Filter device

Abstract

A filter device comprising at least two filter elements (10, 12), which are arranged in series when viewed in the direction of fluid flow, wherein one filter element (10) is used for removing particulate contamination and the other filter element (12) is used for separating gas, particularly air, wherein the filter element (12) for gas separation comprises at least two layers (24, 26), each having fluid passage holes of different sizes, and, when viewed in the direction of fluid flow, the layer (24) having larger fluid passage holes is positioned upstream of the layer (26) having smaller fluid passage holes.

Description

Technical Field

[0001] The present invention relates to a filter device having at least two filter elements, these filter elements being arranged in series with each other along the flow direction of a fluid, one of the filter elements being used for removing particulate contamination and the other filter element being used for gas separation, particularly air separation.

Background Art

[0002] According to Patent Document 1, a filter device belonging to the prior art having at least two filter elements arranged coaxially with each other is known. An annular hollow space, i.e., a fluid space, is formed between these filter elements. On the inner side facing the hollow space of the outer filter element, at least partially, a separation device for gas bubbles such as air bubbles is provided. This hollow space communicates with at least one discharge opening for the gas bubbles at the tip. On this separation device or on the inner peripheral surface of the outer filter element, a suitable medium layer having coalescence characteristics is used. This medium layer is made of a non-woven fabric and has a predetermined pore size gradient, gradually changing from a fine structure on the inner side to a coarser structure towards the outflow side. Thus, when a fluid passes through the outer filter medium, the bubbles finely dispersed in the fluid are combined into larger units in volume due to the coalescence characteristics of the medium layer configured as the separation layer. The fiber material preferred for this application is usually in the form of the above non-woven fabric and can contain polyester fibers, thereby promoting the degassing process from the fluid.

[0003] Patent Document 2 describes a separation element for separating gas bubbles from a liquid, particularly hydraulic fluid, which comprises a volumetric body made of a porous material and contains numerous cells, which are offset from each other, so that numerous channels for guiding gas bubbles extend through the material structure in a labyrinthine manner. This group of channels includes a contact region in which at least two channels are close to each other in at least part, and during operation, gas bubbles guided along these channels come into contact with each other, thereby coupling with each other into larger gas bubbles, which are formed for the purpose of discharge from the liquid. Larger gas bubbles usually have greater buoyancy and can therefore be discharged more easily by rising faster through the liquid. This separation effect based on Archimedes' principle is facilitated by the labyrinthine shape of the channels, which naturally expands the gas bubbles, thereby allowing the gas bubbles to be efficiently separated from the liquid.

[0004] Patent Document 3, in a different context relating to an apparatus for recovering oil from a water surface, confirms that a hydrophobic surface structure forming a lattice structure allows for the retention of a gaseous layer on the surface in water. This property is called the "Salvinia effect" in technical terms and describes the stable presence of a layer of air on a surface beneath a liquid. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] German Patent Application Publication No. 102021002428 [Patent Document 2] International Publication No. 2020 / 165146 [Patent Document 3] German Patent Application Publication No. 102018118139 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Based on this prior art, the object of the present invention is to further improve the conventional solution described at the beginning and to improve the performance of a filter device, particularly gas separation including air separation. [Means for solving the problem]

[0007] These problems are solved by a filter device having the features described in the entirety of claim 1.

[0008] An essential feature of the present invention is that the filter element for gas separation comprises a wire mesh structure (22) with at least three layers. A particularly preferred configuration is one in which a layer with small fluid passage holes, acting as an intermediate layer, is placed between two layers acting as cover layers (outer layers) with larger fluid passage holes. In a filter element for gas separation, the primary objective is gas separation, and depending on the structure, particle removal may be minimal or not performed at all.

[0009] For those skilled in the field of filter devices for gas separation, it is surprising that this special layer structure can yield remarkably superior separation results without constructing a complex labyrinthine structure using cells within the filter element layers. While woven fabrics are preferably used for each layer, net structures and grid structures can also be used.

[0010] In addition to the coalescence properties of a special layered structure, where small air bubbles are coalesced into larger bubbles and separated from the liquid by rising according to Archimedes' principle, actual tests have shown that layered structures, particularly those in the form of a woven fabric, also contribute to the so-called Salvinia effect. In this effect, the gas or air layer becomes somewhat permanently stable on the surface of the woven or layered structure and first adheres to that location. At this time, each opening or mesh edge of the layered structure forms a barrier to the air layer, and during normal filtration operation, this air layer separates from the structure, forming larger gas bubbles that rise through the fluid. Therefore, two different separation mechanisms (coalescence and the Salvinia effect) are at work here, enhancing the separation performance of the filter device. Such a combination is not seen in conventional technology.

