Vent

Abstract

A vent, preferably made of metal, comprises a body (10) having an aperture (24) for the passage of a fluid and a sealing surface (11) surrounding the aperture. A porous membrane (50) lies against the sealing surface (11) and covers the aperture (24). A clamp arrangement may comprise a spring (30) pressing the membrane against the sealing surface (11) to prevent liquid from passing through between the sealing surface (11) and the membrane (50), e.g. by means of a cap (40) secured to the body (10) of the vent. The clamp arrangement is such that upon a reduction of the membrane thickness by 50% in the clamping area the compressive force per unit area does not change by more than 50%.

Claims

1. A vent comprising (a) a body having an aperture for passage of a fluid, wherein the body further comprises a general axis; (b) a sealing surface surrounding the aperture, (c) a porous membrane covering the aperture and lying against the sealing surface, and (d) a clamp arrangement pressing the membrane against the sealing surface in a clamping area of the membrane with a compressive force per unit area so as to prevent a liquid from passing from the aperture through between the sealing surface and the membrane, wherein the clamp arrangement comprises a fastener and at least one spring element, wherein the at least one spring element is configured to provide the compressive force per unit area, wherein the at least one spring element comprises at least one first venting passage and at least one spring leaf, wherein the fastener is in a form of a cap, wherein the cap comprises at least one second venting passage, and wherein the first and second venting passages are configured to be displaced relative to each other such that liquid dripping from the at least one second venting passage of the cap towards the at least one spring element in a direction of the general axis will not drip into the at least one first venting passage of the at least one spring element; wherein the compressive force per unit area does not change by more than 50% upon a change of a thickness of the membrane in a clamping area (A) by 50%.

2. The vent according to claim 1, wherein the clamp arrangement allows for a decrease of the thickness of the membrane in the clamping area against the compressive force by at least 50%.

3. The vent according to claim 1, wherein the fastener is secured to the body of the vent, and wherein the compressive force per unit area results from at least one of: (i) the fastener or (ii) the spring element being secured to the body of the vent.

4. The vent according to claim 3, wherein the spring element is separate from the fastener and clamped between the fastener and the membrane.

5. The vent according to claim 3, wherein at least one of: (i) the body, (ii) at least a part of the clamp arrangement, (iii) the fastener, or (iv) the spring element is made of metal.

6. The vent according claim 1, wherein the at least one spring element has a spring constant (C), and wherein a ratio (R) between the spring constant (C) and the clamping area (A) is lower than or equal to 50,000 N/m/mm.sup.2.

7. The vent according to claim 1, wherein the clamp arrangement provides a contact surface area opposite the sealing surface and abutting the membrane in the clamping area, the contact surface area having a minimum width of between 0.5 and 1.5 mm.

8. The vent according to claim 1, wherein the clamp arrangement provides a contact surface area opposite the sealing surface and abutting the membrane in the clamping area, wherein a surface pressure in the clamping area is in ranges from 1 N/mm.sup.2 to 30 N/mm.sup.2.

9. The vent according to claim 1, wherein the porous membrane is a polymeric membrane comprising a fluoropolymer.

10. The vent according to claim 1, wherein the membrane is secured to the body of the vent, directly or indirectly, solely by interference fit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an exploded view of a vent in accordance with the present invention.

(2) FIG. 2 is a cross-sectional view of the vent of FIG. 1 in an assembled state.

(3) FIG. 3 is a spring model.

(4) FIG. 4 is a cross-sectional view of another embodiment of a vent in accordance with the present invention.

(5) FIG. 5 is a perspective view of the vent of FIG. 4.

(6) FIG. 6 is a cross-sectional view of another embodiment of a vent in accordance with the present invention.

(7) The vent as shown in FIG. 1 comprises a body 10 having an aperture 24 for the passage of a fluid, such as gas or vapor. A sealing surface 11 surrounds the aperture 24. A porous membrane 50 is provided to lie against the sealing surface 11 and cover the aperture 24. The clamp arrangement in the form of a spring element 30 and a cap 40 is provided to press the membrane 50 against the sealing surface 11 in a clamping area A of the membrane. The clamping area A of the membrane is the area in which the membrane 50 is compressed between the clamp arrangement, in this embodiment the spring element 30, and the sealing surface 11. Securing the cap 40 to the body 10 causes the spring element 30 to be sandwiched between the membrane 50 and the cap 40, thereby generating a compressive force and compressing the spring element 30.

