, the sealing edge 30 and the opening 32 preferably have a circular cross-section

when viewed against the direction of flow of the fluid. The opening in the mesh body 12 preferably has a cross-sectional area that at least corresponds to the size of the opening 32'. The flexible flap 24 naturally covers an area larger than the opening 32 and has a size that at least corresponds to the area surrounded by the sealing edge 30. The opening 32 preferably has a cross-sectional area of 2- 6 cm<2>, and more preferably 3-4 cm<2>. An opening of this size equips the face mask with an aspiration effect that helps in blowing out warm, moist exhaled air. An upper limit on orifice size may be important when aspiration occurs, because a larger orifice creates an opportunity.

so that the ambient air can enter the face mask through the opening in the education valve instead of through the filter, which creates unsafe breathing conditions.

Fig. 3 shows the flexible flap 24 in the closed position, resting on the sealing edge 30, and in the open position, shown with dashed lines 24a. The sealing edge 30 has a concave curvature when viewed in the direction shown in fig. 3. This concave curvature, as indicated above, corresponds to the deformation curve exhibited by the flexible flap when attached as a cantilever beam. The concave curvature shown in fig. 3 is free of turning points, and preferably extends along a generally straight line in the profile projection shown in fig. 3. A fluid passes through the valve 14, in the direction indicated by the arrow 36. The top of the concave curvature is located upstream of the fluid flow through the annular opening 32, relative to the extreme points of the concave curvature. The fluid 36 passing through the annular opening 32 exerts a force on the flexible flap 24, which causes the free end 38 of the flap 24 to be lifted from the sealing edge 30 in the valve seat 26, so that the valve 14 opens. The valve 14 is preferably oriented in the face mask 10 in such a way that the free end 38 of the flexible flap 24 is below the attached end 28 when the mask 10 is in the upright position as shown in fig. 1. This enables the exhaled air to be deflected downwards so that moisture is prevented from condensing on the wearer's eye protection.

As shown in fig. 3 and 4, the valve seat 26 has a flap-holding surface 40 placed on the outside of the area encompassed by the opening 32, outside the outer limits of the sealing edge 30. The flap-holding surface 40 preferably crosses the valve 14 at a distance that is at least as large as the width of the opening 32 The flap retaining surface 40 may extend in a straight line in the direction that the surface 40 crosses the valve seat 26. The flap retaining surface 40 may have pins 41 to hold the flexible flap 24 in place. When the pins 41 are used as part of a means of attaching the flexible flap 24 to the valve seat 26, the flexible flap 24 will be provided with corresponding openings so that the flexible flap 24 can be placed over the pins 41, and preferably rest against the flap holding surface 40. The flexible flap 24 can also be attached to the flap-holding surface by ultrasonic welding, glue, mechanical clamping, or other suitable means.

The flap-holding surface 40 is preferably placed on the valve seat 26 so that the flexible flap 24 is allowed to be pressed into a relationship where it rests against the sealing edge 30 when a fluid does not pass through the opening 32. The flap-holding surface 40 can be placed on the valve seat 26 as tangent to the curvature of the sealing edge 30 when this is viewed in a horizontal projection (fig. 3). The flap-holding surface 40 is separated from the opening 32 and the sealing edge 30, so that a moment arm is produced which helps with the deflection of the flap during an exhalation. The greater the distance between the flap-holding surface 40 and the opening 32, the larger the torque arm becomes, and the lower the torque from the flexible flap 24, the easier it thus becomes for the flexible flap 24 to open when a force from the exhaled air is applied to it. However, the distance between the surface 40 and the opening 32 should not be so great that it causes the flexible flap to dangle freely. Preferably, the flexible flap 24 should be pressed against the sealing edge 30 so that there is a substantially uniform seal when the valve is in the closed position. The distance between the flap-holding surface and the nearest part of the opening 32 is preferably approx. 1-3.5 mm, more preferably 1.5-2.5 mm.

