Filter device without clamping pins

Abstract

The invention relates to a filter device for filtering fluid, which filter device comprises a membrane insert which is arranged in a housing and has multiple membranes for filtering the fluid. The housing comprises a cylindrical housing tube which is provided at a first tube end with a first end element and at a second tube end with a second end element, wherein the membrane insert is arranged between the first end element and the second end element. The filter device does not comprise any pin element which interconnects the end elements in order to preload the first end element and the second end element in the direction of the membrane insert.

Description

[0001] Filter device without clamping bolt

[0002] The present invention relates to a filter device for filtering a fluid by means of membranes.

[0003] The use of membranes for the filtration of fluids is generally known. Such filter devices are used, for example, for drinking water treatment and typically comprise a housing with an inlet for the fluid, a permeate outlet for the permeate separated from the fluid, and a retentate outlet for the retentate (concentrate) separated from the fluid. Within the housing is a membrane insert carrying one or more membranes for separating or filtering the fluid. Advantageously, the membrane insert is arranged in a cylindrical housing tube, which is closed at the end with end elements. In this way, the housing can be designed to be particularly pressure-tight, so that the fluid to be filtered can be pumped through the membrane insert even at high pressure.

[0004] When the filter device is used as intended, the membranes are exposed to the fluid to be filtered by passing the fluid through the inlet into the housing tube and forcing it through the membrane insert to obtain the permeate and retentate. The permeate is the portion of the fluid that passes through the membranes and is thus freed of unwanted components. The retentate is retained in the permeate.

[0005] When using a large number of fine-pored membranes, such as for ultrafiltration, the fluid is pressurized from the inlet side in order to separate the fluid as quickly as possible into the permeate and the retentate. This creates an internal pressure within the housing, which acts on the housing wall and in particular on the two end elements that close the housing. Depending on the filter application (e.g. microfiltration, ultrafiltration and nanofiltration), the pressure can be up to 120 bar or more, especially when using very fine-pored membranes. To prevent pressure-related damage to the housing or leaks during operation of the filter device, the end elements have so far been connected to one another with a clamping bolt extending through the membrane insert.The clamping bolt pre-tensions the end elements in the direction of the membrane insert so that the compressive forces acting against the end elements from the inside are reliably compensated.

[0006] However, the clamping bolt does have disadvantages. On the one hand, the clamping bolt reduces the space available inside the housing for the membrane insert and thus for filtration. Consequently, the fluid flow induced during filtration is impaired by the clamping bolt, so that the amount of fluid that can be filtered per unit of time is limited by the clamping bolt. The flow rate is also limited when the clamping bolt is positioned downstream of the membranes in the flow direction, e.g., when the clamping bolt is guided through a permeate tube extending through the membrane insert. In other words, the space available on the permeate side also affects the filter performance.

[0007] The clamping bolt also increases the weight of the filter device and the effort required for reliable sealing.

[0008] It is an object of the invention to provide an improved filter device that, in particular, allows a higher flow rate for the retentate. This object is achieved according to a first aspect by the subject matter of claim 1.

[0009] Accordingly, the filter device does not have a bolt element connecting the first and second end elements to each other in order to prestress the first end element and the second end element in the direction of the membrane insert.

[0010] It has been shown that sufficient pressure resistance of the housing can be ensured even without the clamping bolt. In other words, the clamping bolt can be omitted without compromising the function and safety of the filter device. The flow rate of the fluid to be filtered, especially the permeate portion, can be significantly increased in this way. Furthermore, weight and the risk of leakage can be reduced.

[0011] The clamping bolt can be omitted, especially in applications that do not require particularly high filter pressures, e.g., in the range of 120 bar and above. On the other hand, the filter device can be designed using various structural measures so that the end elements are always securely held to the housing tube, even without a clamping bolt, and no leaks occur. Examples of suitable measures are described below.

[0012] The described filter device can, in principle, be used for various filtering purposes. Examples include ultrafiltration, reverse osmosis, and nanofiltration.

[0013] Embodiments are disclosed in the description, the dependent claims, and the figures. According to one embodiment, the filter device preferably does not have a bolt element extending through the membrane insert and the first and / or second end element. The effective area of ​​the membrane insert can be increased in this way. On the other hand, there are lower design requirements for at least one of the end elements, in particular with regard to the reliable sealing of an opening formed in the end element. For example, an end element can be designed without an opening for the bolt element, thus reducing the risk of leaks.

