Gas Filter System

Abstract

The present invention relates to a gas filter system (10) comprising an outer filter element (20) having a first filter medium (22) disposed between a first end cap (24) and a second end cap (26), and an inner filter element (30) having a second filter medium (32) disposed between a third end cap (34) and a fourth end cap (36), wherein the first filter medium (22) is positionable to surround the inner filter medium (32), and the first, second, third, and fourth end caps (24, 26, 34, 36) are open.

Description

[Technical Field]

[0001] The present invention relates to a gas filter system comprising an outer filter element having a first filter medium disposed between a first end cap and a second end cap, and an inner filter element having a second filter medium disposed between a third end cap and a fourth end cap, wherein the first filter medium can be positioned to surround the second filter medium. [Background technology]

[0002] Such a filter system is known from DE 10 2018 215 603 A1.

[0003] In some applications, a gas stream must be filtered through two filter elements. Typically, the gas flows through the first filter element, followed by the pre-filtered gas flowing through the second filter element. The filter elements can be located within a common housing. This type of filter system is used, for example, to filter combustion air for large combustion engines such as trucks and construction vehicles. Another application is filtering air for fuel cells.

[0004] U.S. Patent Application Publication No. 2006 / 0107836 discloses an air filter for an internal combustion engine, which includes a circular filter element sealed between an unfiltered air inlet and a filtered air outlet of a housing, and an adsorption element disposed on the inner wall of the housing so as to be disposed within the circular filter element.

[0005] WO 2015 / 092681 discloses a multi-layer filter element having two layers of pleated paper filter media, which are held in place by a sealing gasket made of a plastic material in which the paper layers are partially embedded.

[0006] German Patent Application No. DE 10 2017 005 797 A1 discloses a filter system having a central tube in a housing. A secondary element is arranged within the filter element and is slidable along the central tube. In a first position, the secondary element opens a fluid path through the open area of ​​the central tube, and in a second position, the secondary element closes the fluid path through the open area of ​​the central tube.

[0007] German Patent Application Publication No. 102018215603 discloses a gas filter system having a first filter element surrounding a second filter element. At first axial ends, the open end caps of the two filter elements are associated with a clean air outlet. At second axial ends, the first (outer) filter element has an open end cap, and the second (inner) filter element has a closed end cap. The closed end cap of the inner filter element is arranged to close the opening of the end cap of the outer filter element at the second axial end.

[0008] SUMMARY OF THE INVENTION It is an object of the present invention to facilitate the manufacture and installation of a gas filter system having two filter elements suitable for joint use.

[0009] This is achieved by the use of a gas filter system according to claim 1 and a filter element according to claim 17. Advantageous embodiments are set out in the dependent claims and the description. Summary of the Invention

[0010] According to the present invention, a gas filter system is provided, comprising an outer filter element having a first filter medium disposed between first and second end caps, and an inner filter element having a second filter medium disposed between third and fourth end caps.

[0011] The first filter medium can be arranged to surround the second filter medium. The filter medium may be hollow cylindrical or conical, preferably having a generally circular or elliptical cross section. The filter mediums each surround a longitudinal axis. In particular, the filter mediums are arranged concentrically about a common longitudinal axis. Directions such as radial and axial refer to the longitudinal axis of the filter system. In principle, the first and third end caps are associated with the first axial end, and the second and fourth end caps are associated with the second axial end.

[0012] During use of the gas filter system, the gas flow typically first passes through the first filter medium in the outer filter element and then through the second filter medium in the inner filter element. As described below, the filter elements may be suitably sealed to the housing or between the filter elements.

[0013] According to the present invention, the first, second, third, and fourth end caps are open. The first, second, third, and fourth end caps typically have a central opening. Open end caps require less material than closed end caps. Furthermore, simpler tools can be used to manufacture open end caps. The use of open end caps also facilitates installation of the filter elements. In particular, it is possible to access the outer filter element from one axial end while inserting the inner filter element from the other axial end. Furthermore, the open end caps allow for visual inspection of the interior of the filter element before and during installation.

[0014] Preferably, the first end cap of the outer filter element and the third end cap of the inner filter element are sealed to each other. The first end cap may have a (second) seal for sealingly abutting against the third end cap, preferably in the radial direction. Alternatively, the third end cap may have a (second) seal for sealingly abutting against the first end cap, preferably in the radial direction. The second seal may be integral with the first or third end cap, respectively.

