Filter apparatus

Abstract

The invention relates to a filter apparatus at least consisting of two filter elements (10, 12) disposed one behind the other in the fluid through-flow direction, of which one filter element (10) is used to filter out particulate contamination and the other filter element (12) is used for gas separation, in particular air separation, characterized in that the gas-separating filter element (12) has at least two layers (24, 26) having fluid passages of different size and in that, in the fluid through-flow directions, the layer (24) having the larger fluid passages precedes the layer (26) having the smaller fluid passages.

Description

[0001]RT-Filtertechnik GmbH Buchholz 4, 88048 Friedrichshafen, Germany Filter device The invention relates to a filter device comprising at least two filter elements which are arranged one behind the other in the direction of fluid flow, of which one filter element serves to remove particulate contamination and the other filter element serves to separate gases, in particular air. DE 102021002428 A1 discloses a generic filter device comprising at least two coaxially arranged filter elements which define an annular cavity or fluid space between them, wherein the inner side of the outer filter element facing the cavity at least partially comprises a separation device for gas bubbles, such as air bubbles.and wherein the cavity opens at the top into at least one discharge opening for gas bubbles. For the separation device mentioned, or on the inner peripheral side of the outer filter element, a suitable media layer with coalescence properties is used, which consists of a fleece with a predetermined pore size gradient, which, starting from an innermost fine structure, is gradually transformed into a coarse structure towards the downstream side. This leads, when fluid flows through the outer filter medium with fluid, to the bubbles, which are regularly finely dispersed in the fluid, being combined into volumetrically larger units due to the coalescence property of the media layer, which is designed as a discharge layer. The fiber material preferably used in each case, usually in the form of the aforementioned fleece, can comprise polyester fibers,which facilitates the degassing processes from the fluid. WO 2020 / 165146 A1 discloses a separation element for separating gas bubbles from a liquid, in particular from hydraulic oil, comprising a volume body with an open-pore material structure having a plurality of cells arranged offset from one another in such a way that a plurality of flow paths for guiding gas bubbles run labyrinthine through the material structure, which comprises a contact area in which at least two of the flow paths approach one another at least in sections, so that during operation, the gas bubbles guided along the flow paths contact one another and thus combine to form a larger gas bubble for the purpose of its discharge from the liquid. A larger gas bubble generally has a higher buoyancy force, so that it can be more easily discharged from the liquid.by rising faster in the liquid. This separation effect, based on Archimedes' principle, is promoted by the labyrinthine course of the flow paths, which naturally causes the gas bubbles to enlarge, allowing them to be efficiently separated from the liquid. In another context, DE 102018118139 A1 has established that hydrophobic surface structures in the form of grid-like structures offer the possibility of maintaining a layer of gas on the surface underwater. This property is technically referred to as the Salvinia effect, which describes the stabilization of an air layer on a surface beneath a liquid. Based on this prior art, the invention is based on the object of further improving the generic solution described above in such a way thatthat a filter device achieves improved gas separation, in particular air separation. This object is achieved by a filter device having the features of patent claim 1 in its entirety. It is considered essential to the invention that the gas-separating filter element has at least a three-layer wire mesh structure (22). It is particularly preferred that the layer with the smaller fluid passages, as an intermediate layer, is accommodated between two layers with, in contrast, larger fluid passages, as cover layers. When discussing a gas-separating filter element, gas separation is the primary focus, and particulate cleaning occurs only to a small extent or, depending on the design of the element, is completely absent. It is surprising to an average person skilled in the art in the field of filter devices dealing with the topic of gas separation,that this special layer structure achieves significantly better separation results without first having to build complex labyrinth structures using cells in a filter element layer. Fabrics are preferably used as the respective layers, but mesh or grid structures are also used. In addition to the coalescence property of the special layer structure, in which smaller air bubbles are combined to form larger air bubbles and separated from the liquid by rising in the liquid according to the Archimedes' principle, practical tests have shown that the layer structure, particularly in the form of a fabric structure, also contributes to the so-called Salvinia effect, in which a gas layer or air layer stabilizes more or less permanently on the surface of a fabric or layer structure and thus initially accumulates,The respective