The distance between the opening 32 and the flap-holding surface 40 also provides the flexible flap 24 with a transition area that allows the flexible flap 24 to more easily assume the curvature of the sealing edge-30. The flexible flap 24 is preferably sufficiently flexible to accommodate tolerance variations. The flap retaining surface 40 may be a flat surface, or it may be a continuous extension of the curved sealing edge 30; i.e. that it may be a curved extension of the deformation curve exhibited by the flexible flap. As such, however, it is preferred that the flexible flap 24 has a transition area between the point of attachment and the point of contact with the sealing edge 30.

The valve seat 26 is preferably produced from a relatively light plastic, which is formed into an integrated body in one piece. The valve seat can be produced using injection molding techniques. The surface 31 of the sealing edge 30 which is in contact with the flexible flap 24 (the contact surface) is preferably shaped so that it is mainly uniformly smooth, to ensure that a good seal is achieved. The contact surface preferably has a width large enough to form a seal with the flexible flap 24, but not so large as to allow adhesion forces caused by condensed moisture to make the flexible flap 24 substantially more difficult to open. The width of the contact surface is preferably at least 0.2 mm, and is preferably in the range of approx. 0.25mm -0.5mm.

The flexible flap 24 is preferably made of a material capable of presenting an inclined abutment against the sealing edge 30 when the flexible flap 24 is attached to the valve seat 26, in surface 40. The flexible flap preferably assumes a flat configuration when not exposed. for forces, and is elastomeric and resistant to permanent seals and creep. The flexible flap can be made of an elastomeric material, such as cross-linked natural rubber (eg cross-linked polyisoprene) or a synthetic elastomer such as neoprene, butyl rubber, nitrile rubber or silicone rubber. Examples of rubbers that can be used as flexible flaps include: Compound No. 40R149 available from West American Rubber Company, Orange, California; compound 402A and 330A available from Aritz-Optibelt-KG, Hoxter, Germany; and RTV-630 available from General Electric Company, Waterford, New York. A preferred flexible flap has a stress relief sufficient for the flexible flap to abut against the sealing edge in any static orientation for 24 hours at 70°C; see European Standard from the European Committee for Standardization (CEN), European norm (EN) 140, part 5.3 and 149 part 5.2.2, which applies to a test that measures stress relief under these conditions. The flexible flap preferably provides a leak-free seal according to the standards set forth in 30 C.F.R. Section 11.183-2 (July 1, 1991). A cross-linked polyisoprene is preferred because it exhibits a lower degree of stress relief. The flexible flap will typically have a Shore A hardness of approx. 30 to 50.

The flexible flap 24 may be cut from a flat sheet of material of generally uniform thickness. In general, the plate has a thickness of approx. 0.2 to 0.8 mm; more typically from 0.3 to 0.6 mm, and preferably from 0.35 to 0.45 mm. The flexible flap is cut

preferably to a shape such as a rectangle, and has a free end 38 which is cut so that it corresponds to the shape of the sealing edge 30 where the free end 38 has contact with it. For example, as shown in fig. 1, the free end 38 has a curved edge 42 corresponding to the circular sealing edge 30. By cutting the free end 38 in this way, weighing

the free end 38 is smaller, and can therefore be more easily lifted from the sealing edge 30 during exhalation, and closes more easily when the face mask is turned upside down. The flexible flap 24 preferably has a width that is greater than approx. 1 cm, more preferably it has a width in the range from approx. 1.2 to 3 cm, and is approx. 1-4 cm long. The attached end of the flexible flap will typically make up 10-25 percent of the flexible flap's total circumference, with the remaining 75-90 percent free to be lifted from the valve seat 26. A preferred flexible flap according to the present invention is approx. 2.4 cm wide and approx. 2.6 cm long, and has a rounded free end 38 with a radius of approx. 1.2 cm.

