Abstract:
The invention relates to a filter module ( 1 ) comprising filters layers ( 4   a, b ) made of a filter medium, especially comprising filter layers made of filter strata. Said filter layers alternate with layers made of draining spacer elements  910, 10   a, b, 20 ), the first and last layer of the filter module ( 1 ) consisting respectively of a draining spacer element ( 10   a, b,    20 ). The draining spacer elements respectively and mutually comprise flow elements ( 12   a, b ) and sealing elements ( 11   a, b ) for the filtrate chamber and the non-filtrate chamber ( 40, 41 ). Means are provided for the mutual connection thereof The aim of the filter module ( 1 ) is to combine the advantages of known filter modules with improved sealing at the edges of the filter layers, and to make the filter module backwashable. The filter module ( 1 ) comprises draining spacer elements ( 10, 10   a, b,    20 ) which are embodied in such a way that they enable the filter layers to be pressed in a sealing manner. At least some of the draining spacer elements ( 10, 10   a, b,    20 ) comprise connecting means in the region of at least one filtrate chamber or non-filtrate chamber ( 40, 41 ), which co-operate with the connecting means of at least one other spacer element. The connecting means include lugs, stirrup straps ( 16   a, b,    23   a, b ), and T and arrow-shaped catch elements. In this way, a stable and both backwashable filter module ( 1 ) is created.

Description:
DESCRIPTION  
         [0001]    The present invention concerns a filter module having filter layers made of a filter medium, especially having filter layers made of filter strata. Said filter layers alternate with layers made of draining spacer elements, and the draining spacer elements have respectively and mutually flow elements on one side and sealing elements on the other for the filtrate chamber and non-filtrate chamber. Means for mutual connecting thereof are provided.  
           [0002]    Such filter modules are known in a variety of constructive forms. A common trait of the majority of these filter modules is that the filter layers are manufactured from flat materials, e.g., filter cartons, papers, fleeces, or fabrics.  
           [0003]    Filter strata consist as a rule of deep filter material that contains organic and/or inorganic fibrous, and/or granular matter. Used as a rule as a basic material for filter strata are cellulose or synthetic material fibers, in which Kieselgur, perlite, metal oxides, or other filtration-active substances can be stored. Kieselgur and perlite hereby serve to enlarge the inner surface and thus to enlarge the ability to collect impurities.  
           [0004]    The range of use for the filter strata includes clarifying and treating fluids for the entire beverage industry, as well as the pharmaceutical industry, and the chemical industry. Filter strata have not only a straining effect, in which coarse particles are retained on the surface of the filter layer, but also especially a deep effect for fine particles that are retained in the hollow spaces within the deep filter material. Depending on the type of materials used, these filter strata can also have an absorption effect and the surface can be treated afterwards for specific purposes so that fibrous particles cannot be loosened when they are in a dry or damp state.  
           [0005]    A filter module is known form U.S. Pat. No. 4,347,208, made of filter cells whose core consists of a draining spacer made of synthetic material on which a filter layer made of a filter medium in the form of flat disks on both sides lies. A filtrate opening is provided in the center of the filter cell. The outer edge of filter cells of this type must be extruded with a synthetic material for sealing purposes, which is expensive, because special forms must be used that have to be adapted to the geometry of the filter cell. Sealing the filter cell from the non-filtrate chamber is performed by pressing together both filter material layers, which are in contact with each other only in the edge region, and by forming a U-shaped plastic element that grips along the edge region.  
           [0006]    In EP 0,233,999, such a filter module is also described in which so-called outer spacers are also arranged between the filter cells. They keep the filter cells at a distance in order to prevent the filter cells from being damaged, collapsing, or being saturated in the filter cells. Moreover, the radial flow between the filter cells should be improved. The inner and outer spacers are shaped variously, so that different tools are needed for manufacturing. Extruded filter cells are used in this filter module as well.  
           [0007]    EP 0,291,883 describes a filter module made of filter cells stacked on top of one another. To make the described module, filter pockets having drainage material within them are manufactured, which are enclosed by a sealing element and a synthetic material mass in a leak-proof manner. The pockets are stacked on top of one another in such a way that the fluid can penetrate between the cells. Additional components for the spaced arrangement of the filter strata are necessary for this filter module as well. The flow through the filter module occurs in the plane of the filter strata, which then must still be flowed through perpendicular to the strata planes in order for filtration to take place. Unless special measures are taken, these filter cells cannot be back-washed.  