perforation or mesh edge of the layered structure forms a barrier for the air layer, which then, during normal filtration operation, forms an enlarged gas bubble that rises upwards in the fluid, yet is detached from the layered structure. In this respect, two different separation mechanisms (coalescence and Salvinia effect) come into play, increasing the separation capacity for the filter device. This has no equivalent in the prior art. In a preferred embodiment of the filter device according to the invention, all fabric layers used are made of plain weave.which allows a close crossing of warp and weft threads. This type of plain weave is also technically referred to as a "smooth" weave. In addition to being cost-effective to produce, such a plain weave also proves to be extremely inherently stable, and the desired aperture or pore size in the fabric composite can be specified very precisely. In a further preferred embodiment of the filter device according to the invention, the two cover layers are the same and the intermediate layer is different. Regardless of the design of the cover layers and intermediate layer, they lie flat against one another without being woven or interwoven with one another and are pleated together during the production of a filter element. Preferably, the respective cover layer has individual - apertures, each approximately 5 to 11 times as large as the respective aperture of the subsequent layer, viewed in the flow direction, and - thread diameters,which are each approximately 2 to 5 times the respective thread diameter of the subsequent layer. Thus, the individual layers, in particular fabric layers, are preferably made of metal wire; however, plastic wires or suitable fiber material can also be used without difficulty. Depending on the specific design of the respective fabric layer, gas separation can occur on the upstream side of the gas-separating filter element and / or when flowing through it. In principle, the two filter elements can be arranged one behind the other with a fluid flow direction from the inside to the outside, which is technically referred to as in-to-out, or in the opposite flow direction from the outside to the inside, which is technically referred to as out-to-in. In a further preferred embodiment of the filter device according to the invention,that the two pleated filter elements are arranged concentrically to each other, defining an annular hollow or fluid space between them. This hollow or fluid space leads to a homogenization of the fluid during flow and can thus form a kind of rest zone, which helps to facilitate the removal of gas from the fluid, for example in the form of hydraulic medium. Alternatively, in a space-saving manner, it can be provided that the gas-separating filter element is folded into the particle-separating filter element with its layers without any gaps. In a further preferred embodiment of the filter device according to the invention, it is provided that both filter elements form a replaceable filter unit as a whole, or that one filter element remains in the device housing and only the other filter element is replaceable. Since it is to be expected,Since the particle-separating filter element clogs up more quickly and therefore needs to be replaced more frequently, the gas-separating filter element, which is subject to less wear, can remain in the device with its device housing in the form of a filter housing. Preferably, the replaceable filter element is received at least at one free end in an end cap, which has an annular sealing device on its outer circumference, by means of which a sliding guide for the engagement of the respective filter element in a bottom-side housing connection of the device housing is realized. This allows a filter element to be replaced in a particularly rapid time sequence. Preferably, the device housing of the filter device is provided with at least one venting device on the head side,discharged or separated gas bubbles can be released into the environment or into a fluid storage tank in which the device housing is accommodated. The invention also relates to a filter element, in particular intended for a filter device as described above, which consists of at least one two-layer, preferably pleated, fabric and in which all fabric layers are plain weave, with a mesh size between 300 and 600 µm and a thread diameter between 100 and 200 µm for the respective cover layer and with a mesh size of 40 to 120 µm and a thread diameter of 30 to 80 µm for the respective intermediate layer. Particularly preferably, the respective cover layer has a passage or mesh size of 530 µm and a thread diameter of 160 µm. The respective intermediate layer can be designed differently, for example, have a passage or mesh width of 50 µm,with a thread diameter of 35 µm. With a differently constructed intermediate layer, the mesh size is 100 µm, with a wire diameter of 60 µm. The filter device according to the invention, including the filter element, is explained in more detail below using exemplary embodiments according to the drawing. Figures 1 to 7 show, in a purely schematic representation, the possible construction of a filter device with two filter elements and a partially illustrated filter or device housing; Figure 8 shows, in a schematic representation, air separation on the upstream side or when flowing through a filter element shown in Figures 1 to 7, consisting of three fabric layers; Figure 9 shows, in