As can best be seen from fig. 1 and 4, a flange 43 extends on the side of the valve seat 26 so that a surface is provided on which the exhalation valve 14 can be attached to the mask body 12. The flange 43 preferably extends around the entire circumference of the valve seat 26. When the mask body 12 is a fibrous face filter mask, the exhalation valve 14 can be attached to the mask body 12 in the flange 43 by means of ultrasonic welding, adhesion attachment, mechanical attachment, or the like. It is preferred that the exhalation valve 14 is attached by ultrasonic welding to the mask body 12 in the face filter mask 10. A preferred one-way fluid valve according to the present invention is advantageous in that it has a single flexible flap 24 with one free end 38, as opposed to 2 flaps each having a free end. By having a single flexible flap 24 with one free end 38, the flexible flap 24 can have a longer moment arm, which allows the flexible flap 24 to be more easily lifted from the sealing edge 30 by the dynamic pressure of a user's exhaled air. A further advantage of using a single flexible flap with one free end is that the exhaled air can be deflected downwards, preventing misting of a user's eye protection or face shield (eg a welding helmet).

Fig. 5 illustrates a flexible flap 24 which is deformed by a uniform force being applied to the flexible flap. The flexible flap 24 is in a first part 28 attached to an attachment surface 46, and has a second or free part which is held up therefrom as a cantilever beam. Surface 46 is, if desired, planar, and the flexible flap 24 is preferably attached to the planar surface along the entire width of portion 28. The uniform force includes a series of force vectors 47 of equal magnitude, each of which is applied in a direction normal to the curvature of the flexible flap. The resulting deformation curve can be used to define the curvature of a valve seat sealing edge 30, so that a flexible flap is produced which exerts a substantially uniform force on the sealing edge.

Determining the curvature of a sealing edge 30 which produces a substantially uniform sealing force is not easy to do empirically. However, it can be determined numerically by applying finite element analysis. The procedure is to model a flexible flap attached at one end with a uniform force applied to the free end of the flexible flap. The applied force vectors are placed normally in relation to the curvature of the flexible flap 24, because the sealing force exerted by the flexible flap 24 on the sealing edge 30 will act normally on it. The deformed shape of the flexible flap 24 when subjected to this uniform, normally directed force is then used to form the concave curvature of the sealing edge 30.

By applying element analysis, the flexible flap can be modeled in a two-dimensional element model, as a bent beam fixed at one end, where the free end of the flexible flap is divided into a large number of connected sub-areas or elements, in which approximate functions are used to represent beam deformation. The total beam deformation is derived from linear combinations of the behavior of the individual elements. The material properties of the flexible flap are used in the model. If the stress-strain behavior of the material in the flexible flap is non-linear, as with elastomeric materials, the Mooney-Rivlin model can be used (see R. S. Rivlin and D. W. Saunders(1951)), Phil. Trans. R. Soc. A243, 251-298 "Large Elastic Deformation of Isotropic Materials: VII Experiments on the Deformation of Rubber"). To use the Mooney-Rivlin model, a set of numerical constants representing the stress-strain behavior of the flexible flap must be determined using experimental test data. These constants are introduced in the Mooney-Rivlin model which is then used in the two-dimensional element model. The analysis is of the large deflection, non-linear analysis type. The numerical solution is typically iterative, because the force vectors are kept normal to the surface. A solution is calculated based on the previous force vector. The direction of the force vector is then updated, and a new solution is calculated. A converged solution is reached when the bent shape does not change from one iteration to the next by more than a preset minimum tolerance. Most finite element analysis programs for computers allow a uniform force as input data to be given as a pressure on the elements, which pressure is eventually transferred to forces at the nodes, or for the input data to be given directly as forces at the nodes. The total magnitude of the forces in the nodes can be equal to the mass of the flexible flap's free part multiplied by the acceleration of gravity acting on the mass of the flexible flap, or any factor of the acceleration of gravity if this is desired. Preferred gravity factors are discussed below. The final X, Y position of the bent nodes representing the flexible flap can be curve fitted to a polynomial equation which will then define the shape of the concave sealing edge.

Fig. 6 shows a flexible flap 24 deformed by the acceleration of gravity, g. The flexible flap 24 is fixed as a cantilever beam at one end 28, to the surface 46 of a fixed body 48. Fixed in this way, the flexible flap 24 exhibits a deformation curve caused by the acceleration of gravity, g. As indicated above, the profile projection of the curvature of a valve seat sealing edge can be shaped to correspond to the deformation curve of the flexible flap 24 when it is subjected to a force in the direction of gravity, which is equal to the mass of the free part of the flexible flap 24 multiplied by at least one unit of the acceleration of gravity, g.