[0014] According to a further embodiment, the membrane insert has a permeate tube connected to the membranes for receiving and discharging the permeate. The permeate tube preferably extends centrally through the membrane insert and the housing tube. For example, the permeate tube and the housing tube can be arranged concentrically or axially parallel.

[0015] The permeate tube is completely free, particularly along its tube axis, and in particular, free of any bolt element. The central outflow area of ​​the permeate is thus neither obstructed by a bolt element nor by any other connecting element that could reduce the tube volume of the permeate tube. The flow rate of the fluid through the filter device, especially of the permeate portion, can be further increased by this measure.

[0016] According to a further embodiment, at least one of the ends of the permeate tube rests against one of the end elements of the housing.

[0017] For example, the first tube end of the permeate tube rests against the first end element. Alternatively or additionally, the second tube end can rest against the axially opposite second end element. Movement of the permeate tube can be effectively restricted in this way, so that the membrane insert is held in a fixed position in the housing tube. Furthermore, the end elements can advantageously be supported centrally on the permeate tube. For example, the permeate tube can directly support the end elements, eliminating the need for separate pressure elements.

[0018] According to a further embodiment, the first tube end of the permeate tube engages in sections with a central recess of the first end element to limit the movement of the permeate tube in the axial direction toward the first end element. The first tube end can optionally be provided with a sealing element to particularly reliably prevent the fluid from penetrating the permeate tube. The sealing element is preferably designed as a sealing ring. This can help to hold the permeate tube in the recess and, in particular, prevent it from slipping out of the recess.

[0019] It is preferred that the second tube end of the permeate tube partially engages a central opening in the second end element. The permeate tube can thus advantageously be stored in both end elements. The opening allows access to the interior of the permeate tube as needed. For example, the opening can be provided with an internal thread into which a connector for the permeate tube or the permeate outlet is screwed. The connector can be optionally removed by unscrewing it to expose the end of the permeate tube and, if necessary, to clean it.

[0020] Furthermore, measures can be taken to compensate for gaps caused by manufacturing or operation. For example, the connector can define a stop for the permeate tube, which can be variably adjusted depending on the screw-in depth. In particular, the movement of the permeate tube can be limited in such a way that the mobility of the permeate tube and the membrane insert in the axial and radial directions is minimized.

[0021] The connector preferably has a sealing element to prevent fluid from escaping from the housing. Furthermore, the second end of the permeate tube can also have a sealing element to prevent retentate from entering the permeate tube and / or to improve the fit of the permeate tube in the opening.

[0022] The permeate outlet is preferably located centrally on the second end element. For example, the permeate outlet can be formed on the aforementioned connector. The achievable permeate discharge rate can thereby be further increased.

[0023] According to a further embodiment, the inlet is arranged decentrally on the first end element, and the retentate outlet is arranged decentrally on the second end element. The inlet and retentate outlet can also be interchanged if necessary to operate the filter device with a reversed fluid flow.

[0024] The arrangement of all inlets and outlets at the end elements is advantageous in order to be able to form the housing tube without interruption, i.e. without openings for connections or the like. The design requirements for the housing tube can be reduced in this way. For example, the housing tube can advantageously be made of a plastic. This can be reinforced with fibers, in particular glass fibers, for high-pressure applications. In addition, the risk of leakage in the housing tube is minimized. Preferably, the first end element and / or the second end element are each releasably secured with a retaining ring to prevent them from falling out of the housing tube. The retaining ring engages on an inner side of the housing tube in a groove running around the tube axis and is preloaded radially outwards.

[0025] According to a further embodiment, the filter device is equipped with a prestressing element, in particular an adjusting flange, which is provided with at least one threaded hole. The threaded hole preferably extends axially parallel to the tube axis of the housing tube and serves to accommodate a screw for prestressing the first and / or second end element in the direction of the membrane insert. The screw is preferably screwed into the threaded hole from the outside until it interacts with the adjacent end element in the axial direction. In this way, the end element can be prestressed in the axial direction against the membrane insert depending on the screw-in depth in order to reliably hold the end element and the membrane insert in a fixed position in the housing tube. Tolerances resulting from manufacturing or operation can be compensated for by readjusting the screw as needed.