the form of a longitudinal section, a filter device with a filter housing in which two filter elements are accommodated.which are interchangeable with one another; Figure 10 shows a half-side section and only partially shows the essential components of a bottom-side receptacle of the filter device according to Figure 9; Figure 11 shows a solution corresponding to Figure 9, in which only the innermost filter element is interchangeable and the outer filter element remains in the device housing; Figure 12 shows a representation of the lower connection area for the filter device according to Figure 11, corresponding to Figure 10; and Figures 13 and 14 show further device solutions for the filter device according to Figures 9 to 12; one with an exchange option for both filter elements and one with an exchange option for the inner element, with the outer element remaining in the device housing. In a purely basic representation and greatly simplified, Figure 1 shows the essential elements of a filter device as a whole. The filter device has two filter elements 10,12, which are arranged one behind the other in the fluid flow direction. The respective fluid flow direction is indicated by arrows in Figures 1 to 8. In the embodiment according to Figure 1, the inner filter element 10 serves to clean off particle contamination, and the other, outer filter element 12 serves to separate gases, particularly in the form of air separation. The two filter elements 10, 12 are multi-layered and pleated, with the particle-cleaning filter element 10 being constructed in a conventional manner. The two concentrically arranged filter elements 10, 12 are arranged at a distance from each other and delimit with their respective outer circumference and inner circumference an annular cavity as fluid space 14. Furthermore, the two filter elements 10, 12 are enclosed at their free end faces by two end caps, as seen in the direction of Figure 1,by an upper end cap 16 and a lower end cap 18. This structure is also conventional, so it will not be discussed in detail here. The lower end cap 18 has a central opening 20 through which the unfiltered stream is fed, indicated by a dashed arrow. The flow through the filter device according to Figure 1 is accordingly from the inside to the outside (in-to-out). As can be seen particularly from the illustration in Figure 8, the gas-separating filter element 12 has a three-layer fabric structure 22,with two cover fabric layers 24 and an intermediate layer 26 accommodated therebetween. The mesh size or the fluid passage of the intermediate layer 26 is smaller than the mesh size or the fluid passage of the two adjacent cover fabric layers 24. Furthermore, the thread diameter for the fabric structure 22 of the respective cover fabric layer 24 is larger than the thread diameter for the intermediate layer 26. The respective mesh sizes and thread diameters relating to the fabric structure 22 are in any case selected such that, in the embodiment according to Figure 1 as shown in the illustration in Figure 8 below, a coalescence of air bubbles 28 occurs as they flow through the outermost filter element 12. The small-volume air bubbles 28 initially located on the upstream side A, which may even be in finely dispersed form in the fluid flow, are, by the aforementioned coalescence effect, by means of the fabric structure 22,preferably a wire mesh structure, on the right-hand outflow side B (as viewed in Figure 8) are combined to form larger air bubbles 30, which then rise in the fluid due to buoyancy due to the Archimedes' principle and can thus be discharged into the environment. Since the filter devices discussed here are regularly so-called in-tank solutions, the air bubbles thus reach the upper side of the fluid held or stored in a fluid storage tank. It may also be sufficient to provide only two layers, with layer 24 with the larger fluid passages preceding layer 26 with the smaller passages in the direction of fluid flow. In this respect, a layer structure from coarse to fine is realized. All fabric layers 24, 26, 28 used26 are designed in a so-called plain weave and preferably the two cover layers 24 are of the same design and the intermediate layer 26 is different from this. Fabric layers 24, 26 made of metal and / or plastic wires can be used. In particular, it is provided that the respective cover layer 24 has a passage or mesh size that is approximately 5 to 11 times as large as the passage or mesh size of the respective intermediate layer 26. Furthermore, the respective cover layer 24 has a thread or wire diameter that is approximately 2 to 5 times as large as the thread or wire diameter of the respective intermediate layer 26. In particular, the respective cover layer 24 has a mesh size between 200 and 800 µm and a thread diameter between 100 and 200 µm. For the respective intermediate layer 26, the mesh size is at least 20 µm and extends up to 120 µm,with a thread diameter of 30 to 80 µm. It has proven particularly preferable for gas separation in the context of the treatment of common fluids, such as hydraulic media, to provide the respective cover layer 24 with a mesh size of 530 µm, with a thread diameter of 160 µm. The respective intermediate layer 26, in contrast, is designed differently, for example, in one embodiment, it has a mesh size of 50 µm, with a thread diameter of 35 µm. However, with an intermediate layer 26 constructed differently, the mesh size is 100 µm, with a thread