[0015] Generally, the seals described in the context of the present invention are softer than the mating parts they seal. In particular, each seal is made of polyurethane, preferably foamed polyurethane. The respective mating parts may be made of hard plastic.

[0016] Preferably, the second end cap of the outer filter element and the fourth end cap of the inner filter element are sealed to each other. The second end cap may have a (fourth) seal for sealingly abutting against the fourth end cap, preferably in the radial direction. Alternatively, the fourth end cap may have a (fourth) seal for sealingly abutting against the second end cap, preferably in the radial direction. The fourth seal may be integral with the second or fourth end cap, respectively.

[0017] The first end cap of the outer filter element may have a first seal for sealingly abutting the housing, preferably axially. Alternatively or additionally, the first seal may provide a radial sealing abutment against the housing. The first seal may be integral with the first end cap.

[0018] The third end cap of the inner filter element may have a third seal for sealingly abutting the housing, preferably axially. Alternatively or additionally, the third seal may provide a radial sealing abutment against the housing. The third seal may be integral with the third end cap.

[0019] Preferably, the gas filter system further includes a housing in which the inner and outer filter elements can be disposed. In the installed state, the filter elements are disposed within the housing. Typically, the housing includes a first housing portion associated with the first end and a second housing portion associated with the second end. The inlet may be formed in either the first or second housing portion. The outlet is preferably formed in the first housing portion. The outlet may be in fluid communication with the clean side of the inner filter element.

[0020] The housing may have a central tube that extends into the inner filter element at the third end cap when the filter system is installed, the central tube providing a guide for the inner filter element and supporting the second filter medium.

[0021] The housing may have a dome. Preferably, the dome protrudes into the central tube. In other words, the dome and the central tube may overlap each other in the axial direction. The dome can provide a guide during installation. This design can effectively suppress undesired movement of the filter element during operation. In the case of large vibrations, the central tube can contact the dome to suppress the vibration movement of the filter element.

[0022] The central tube can be held in an axial collar of the housing, which is advantageous in manufacturing the filter housing, and a snap fit may be provided between the collar and the central tube.

[0023] The third end cap may be sealed to the collar or the central tube, and in particular, the third seal of the third end cap sealingly abuts the collar or the central tube, particularly in a radial direction, thereby advantageously sealing the interior of the inner filter element to the housing.

[0024] The central tube may be closed at the bottom, allowing it to be used to seal the filter element at the second end.

[0025] The fourth end cap may be sealed to the central tube. In particular, the fourth end cap may have a fifth seal for sealingly abutting, preferably radially, against the central tube. The fifth seal may be integral with the fourth end cap.

[0026] The second end cap may be sealed to the central tube. In particular, the second end cap may have a sixth seal for sealingly abutting, preferably radially, against the central tube. The sixth seal may be integral with the fourth end cap.

[0027] Preferably, the outer filter element includes a support tube having a radially inward end face that may be embedded in the second end cap. The end face of the support tube reinforces the second end cap, facilitating sealing of the second end cap to the central tube.

[0028] The housing may have a first skirt protruding between the second end cap and the fourth end cap. The first skirt provides guidance and support for the filter element at the second end. The first skirt may have a radially outwardly facing sealing surface and / or a radially inwardly facing sealing surface.

[0029] The second end cap may be sealed against the first skirt. In particular, the second end cap may have a seventh seal for sealingly abutting, preferably radially, against the first skirt. The seventh seal may be integral with the second end cap.

[0030] The fourth end cap may be sealed against the first skirt. In particular, the fourth end cap may have an eighth seal for sealingly abutting, preferably radially, against the first skirt. The eighth seal may be integral with the fourth end cap.

[0031] The housing may have a second skirt at the fourth end cap that protrudes into the inner filter element. The second skirt provides guidance and support for the inner filter element at the second end. The second skirt may have a sealing surface facing radially outward. The second skirt and the central tube may overlap each other in the axial direction. In particular, the central tube extends into the second skirt.

[0032] The fourth end cap may be sealed against the second skirt. In particular, the fourth end cap may have a ninth seal for sealingly abutting, preferably radially, against the second skirt. The ninth seal may be integral with the fourth end cap.

[0033] The first or second skirt is typically formed on the second housing part. Radial sealing of the second and / or fourth end caps against the first and / or second skirts allows the filter element to be tightly fitted to the second housing part when the housing is opened. This allows the filter element to be advantageously removed and replaced. During installation, the filter element can be held by the first and / or second skirts. This allows for common installation of the filter element and the second housing part.