[0026] In a preferred embodiment, the preload element is annular and has a plurality of threaded holes arranged along the ring. For example, the preload element can be designed as an annular flange. The threaded holes are each designed to accommodate a screw to apply pressure to the end element in the direction of the diaphragm insert. By using multiple screws, tilting of the end element in the housing tube can be reliably prevented. Furthermore, the point load on the end element is reduced because the preload force is distributed across the multiple screws.

[0027] According to a further embodiment, at least one deflection device is arranged between the membrane insert and the inlet in order to deflect the fluid flow in the housing tube. The fluid flow can in particular be deflected in such a way that partial mechanical overloading of the membranes by inflowing fluid is avoided. For example, the deflection device can be designed as a disk that extends transversely to the tube axis of the housing and forms a fluid barrier in the direction towards the membranes. The fluid must therefore flow around the disk before the fluid hits the membranes. The flow velocity per unit area can be effectively reduced or limited in this way. The total flow rate, however, is not impaired, so that a high filter performance can still be achieved.

[0028] The deflection device is preferably attached to the end element that has the fluid inlet. A further deflection device can be arranged between the membrane insert and the retentate outlet. In this way, the membrane side facing the retentate outlet is also protected from overload. This is particularly advantageous when the retentate outlet is optionally used as the inlet for the fluid to be filtered.

[0029] According to a further embodiment, the membrane insert has a grid-like intermediate element on each of its sides facing the end elements for enclosing the membranes. The intermediate elements effectively hold the membranes in position. Furthermore, the membranes are mechanically protected. For example, damage during assembly can be better prevented.

[0030] The housing tube is preferably made of a plastic. The plastic can advantageously be reinforced with fibers, e.g., glass fibers, to ensure its shape stability even under high internal pressures.

[0031] According to a second aspect of the invention, a filter device for filtering a fluid is described. The filter device comprises a housing with an inlet for the fluid, a permeate outlet for the permeate separated from the fluid, a retentate outlet for the retentate separated from the fluid, and a membrane insert with a plurality of membranes for filtering the fluid. A deflection device is arranged between the membrane insert and the inlet, which is designed to deflect a fluid flow when the filter device is used as intended. The deflection device allows operation of the filter device with higher fluid flows. In particular, partial overloading of the membranes by the incoming fluid flow is reliably prevented.

[0032] The deflection device is preferably designed, as described above, as a disc element that ensures a uniform distribution of the fluid flow. For example, the disc element can define an inlet channel for the fluid in the direction of a tube axis of the housing. The disc element is preferably attached directly to an end element arranged in the housing, which end element has the inlet for the fluid.

[0033] The end elements are preferably made of a metal, in particular stainless steel. The robustness of the housing can thus be even better ensured even without a clamping bolt. It should be understood that the features disclosed in connection with the filter device according to the first aspect can also be implemented in a corresponding manner in the last-described filter device according to the second aspect, and vice versa. For example, the housing can also comprise a housing tube made of plastic, into which the end elements are inserted at the ends.

[0034] According to a third aspect of the invention, a filter device for filtering a fluid is disclosed. This comprises a housing with an inlet for the fluid, a permeate outlet for the permeate separated from the fluid, and a retentate outlet for the retentate separated from the fluid. The housing has a cylindrical housing tube in which a membrane insert with a plurality of membranes for filtering the fluid is arranged. The membrane insert also has a permeate tube connected to the membranes for receiving and discharging the permeate. The permeate tube extends centrally through the membrane insert and is free along its tube axis, in particular free of a bolt element.

[0035] It should be understood that features of the filter devices described according to the first two aspects can also be implemented in a corresponding manner in the last-described filter device according to the third aspect, and vice versa. For example, the embodiments disclosed in the dependent claims can be implemented in the filter device according to the third aspect.

[0036] The invention will be described in a preferred embodiment purely by way of example with reference to the drawings, wherein further advantageous details are disclosed. Functionally identical parts are provided with the same reference numerals.