           [0008]    Another filter module is known from DE 37 41 552 A1. This filter module, in which a number of filter cells is combined, is equipped with a central support tube, on which filter cells are pressed together axially between two adapter pieces attached to both ends of the support tube and are held sealed against one another. The interior of the support tube is connected to the inner chamber of each of the filter cells via flow channels arranged in the circumferential wall of the support tube and thus forms a common outlet channel for the filtrate for all filter cells.  
           [0009]    Because many modules are not backwashable, the trend in recent times has been towards filter strata having no opening in their arrangement.  
           [0010]    From 198 36 949.2-27 a filter module is known having collecting/distributing strata for the filtrate and the non-filtrate. Between said respective strata, at least one filter stratum made of deep filter material is arranged. Both filter strata and the collecting/distributing strata are produced form the same basic material, but have different separation efficiencies. The collecting/distributing strata are reciprocally sealed to the filtration/non-filtration chamber. The sealing elements can consist of molded parts that have means for mutual connection.  
           [0011]    From DE 198 37 257 a filter module is known that has layers made of a filter medium. Draining spacer elements are arranged between said layers. The draining spacer elements are likewise reciprocally sealed to the filtrate/non-filtrate chamber. Furthermore the draining strata likewise have reciprocal flow elements that comprise a solid frame having a bore hole or grooves lying in the plane of the draining strata. The sealing elements and/or the flow elements have means for mutual connection, either the flow elements or the sealing elements still being able to be connected.  
           [0012]    The draining spacer elements are implemented with sealing element and flow element in one unit, whereby cost-effective components can be produced that only need to be combined with the filter strata and assembled. Since the flow and seal elements have the same thickness as the draining spacer elements, the filter strata are not compressed in the edge region when the filter module is assembled, with the result that bypasses cannot be excluded in this area. The filter strata are open for flow-through in the side edge region.  
           [0013]    The connecting means serve only to attach the entire module, without there thus being an improvement in the sealing.  
           [0014]    The task of the present invention is a filter module that combines the advantages of this known filter module with an improved sealing in the edge region and that is backwashable and can be moved in any direction of flow.  
           [0015]    The solution for this problem is a filter module that is characterized in that the draining spacer elements are implemented so as to press and seal off the filter layers, and so that at least some of the draining spacer elements have connecting means in the region of at least one filtrate or non-filtrate chamber, wherein the connecting means of these spacer elements cooperate with the connecting means of at least one other spacer element.  
           [0016]    The filtrate or non-filtrate chambers are understood to be the spaces surrounding the filter module and the collecting channels(s) extending in the axial direction of the filter module for the filtrate or non-filtrate. Customarily, the filter module possesses a filtrate/non-filtrate chamber arranged in the middle. But multiple filtrate/non-filtrate chambers of a type extending through the filter module are also possible.  
           [0017]    This filter module has a series of advantages.  
           [0018]    Due to the flat position of the filter layers on the draining spacer elements, wherein the filter layers are attached in the edge region between the spacer elements, and due to the reciprocal connection of the draining spacer elements via connecting means, an overall stable filter module is created that cannot be distorted and that is also backwashable. The filter layers are prevented from being deformed during backwashing.  
           [0019]    Because the draining spacer elements are arranged on the filter layers on both sides and the filter layers are thus supported on both sides, for purposes of filtration, filter materials can be used the have a low inherent stiffness.  
           [0020]    The rigid connection, especially on the outer edge, helps to create a filter module with a stable design that can withstand all strains on it during storage, delivery, and use. Further, damages to the filter layers when they are inserted and taken out from the filter housing. If ring-shaped filter layers are used, the filtrate/non-filtrate channel is, as a rule, arranged in the middle, where the draining spacer elements likewise have connecting elements. Stability is thereby increased additionally.  
           [0021]    These inventive measures decidedly improve the resistance to back-pressure in the filter module, an important factor when vacuum forces or pressure shocks occur due to hookup errors.  
           [0022]    Since the draining spacer elements are connected to each other, the height of the filter module can be whatever is desired. Furthermore, the diameters of the filter layers and the draining spacer elements can be adapted to the diameters of conventional filter housings, so that effective filter area is not lost and usage in known filter housings presents no problems.  
           [0023]    While the filter layers in the core region of the filter cells cannot be prevented from sticking together in conventional filter cells, this is not a problem here, because of the draining spacer elements on both sides of the filter layers. The filter layers are exploited to the fullest advantage, especially even during low differential pressure.  
