Filter device

Abstract

Filter device for a liquid medium, in particular for water, comprising a hollow support body (6) with passages (14) for the liquid medium, wherein a first filter (8) is assigned to the hollow support body (6), wherein the first filter (8) is designed as a surface filter, wherein the filter device has a backwash device (11) in order to remove impurities from the first filter (8), characterized in that a second filter (9) is assigned to the support body (6), wherein the second filter (9) is designed as a depth filter and wherein the second filter has a porous body (17) made of a sintered plastic material.

Description

The invention relates to a filter device for a liquid medium, in particular for water, comprising a hollow support body with passages for the liquid medium, wherein a first filter is associated with the hollow support body, wherein the filter device has a back flushing device for removing contaminants from the first filter.The filtering of liquid media is performed to remove contaminants from the liquid medium. For example, it is already known to filter water of a domestic installation, for example in order to filter out particulate contaminants.US 2005 / 0115886 A1 describes a filter device for liquid media, which filter device comprises a plurality of filters.RU 174 088 U1 and US 2006 / 0049096 A1 disclose filter elements for drinking water which comprise activated carbon. With activated carbon, dissolved substances, such as chlorine, can also be removed from water.There is a need for filter devices that achieve good filtering action even for small particles. For this purpose, fine filters can be used which in turn have the disadvantage that they tend to clog relatively quickly. This then requires manual intervention, such as in particular replacement of the filter.The object of the invention is to specify a filter device which nevertheless has a long service life for small particles with a good filtering effect.The object is achieved with the features of claim 1. Accordingly, a filter device for a liquid medium, in particular for water, is provided, comprising a hollow support body with passages for the liquid medium, wherein a first filter is associated with the hollow support body, wherein the first filter is formed as a surface filter, wherein the filter device has a back flushing device for removing contaminants from the first filter, wherein a second filter is associated with the support body, wherein the second filter is formed as a depth filter and wherein the second filter has a porous body made of a sintered plastic material.With these measures it is possible to achieve multiple filtering of the liquid medium. For this purpose, the filter device provides a first filter, which is designed as a surface filter. With the surface filter, contaminants can be predominantly retained on the surface of the first filter. In addition, the second filter is provided, which is formed as a depth filter and has a porous body made of a sintered plastic material. The depth filter comprises a depth filter material, in which particles to be filtered can be retained in recesses of the depth filter material. With this multistage combination, particulate impurities, even those with a small size, can be separated from the liquid medium particularly effectively. In particular, particles which are larger than the pores of the respective filter are separated out when flowing through the first and second filters. With the combination according to the claims, the tendency of the filters to clog is considerably reduced. In addition, contaminants can be removed from the first filter with the backwash device without replacing the first filter, for example by the flow direction being temporarily reversed. With all these measures, the service life of the filter device can be considerably increased. This significantly reduces maintenance and maintenance costs. In addition, an undesired pressure drop at the filter is avoided. The claimed filter is particularly suitable for filtering water from a public water supply when entering a domestic installation. The porous body may preferably be made of plastic particles which are joined by sintering. The filter device is suitable for different liquid media. Although it is particularly suitable for water, it can also be used for other liquid media, such as dispersions.Preferred features of the filter device are described below, which promote the aforementioned advantages individually and jointly.A preferred embodiment of the invention provides that one of the first and second filters is arranged on the inside of the hollow support body and the other of the first and second filters is arranged on the outside of the hollow support body. Preferably, the first filter is arranged on the inner side and the second filter is arranged on the outer side of the hollow support body.According to the invention, it is preferred that the sintered thermoplastic has hydrophobic properties. This surprisingly contributes to a good filtering action. In particular, the thermoplastic may be non-polar.Preferably, the porous body comprises sintered thermoplastic, as in particular. Polyethylene. The material not only permits a good filtering action, but is also resistant to acids and alkalis. With polyethylene (PE), advantageous hydrophobic properties can also be obtained.The porous body is preferably open-pored.Preferably, the porous body has filter channels through which the liquid medium can pass through the porous body.According to the invention, it is preferred that the porous body has pores with a pore width between 5 μm and 100 μm. Particularly preferably, an average pore width of the porous body is between 10 μm and 30 μm. The average pore width can be determined by the bubble pressure test described below. Filter particles larger than the pore width are retained. The second filter thus makes it possible to filter particles of very small size.A further improvement provides that the porosity of the porous body is between 40% and 60%. This contributes to a good filtering effect at high filter lives. The porosity represents the ratio of the void volume and the total volume of the porous body.Preferably, the porous body has a density comprised between 1.6 g / cm 3 and 1.7 g / cm 3. This contributes to a good filtering effect at high filter lives. These densities can be achieved by sintering under pressure and / or the use of fillers.An advantageous embodiment of the invention provides that the porous body in the bubble pressure test has a bubble point at a pressure difference on the porous body of between 0.003 bar and 0.005 bar. It has been found that good filtering can then be achieved with a particularly long service life.The pressure difference at the bubble point can be determined by the bubble point test (bubble point