[0037] The drawings show in detail:

[0038] Figure 1 : a longitudinal sectional view of a filter device for

[0039] Filtration of a fluid;

[0040] Figures 2a and 2b: side views of the front sides of the filter device of Fig. 1;

[0041] Figures 3a and 3b: side views of end elements of the filter device of Fig. 1;

[0042] Figure 4: a side view of an intermediate element of the

[0043] Filter device of Fig. 1 ;

[0044] Figures 5a and 5b: a side view (Fig. 5a) and a cross-sectional view (Fig. 5b) of a disc-shaped deflection device for the filter device of Fig. 1;

[0045] Fig. 6: an exploded view of the filter device of Fig.

[0046] 1.

[0047] A filter device for filtering fluids is described below with reference to the figures. Fig. 1 shows the filter device in an assembled state in a longitudinal section. The longitudinal axis of the device is defined by a central geometric axis A, which lies in the section plane. Individual parts of the filter device are further illustrated in the exploded view of Fig. 6.

[0048] The filter device comprises a hollow cylindrical housing tube 2 in which a membrane insert 1 is arranged. The membrane insert 1 has a cylindrical outer shape adapted to the housing tube 2, with the membrane insert 1 resting along its peripheral surface against the inside of the housing tube 2. The housing tube 2 is made of glass-fiber-reinforced plastic. However, other plastics and materials are also conceivable.

[0049] The membrane insert 1 comprises a plurality of flat membranes 33 wound around a hollow cylindrical permeate tube 21. The permeate tube 21 extends coaxially with the housing tube 2 with respect to the axis A. The membranes 33 are arranged in the form of membrane cushions, as described, for example, in document EP 1 445 013 A1.

[0050] The individual membrane surfaces extend parallel to axis A and are stacked one above the other in a radial direction (see dashed lines in Fig. 1). The membranes 33 are designed to separate a fluid to be filtered, e.g., contaminated water, into the permeate that permeates the membranes 33 and the retained retentate. The membranes 33 engage sectionally in the permeate tube 21 to discharge the obtained permeate into the permeate tube 21.

[0051] When the filter device is used as intended, the fluid to be filtered is passed through a hollow cylindrical inlet tube 5 into the interior of the housing tube 2, where it is filtered by means of the membrane insert 1. The inlet tube 5 engages at its end in a first disc-shaped end element 3, which closes the housing tube 2 at a first opening side (see Fig. 1 and Fig. 2a).

[0052] The end element 3 has a decentrally arranged opening 27 into which the inlet pipe 5 is screwed in sections. A pipe axis B of the inlet pipe 5 extends in the axial direction parallel to the axis A of the housing pipe 2 and in the radial direction between the

[0053] Axis A and the wall of the housing tube 2 (see Fig. 1 ).

[0054] The end element 3 has a circumferential groove with a lip seal ring 11 to seal the end element 3 against the inside of the housing tube 2 (see Fig. 1). Additionally, the end element 3 is secured against falling out of the housing tube 2 by a retaining ring 16, also called a circlip (see Fig. 1 and Fig. 2a). The retaining ring 16 engages in an inner groove of the housing tube 2, which extends around the axis A, and is preloaded radially outward.

[0055] An annular flange 8 is arranged between the retaining ring 16 and the end element 3 (see Fig. 2a). The flange 8 is immediately adjacent to the end element 3 in the direction of the axis A and is designed to axially displace and preload the end element 3 towards the diaphragm insert 1. For this purpose, the flange 8 has a plurality of threaded holes into which a respective threaded pin 15 is screwed (see Fig. 1 and Fig. 2a). The threaded pins 15 act on the end element 3 depending on their screw-in depth in order to load it along the axis A in the direction of the diaphragm insert 1. Advantageously, the flange 8, as shown in Fig. 2a, has a plurality of threaded holes 15 distributed along the flange 8. The end element 3 can therefore be evenly loaded by successively screwing in the threaded pins 15 without becoming jammed or deformed in the housing tube 2.

[0056] The end element 3 has, on its side facing the membrane insert 1, a central circular recess 26 in which the permeate tube 21 is supported at one end (see Fig. 1 and Fig. 3b). The end of the permeate tube 21 engaging in the recess 26 is sealed by a sealing ring 13 so that the fluid does not pass unfiltered along the recess 26 into the permeate tube 21. The recess 26 has a bottom that limits the axial mobility of the permeate tube 21 (see Fig. 1).