[0034] The first or second filter medium, especially the second filter medium of the inner filter element, may have gas adsorption properties and preferably comprises activated carbon. Typical harmful gases include SO2, NO X , NH3.

[0035] The first or second filter medium, particularly the first filter medium of the outer filter element, may be composed of cellulose.

[0036] The first and / or second filter media may be pleated.

[0037] The end cap with at least one seal may be made of polyurethane, in particular foamed polyurethane. Preferably, the end cap with at least one seal is integral with the seal.

[0038] The end caps against which the seals abut can be constructed of hard plastic, and the hard plastic end caps can be glued to the respective filter media.

[0039] The present invention also relates to the use of the outer filter element and / or the inner filter element in a gas filter system according to the invention, as described above, which can be used for cathode air filtration in fuel cells of electric vehicles.

[0040] Other advantages and features of the present invention will be apparent from the following description of embodiments of the invention, with reference to the drawings showing important details, and from the claims. The individual features as described above or below may be implemented individually or in any useful combination in variants of the invention. [Brief explanation of the drawings]

[0041] [Figure 1] 1 is a schematic cross-sectional view of a first embodiment of a gas filter system according to the present invention, comprising an outer filter element, an inner filter element, and a housing. [Figure 2] 2 is a schematic cross-sectional view of an outer filter element of the gas filter system of FIG. 1. [Figure 3] 2 is a schematic cross-sectional view of an inner filter element of the gas filter system of FIG. 1. [Figure 4] FIG. 2 is an enlarged view of a first end of the filter system of FIG. 1. [Figure 5] FIG. 2 is an enlarged view of a second end of the filter system of FIG. 1. [Figure 6] 4 is a schematic cross-sectional view of a second end of a second embodiment of a filter system according to the present invention. FIG. [Figure 7]FIG. 10 is a schematic cross-sectional view of a first end of a third embodiment of a filter system according to the present invention. [Figure 8] FIG. 10 is a schematic cross-sectional view of a first end of a fourth embodiment of a filter system according to the present invention. [Figure 9] FIG. 10 is a schematic cross-sectional view of a second end of a fourth embodiment of a filter system according to the present invention. [Figure 10] FIG. 10 is a schematic cross-sectional view of a first end of a fifth embodiment of a filter system according to the present invention. [Figure 11] FIG. 10 is a schematic cross-sectional view of a second end of a fifth embodiment of a filter system according to the present invention. [Figure 12] FIG. 10 is a schematic cross-sectional view of a second end of a sixth embodiment of a filter system according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0042] 1 illustrates a gas filter system 10. The filter system 10 includes a housing 12. The housing has a first housing portion 14 and a second housing portion 16 that are attachable to one another. An inlet 18 allows gas to enter the housing 12. Here, the inlet is formed in the first housing portion 14. A filtered gas outlet 19 is also formed in the first housing portion 14. The housing portions 14, 16 may be made of metal and / or rigid plastic.

[0043] The filter system 10 further includes an outer filter element 20 (see also FIG. 2). The outer filter element 20 has a first filter medium 22. The first filter medium 22 is housed between a first end cap 24 and a second end cap 26. The first filter medium 22 circumferentially surrounds a longitudinal axis 28. The first filter medium 22 may be constructed from pleated cellulose paper.

[0044] The filter system 10 further includes an inner filter element 30 (see also FIG. 3). The inner filter element 30 has a second filter medium 32. The second filter medium 32 is housed between a third end cap 34 and a fourth end cap 36. The second filter medium 32 also circumferentially surrounds the longitudinal axis 28. The second filter medium 32 may include activated carbon for gas adsorption properties.

[0045] The inner filter element 30 is disposed inside the outer filter element 20. Both filter elements 20, 30 are disposed within the housing 12, where the first and second filter media 22, 32 are concentric with each other and with respect to the longitudinal axis 28.

[0046] At the first end of the filter system 10, a first end cap 24 is positioned to surround a third end cap 34 (see also FIG. 4). The first end cap 24 and the third end cap 34 each have a central opening. The outlet 19 is in fluid communication with the clean side 40 within the inner filter element 30 (see FIG. 1).

[0047] The first seal portion 42 protrudes axially from the first end cap 24. The first seal portion 42 is in axial sealing contact with the first housing portion 14. Here, the first end cap 24 having the first seal portion 42 is integrally formed from foamed polyurethane.