           [0024]    Moreover, filtration is possible in both directions, i.e., the module can work when the flow direction is switched. An absolute filtration of remnants is thus possible, i.e., after filtration there is no more non-filtrate in the housing. This is especially important for the filtration of expensive solutions. The filter housing does not need to be cleaned after filtrating toxic fluids, for example, so that contact with toxic materials is thereby prevented.  
           [0025]    The highest and lowest filter layer of the filter module can be capped with non-draining spacer elements, for example. It is also possible to use conventional filter cells as upper and lower caps, said cells having connecting means on the extruded outer edge.  
           [0026]    Preferably, the connecting means of adjacent spacer elements cooperate. It is also possible that the connecting means encompass respectively one or more adjacent spacer elements and first cooperate with the connecting means of one or more successive spacer elements.  
           [0027]    The spacer element preferably includes a drainage element, at least one sealing element and/or a flow element. The number of sealing and/or flow elements corresponds to the number of filtrate and/or non-filtrate chambers to which the respective spacer element is adjacent.  
           [0028]    Advantageously, two different draining spacer elements (first and second draining spacer elements) are provided that alternate in their arrangement in the filter module.  
           [0029]    Preferably, the first spacer element has the sealing element on the inner circumference and the second spacer element has the sealing element on the outer circumference.  
           [0030]    Preferably, the sealing elements and the flow elements of the first draining spacer elements are thicker than the sealing and flow elements of the second draining spacer elements. Between the first draining spacer element and the filter layer in the non-attached region, a more or less wide opening is thereby formed, depending on the thickness of the filter layer after the filter module is assembled.  
           [0031]    Preferably, the first spacer element has a corresponding inner wedge-shaped connecting element and/or an outer wedge-shaped connecting element between the drainage element and the sealing element and/or the flow element.  
           [0032]    The wedge-shaped connecting elements have at least one upper and at least one lower wedge area with an inclination between 10° and 60°. Tapering radially until the thickness of the drainage element is reached, the wedge-shaped connecting elements preferably have a thickness that corresponds to the sealing element and/or the flow element. A smooth transition is thereby made between the sealing element and/or flow element and the drainage element, which is advantageous for sealing purposes. During assembly, the filter stratum is continuously compressed with the second spacer elements toward the edge region of the spacer elements so that the filter stratum is not subjected to any uncontrolled deformations that could lead to bypasses.  
           [0033]    The wedge-shaped connecting elements preferably have respectively two wedge areas, wherein the wedge in the x&lt;1 range mm is at an angle α 2 &lt;20°.  
           [0034]    Advantageously, the drainage element formed in one piece with the sealing element and/or the flow element and/or the wedge-shaped connecting element, so that a one-piece plastic extruded part, for example, can be manufactured.  
           [0035]    A further simplification is possible when the connecting means are likewise formed in one piece with the spacer element.  
           [0036]    The connecting means can be implemented in various ways. Preferably, the connecting means of the spacer elements are form-locking. In another embodiment, the connecting means of the spacer elements are positive-fitting.  
           [0037]    Since the spacer elements have flow and/or sealing elements in their edge regions, the connecting means are preferably arranged on, and especially formed onto, the flow and/or sealing elements when the embodiment is of one piece.  
           [0038]    Advantageously, the connecting elements comprise clips in which catch lugs grip. The clips can be U-shaped or L-shaped, for example.  
           [0039]    The clips point upward and downward. An alternating arrangement of upward and downward pointing clips is preferred.  
           [0040]    To create the most rigid module unit possible, the clips are arranged in the circumferential direction of the spacer elements, preferably directly next to one another.  
           [0041]    In another preferred embodiment, the clips can be arranged at intervals to one other in the circumferential direction of the spacer element, whereby the interval may be a max. 500 mm. The connecting elements are distributed uniformly over the circumference, the number depending on the circumference size. The connecting means, especially the clips, help protect against the impact on the clipped filter layers edge in the radial direction.  
           [0042]    In another embodiment connecting means are arranged in a slot that runs around on a spacer element, with catch hooks on another spacer element that reach into the slot. The circular-running slot can be arranged in the sealing element of the spacer element or in the flow element. The slot is preferably delimited by catch rings.  
           [0043]    Preferably, the catch lugs, hooks, rings, and/or clips have gliding bevels on their outer sides. Combining and locking the connecting means is thus made easier. When the filter module is assembled, the filter layers and the draining spacer elements are stacked onto one another and the entire package is then pressed together, whereby the clips, catch lugs, etc., catch in one another. The corresponding connecting means must run over the outer surfaces of the connecting partners, whereby the gliding bevels make this process easier.  