[0057] The end element 3 acts upon the permeate tube 21 when subjected to pressure through the flange 8 or the threaded pins 15. This improves the reliable sealing of the permeate tube 21.

[0058] The housing tube 2 is closed at a second opening side, which is opposite the first opening side, with a second disc-shaped end element 4 (see Fig. 1). Like the first end element 3, the second end element 4 is sealed with a circumferential lip seal 11 on the inside of the housing tube 2 and secured against falling out of the housing tube 2 by a retaining ring 20.

[0059] An outlet pipe 6 for the retentate is screwed from the outside into a decentralized opening 25 of the end element 4 (see Fig. 1, Fig. 2b, and Fig. 3a). An axis C of the outlet pipe 6 extends parallel to the axis A and in the radial direction between the axis A and the wall of the housing tube 2. Furthermore, the axis C, as shown in Fig. 1, is arranged coaxially with the axis B of the inlet pipe 5. However, a non-coaxial arrangement of the axes is also conceivable.

[0060] The end element 4 has a central circular opening 24 (cf. Fig. 1 and Fig. 3a) which extends in the direction of the axis A through the end element 4 and is arranged coaxially to the axis A. A connecting piece 7 is screwed into the opening 24 from the outside and partially closes the opening 24. On the inside, one end of the permeate tube 21 engages in the opening 24, wherein the permeate tube 21 opens directly into a cylindrical cavity 36 of the connecting piece 7 (cf. Fig. 1). The permeate tube 21 and the connecting piece 7 together define a linear outflow channel for the permeate.

[0061] The end of the permeate tube 21 engaging the opening 24 is provided with a sealing ring 37. In addition, the portion of the connecting piece 7 engaging the opening 24 has a sealing ring 14 to seal the transition between the permeate tube 21 and the connecting piece 7 to the outside.

[0062] The connecting piece 7 is provided with a flange section 38, which defines an axial stop and, in particular, prevents the connecting piece 7 from being screwed too far into the opening 24. Mechanical overloading of the permeate tube 21 can thus be reliably prevented. The connecting piece 7 is equipped on the outside with a pipe section and an optionally screwed-on nut 10, which serves to connect a drain line (not shown) for the permeate.

[0063] The membrane insert 1 has, in the axial direction, between the membranes 33 and the end elements 3 and 4, an intermediate element 22, 23 which encloses the membranes 33 laterally, i.e., in the direction of the axis A and in the radial direction. The intermediate element 22 is shown in Fig. 4 in a side view of the axial end face (the axis A extends perpendicular to the plane of the paper in Fig. 4). It can be seen that the intermediate element 22 is designed in a lattice shape with a plurality of webs 32 which extend in a star shape in the radial direction around the permeate tube 21. Trapezoidal openings 31 are formed between the webs 32 and allow a fluid flow towards the membranes 33 (not shown in Fig. 4).

[0064] The permeate tube 21 has on its inner side a plurality of circumferentially spaced ribs 30 which extend parallel to the axis A. The inner side can alternatively be designed without ribs, i.e., in the manner of a smooth-walled hollow cylinder. However, in the region of the axis A, the permeate tube 21 does not have any bolt element or similar connecting elements that could extend axially through the permeate tube 21. In other words, the permeate tube 21 is free or hollow along its entire axial length, particularly when the filter device is used as intended. This enables a very high flow rate for the permeate.

[0065] A deflection disk 9 is arranged on the end element 3, which deflects the fluid flow through the inlet pipe 5 in a radial direction. This prevents the fluid flow along axis B from directly impinging on the membranes 33 (see Fig. 1, Fig. 5a and Fig. 5b). In other words, the fluid must first flow around the deflection disk 9, thereby protecting the membranes 33 from partial overloading by incoming fluid. The fluid can therefore be easily pumped through the inlet pipe 5 at high pressure in order to filter a high volume of fluid per unit time.

[0066] The deflection pulley 9 has two decentrally arranged holes 34 and 35 for the passage of a respective screw 19 in order to fasten the deflection pulley 9 directly to the end element 3. The holes 34, 35 are preferably provided, as shown in Fig. 5b and Fig. 5b, with a countersunk recess for receiving a countersunk head of the screw 19. In the fastened state, the side of the deflection pulley 9 facing the membrane insert 1 has a smooth surface (see Fig. 1).