or wire diameter of 60 µm. The other embodiments essentially correspond to the embodiment according to Figure 1 and will only be explained insofar asas they differ significantly from the solution according to Figure 1. In the embodiment according to Figure 2, the element structure is as in Figure 1; only in the upper end cap 16 are individual passages 32 introduced, which serve to remove gas bubbles from the filter device, with the removal taking place via a limiting gap between the upper side of the upper end cap 16 and the underside of a plate-shaped housing cover 34. The direction of the possible gas bubble discharge across this gap-shaped distance area is indicated by an arrow 36. In the embodiment according to Figure 2, the gas or air separation therefore takes place on the upstream side A of the filter element 12, as shown in Figure 8 above. Therefore, the smaller gas bubbles 28 are combined into the larger bubbles 30 in the area of ​​the leftmost cover layer 24 before flowing through the filter element 12.which then, due to buoyancy, rise from the fluid, as already explained, for a separation process. In the variant according to Figure 3, the two filter elements 10, 12 are swapped in position, i.e., the gas-separating filter element 12 is now arranged on the inside of the filter device. Here, too, gas or air separation occurs on the upstream side A of the inner filter element 12, as shown in Figure 8 above, and the enlarged air bubbles 30 are discharged in the direction of arrow 36 via a channel-like central opening 38 in the upper end cap 16. The embodiment according to Figure 4 largely corresponds to the embodiment according to Figure 1 with the proviso that the flow direction for the fluid is now reversed, i.e. the unfiltered material flows from the outside to the inside (out-to-in) through the filter device with the two filter elements 10, 12,whereby the flow first passes through the filter element 12 before the element 10. Since in the embodiment according to Figure 4 there is no passage opening 32 in the upper end cap 16, the gas separation process also takes place on the upstream side A of the filter element 12 in the variant according to Figure 4, as shown in Figure 8 above. The filtrate flow is discharged in the direction of arrow 40 via the central opening 20 in the lower end cap 18. The embodiment according to Figure 5 largely corresponds to the embodiment according to Figure 4 with the proviso that again the unfiltrate flow is first passed from the outside to the inside over the filter element 10. While the filtrate flow leaves the filter device in the direction of arrow 40,The gas escapes again via the upper passages 32 in the upper end cap 16, as indicated by arrow 36. In this respect, too, the separation takes place on the upstream side A of the internal gas-separating filter element 12. In the embodiment according to Figure 6, the flow also occurs from the outside to the inside, and any separated gas is discharged via the channel-like central opening 38 in the upper end cap 16 in the direction of arrow 36. In the special embodiment according to Figure 7, the two filter elements 10, 12 are arranged one behind the other in the longitudinal direction, with the particle-separating filter element 10 being arranged upstream of the gas-separating filter element 12. The filter element 10 is accommodated in a separate pot-shaped filter housing 42, which has an inlet 44 for the unfiltered stream at the top.which, guided in the direction of the arrow, flows through the filter element 10 from the inside outwards and is thereby cleaned of possible particle contamination. The filtrate guided to the clean side 46 of the filter housing 42 then passes through a bottom-side channel 48 in the filter housing 42 to the inside 46 of the gas-separating filter element 12, through which the gas is thus flowed from the inside outwards. During this flow, comparable to the solution according to Figure 8 below, the gas is discharged on the downstream side B of the fabric structure 22, from which the second filter element 12 consists. At the bottom, the filter element 12 is again closed with a lower end cap 18. To separate the unfiltered side from the filtrate side within the filter housing 42, a horizontally extending partition wall 50 is integrated into the latter.which also serves as a holder for the particle-separating filter element 10 in the manner of an upper end cap 16. The filter device solution shown in Figure 9 shows a constructive implementation of the principle diagram according to Figure 1. The statements made in this regard regarding Figure 1 also apply to the solution according to Figure 9. The two filter elements 10, 12 according to Figure 9 are again accommodated in a concentric arrangement in a filter housing 42, which is provided with fluid passages 52, at least in the lower region. The aforementioned fluid passages 52 are accommodated in a casing 54 of the filter or device housing 42, which extends between a housing head 56 and a base part 58 of the housing 42. The base part 58 has a fluid inlet 60,which corresponds to the unfiltered material inlet via the central opening 20 in Figure 1. The unfiltered material flow is deflected upwards by 90° via the fluid inlet 60 and reaches the inside 64 of the filter device shown, and thus its unfiltered material side, via a distributor plate 62. The filter device shown in Figure 9 can be accommodated as a so-called in-tank solution in a fluid