[0048] The third seal portion 44 projects axially from the third end cap 34. The third seal portion 44 sealingly abuts against the first housing part 14 in the radial direction. In particular, the third seal portion 44 sealingly abuts against a collar 46 that projects axially into the housing 12 at the outlet 19. Here, the third end cap 34 and the third seal portion 44 are integrally formed from foamed polyurethane.

[0049] At the second end of the filter system 10, a second end cap 26 is positioned to surround a fourth end cap 36 (see also FIG. 5). The second end cap 26 and the fourth end cap 36 each have a central opening (see FIGS. 2 and 3, respectively).

[0050] The second end cap 26 and the fourth end cap 36 are sealed to one another. In the illustrated embodiment, a radial seal is established. The fourth end cap 36 has a fourth seal portion 48 on its outer periphery. The fourth seal portion 48 sealingly abuts the second end cap 26 in the radial direction.

[0051] The second end cap 26 may be constructed from a hard plastic and is preferably glued to the first filter media 22. The second housing portion 16 may have a lower support ridge 50 that axially abuts the second end cap 26.

[0052] A central tube 52 of the housing 12 is retained in the axial collar 46. The central tube 52 extends through an opening in the third end cap 34 and beyond the fourth end cap 36. The central tube 52 may be constructed of a hard plastic. In a first embodiment, the central tube 52 has a closed bottom surface 54 (see, in particular, FIGS. 1 and 5).

[0053] In the first embodiment, the fourth end cap 36 is sealed to the central tube 52. A fifth seal 56 is formed in the opening of the fourth end cap 36. The fifth seal 56 sealingly abuts the central tube 52 in a radial direction. The central tube 52 may have an annular protrusion 58 disposed beyond the closed bottom surface 54 when viewed from the first end having the outlet 19. The annular protrusion 58 is formed with a radially outward sealing surface for abutting the fifth seal 56.

[0054] The fourth end cap 36, including the fourth seal 48 and the fifth seal 56, may be integrally formed from foamed polyurethane. In other words, the fourth end cap 36, including the seals 48, 56, is a monolithic part.

[0055] The housing may have a dome 60 (see FIGS. 1 and 5). Here, the dome 60 is formed on the second housing part 16, which may be, for example, a removable cover. The dome 60 extends toward the inside of the inner filter element 30. In particular, the dome 60 extends axially into the central tube 52 at the axial protrusion 58. In other words, the central tube 52 and the dome 60 overlap each other in the axial direction. The closed bottom surface 54 of the central tube 52 is located slightly above the dome 60.

[0056] The second end cap 26 and the fourth end cap 36 may have a circular cross section. To position the filter elements 20, 30 at a predetermined circumferential location, the end caps 26, 36 and the housing may have a radial protrusion / recess arrangement. For example, a radially outward protrusion on the fourth end cap 36 may protrude into a recess in the second end cap 26. Similarly, an outward protrusion on the second end cap 26 may protrude into a recess in the wall of the housing, and a protrusion on the inner wall of the housing may protrude into a recess on the outer periphery of the second end cap 26.

[0057] The second embodiment of the gas filter system 10, the first end of which is partially shown in Figure 6, substantially corresponds to the first embodiment of the gas filter system 10 (see Figures 1 to 5 and the description above).

[0058] In the second embodiment, the second housing portion 16 is formed with a second skirt 62. The second skirt 62 protrudes into the inner filter element 30 at the fourth end cap 36. The central tube 52 and the second skirt 62 overlap each other in the axial direction. In particular, the central tube 52 has ends that extend into the second skirt 62, and the ends of the central tube 52 have a smaller diameter than the middle portion.

[0059] In the second embodiment, the fourth end cap 36 is sealed to the second skirt 62. A ninth seal 64 is formed at the opening of the fourth end cap 36. The ninth seal 64 sealingly abuts against the second skirt 62 in the radial direction.

[0060] The third embodiment of the gas filter system 10, the second end of which is partially shown in Figure 7, substantially corresponds to the first embodiment of the gas filter system 10 (see Figures 1 to 5 and the description above).

[0061] In the third embodiment, the first end cap 24 and the third end cap 34 are sealed to one another, establishing a radial seal. The third end cap 34 has a second seal 66 that sealingly abuts the first end cap 24 in the radial direction.