[0011] In a preferred embodiment of the filter device according to the present invention, all the fabric layers used are made of plain weave, which allows the warp and weft threads to intersect closely. This plain weave is also known in technical terms as "glatt" weave. Such plain weaves not only have low manufacturing costs but also high shape stability, making it possible to set the size of the desired through holes or pores in the fabric composite with great precision.

[0012] In yet another preferred embodiment of the filter device according to the present invention, the two outer layers (coating layers) are identical, while the intermediate layer has a different configuration. Regardless of the specific structure of the outer and intermediate layers, these layers are in planar contact with each other without being woven or interwoven, and are integrally pleated (folded) during the manufacturing process of the filter element.

[0013] Preferably, each outer layer has the following: - Individual through holes having a size approximately 5 to 11 times larger than the through holes of subsequent layers in the direction of fluid flow, and - Similarly, a thread diameter that is approximately 2 to 5 times thicker than the thread diameter of the subsequent layer.

[0014] In this way, each layer, especially the woven layer, is preferably composed of metal wires, but plastic wires or suitable fiber materials can also be used without any problems.

[0015] Depending on the specific configuration of each fabric layer, gas separation may occur on the inlet side of the gas separation filter element, or it may occur during the process of passing through the element. Basically, the two filter elements are arranged in series, and the fluid flows either from inside to outside (technically called "in-to-out") or in the opposite direction, i.e., from outside to inside (technically called "out-to-in").

[0016] In yet another preferred embodiment of the filter device according to the present invention, it is envisioned that two pleated filter elements are arranged concentrically with respect to each other, forming an annular hollow space or fluid space between them. This hollow or fluid space can provide homogenization during fluid flow and thus form a kind of static area, which helps to facilitate gas discharge from the fluid, such as hydraulic fluid.

[0017] Alternatively, as a space-saving method, the filter elements for gas separation can be folded and placed within the filter elements for particle separation, along with their layers, without any gaps between them.

[0018] In yet another preferred embodiment of the filter device according to the present invention, it is assumed that two filter elements form a replaceable filter unit as a whole, or that one filter element remains within the device housing while only the other is replaceable. The filter element for particle separation is expected to clog relatively quickly and therefore requires more frequent replacement with a new element, whereas the less load-bearing filter element for gas separation can be retained within the device as a filter housing along with the housing.

[0019] Preferably, each replaceable filter element is housed in an end cap at at least one free end, and an annular sealing mechanism is housed on the outer peripheral side of the end cap. By this sealing mechanism, a sliding guide (slide guide) is realized when the filter element is inserted into the connection part on the bottom side of the device housing. Thereby, it becomes possible to perform the replacement work of the filter element in a very quick procedure.

[0020] Preferably, when the housing of the filter device has at least one degassing device on the upper end side, the discharged or separated gas bubbles can be released to the surrounding environment or released into the fluid storage tank in which the housing is accommodated.

[0021] The subject of the present invention also relates to a filter element intended to be used particularly in a filter device as described above, which is composed of at least two layers, preferably a pleated fabric, and all fabric layers are composed of plain weave. And for each outer layer, it has a mesh size of 300 to 600 μm and a yarn diameter of 100 to 200 μm, and for each intermediate layer, it has a mesh size of 40 to 120 μm and a yarn diameter of 30 to 80 μm.

[0022] Particularly preferably, each outer layer has a through-hole or mesh size of 530 μm and a yarn diameter of 160 μm. Each intermediate layer can take a different configuration. For example, there may be a configuration with a through-hole or mesh size of 50 μm and a yarn diameter of 35 μm. In another configuration, the mesh size of the intermediate layer is 100 μm and the wire diameter is 60 μm.

[0023] Hereinafter, the filter device and its filter element according to the present invention will be described in more detail using embodiments based on the drawings.