A unit of the acceleration of gravity, g, is determined to be 9.807 meters per second. second per second (m/s ). Although a sealing edge having a curvature corresponding to a deformation curve exhibited by a flexible flap subjected to one g may be sufficient to hold the flexible flap in the closed position, it is preferred that the sealing edge has a curvature corresponding to a deformation curve exhibited by a flexible flap subjected to a force caused by an acceleration of more than one g, preferably 1.1-2 g. More preferably, the sealing edge has a curvature corresponding to the deformation curve of the flexible flap at an acceleration of 1.2 -1.5 g A most preferred sealing edge has a curvature in the profile projection corresponding to a deformation curve exhibited by a flexible flap subjected to a force caused by an acceleration of 1.3 g. The additional gravity acceleration is used to produce a safety factor that ensures a good seal against the valve seat at any position of the face mask, taking into account variations in the thickness of the flap, and extra weight of the flap caused by condensation t humidity.

In practice, it is difficult to apply a preload greater than 1 g (eg 1.1, 1.2, 1.3 g, etc.) to a flexible flap. The deformation curve corresponding to such magnitudes of the acceleration of gravity can, however, be determined by elemental analysis.

To mathematically describe the deflection of a flexible flap due to gravity, the two-dimensional element model is defined as fixed at one end in all degrees of freedom. A set of algebraic equations is solved, giving the beam deformation at the element nodes of interest, which when combined form the full deformation curve. A curve fit to these points gives an equation for the curve, and this equation can be used to generate the curvature of the sealing edge in the valve seat.

The versatility of finite element analysis means that the magnitude and direction of the acceleration of the gravity constant can be varied to create the desired preload on a flexible flap. For example, if a preload of 10 percent of the weight of the flexible flap is required, the deformation curve generated at 1.1 g will be used as a horizontal projection of the seal edge curvature. The direction can be changed by rotating the acceleration vector of gravity with respect to a horizontal attachment surface, or by rotating the attachment surface with respect to the gravity vector. Although a suitable deformation curve can be determined by allowing the attachment surface 46 to be parallel to the horizontal plane, in the research leading to this design it was found that the greatest deformation of the flexible flap 24 does not occur when the flexible flap 24 is supported in the horizontal plane, but when the flexible flap 24 is held raised above the horizontal plane as shown in fig. 5, and the attachment surface 46 has an angle 9 in the range 25-65°. It was discovered that by rotating the attachment surface at an angle to the horizontal plane, a deformation curve can be generated which is a close approximation to a deformation curve which has been subjected to uniform forces normal to the curved flap. For a fixed length of the flexible flap, the best rotation angle is 6

depending on the magnitude of the gravitational constant and the thickness of the flexible flap. In general, however, a preferred deformation curve can be shown by placing the attachment surface 46 at an angle 0 of approx. 45°.

The mathematical expression that defines the deformation curve of a flexible flap

subjected to either a uniform force and/or a force of a factor of at least one unit of the acceleration of gravity, is a polynomial mathematical expression, typically a polynomial mathematical expression of at least third order. The particular polynomial mathematical expression that defines the deformation curve can vary with regard to parameters such as thickness, length and composition of the flexible flap, and the applied force or forces and their direction.

The exhalation valve 14 may be provided with a valve cover to protect the flexible flap 24 and to help prevent contaminants from entering through the exhalation valve. In fig. 7 shows a valve cover 50 which can be attached to the exhalation valve 14 with a friction fit to the wall 44. The valve cover 50 can also be attached to the exhalation valve 14 by means of ultrasonic welding, an adhesive or other suitable means. The valve cover 50 has an opening 52 so that fluid can pass. The opening 52 is preferably at least as large as the opening 32, and preferably larger than the opening 32. The opening 52 is preferably placed on the valve cover 50, directly in the direction of the fluid flow 36 so that the vortex flow is minimized. In this respect, the opening 52 is approximately parallel to the path drawn by the free end 38 of the flexible flap 24 during its opening and closing. Like the flexible flap 24, the valve cover opening 52 directs fluid flow preferentially downward to