[0067] The deflection disc 9 limits the fluid channel formed by the inlet pipe 5 in the direction of the axis B. However, a gap is formed between the deflection disc 9 and the end element 3, so that when the filter device is used as intended, the fluid is deflected in a substantially radial direction and flows to the membrane insert 1. The gap width is defined by a nut 17 and a washer 18 (see Fig. 1). However, the gap width can be adjusted as needed by using additional and / or different spacer elements.

[0068] The diameter D1 of the deflection disk 9 is adapted to the pipe diameter D2 of the inlet pipe 5 or the diameter of the opening 27 (see Fig. 5a and Fig. 3b). In particular, the diameter D1 is approximately twice the diameter D2. This ensures particularly good protection of the membranes 33. Furthermore, the deflection disk 9 forms a negligible flow resistance for the fluid.

[0069] The end element 3 has two threaded holes 28 and 29 on the side facing the membrane insert 1, which are arranged adjacent to the opening 27 and diametrically opposite each other with respect to the opening 27 (see Fig. 3b). The distance between the threaded holes 28, 29 corresponds to the distance between the holes 34, 35 of the deflection disc 9. The threaded holes 28, 29 serve for screwing in the screws 19 to fasten the deflection disc 9 to the end element 3.

[0070] The filter device enables exceptionally high filter performance through high fluid flows. For this purpose, the fluid can also be pumped into the inlet pipe 5 at high pressure. However, the use of a conventional clamping bolt, which connects the end elements 3 and 4 to one another through the permeate pipe 21 and preloads them inwards, i.e., towards the membrane insert 1, can be dispensed with. Consequently, the free outflow of the permeate through the permeate pipe 21 can be particularly well ensured. Furthermore, by omitting a bolt element, the permeate pipe 21 can advantageously be mounted in the end elements 3 and 4 as described, with the end elements 3 and 4 supporting one another via the permeate pipe 21. A further advantage of the described filter device lies in the deflection disk 9, which reliably prevents partial overloading of the membranes 33 due to high fluid flows.