(8) This is further shown in a cross-sectional view as depicted in FIG. 2. As can be seen, the cap 40 is snap fitted into a circumferential groove 13. Other means for securing the cap 40 of the clamp arrangement to the body 10 of the vent may include and are not limited to the following: threaded engagement, bayonet coupling, press fitting and other pure interference fits, but likewise bonding, soldering, welding and the like.

(9) As can be seen, the height of the spring element 30 is reduced by means of the cap 40, thereby generating an axial force in the direction of the aperture 24 of the vent body 10, which force is translated into a compressive force per unit area in the clamping area. The clamping area in this case substantially corresponds to the size of the sealing surface 11. However, depending on the geometry of the membrane 50 and/or spring element 30, the clamping area may be smaller than the sealing surface 11. In the embodiment of FIG. 2, the sealing surface 11 is formed by an outer circumferential shoulder slightly protruding beyond an inner circumferential base 15, so that the central region of the membrane 50 is at a distance from the base 15. The effective area for gas and vapor transport through the pores of the porous membrane 50 therefore covers the aperture 24 and the base 15.

(10) The spring element 30 is generally cone shaped and forms a coned-disc spring type spring element. An outer area 31 of the spring element 30 is flat and resembles a washer. It may surround the central region of the membrane 50 along a continuous line in order to seal the membrane 50 against the sealing surface 11 around the membrane's entire circumference. An inner region of the spring element 30 comprises at least one spring leaf 33, the number being eight in the embodiment shown but possibly being higher or lower. The free ends 34 of the at least one spring leaf 33 are in contact with a bottom side 41 of the cap 40 and are bent downwards in the direction of the aperture 24, thereby generating the compressive force. The compressive force is directed onto the membrane 50 via a contact surface area of the spring element 30 by which the spring element 30 abuts the surface of the membrane 50.

(11) In an alternative embodiment, not shown, the spring element 30 may be integrally formed with the cap 40. For instance, the spring element 30 may depend from the bottom 41 of the cap 40. It may be slit in a radial, spiral or different direction so that it can build up a spring force as it is compressed by the cap 40 being secured to the vent body 10.

(12) As stated above, the compressive force per unit area in the membrane's clamping area is sufficiently high to prevent liquid from passing through between the sealing surface 11 and the membrane 50. Due to the compressive force, the membrane has a certain thickness in the clamping area. This thickness may change during use because of various influences, such as creep and swelling. The arrangement of the vent as shown in FIGS. 1 and 2 is such that, upon a reduction of the thickness of the membrane in the clamping area by 50%, the compressive force per unit area does not change by more than 50%, preferably by more than 20%, even more preferably by more than 10%, and most preferably by more than 5%. This is achieved by the spring element 30 being chosen to have a low spring constant C and, more specifically, by choosing a ratio R of the spring constant C relative to the clamping area A smaller than 50,000 N/m/mm.sup.2. More preferably, the ratio R is smaller than 15,000 N/m/mm.sup.2, and even more preferably it is smaller than 1,500 N/m/mm.sup.2.

(13) Thus, if a different spring element 30 is employed, e.g. a spring element with a relatively high spring constant C, the clamping area A has to be chosen accordingly larger so as to meet the ratio R.

(14) FIG. 3 shows the principle of the vent schematically. Accordingly, cap 40 is used to compress the spring element 30 against the membrane 50. Compressing the at least one spring leaf 33 of the spring element 30 by an amount of x causes a spring force F=C.Math.x to be generated, the spring force F being directed via the outer area 31 of the spring element 30 onto the clamping area A of the membrane 50. Depending on the size of the contact surface area by which the outer area 31 of the spring element 30 contacts the membrane 50, the compressive force per unit area may vary.