storage tank (not shown in detail), and the fluid inlet 60 shown can be connected via piping (not shown in detail) to an unfiltered material supply line leading out of the fluid storage tank. This design is conventional, so it will not be discussed in detail here. A spring-loaded bypass valve 66 is integrated into the cover-like housing head 56, which, in the event of blockage of the filter element assembly 10,12 connects the unfiltered side directly to the filtrate side of the filter device. Furthermore, devices 68 are provided in the housing head 56 in the usual manner, which can be used to connect a pressure difference measuring device. Other uses are possible here. According to the illustration in Figure 1, the gas-separating filter element 12 again surrounds the internal particle-separating filter element 10, and with the intended flow direction, from the inner side 64 or inflow side A to the outside, the gas discharge occurs on the outflow side B of the outer filter element 12, and the individual gas bubbles 30 are then guided from the outflow side B via the individual fluid passages 52 in the casing 54 of the filter housing 42 to the inside of the fluid storage tank (not shown in detail).rise within it and are separated into the environment above the fluid level in the storage tank. This not only allows an unfiltered stream to be cleaned extremely effectively of particle contamination; rather, a high degree of gas removal from the fluid also occurs, particularly in the form of hydraulic oil. This also prevents unwanted foaming within the hydraulic oil during operation of a hydraulic system through the gas separation stage. As a kind of calming section for outgassing, a radial distance is provided between the casing 54 and the outer circumference of the second filter element 12. As shown in particular in Figure 10, both filter elements 10, 12 are jointly received at the bottom in the lower end cap 18, which carries the distributor plate 62 in one piece, projecting upwards, and a projection 70 is provided at the bottom.which has an annular sealing device 72 in the form of an O-ring on the outer circumference, which in this respect forms a type of sliding guide with the inner wall 74 of the base part 58, which is circular in cross-section, and has the supply opening in the form of the fluid inlet 60. If a removable housing cover 76 of the housing head 56 is now removed, the element combination comprising filter element 10 and filter element 12 can be removed together via the upper opening in the filter housing 42, the sealing device 72 thus disengaging from the base part 58 within the scope of the sliding guide. In the reverse sequence, a new element comprising the first 10 and second filter element 12 can then be inserted into the device housing 42 in order to carry out further filtration processes. As can be seen from Figure 10, a further support layer 78 can be introduced into the fluid space 14 between the two elements 10, 12,in addition to the fluid-permeable support layer 80 on the outer peripheral side of the gas-separating filter element 12. The fluid-permeable support layers 78, 80 ensure that, when the element structure flows from the inside to the outside, the respective pleated element layers can be supported on the adjacent support layer 78 or 80, respectively, in the sense of a pressure-stable structure. A further embodiment of a filter device according to Figures 11 and 12 largely corresponds to the solution according to Figures 9 and 10.so that the same reference numerals are used for the same components, and the previous explanations also apply to the modified embodiment according to Figures 11 and 12. In the latter solution, the gas-repellent filter element 12 is now firmly integrated into the filter housing 42 with the casing 54, and only the particle-separating inner filter element 10 can be removed for replacement via the associated lower end cap 18 with the already mentioned sliding guide via the sealing device 72 and the inner wall 74 of the base part 58. As can be seen in particular from Figure 12, the already mentioned fluid passages 52 in the casing 54, which can also extend over its entire outer circumference while maintaining axial and radial distances from one another,be designed in the manner of window-shaped openings in the casing 54. The embodiments according to Figures 13 and 14 show, based on the basic design solution according to Figures 9 to 12, further embodiments of comparable filter devices, wherein in the embodiment according to Figure 13, both filter elements 10, 12 are again removable together from the device housing 42 with the casing 54, whereas in the solution according to Figure 14, only the inner element 10 is replaceable and the gas-separating outer element 12 remains in the device housing 42. Otherwise, the statements made regarding the separation with the first and second filter elements 10 and 12 also apply to the embodiments according to Figures 13 and 14. Further device solutions with improved separation rates of gas bubbles are possible here. Due to the special fabric layer structure 22, as already described, not only separation via coalescence,but also by incorporating the Salvinia effect. This has not been implemented in this way in the field of filter devices to date. It is also possible to replace the two filter elements 10, 12 as a single, replaceable unit by using the two end caps 16, 18 to limit the elements 10, 12 on both sides.