[0071] LIST OF REFERENCE SYMBOLS

[0072] 1 membrane insert

[0073] 2 housing tube

[0074] 3 First end element

[0075] 4 Second end element

[0076] 5 Inlet pipe

[0077] 6 Outlet pipe

[0078] 7 connecting piece

[0079] 8 Flange

[0080] 9 Deflection pulley

[0081] 10 Mother

[0082] 11 Sealing ring

[0083] 12 Sealing ring

[0084] 13 Sealing ring

[0085] 14 Sealing ring

[0086] 15 threaded pin

[0087] 16 Retaining ring

[0088] 17 Mother

[0089] 18 Washer

[0090] 19 Screw

[0091] 20 retaining ring

[0092] 21 Permeate tube

[0093] 22 Intermediate element

[0094] 23 Intermediate element

[0095] 24 Opening

[0096] 25 Opening

[0097] 26 Deepening

[0098] 27 Opening

[0099] 28 Deepening

[0100] 29 depression 30 rib

[0101] 31 Opening

[0102] 32 bridge

[0103] 33 Membranes 34 Opening

[0104] 35 Opening

[0105] 36 cavity

[0106] 37 Sealing ring

[0107] 38 Flange section D1 diameter

[0108] D2 diameter

Claims

PATENT CLAIMS Filter device for filtering a fluid, comprising: a housing with an inlet (5) for the fluid, a permeate outlet (7) for a permeate separated from the fluid, and a retentate outlet (6) for a retentate separated from the fluid; a membrane insert (1) with a plurality of membranes (33) for the filtration of the fluid; wherein the housing has a cylindrical housing tube (2) which is provided with a first end element (3) at a first tube end and with a second end element (4) at a second tube end, wherein the membrane insert (1) is arranged between the first end element (3) and the second end element (4), and wherein the filter device does not have a bolt element connecting the first and second end elements (3, 4) to one another in order to prestress the first end element (3) and the second end element (4) in the direction of the membrane insert (1).Filter device according to claim 1, wherein the filter device does not have a bolt element which extends through the membrane insert (1) and the first and / or second end element (3, 4). Filter device according to claim 1 or 2, wherein the membrane insert (1) has a permeate tube (21) connected to the membranes (33) for receiving and discharging the permeate, wherein the permeate tube (21) extends centrally through the membrane insert (1) and the housing tube (2), in particular wherein the permeate tube (21) extends along a tube axis. (A) is free of a bolt element connecting the first and second end elements (3, 4) to one another. Filter device according to claim 3, wherein the permeate tube (21) bears against the first end element (3) with a first tube end, and / or wherein the permeate tube (21) bears against the second end element (4) with a second tube end. Filter device according to claim 4, wherein the first tube end of the permeate tube (21) partially engages in a central recess (26) of the first end element (3), which limits movement of the permeate tube (21) in the direction towards the first end element (3), in particular wherein the first tube end of the permeate tube (21) has a sealing element (13). Filter device according to claim 4 or 5, wherein the second tube end of the permeate tube (21) engages in sections into a central opening (24) of the second end element (4), in particular wherein the second tube end of the permeate tube (21) has a sealing element (37).Filter device according to claim 6, wherein the opening (24) has an internal thread into which a connecting piece (7) is screwed, which limits a movement of the permeate tube (21) in the direction towards the second end element (4), in particular wherein the connecting piece (7) has a sealing element (14). Filter device according to one of the preceding claims, wherein the permeate outlet is arranged centrally on the second end element (4). Filter device according to one of the preceding claims, wherein the inlet (5) is arranged decentrally on the first end element (3) and the retentate outlet (6) is arranged decentrally on the second end element (4), or wherein the inlet (5) is arranged decentrally on the second end element (4) and the retentate outlet (6) is arranged decentrally on the first end element (3). Filter device according to one of the preceding claims, wherein the first end element (3) and / or the second end element (4) are each secured against falling out of the housing tube (2) by a retaining ring (16, 20), and wherein the retaining ring (16, 20) releasably engages in a wall on an inner side of the housing tube (2).Filter device according to one of the preceding claims, wherein the filter device comprises a prestressing element (8) with at least one threaded hole, wherein the threaded hole on the prestressing element (8) is designed to receive a screw (15) for prestressing the first and / or second end element (3, 4) in the direction of the membrane insert (1). Filter device according to claim 11, wherein the prestressing element (8) is annular and has a plurality of threaded holes distributed on the prestressing element (8) for receiving a respective screw (15) for prestressing the respective end element (3) in the direction of the membrane insert (1). Filter device according to one of the preceding claims, wherein at least one deflection device is arranged between the membrane insert (1) and the inlet (5) and / or the retentate outlet (6), which deflection device is designed to deflect a fluid flow when the filter device is used as intended. Filter device according to claim 13, wherein the deflection device is designed as a disk element (9) that is preferably attached to the first or second end element (3, 4). Filter device according to one of the preceding claims, wherein the membrane insert (1) has a grid-shaped intermediate element (22, 23) for enclosing the membranes (33) on each of the sides of the membrane insert (1) facing the first and second end elements. Filter device according to one of the preceding claims, wherein at least some of the membranes (33) engage in sections of the permeate tube (21) and are wound around a permeate tube (21) of the membrane insert (1).Filter device according to one of the preceding claims, wherein the housing tube (2) is formed from a plastic. Filter device for filtering a fluid, comprising: a housing with an inlet (5) for the fluid, a permeate outlet (7) for a permeate separated from the fluid, and a retentate outlet (6) for a retentate separated from the fluid; a membrane insert (1) with a plurality of membranes (33) for. the filtration of the fluid; wherein a deflection device is arranged between the membrane insert (1) and the inlet (5) and / or the retentate outlet (6), which deflection device is designed to deflect a fluid flow when the filter device is used as intended. The filter device according to claim 18, wherein the deflection device is designed as a disc element (9).A filter device for filtering a fluid, comprising: a housing with an inlet (5) for the fluid, a permeate outlet (7) for a permeate separated from the fluid, and a retentate outlet (6) for a retentate separated from the fluid, wherein the housing has a cylindrical housing tube (2); a membrane insert (1) with a plurality of membranes (33) for the filtration of the fluid, wherein the membrane insert (1) has a permeate tube (21) connected to the membranes (33) for receiving and discharging the permeate, wherein the permeate tube (21) extends centrally through the membrane insert (1) and the housing tube (2), and wherein the permeate tube (21) is free along its tube axis (A).

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