[0062] The third end cap 34, including the second seal portion 66 and the third seal portion 44, may be integrally formed from foamed polyurethane. In other words, the third end cap 34, including the seal portions 44, 66, is a monolithic part.

[0063] The first end cap 24 may be constructed from a hard plastic and is preferably glued to the first filter media 22. The first housing portion 14 may have an upper support projection 68 that axially contacts the first end cap 24.

[0064] The fourth embodiment of the gas filter system 10, the first and second ends of which are partially shown in Figures 8 and 9, corresponds in basic structure to the first embodiment of the gas filter system 10 (see Figures 1 to 5 and the above description).

[0065] In the fourth embodiment, the third end cap 34 of the inner filter element 30 is sealed to the central tube 52 (see FIG. 8). The third seal portion 44 radially defines an opening in the third end cap 34. The third seal portion 44 radially sealingly abuts the central tube 52 of the housing 12. Here, the third end cap 34 and the third seal portion 44 are integrally formed from foamed polyurethane.

[0066] As with the first embodiment, in the fourth embodiment, the fourth end cap 36 of the inner filter element 30 is sealed to the center tube 52 via a fifth seal 56 (see FIG. 9).

[0067] On the other hand, in the fourth embodiment, a first skirt 70 of the second housing portion 16 protrudes axially between the second end cap 26 and the fourth end cap 36. The second end cap 26 is sealed against the first skirt 70. A seventh seal 72 radially defines an opening in the second end cap 26. The seventh seal 72 sealingly abuts the first skirt 70 in the radial direction. Here, the second end cap 26 and the seventh seal 72 are integrally formed from foamed polyurethane.

[0068] The fifth embodiment of the gas filter system 10, the first and second ends of which are partially shown in Figures 10 and 11, substantially corresponds to the fourth embodiment of the gas filter system 10 (see Figures 8, 9 and the above description).

[0069] In the fifth embodiment, an axial seal is established between the third end cap 34 and the first housing part 14 (see FIG. 10). A third seal part 44 protrudes axially from the third end cap 34. The third seal part 44 sealingly abuts the first housing part 14 in the axial direction. Here, the third end cap 34 and the third seal part 44 are integrally formed from foamed polyurethane.

[0070] As in the first and fourth embodiments, in the fifth embodiment, the axial seal between the first end cap 24 and the first housing part 14 is established via the first seal part 42.

[0071] As in the fourth embodiment, in the fifth embodiment, a radial seal is established between the second end cap 26 and the first skirt 70 via a seventh seal 72. Meanwhile, in the fifth embodiment, the fourth end cap 36 is also sealed to the first skirt 70. An eighth seal 74 is formed on the outer periphery of the fourth end cap 36. The eighth seal 74 sealingly abuts the first skirt 70 in the radial direction. Here, the fourth end cap 36 and the eighth seal 74 are integrally formed from foamed polyurethane.

[0072] A radial seal is established at the second end (second and fourth end caps 26, 36) and an axial seal is established at the first end (first and third end caps 24, 34), so that the filter elements 20, 30 are retained in the second housing portion 16 when the housing is opened. This allows for easy inspection of the gas filter system and replacement of the filter elements 20, 30.

[0073] The sixth embodiment of the gas filter system 10, the second end of which is partially shown in Figure 12, substantially corresponds to the first embodiment of the gas filter system 10 (see Figures 1 to 5) or the fourth embodiment (see Figures 8, 9 and the above description).

[0074] As with the first or fourth embodiment, in the sixth embodiment, a radial seal between the fourth end cap 36 and the central tube 52 is established via the fifth seal 56. Note that the central tube 52 may be circumferentially closed slightly above the closed bottom surface 54 due to the sealing abutment of the fifth seal 56.

[0075] In the sixth embodiment, the second end cap 26 of the outer filter element 20 is sealed to the central tube 52. The outer filter element 20 is longer (axially) than the inner filter element 30. The outer filter element 20 may include a support tube 76. The support tube 76 has an end face 78 extending radially inward in the second end cap 26. Specifically, the end face 78 is embedded in the second end cap 26. A sixth seal 80 radially defines an opening in the second end cap 26. The sixth seal 80 is disposed radially inward of the end face 78. The sixth seal 80 sealingly abuts the central tube 52 in the radial direction. Specifically, the sixth seal 80 abuts the annular protrusion 58 of the central tube 52. The second end cap 26 and the sixth seal 80 are integrally formed from foamed polyurethane. [Explanation of symbols]