Claims

Patent claims 1. A filter device comprising at least two filter elements (10, 12) arranged one behind the other in the fluid flow direction, one of which filter elements (10) serves to remove particulate contamination and the other filter element (12) serves to separate gases, in particular air, characterized in that the gas-separating filter element (12) has at least two layers (24, 26), each having fluid passages of different sizes, and that, viewed in the fluid flow direction, the layer (24) with the larger fluid passages precedes the layer (26) with the smaller fluid passages.

2. A filter device according to claim 1, characterized in that the layer (26) with the smaller fluid passages is accommodated as an intermediate layer between two layers (23) with larger fluid passages, as cover layers. 3.Filter device according to claim 1 or 2, characterized in that the respective layer (24, 26) is formed from a fabric that is preferably plain weave.

4. Filter device according to one of the preceding claims, characterized in that each layer (24) has individual - passages that are each approximately 5 to 11 times as large as the respective passage of the subsequent layer (26) viewed in the flow direction, and - thread diameters that are each approximately 2 to 5 times as large as the respective thread diameter of the subsequent layer (26).

5. Filter device according to one of the preceding claims, characterized in that gas separation occurs on the upstream side A of the gas-separating filter element (12) and / or when flowing through the same.

6. Filter device according to one of the preceding claims, characterized in that the two, preferably pleated, filter elements (10, 12) are arranged concentrically to one another and define an annular fluid space (14) between them, or the gas-separating filter element (12) is folded into the particle-separating filter element (10) without any gap.

7. Filter device according to one of the preceding claims, characterized in that both filter elements (10, 12) form a replaceable filter unit as a whole, or in that one filter element (12) remains in the device housing (42) and only the other filter element (10) is replaceable. 8.Filter device according to one of the preceding claims, characterized in that the respective replaceable filter element (10, 12) is received at least at one free end in an end cap (18), which receives an annular sealing device (72) on the outer circumference, by means of which a sliding guide for the engagement of the respective filter element (10, 12) is realized, preferably in a bottom-side housing connection (58) of the device housing (42).

9. Filter device according to one of the preceding claims, characterized in that the device housing (42) is provided on the head side with at least one vent opening (32) for the purpose of discharging separated gas bubbles (30) into the environment or into a fluid storage tank in which the device housing (42) is received.

10. Filter element (12), in particular intended for a filter device according to one of the preceding claims, characterized in that it consists of at least one two-layer, preferably pleated, fabric structure (22) and that all fabric layers (24, 26) are designed in plain weave, with a mesh size between 200 to 800 µm and a thread diameter between 100 to 200 µm for the respective one layer (24), and with a mesh size of at least 20 to 120 µm and a thread diameter of 30 to 80 µm for the respective further layer (26).

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