           [0044]    To ensure a secure hold, the contact surfaces of the form-locking connecting means are preferably slanted, whereby, preferably, the corresponding overarching contact surface is slanted inwardly counter to the connecting means that is being gripped. A clip-type connection is thereby created.  
           [0045]    Other embodiments of the connecting means can be sleeves and dowels with or without teeth, T-shaped or arrow-shaped locking elements gripping one another on both sides.  
           [0046]    According to another embodiment, fastening means running around on the spacer elements, e.g., hook rings, can be provided onto which a web or grid is attached that wraps around the filter modules. The web or grid in this embodiment serves also as a connecting means that holds the spacer elements and thus the filter module together.  
           [0047]    The connecting means can be provided exclusively on the outer circumference of the spacer elements. It is also possible that, besides being arranged on the outer circumference of the spacer elements, the connecting means are also arranged on the inner circumference, wherein the inner circumference means the edge region, which borders the collecting and thus filtrate and/or non-filtrate chambers arranged in the interior of the filter module.  
           [0048]    Preferably, the sealing and/or flow elements are formed as bead-like swellings of the draining spacer elements.  
       
    
    
       [0049]    Example embodiments of the present invention are further explained by means of the following drawings.  
         [0050]    [0050]FIG. 1 shows a view of the filter module;  
         [0051]    [0051]FIG. 2 shows a section through the filter module shown in FIG. 1, along line A-A;  
         [0052]    [0052]FIG. 2 b  shows a section through a first draining spacer element;  
         [0053]    [0053]FIG. 3 a  shows an enlarged view of the clips;  
         [0054]    [0054]FIGS. 3 b,c  show a view from above of a section of the circumferential edge of a spacer element according to two embodiments;  
         [0055]    [0055]FIG. 4 shows a section through a filter module according to another embodiment;  
         [0056]    [0056]FIG. 5 shows a partial view from above of the filter module shown in FIG. 4;  
         [0057]    [0057]FIGS. 6 a,b  show top-views of segments of the draining spacer elements; and  
         [0058]    [0058]FIG. 7 shows a section through a filter module according to another embodiment. 
     
    
       [0059]    A complete filter module  1  is depicted in FIG. 1. Filter layers in the form of filter strata  4  alternate with first and second draining spacer elements  10 ,  20 . All components of the filter module  1  are lined up on a central tube  2 , which has a lower end piece  8  (see FIG. 2) and an upper end piece  3 , which attaches the filter strata  4  and the draining spacer elements  10 ,  20  on the central tube  2 .  
         [0060]    On their outer side, the second draining spacer elements  20  have U-shaped clips  23  pointing up and down, in which the catching lugs  13 ,  14  of the first draining spacer elements  10  reach. The clips  23  and the catching lugs  13 ,  14  together respectively form a clip-type connection. In the embodiment depicted in FIG. 1, the clips are arranged continuously on the outer circumference, so that a stable filter module  1  is created that is easily wielded and that cannot be distorted during use.  
         [0061]    In FIG. 2 a  is shown a section line A-A through the filter module  1  shown in FIG. 1 for the sake of simplicity, only two filter strata  4   a  and  4   b  are shown, with the draining spacer elements  10   a, b    20  that pertain to them.  
         [0062]    The first draining spacer elements  10   a, b  have ring-shaped sealing elements  11   a,    11   b  that have a hexagonal cross-section in the embodiment shown here. Connecting radially outward over the outer circumference of the ring-shaped sealing elements  11   a,    11   b  are distributed inner wedge-shaped connecting elements  103  that have an upper and lower wedge-surface  104 ,  105 . These wedge-shaped connecting elements  103  taper outward radially, wherein the thickness lessens fro the thickness of the corresponding sealing elements to the thickness of the drainage element  100  or the thickness of the corresponding straps  118 ,  118 ′ of the drainage element  100  (see also FIG. 6 a ). Connecting radially outward to the drainage element  100  are outer wedge-shaped connecting elements  107  with upper and lower wedge-surfaces  108 ,  109 . The wedge-shaped connecting elements  107  transition into the flow elements  12   a ,  12   b , which for a ring whose thickness corresponds to the thickness of the sealing element  11   a,    11   b.  The catching lugs  13  are formed to the flow elements  12   a, b,  and the flow channels  18  are arranged in the flow elements  12   a, b  in the middle. The draining spacer elements, the wedge-shaped connecting elements, the sealing elements, and the flow elements are formed in one piece, for example as a mold part made of plastic.  