(15) The components of the vent are preferably made of metal, more preferably of stainless steel, such as V4A/1.4404/316L, namely, the vent body 10, the cap 40 and/or the spring element 30.

(16) The vent body 10 includes an elongated root 12 and a flared head 16 for holding the porous membrane 50. The aperture 24 extends through the vent body from the root 12 to the head 16, providing fluid communication between the housing and the atmosphere. The root 12 may be of any shape, but typically is cylindrical to match vent holes drilled or formed into a housing. The root 12 may be tapered at its end to facilitate insertion or to permit the vent to be driven into the housing. Alternatively, threads may be cut or rolled into the outside of the root 12 which cooperate with a tapped hole in the housing. A variety of other securing mechanisms may also be incorporated into the root to retain the vent. For example, a groove may be incorporated in the root to receive a snap ring to retain the vent. Alternatively, a locking ring could be pressed onto the root after insertion into the housing. Preferably, the root is threaded 14 to match a tapped hole in the housing.

(17) The sealing surface 11 is typically round to match the cylindrical aperture 24, but may be of any shape and size. The shape of the head 16 of the vent body is not critical. It may be cylindrical or of any shape, depending on the application. For example, the head may include a hexagonal part, as shown, so that a wrench can be used to drive a threaded vent into a tapped housing. For instance, the threading 14 on the root may be M12×1.5 and the wrench size may be 18 mm.

(18) The aperture 24 may be machined or formed into the vent body 10 and may be straight, tapered or of any other configuration. For example, the aperture 24 may be a tapered hole, which is narrow at the root and gradually increases in diameter in the direction of the top. Alternatively, the hole diameter may increase incrementally, with the diameter at the shaft typically being narrower than at the top. The larger area near the head permits a large porous membrane to be used, which may improve venting in some applications.

(19) The cap is preferably secured to the vent by an interference fit, as described above, and includes venting passages 44 which may be provided at its outer perimeter. There may be more or fewer than the six venting passages 44. For instance, a single venting passage 44 may be sufficient. The venting passages may be formed as holes in the cap 40 or as recesses on a circumferential surface of the cap 40, as shown, so as to form holes in cooperation with the vent body 10. The venting passages 44 may be formed in many different ways, such as by cut-outs as shown in FIG. 2, or by material deformation as shown in FIG. 1 where the venting passages 44 are formed by downwardly bent regions of the outer border of the cap 40 at a plurality of locations.

(20) The spring element 30 as described above likewise has venting passages 35 which may be provided between the spring leaves 33. The venting passages 44 of the cap 40 and the venting passages 35 of the spring element 30 are displaced relative to each other such that liquid dripping from the venting passages 44 in the cap 40 downwards onto the spring element will not drip into the venting passages 35 of the spring element 30. More specifically, the venting passages 44 of the cap 40 are positioned radially outside the conical part of the spring element 30, and the venting passages 35 of the spring element 30 are positioned on the conical part of the spring element 30.

(21) The width of the contact surface area of the spring element 30, which contact surface area corresponds to the clamping area A of the membrane 50 in the embodiment shown in FIGS. 1 and 2, is sufficiently large to avoid the spring element cutting into the membrane, which could lead to rapture of the membrane. Preferably, the minimum width of the contact surface area of the spring element 30 is 0.1 mm, preferably between 0.5 and 1.5 mm.

(22) In order to allow swelling of the membrane, the outer area 31 of the spring element 30 is held in the head 16 of the vent body 10 in a non-restrained manner so that an increase of the thickness of the membrane in the clamping area by at least 50% is possible, e.g. if the membrane swells due to moisture absorption.

(23) Preferred materials for the membrane 50 have been specified above. The size of the central area of the membrane 50 and the properties of the membrane 50 are selected such that a pressure equalization of typically 1600 ml/min @ 70 mbar pressure drop is achieved through the membrane under standard conditions. Other selections may be made depending on the specific boundary requirements.