Brief Description of the Drawings

[0024] [Figure 1]FIG. 1 is a diagram purely conceptually showing a configuration example of a filter device including two filter elements and a partially shown filter or device housing. [Figure 2] FIG. 2 is a diagram purely conceptually showing a configuration example of a filter device including two filter elements and a partially shown filter or device housing. [Figure 3] FIG. 3 is a diagram purely conceptually showing a configuration example of a filter device including two filter elements and a partially shown filter or device housing. [Figure 4] FIG. 4 is a diagram purely conceptually showing a configuration example of a filter device including two filter elements and a partially shown filter or device housing. [Figure 5] FIG. 5 is a diagram purely conceptually showing a configuration example of a filter device including two filter elements and a partially shown filter or device housing. [Figure 6] FIG. 6 is a diagram purely conceptually showing a configuration example of a filter device including two filter elements and a partially shown filter or device housing. [Figure 7] FIG. 7 is a diagram purely conceptually showing a configuration example of a filter device including two filter elements and a partially shown filter or device housing. [Figure 8] FIG. 8 is a diagram schematically showing the state of air separation on the inflow side or during its passage in a filter element made of a three-layer fabric shown in FIGS. 1 to 7. [Figure 9] FIG. 9 is a longitudinal sectional view of a filter device with a filter housing in which two filter elements are accommodated and are integrally replaceable. [Figure 10] FIG. 10 is a diagram showing, in a half section, a part of the main components of the accommodation structure on the bottom side in the filter device of FIG. 9. [Figure 11] FIG. 11 is a configuration example corresponding to FIG. 9, showing a configuration in which only the inner filter element is replaceable and the outer filter element remains in the device housing. [Figure 12]Figure 12 is a diagram showing the lower connection area of ​​the filter device in Figure 11, corresponding to Figure 10. [Figure 13] Figures 13 and 14 show further configuration examples for the filter apparatus shown in Figures 9 to 12, one in which both filter elements are interchangeable, and the other in which only the inner elements are interchangeable, while the outer elements remain within the apparatus housing. [Figure 14] Figures 13 and 14 show further configuration examples for the filter apparatus shown in Figures 9 to 12, one in which both filter elements are interchangeable, and the other in which only the inner elements are interchangeable, while the outer elements remain within the apparatus housing. [Modes for carrying out the invention]

[0025] Figure 1 shows the main components of the filter device as a whole, in a purely conceptual and greatly simplified representation. The filter device comprises two filter elements 10 and 12 arranged in series along the direction of fluid flow. In Figures 1 to 8, the direction of fluid flow for each is indicated by an arrow. In the embodiment shown in Figure 1, the inner filter element 10 is used for removing particulate contamination, and the outer filter element 12 is used for gas separation, particularly air separation. These two filter elements 10 and 12 are multilayered and pleated, and the filter element 10 for particle separation has a common structure. The two filter elements 10 and 12 are arranged concentrically and spaced apart from each other, and their outer and inner circumferences form a fluid space 14 as an annular hollow space. Furthermore, at their free ends, the two filter elements 10 and 12 are surrounded by an upper end cap 16 and a lower end cap 18, as viewed from the perspective of Figure 1. This structure itself is also common, so a detailed explanation is omitted here. The lower end cap 18 is provided with a central opening 20, through which an unfiltered fluid flow is supplied as indicated by the dotted arrow. Based on Figure 1, the flow direction of the filter device is from inside to outside (In-to-Out).

[0026] As is particularly clear from the illustration in Figure 8, the gas separation filter element 12 has a three-layer fabric structure 22 comprising two outer fabric layers 24 and an intermediate layer 26 positioned between them. The mesh size of the intermediate layer 26, i.e., the fluid passage holes, is smaller than that of the two adjacent outer fabric layers 24. Also, the yarn diameter of each outer fabric layer 24 in the fabric structure 22 is larger than the yarn diameter of the intermediate layer 26. The respective mesh size and yarn diameter are selected so that, in the embodiment of Figure 1, as shown at the bottom of Figure 8, air bubbles 28 undergo coalescence (combination) as the fluid passes through the outer filter element 12. The small volume of air bubbles 28 initially present on the inlet side A may exist in a finely dispersed state in the fluid flow, and due to the aforementioned coalescence effect, they pass through the fabric structure 22, preferably a wire fabric structure, and combine into larger air bubbles 30 on the outlet side B, located on the right side in the view of Figure 8. These large air bubbles can rise through the fluid due to buoyancy, according to Archimedes' principle, and thus be discharged into the surrounding environment.

[0027] The filter devices mentioned here are generally so-called in-tank solutions, so that air bubbles reach the surface of the fluid contained or stored in the fluid storage tank. In some cases, a two-layer configuration is sufficient, in which case, in the direction of fluid flow, layer 24 with larger fluid passage holes is positioned before layer 26 with smaller passage holes. In this respect, a layer structure from coarser to finer layers is realized.