[0076] Gas filter systems 10 Housing 12 First housing part 14 Second housing part 16 Inlet 18 Outlet 19 Outer filter element 20 First filter element 22 First End Cap 24 Second End Cap 26 Longitudinal axis 28 Inner filter element 30 Second filter element 32 Third End Cap 34 4th end cap 36 Clean side 40 First seal portion 42 Third seal 44 Color 46 Fourth seal 48 Lower support protrusion 50 central tube 52 Bottom 54 Fifth seal 56 Projection 58 Dome 60 Second Skirt 62 9th seal 64 Second seal part 66 Upper support protrusion 68 First Skirt 70 Seventh seal part 72 8th seal 74 Support tube 76 End face 78 Sixth seal part 80

Claims

1. A gas filter system (10) comprising: an outer filter element (20) having a first filter medium (22) disposed between a first end cap (24) and a second end cap (26); an inner filter element (30) having a second filter medium (32) disposed between a third end cap (34) and a fourth end cap (36); The first filter medium (22) can be arranged to surround the second filter medium (32) inside, The gas filter system (10), wherein the first, second, third, and fourth end caps (24, 26, 34, 36) are open.

2. 10. The gas filter system (10) of claim 1, wherein the first end cap (24) of the outer filter element (20) and the third end cap (34) of the inner filter element (30) are sealed to one another.

3. 3. The gas filter system (10) of claim 2, wherein the third end cap (34) has a second seal portion (66) for sealingly abutting against the first end cap (24), preferably in a radial direction.

4. 4. The gas filter system (10) of claim 1, wherein the second end cap (26) of the outer filter element (20) and the fourth end cap (36) of the inner filter element (30) are sealed to one another.

5. 5. The gas filter system (10) of claim 4, wherein the fourth end cap (36) has a fourth seal portion (48) for sealingly abutting, preferably radially, against the second end cap (26).

6. 6. The gas filter system (10) of claim 1, wherein the first end cap (24) of the outer filter element (20) has a first seal (42) for sealingly abutting, preferably axially, against a housing (12).

7. 7. The gas filter system (10) of claim 1, wherein the third end cap (34) of the inner filter element (30) has a third seal portion (44) for sealingly abutting against the housing (12).

8. The gas filter system (10) of any one of claims 1 to 7, further comprising a housing (12) in which the outer and inner filter elements (20, 30) are positionable.

9. 9. The gas filter system (10) of claim 8, wherein the housing (12) has a center tube (52) that extends into the inner filter element (30) at the third end cap (34).

10. 10. The gas filter system (10) of claim 9, wherein the housing (12) has a dome (60) that projects into the central tube (52).

11. 11. The gas filter system (10) of claim 9 or 10, wherein the central tube (52) is retained in an axial collar (46) of the housing (12).

12. The gas filter system (10) of claim 11, wherein the third end cap (34) is sealed to the collar (46) or the center tube (52).

13. A gas filter system (10) as claimed in any one of claims 8 to 12, wherein the fourth end cap (36) has a fifth seal portion (56) for sealingly abutting, preferably radially, against the central tube (52).

14. A gas filter system (10) as claimed in any one of claims 8 to 13, wherein the second end cap (26) has a sixth seal portion (80) for sealingly abutting, preferably radially, against the central tube (52).

15. 15. The gas filter system of claim 14, wherein the outer filter element includes a support tube having a radially inwardly facing end face, the end face being embedded in the second end cap.

16. The gas filter system (10) of any one of claims 8 to 15, wherein the housing (12) has a first skirt (70) protruding between the second end cap (26) and the fourth end cap (36).

17. 17. The gas filter system (10) of claim 16, wherein the second end cap (26) has a seventh seal portion (72) for sealingly abutting, preferably radially, against the first skirt (70).

18. 18. A gas filter system (10) as claimed in claim 16 or 17, wherein the fourth end cap (36) has an eighth seal portion (74) for sealingly abutting, preferably radially, against the first skirt (70).

19. The gas filter system (10) of any one of claims 8 to 18, wherein the housing (12) has a second skirt (62) at the fourth end cap (36) that protrudes into the inner filter element (30).

20. 20. The gas filter system (10) of claim 19, wherein the fourth end cap (36) has a ninth seal portion (64) for sealingly abutting, preferably radially, against the second skirt (62).

21. Use of an outer filter element (20) and / or an inner filter element (30) in a gas filter system (10) according to any one of claims 1 to 20.

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