         [0063]    Between drainage elements  100  and the respective adjacent filter strata  4   a ,  4   b , there is a gap-shaped intermediate chamber  130 , so that the filter stratum  41   b  is not subject to any load in this area and can be extended by swelling without impediment. The complete functionality and effectiveness of the filter stratum  4   a,b.  Without having to change the draining spacer elements  10   a,b,    20 , filter layers of various thickness can be installed. When the filter module is operated in a reverse direction of flow, the gap  130  can be closed depending on the thickness of the filter stratum  4   a,b,  and a gap can be formed between the drainage element  200  and the adjacent filter stratum or filter layer.  
         [0064]    During assembly, the wedge-shaped connecting elements cooperate with the second draining spacer elements  20  in a radial direction to continually pres the filter stratum, whereby the seal is improved. The second draining spacer elements  20  have a ring-shaped flow element  22  with flow channels  33 . The ring-shaped flow element  22  has a greater thickness than the drainage element  200  connecting radially outward, to which the ring-shaped sealing element  21  connects radially outward. The second draining spacer element  20  is preferably manufactured in one-piece out of plastic. The clips  23  are formed on the outer side of the sealing element  21 , which is formed as a seal ring having a thickness corresponding to the thickness of the draining spacer element  20 . The clips  23  extend upward and downward and possess clip lugs  26  and contact surfaces  27  on their inner side and gliding bevels  30  on their outer side.  
         [0065]    The filter strata  4   a,b  and the spacer elements  10   a,b,    20  are aligned on the central tube on which the lower end piece  8  and the upper end piece  3  are fastened. On their front, these end pieces  3  and  8  bear ring-shaped seal elements  50  that are formed as flat seals. The interior of the central tube  2  forms the filtrate/non-filtrate channel  40 .  
         [0066]    Between the end pieces  3  and  8  equipped with pins, the following components are clipped from above to below: intermediate element  9  made of filter material, seal element  11   a,  filter stratum  4   a , flow element  22 , filter stratum  4   b , sealing element  11   b,  and intermediate element  9 . The sealing elements  11   a  and  11   b  are formed on both sides as bead-like swellings of the drainage elements  100  on the basis of the wedge-shaped connecting elements  103  and in the embodiment shown here possess a hexagonal cross-section. The bead-like sealing elements  11   a  and  11   b  are adjacent in a sealing manner on one side to the intermediate element  9  and on the other to the inner wall  5  of the filter stratum  4   a  and  4   b.    
         [0067]    The flow element  22 , which forms a connection via flow channels  33  between the chamber between the filter strata  4   a  and  4   b  and the filtrate/non-filtrate  40 , is a bead-like swelling of the second draining spacer element  20  on both sides.  
         [0068]    When the components for filter module  1  are put together, the filter strata  4   a  and  4   b  are pressed together and sealed on the inner wall  5  as a result of the design of the sealing elements  11   a  and  11   b  and the flow element  22 , so that bypasses are prevented in this area.  
         [0069]    On the outer circumference, the second draining spacer element  20  possesses a sealing element  21  in order to form a seal against the surrounding chamber that forms the filtrate/non-filtrate chamber  41 .  
         [0070]    The flow elements  12   a, b  represent the connection between the chamber above and below the filter strata  4   a, b  and the filtrate and/or non-filtrate chamber  41 . Above and below the flow channels  18  are arranged catch lugs  13 ,  14  with gliding bevels  31  that cooperate with the clip lugs  26  in the assembled state and form a clip-type connection.  
         [0071]    Between the sealing element  21  and the flow element  22 , the outer edge  6  of the filter layers  4   a  and  4   b  are pressed together.  
         [0072]    The arrows indicate the flow direction of the non-filtrate and/or filtrate. The non-filtrate is fed out of the non-filtrate chamber  41  and reaches the filter strata  4   a  and  4   b  through the flow channels  18 . After entering through the filter strata  4   a  and  4   b , the filtrate collects in the area of the second draining spacer element  20  and flows down through its flow element  22  into the filter chamber  40  within the central tube  7 . The flow direction can also be reversed. In this case, the chamber  40  forms the non-filtrate chamber and the chamber  41  forms the filtrate chamber.  