(24) Once assembled, the vent may be installed and sealed to a housing by any known means. Such means may include flaring, swaging, coating the threads of the shaft with sealant, or providing an O-ring around the shaft. Where an O-ring is used, it is compressed between the lower surface of the head 16 of the vent body 10 and the housing. Preferably, silicon O-rings are used. A typical O-ring may have an inner diameter of 10 mm and a cross-sectional diameter through the material of 2 mm. Silicon is preferred as a sealing material because of its large temperature range which covers typical applications between −40° C. and over 125° C.

(25) Preferably, the vent provides ingress protection according to the standardized IP rating system regarding protection against environmental factors such as liquids and solids, preferably IP69K. Accordingly, the vent is able to resist ingress of high temperature steam and high water pressure. Burst pressures achieved with metal vents of the structure described above and loaded with spring forces of between 75 N and 150 N, respectively, were between 1.3 and 2.5 bar and between 3.3 and 3.6 bar, respectively, i.e. above these pressures water leaked between the membrane 50 and the sealing surface 11.

(26) FIG. 4 and FIG. 5 show a different, second embodiment of a vent in cross-sectional and perspective views. The construction is identical to the construction as shown and described in relation to FIGS. 1 and 2 of EP 1 740 861 B1, and to this extent the content of EP 1 740 861 B1 is incorporated herein by reference. The vent according to this second embodiment substantially corresponds to the vent according to the embodiment described above and, therefore, like reference numerals are used for like elements. The difference between the two embodiments lies in the clamp arrangement. That is, in this second embodiment, the cap 40 does not form part of the clamp arrangement because it does not contribute to the compressive force by which the spring element 30 presses the membrane 50 against the head 16 of the vent body 10. Instead, the tension of the spring element 30 results from the spring element being directly secured to the body 10 of the vent. In this particular embodiment, a snap ring 38 formed on the spring element 30 cooperates with a groove 22 in the head 16 of the vent body 10 to secure the spring element 30 to the vent body 10. The spring element has in general a cross-sectional S-shape which includes a baffle 32 extending toward the cap 40. The sole purpose of the baffle 32 is to prevent liquid dripping from the venting passages 44 down towards the spring element 30 from reaching the membrane 50. In a different arrangement, the cross-section of the spring element would be generally C-shaped without such baffle 32.

(27) The spring element 30 is shown only schematically. However, the spring constant C of the spring element 30 as well as the size of a contact surface area by which the spring element 30 compresses the membrane 50 against the head 16 of the vent body 10 (=clamping area) are again selected such that, upon a reduction of a thickness of the membrane 50 in the clamping area by 50%, the compressive force per unit area does not change by more than 50%.

(28) FIG. 6 shows a third embodiment of a vent as a cross-sectional view, similar to the second embodiment shown in FIG. 4. In this third embodiment, the spring element 30 is C-shaped. The central area 31 of the spring element 30 contacting the upper surface of the membrane 50 has a substantially larger width as compared to the second embodiment of FIG. 4. Thus, the spring constant C of this spring element 30 may be chosen accordingly higher to yield the same ratio R as in the second embodiment. Due to the relatively large clamping area A, the danger of rupture of the membrane due to the spring's compressive force is reduced.

(29) Comparative examples with spring elements having a contact surface area of about 45 mm.sup.2 in combination with four spring elements having different spring constants C are given in Table 1 for an ePTFE membrane having a normal thickness of 1 mm. The initial clamping forces were chosen to achieve an initial spring compression by about 0.6 mm in three of the four examples. This yielded different surface pressure values p and different ratios R, respectively. As can be seen, a relatively soft spring element with a low spring constant C of only 57742 N/m, thus yielding a low ratio R, is sufficient to achieve a surface pressure of above 1 N/mm.sup.2, here about 1.65 N/mm.sup.2. But in this case it was necessary to set the initial spring compression to more than twice the value of the other comparative examples, namely 1.275 mm, to provide a sufficiently high initial force F.

(30) TABLE-US-00001 TABLE 1 Initial Spring Spring force compression constant Surface F x C Ratio R pressure p [N] [mm] [N/m] [N/m/mm.sup.2] [N/mm.sup.2] 74 1.28 57741 1290 1.637638745 400 0.59 677966 15081 8.897550976 1350 0.59 2288136 50897 30.02923455 3150 0.59 5338983 118760 70.06821394