prevent fogging of a user's eye protection. All exhaled air can be directed downward by providing the valve cover with fluid-impermeable side walls 54. The opening 52 may have transverse members 56 that provide structural support and aesthetics to the valve cover 50. A set of ribs 58 may be provided on the valve cover 50 for additional structural support and appearance. The valve cover 50 can have its interior shaped in such a way that there are female elements (not shown) which are connected together with pins 41 in the valve seat 14. The valve cover 50 can also have a surface (not shown) which holds the flexible flap 24 against the flap retaining surface 40. The valve cover 50 preferably has a fluid-impermeable top 60 which increases in height in the direction of the flexible flap, from the secured end to the free end. The interior of the top 60 may be provided with a rib-like or rough pattern or a release surface to prevent the free end of the flexible flap from adhering to the top 60 when moisture is present on the top or the flexible flap. The design of the valve cover (50) is fully shown in US patent application 29/000,382. One

another valve cover which can also be suitable for use on a one-way fluid valve according to this invention is shown in pattern application 29/000,384.

Although the one-way fluid valve according to this invention has been described with regard to use as an exhalation valve, it may also be possible to use the valve in other applications, e.g. as an exhalation valve for a respirator or as a deaeration valve for overpressure suits or helmets.

Advantages and other features of this invention are further illustrated in the following examples. However, it must be expressly understood that even if the examples fulfill this purpose, the materials chosen and quantities used, as well as other conditions and in detail, must not be perceived in a way that unreasonably limits the scope of the invention.

Example 1 ( element analysis: flexible flap subjected to 1. 3 gl

In this example, finite element analysis was used to define the curvature of a valve seat's sealing edge. The curvature corresponds to the deformation curve exhibited by the free part of a flexible flap after it is subjected to an acceleration of 1.3 g. The flexible flap was manufactured from a natural rubber compound, containing 80 wt.% polyisoprene, 13 wt.% zinc oxide, 5 wt.% of a long-chain fatty acid ester that was used as a plasticizer, stearic acid, and an anti-oxidant. The flexible flap had a material density of 1.08 grams per cubic centimeter (g/cm<3>), an elongation at break of 670 percent, a breaking strength of 19.1 meganewton per square meters, and Shore A hardness of 35. The flexible flap had a freely movable length of 2.4 cm, a width of 2.4 cm, a thickness of 0.43 mm, and a rounded free end with a radius of 1.2 cm. The overall length of the flexible flap was 2.8 cm. The flexible flap was subjected to a tensile test, a pure shear test, and a biaxial tensile test, resulting in three data sets from real-world behavior. This data was transformed into structural stress and structural strain. The Mooney-Rivlin constants were then generated using the finite element computer program ABAQUS (available from Hibbitt, Karlsson and Sorensen, Inc., Pawtucket, RI). After checking the computer simulations of the stress/strain tests against the empirical data, the two Mooney-Rivlin constants were determined to be 24.09 and 3.398. These constants gave numerical results that were close to the real data from the samples of the flexible flap material.

The input data parameters for the description of grid points, boundary conditions and loading were selected, and these parameters and the Mooney-Rivlin constants were then entered into the computer element program ABAQUS. The individual element shape functions were chosen to be quadratic with mid-side nodes. The gravitational constant was chosen to be 1.3 g. The angle 8 for rotation relative to the horizontal plane, to achieve maximum deformation curvature, was determined to be 34° by rotating the gravity vector. A regression of the data gave a curve for the valve seat defined by the following equation: y = + 0.052559x - 2.445429x<2> + 5.785336x<3> - 16.625961x<4> + 13.787755xs where x is the abscissa and y is the ordinate. The square of the correlation coefficient was 0.99, indicating an excellent correlation between this equation and the data from the elemental analysis.

A valve seat was machined out of aluminium, and was provided with a sealing edge which had a curvature in the profile projection corresponding to the deformation curve above. A circular opening of 3.3 cm 2 was provided in the valve seat. The flexible flap was clamped to a flat flap-holding surface. The flap-holding surface was placed at a distance of

1.3 mm from the nearest part of the opening, tangential to the curved sealing edge. The valve-holding surface was 6 mm long, crossing the valve seat at a distance of 25 mm. The curved sealing edge had a width of 0.51 mm. The flexible flap remained in contact with the sealing edge no matter how the valve was oriented. The seal between the flexible flap and the valve seat was found to be leak-free.