[0028] All the woven layers 24 and 26 used are made of a so-called plain weave, preferably the two outer layers 24 have the same structure and the intermediate layer 26 has a different structure. Metal wires and / or plastic wires can be used for the woven layers 24 and 26.

[0029] In particular, each outer layer 24 is configured to have through holes or a mesh size approximately 5 to 11 times larger than the through holes or mesh size of the corresponding intermediate layer 26. Furthermore, each outer layer 24 has a thread or wire diameter approximately 2 to 5 times thicker than the thread or wire diameter of the corresponding intermediate layer 26. Specifically, each outer layer 24 has a mesh size of 200 to 800 μm and a thread diameter of 100 to 200 μm, while each intermediate layer 26 has a mesh size of at least 20 μm and a maximum of 120 μm, and a thread diameter of 30 to 80 μm.

[0030] When processing common fluids, such as hydraulic media, it has been shown that a configuration of each outer layer 24 with a mesh size of 530 μm and a thread diameter of 160 μm is particularly preferable for gas separation. On the other hand, each intermediate layer 26 has a different configuration; for example, in one embodiment, it has a mesh size of 50 μm and a thread diameter of 35 μm. In another configuration of the intermediate layer 26, the mesh size is 100 μm and the thread or wire diameter is 60 μm.

[0031] Other embodiments basically correspond to the embodiment shown in Figure 1, and only the points that are essentially different from the configuration example in Figure 1 will be explained.

[0032] In the embodiment shown in Figure 2, the element structure is the same as in Figure 1. However, the upper end cap 16 is provided with a plurality of openings 32 used for discharging bubbles (gas bubbles) from the filter device, and the discharge occurs through the gap between the upper surface of the upper end cap 16 and the lower surface of the plate-shaped housing cover 34. The direction of gas bubble discharge through this gap-like region is indicated by the arrow 36.

[0033] In the embodiment shown in Figure 2, the separation of gas or air takes place on the inlet side A of the filter element 12, as shown at the top of Figure 8. In this regard, the small bubbles 28 are combined into larger bubbles 30 in the leftmost outer layer 24 region before passing through the filter element 12, and these rise in the fluid by buoyancy as already described, and the separation process takes place.

[0034] In the modified example shown in Figure 3, the positions of the two filter elements 10 and 12 are swapped, meaning that the gas separation filter element 12 is located inside the filter device. Here as well, as shown at the top of Figure 8, gas or air separation is performed on the inlet side A of the filter element 12 located inside, and the enlarged air bubble 30 is discharged in the direction of arrow 36 through the channel-shaped central opening 38 provided in the upper end cap 16.

[0035] The embodiment in Figure 4 is basically the same as the embodiment in Figure 1, but the direction of fluid flow is reversed, meaning that the unfiltered fluid flows from outside to inside (Out-to-In) through the two filter elements 10 and 12 within the filter device. In this case, it first passes through filter element 12, and then through element 10. In the embodiment of Figure 4, since there is no opening 32 in the upper end cap 16, the gas separation process is performed on the inlet side A of filter element 12, as shown in the upper part of Figure 8. The filtered fluid (filtered) is discharged through the central opening 20 of the lower end cap 18 in the direction of arrow 40.

[0036] The embodiment in Figure 5 is basically the same as the embodiment in Figure 4, but with the difference that the unfiltered fluid still flows from the outside to the inside, although in this case it first passes through the filter element 10. Meanwhile, the filtered fluid is discharged from the filter device in the direction of arrow 40, and the gas is similarly discharged in the direction indicated by arrow 36 through the opening 32 provided in the upper end cap 16. In this respect as well, gas separation is performed on the inlet side A of the gas separation filter element 12 located on the inside.

[0037] In the embodiment shown in Figure 6, the flow is from the outside to the inside, and the separated gas is discharged in the direction of arrow 36 through a channel-shaped central opening 38 provided in the upper end cap 16.

[0038] In the special embodiment shown in Figure 7, two filter elements 10 and 12 are arranged in series along the longitudinal direction, with the particle separation filter element 10 preceding the gas separation filter element 12. The filter element 10 is housed in an independent pot-shaped filter housing 42, with an inlet 44 for unfiltered fluid at its upper end. This unfiltered fluid passes through the filter element 10 from inside to outside in the direction of the arrow, removing particulate contaminants in the process. The filtered fluid is led to the clean side 46 of the filter housing 42 and, through a channel 48 at the bottom of the housing, reaches the inside 46 of the gas separation filter element 12, where it also flows from inside to outside. During this flow, as in the configuration example shown at the bottom of Figure 8, the gas is discharged at the outlet side B of the woven structure 22 that constitutes the filter element 12. The bottom of the filter element 12 is again sealed with a lower end cap 18. Within the filter housing 42, a partition wall 50 extending horizontally is provided to separate the unfiltered side from the filtered side. This partition wall also serves as a support for the particle separation filter element 10 and acts as an upper end cap 16.