         [0073]    In FIG. 2 b , another embodiment of the wedge-shaped connecting element  103  is depicted. Instead of an individual wedge surface, two wedge-shaped surfaces  104   a, b  and  106   a, b  are provided on the upper and lower side respectively. The wedge surfaces  104   a ,  106   a  are more inclined than the wedge surfaces  104   b ,  106   b,  which border the drainage element  100 . This means that α 1 &gt;α 2  is valid for the pertinent angle. The wedge-shaped connecting element  107  (see FIG. 2 a ) can be formed accordingly.  
         [0074]    In FIG. 3 a , four clips  23  are depicted. These clips are formed to the ring-shaped sealing element  11  as U-shaped clips pointing up and down. Each clip  23  possesses two vertical members  24  and a connecting cross-member  25 , on whose corresponding back side is arranged a clip lug  26  is arranged.  
         [0075]    In FIG. 3 b , a top-view of a section of the circumferential edge of a draining spacer element  10   a  is shown. In the middle, the flow channels  18  are arranged and above and below the flow channels  18  are arranged catch lugs  13  and  14  that are distributed uniformly over the circumferential edge with an interval. The catch lugs  13  and/or  14  possess sliding surfaces  31  on their outer side.  
         [0076]    In FIG. 3 c,  another embodiment is depicted in which, instead of catch lugs  13  and/or  14 , catch rings  102   a ,  102   b  are provided that border an intermediate slot  101  in which the flow channels  18  are arranged. There also exists the possibility of attaching the embodiments shown in FIG. 3 b  and  3   c  to the sealing elements instead of to the flow elements.  
         [0077]    In FIG. 4, another embodiment is depicted in which the sealing elements  21  and the flow elements  12  have ring-shaped pressure shoulders  19  and  32 . the clips  23   a, b  are arranged on the sealing element  21  pointing upward and downward in an alternating manner, as this can be seen in FIG. 5. Accordingly, the catch lugs  14 ′,  14 ″ and  13 ′,  13 ″ are arranged in an alternating manner. The contact surface  15  of the catch lugs  14 ′ and the contact surface  27  of the cross-member  25  of the clip  23   a  are inclined, the contact surface  15  being inclined inwardly (see FIG. 4). A secure hold is thereby ensured so that the clips  23   a  cannot move to the outside under load. A clip-type lock or clip-like connection is thus made.  
         [0078]    In FIG. 6 a  a segment of a circular first spacer element  10  is shown. On the inner circumference, the ring-shaped sealing element  11   a  is located, to which the wedge-shaped connecting elements  103  connect radially outward with the upper wedge surfaces  104 , which transition into the radial straps  118  of the drainage element  100 . Also provided are shortened radial straps  118 ′, which extend inwardly from the ring-shaped flow element  12   a  arranged on the outer circumference of the draining spacer element  10 . The radial straps  118 ,  118 ′ are connected to one another by circular straps  119 . The graph-lined sections of the circular straps  118 ′,  118 ″ and the areas  128 , that are depicted on only one strap  118 ′, have a reduced thickness compared with the remaining straps and strap segments in order to enable cross-flow if necessary.  
         [0079]    On the radial outer end, the straps  118 ,  118 ′ have wedge-shaped connecting elements  107 , of which the upper wedge surface can be seen. The ring-shaped flow element  12   a  connects to this with the flow channels  18  and the catch lugs  13 .  
         [0080]    In FIG. 6 b,  a segment of a circular second spacer element  20  is shown. The clips  23  are formed to the outer circumference of the ring-shaped sealing element  21 . The flow element  22  with the flow channels  33  is located on the inner circumference. Between flow element  22  and dealing element  21  are radially arranged straps  28 ,  28 ′ and circular straps  29 , there being continuous straps  28  and shortened straps  28 ′. The interval of the radial straps  28 ,  28 ′ is adapted to the filter material to ensure an optimal support of the filter layer both during filtration and backwashing. Width, length, and arrangement of straps  28 ,  28 ′, and  29  must be thus adapted respectively to the filter material and the filter&#39;s task. The hatched sections of the circular straps  29  and the areas  228 , that are shown on only one strap  28 , have a reduced thickness compared with the remaining straps and strap segments in order to enable cross-flow, if necessary.  
         [0081]    In FIG. 7, another embodiment is depicted, which shows the connection in the area of the filtrate/non-filtrate channel  40 . In this embodiment a central tube  2  is not used because the first draining spacer elements  10  with the ring-shaped sealing elements  11  have clips  16   a, b  that cooperate with corresponding catch lugs  34  that are formed either to the upper end piece  3  or to the second draining spacer elements  20 . The similar clip-like connection corresponds to the connection that is depicted in FIGS. 4 and 5.