The minimum force required to open this valve was then determined. This was accomplished by attaching the valve to a fluid-permeable mask body, tapering the valve in the closed position, and monitoring the pressure drop as a function of the airflow volume. After a plot of pressure drop versus air flow had been produced for an open-valve face filter mask taped again, the same was done for the open-valve face filter mask. The two datasets were compared. The point where the two data sets diverged represented the beginning of the opening of the valve. After many repetitions, the average opening pressure was determined to be 1.03 mm H<2>0. This pressure was converted to the force required to raise the flexible flap by dividing the pressure required to open the valve by the area of the flexible flap within the opening. The area of the flexible flap within the opening was 3.49 cm<2>. This gave an opening force of 0.00352 newtons. The weight of the freely movable part of the flexible flap was 0.00251 newtons, and the opening force-to-weight ratio gave a preload during the test of 1.40 g. This magnitude is close to the chosen gravitational constant of 1.3 g, and the additional force can is assumed to be the force required to bend the flexible flap during opening.

Example 2 (element analysis: flexible flap subjected to a uniform force)

In this example, finite element analysis was used to define a valve seat where the flexible flap will exert a uniform force on the sealing edge in the valve seat. The flexible flap used in this example was the same as the flexible flap in example 1. The computer program ABAQUS in example 1 was used in the finite element analysis. The analysis was of the large deflection, non-linear analysis type. The force factors used in the analysis were kept normal to the surface of the flexible flap. An iterative calculation was used: a curve was calculated based on the previous set of force vectors, and this curve was updated to produce a new curve. Convergence of the numerical equation for the curve was reached when the deformation curve did not change significantly from one iteration to the next. The final curvature was transferred to the following fifth-order polynomial equation:

where x is abscissa and y is ordinate.

. Example 3 (elemental analysis: flexible flap subjected to 1.3 g)

In this example, as in Example 1, finite element analysis was used to define the curvature of a valve seat sealing edge, which corresponds to the curvature of a free portion of a flexible flap subjected to an acceleration of 1.3 g. This example differs from Example 1 in that the flexible flap was made from compound 330A, available from Aritz-Optibelt KG. The flexible flap had a material density of 1.07 grams per cubic centimeter (g/cm<3>), an elongation at break greater than 600%, a tensile strength of 17»IO<6> newton per square meters, and a Shore A hardness of 47.5. The geometry of the flap was the same as that of the flap in Example 1. When the rubber was subjected to the same testing as in Example 1, the Mooney-Rivlin constants were determined to be 53.47 and -0.9354. The first constant shows that this material is stiffer than that in example 1, also shown by higher Shore A hardness.

When a 0.43 mm thick flap made from this material was installed in the valve seat of Example 1, the rubber sealed uniformly over the entire valve seat curve. However, due to the higher stiffness of this material, the opening pressure drop was slightly higher than that of the material in Example 1. When a thinner 0.38 mm flap was installed to lower this pressure drop, it did not lie evenly over the valve seat, lifting slightly up in the middle of the curve. However, it was possible to make the flap lie evenly and leak-free over the valve seat, by either moving the flap-holding surface closer, or by slightly changing the curve in example 1, so that it became flatter.

The ABAQUS program was used in example 1 to obtain deformation curves for this material. The gravitational constant was chosen to be 1.3 g to give a deformation curve with a preload of 30 percent of the weight of the flexible flap. In this case, the angles 6 indicating rotation relative to the horizontal plane for maximum deformation curvature were determined to be 40° for a flap thickness of 0.38 mm, and 32° for a flap thickness of 0.43 mm. Regression of the data gave valve seat curves with the following fourth-order polynomial equations, for a 0.38 mm flap: and for a 0.43 mm flap:

where x is abscissa and y is ordinate.

These curves are flatter than the curve that appeared for the rubber in example 1, which shows that the preload on the rubber in this example, when applied to the valve seat curve in example 1, will be greater than 30 percent.