[0039] The proposed configuration of the filter device shown in Figure 9 is a structural realization of the conceptual diagram in Figure 1. The explanation given for Figure 1 also applies to the proposed configuration in Figure 9. The two filter elements 10 and 12 shown in Figure 9 are again housed concentrically within a filter housing 42, which has fluid passage holes 52 at least at the bottom. These fluid passage holes 52 are provided in the outer cylindrical portion 54 of the filter or device housing 42, which extends from the upper head 56 of the housing to the lower bottom component 58. A fluid inlet 60 is provided at the bottom 58, which corresponds to the inlet for unfiltered fluid via the central opening 20 in Figure 1. The unfiltered fluid is redirected 90 degrees upward through the fluid inlet 60 and guided through a distribution plate 62 to the inside 64 of the illustrated filter device, i.e., the unfiltered side.

[0040] The filter device shown in Figure 9 can be installed in a fluid storage tank (not shown in detail) as a so-called in-tank solution, and the illustrated fluid inlet 60 may be connected to an unfiltered fluid supply line leading from the fluid storage tank to the outside via piping (not shown in detail). This type of structure is common and will not be described in further detail herein. The lid-shaped housing head 56 incorporates a spring-loaded bypass valve 66, which serves to directly connect the unfiltered side to the filtered side of the filter device in the event of blockage of the filter element complexes 10, 12. Furthermore, the housing head 56 is equipped with a device 68 that can be used in the usual manner to connect a differential pressure measuring device. It can also be used for other applications.

[0041] As shown in Figure 1, the gas separation filter element 12 is also positioned to enclose the particle separation filter element 10 located inside, and in a predetermined flow direction (from the inside 64 or inlet side A to the outside), gas discharge occurs at the outlet side B of the filter element 12 located on the outside. Individual bubbles 30 are guided from the outlet side B through each fluid passage hole 52 provided in the outer cylinder portion 54 of the filter housing 42 to the inside of a fluid storage tank (not shown), where they rise and are discharged into the surrounding environment above the fluid surface in the storage tank. In this way, not only can the unfiltered fluid flow be purified very effectively from particulate contamination, but gas discharge from fluids such as hydraulic fluid is also performed at a high level. In this way, the gas separation stage can also prevent undesirable foaming phenomena that occur in hydraulic fluid during the operation of the hydraulic system. A radial gap is provided between the outer cylinder portion 54 and the outer circumference of the second filter element 12 as a kind of quiet section for degassing.

[0042] In particular, as shown in Figure 10, the two filter elements 10 and 12 are integrally housed within a lower end cap 18 at the bottom, and this lower end cap 18 protrudes upward and integrally supports the distribution plate 62. A projection 70 is provided at the bottom, and an annular sealing mechanism 72 in the form of an O-ring is provided on its outer circumference. This forms a kind of sliding guide between the projection 70 and the inner wall 74 of the bottom component 58, which has a circular cross-section and a supply opening configured as a fluid inlet 60.

[0043] By removing the detachable housing cover 76 attached to the housing head 56, the element complex consisting of the filter element 10 and the filter element 12 can be removed as a single unit through the upper opening of the filter housing 42. At this time, the sealing mechanism 72 located within the slide guide structure is disengaged from the bottom component 58. In the reverse procedure, a new element consisting of the first filter element 10 and the second filter element 12 can be reinserted into the housing 42, enabling a new filtration process to be performed.

[0044] As is further evident from Figure 10, the fluid space 14 between the two elements 10 and 12 may be provided with an additional support layer 78, in addition to the fluid-permeable support layer 80 provided on the outer circumference of the gas separation filter element 12. The fluid-permeable support layers 78 and 80 ensure that each pleated element layer is supported by the adjacent support layer 78 or 80 during flow from inside to outside, thereby achieving a structure that is stable against pressure.

[0045] Since the alternative configurations of the filter apparatus shown in Figures 11 and 12 correspond substantially to the configurations in Figures 9 and 10, the same reference numerals are used for the same parts, and the foregoing description also applies to the modified embodiments based on Figures 11 and 12.

[0046] In the last solution mentioned above, the gas separation filter element 12 is fixedly incorporated into the filter housing 42, which has an outer cylinder 54, and only the inner filter element 10 for particle separation is removable for replacement via the associated lower end cap 18, and the aforementioned slide guide, sealing mechanism 72, and inner wall 74 of the bottom component 58.

[0047] As is particularly clear from Figure 12, the fluid passage holes 52 provided in the outer cylinder portion 54 can be arranged around its entire outer circumference while maintaining axial and radial spacing, and they can be formed as window-shaped openings in the outer cylinder portion 54.

[0048] The embodiments shown in Figures 13 and 14 demonstrate further configurations of a similar filter device, starting from the basic design configuration based on Figures 9 to 12. In the embodiment of Figure 13, both filter elements 10 and 12 are removable as a single unit from the device housing 42, which has an outer cylinder 54, whereas in the configuration shown in Figure 14, only the inner element 10 is replaceable, and the outer element 12 for gas separation remains inside the device housing 42. In other respects, the descriptions regarding separation by the first and second filter elements 10 and 12 also apply to the configurations of Figures 13 and 14. Other device configurations that further improve the gas bubble separation efficiency are also possible.

[0049] As already mentioned, the special woven fabric layer structure 22 allows for separation not only by coalescing but also by incorporating the Salvinia effect. Such a method has not been realized in the field of filter devices until now. Furthermore, by sandwiching elements 10 and 12 with end caps 16 and 18 on both sides, it is possible to completely replace both filter elements 10 and 12 as a single replaceable unit.

Claims

1. A filter device comprising at least two filter elements (10, 12), wherein the at least two filter elements (10, 12) are arranged in series when viewed in the direction of fluid flow, one filter element (10) is used for removing particulate contamination, and the other filter element (12) is used for gas separation, particularly air separation, wherein the filter element (12) for gas separation comprises at least two layers (24, 26) each having fluid passage holes of different sizes, and when viewed in the direction of fluid flow, the layer (24) having larger fluid passage holes is positioned upstream of the layer (26) having smaller fluid passage holes.

2. The filter device according to claim 1, characterized in that the layer (26) having smaller fluid passage holes is housed as an intermediate layer between two layers (23) which serve as cover layers and have larger fluid passage holes.

3. The filter device according to claim 1 or 2, characterized in that each of the aforementioned layers (24, 26) is formed from a woven fabric, preferably composed of a plain weave.

4. Each of the aforementioned layers (24) is, In the flow direction, the subsequent layer (26) has through holes that are approximately 5 to 11 times larger than the corresponding through holes, Each of the subsequent layers (26) has a thread diameter that is approximately 2 to 5 times larger than the corresponding thread diameter. A filter device according to any one of claims 1 to 3, characterized in that

5. The filter device according to any one of claims 1 to 4, characterized in that gas separation occurs on the inlet side (A) of the filter element (12) for gas separation and / or occurs while flowing through the filter element (12).

6. The filter device according to any one of claims 1 to 5, wherein the two filter elements (10, 12), preferably pleated, are arranged concentrically with respect to define an annular fluid space (14) between them, or the filter element (12) for gas separation is folded together with the filter element (10) for particle separation without any gap between them.

7. A filter device according to any one of claims 1 to 6, characterized in that both filter elements (10, 12) form a replaceable filter unit as a whole, or that one filter element (12) remains within the device housing (42) and only the other filter element (10) is replaceable.

8. The filter device according to any one of claims 1 to 7, characterized in that each of the replaceable filter elements (10, 12) is housed in an end cap (18) at at least one free end, the end cap (18) houses an annular sealing mechanism (72) on its outer circumference, the sealing mechanism (72) provides a sliding guide for each of the filter elements (10, 12) when inserted, preferably at the housing connection portion (58) on the bottom side of the device housing (42).

9. The filter device according to any one of claims 1 to 8, characterized in that the device housing (42) is provided with at least one vent port (32) at its top for discharging the separated bubbles (30) into the external environment or into the fluid storage tank in which the device housing (42) is housed.

10. In particular, a filter element (12) for use in a filter device according to any one of claims 1 to 9, wherein the filter element comprises at least one two-layer, preferably pleated, woven fabric structure (22), all of which are plain weave, and each layer (24, 26) has a mesh size of 200 to 800 μm and a yarn diameter of 100 to 200 μm, and each other layer (26) has a mesh size of at least 20 to 120 μm and a yarn diameter of 30 to 80 μm.

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