Example 4-6 (comparison of the valve according to the '362 patent with the valve according to this invention)

In examples 4-6, the exhalation valve according to the invention was compared with the exhalation valve according to patent '362.1 example 4, the exhalation valve in example 1 was tested with regard to the valve's resistance to air flow, by placing the exhalation valve at the opening of a tube with a cross-sectional area of 3.2 cm< 2>, and measure the pressure drop with a manometer. An air flow of 85 l/min was blown through the tube. The measured pressure drop was multiplied by the flexible flap's surface area over the opening, to find the resistance to airflow. The collected data is presented in table 1.

Examples 5 and 6 correspond to examples 2 and 4 of patent '362.1 examples 2 and 4 of patent '362 the length and width of the flaps were changed, and each valve was tested with regard to pressure drop at 85 liters per minute (l/min), through the same nozzle as in example 4. -

In Table 1, the data shows that the valve according to this invention (Example 4) has less resistance to air flow than the exhalation valve in the '362 patent (Examples 5-6).

Example 7 (the aspiration effect)

In this example, a normal exhalation test was used to show how a one-way fluid valve according to the invention can create a negative pressure inside a face mask during exhalation.

A "normal exhalation test" is a test that simulates a person's normal exhalation. The test involves mounting a face filter mask on a 0.5 centimeter (cm) thick flat metal plate having a 1.61 square centimeter (cm<2>) (9/16 inch diameter) circular opening or nozzle. The face filter mask is mounted to the flat metal plate on the base of the mask so that airflow passing through the mouthpiece is directed into the interior of the mask body, directly towards the exhalation valve (ie the airflow is directed along the shortest straight line between from a point on a plane that bisects the base of the mask, to the exhalation valve). The plate is attached horizontally to a vertically oriented pipe. An air stream through the tube passes through the nozzle and enters the interior of the face mask. The speed of the air passing through the nozzle can be determined by dividing the air flow rate (volume/time) by the cross-sectional area of the circular opening. The pressure drop can be determined by placing a manometer probe inside the face filter mask.

The exhalation valve in Example 1 was mounted on a 3M 8810 face filter mask such that the exhalation valve was placed on the mask body directly above where a user's mouth would be when the mask is in use. The air flow through the nozzle was increased to approx. 80 l/min to produce an air flow rate of 8.3 meters per second (m/s). At this speed, a pressure drop of zero was achieved inside the face mask. At a moderate to high work pace, an ordinary person will exhale at an approximate air speed of approx. 5-13m/s, depending on the opening area of the mouth. Negative and relatively low pressures can be produced in a face mask according to this invention over a large part of this air velocity range.

Example 8-13 (face filter mask with one-way fluid valve according to this invention

- measurement of pressure drop and percentage of total flow through the exhalation valve as a function of total air flow through the face mask)

The efficiency of the exhalation valve in exhaling spent air, expressed as a percentage of total exhalation flow at a given pressure drop, is a major factor affecting the user's well-being. In examples 7-12, the exhalation valve in example 1 was tested on a 3M 8810 face filter mask, which at a flow of 80 l/min has a pressure drop of approx. 63.7 pascals. The exhalation valve was placed on the mask body directly opposite where the user's mouth will be when the mask is used. The pressure drop through the valve was measured as described in Example 7, at different vertical volume flow rates, using airflow nozzles with different cross-sectional areas.

The percentage of the total current was determined using the following procedure. First, the linear equation describing the relationship between the filter media volume flow (Qf) and the pressure drop (AP) was found at a closed valve, by comparing experimental data from positive and negative pressure drop data (note: when the pressure drop is positive, Of is also positive). The pressure drop when the valve was allowed to open was then measured at a specified expiratory volume flow (Qt). The flow through the valve alone (Qv) is calculated as Qv = Qt - Qf. with Qf calculated for the applicable pressure drop. The percentage of the total exhalation flow through the valve is calculated as 1 00(Qt - QfVQr- If the pressure drop during exhalation is negative, the inward air flow through the filter media, into the face mask, will also be negative, which gives the ratio that the flow out through the valve opening Qv is greater than the expiratory flow Qt. The data for pressure drop and percentage of total flow are presented in table 2.

1 table 2 the data shows that for airflows with a small amount of movement, an increase in airflow will cause an increase in pressure drop (18.1 cm<2>nozzle). Air currents with a small amount of movement are unusual in typical use of face masks. Nevertheless, the percentage of total current is higher than 50 percent at over approx. 30 l/min (examples 10-13). A typical person will exhale approx. 25-90 l/min, depending on the person's working pace. On average, a person exhales approx. 32 l/min. Thus, the face mask with the valve according to this invention produces high well-being for a user with air currents with a small amount of movement.

For airflows with a greater amount of movement (obtained by using a 2.26 cm nozzle), an increase in airflow caused a lower pressure drop than for the 18.1 cm nozzle<2>. As airflow increases, the effect of aspiration becomes apparent, as the pressure drop reaches a maximum and then begins to decrease with increasing airflow. The percentage of total flow through the exhalation valve increases at higher air flows to over 70 per cent, which provides better well-being for the user.

At the airflows with the greatest amount of movement (using a nozzle of 0.95 cm2), the pressure drop increases slightly, then falls to negative values as the airflow increases. This is the aspiration effect, and is shown in table 2 as a percentage of total flow that is greater than 100 percent. In example 13, e.g. the percentage of total flow at 80 l/min 119 per cent, where 19 per cent of the total volume flow is drawn through the filter medium, into the interior of the face mask, and expelled through the exhalation valve.

Various modifications and changes to this invention will be obvious to a person skilled in the art, without deviating from the scope of the invention. It is therefore to be understood that the invention shall not be unreasonably limited to the illustrated embodiments described above, but shall be governed by the limitations set forth in the claims and any equivalent thereof.

Claims (7)

1. One-way fluid valve (14) comprising a flexible flap (24) with a first part (28) and a second part, where the first part is attached to a valve seat (26), where the valve seat has an opening and a sealing edge (30 ) which has a concave curvature when seen in a profile projection, where the flexible flap (24) is in contact with the concave curvature of the sealing edge (30) when a fluid does not pass through the opening, where the other part of the flexible flap is free to become lifted from the sealing edge when a fluid passes through the opening, which one-way fluid valve (14) is characterized in that the sealing edge of the valve has a concave curvature corresponding to a deformation curve exhibited by the second part of the flexible flap (24), when this is exposed to (i) a uniform force acting along the length of the deformation curve, normal to it, or (ii) a force acting in the direction of gravity of a magnitude equal to the mass of the second part of the flexible flap multiplied by at least one unit of thin gden's acceleration, or a combination of (i) and (»)■ 2. One-way fluid valve (14) according to claim 1, characterized in that the concave curvature corresponds to a deformation curve exhibited by the flexible flap (24) when this is subjected to a uniform force which is not less than the mass of the second part of the flexible flap multiplied by at least one unit of the acceleration of gravity. 3. One-way fluid valve (14) according to claim 2, characterized in that the uniform force has a magnitude in the range of the mass of the second part of the flexible flap multiplied by an acceleration of 1.1 -1.5 times the acceleration of gravity. 4. One-way fluid valve (14) according to claim 1, characterized in that the concave curvature corresponds to the deformation curve exhibited by the second part of the flexible flap (24) when this is subjected to a force acting in the direction of gravity, and has a size equal to the mass of the second part of the flexible flap multiplied by a acceleration of 1.1 -2 times the acceleration of gravity. 5. One-way fluid valve (14) according to claim 4, characterized in that the force has a magnitude equal to the mass of the second part of the flexible flap multiplied by an acceleration of 1.2 -1.5 times the acceleration of gravity. 6. One-way fluid valve (14) according to one of the preceding claims, characterized in that the flexible flap (24) has a stress relief which is sufficient to keep the other part of the flexible flap in leak-free contact with the sealing edge (30) during any static orientation for 24 hours at 70 oC when a fluid does not pass through the opening. 7. One-way fluid valve (14) according to one of the preceding claims, characterized in that the opening has a size of 3-4 cm<2>.