test) according to the standard DIN EN 13443-2:2007-10. In this case, the filter material loaded with a liquid is pressurized with a gas from the one side and the pressure is increased until the gas displaces the liquid from the pores and passes through the filter material. This can be observed on bubbles formed. The pressure at which first bubbles form is referred to as the bubble point. From the pressure at the bubble point, the size of the largest pores can be deduced. With a further increase in the pressure, the open bubble point (open bubble point) can be determined, which can be regarded as a measure of the mean pore size. Preferably, the open bubble point is reached in the porous body at a pressure difference on the porous body between 0.005 bar and 0.02 bar (preferably more than 0.0075 bar and / or less than 0.015 bar).A preferred embodiment of the invention provides that the porous body has a surface which has a mean roughness Ra of more than 15 μm in at least a part of the surface. Preferably, the aforementioned average roughness Ra is more than 17 μm. Preferably, the part of the surface with the mentioned mean roughness Ra comprises at least 25% (particularly preferably at least 40%) of the surface of the porous body. Preferably, the average roughness Ra is less than 30 μm. The average roughness Ra can be determined according to the standard DIN EN ISO 21920-2:2021-12. The invention has recognized that a porous body having the aforementioned average roughness values can achieve a particularly good filtering effect with a long service life.According to the invention, it is preferred that the second filter is cylindrical and has a cylinder surface. The filter unit is preferably configured such that the liquid medium flows through the second filter in a direction perpendicular to the cylinder surface. Preferably, the second filter is tubular and open on both sides.The advantages of the invention are further promoted if the cylinder surface of the second filter has a material thickness that is between 1 mm and 5 mm. The material thickness is preferably more than 1.5 mm and / or less than 3 mm, particularly preferably less than 2.5 mm.A further preferred improvement provides that the filter unit is configured such that, during operation, the first filter is flowed through upstream of the second filter.According to the invention, it is preferred that the first filter has filter openings whose opening width is greater than 20 μm. In particular, the opening width of the filter openings of the first filter can be more than 25 μm. The opening width is preferably less than 50 μm, particularly preferably less than 35 μm. This contributes to good deposition and a long service life.Preferably, the first filter comprises a sheet of fibers, wherein passages are formed between the fibers. The passages form the filter openings. The fibers can be made in particular of plastic and / or metal. Stainless steel is particularly preferred as the metal material. The plastic material preferably comprises a polysulfone compound, such as in particular polyethersulfone (PES), which results in particularly good filter properties with a long service life in the described combination.Preferably, the fibers are arranged in a laid fiber fabric.A preferred embodiment provides that the fiber fabric has warp threads and weft threads which are arranged with a mesh width of more than 20 μm and less than 50 μm. The mesh width is preferably more than 25 μm and / or less than 35 μm. In this way, the passages forming the filter openings can be formed.The first and the second filter are preferably designed as particle filters. In this case, it can be provided in particular that the first filter is designed for coarse filtration and the second filter is designed for fine filtration.Preferably, the passages connect the interior of the support body to the outside of the support body. Preferably, the passages comprise elongated slots formed in the support body. Preferably, a maximum length of one of the slots is more than twice the shortest width of the slot.According to the invention, it can be provided that the support body comprises a cylindrical section, wherein the elongated slots are arranged in the cylindrical section. Preferably, the cylindrical portion of the support body and the second filter are arranged coaxially.Preferably, the first filter is arranged on the inside of the cylindrical portion and the second filter is arranged on the outside of the cylindrical portion. Preferably, an inner side of the support body forms a contact surface for the first filter.Preferably, the elongated slots have a longitudinal direction, the longitudinal direction extending in a circumferential direction of the cylindrical portion.Preferably, the elongated slots are arranged in rows. Preferably, each of the rows comprises more than 10 elongated slots. Preferably, between 4 and 15 rows of elongated slots are provided in the cylindrical portion.Preferably, continuous longitudinal webs are formed between the rows, which separate two rows of elongate slots in each case.The filter unit preferably has a feed line for the liquid medium to be filtered and a discharge line for the filtered liquid medium. Preferably, the filter unit further comprises a drain for the liquid medium obtained during the flushing. Preferably, the feed line and the discharge line are arranged coaxially in a single connection element.A preferred embodiment provides that the filter unit has a pressure reducer. The pressure reducer is preferably integrated into the filter unit. It is furthermore preferred if the pressure reducer has an actuator by means of which the pressure reduction can be adjusted.According to the invention, it is preferred that the filter unit has a housing which encloses the supporting body. Preferably, a control window is arranged in the housing, through which the second filter is visible.According to the invention, it is preferred that the filter device has a control which automatically activates the backwash device. For this purpose, the backwash device can comprise a solenoid valve which opens a flow channel in order to carry out the backwash.Furthermore, the backwash device may comprise a spring which is configured to close a flushing valve of the backwash device.The backwash device can be activated by the controller regularly after a time period stored in the controller has elapsed.It can advantageously be provided that the controller comprises a sensor device which detects a differential pressure at the first filter and / or at the second filter and activates the backwash device if the measured differential pressure is above a setpoint value for the differential pressure stored in the controller.The second filter is preferably designed as a tubular cartridge, which is arranged interchangeably in the filter device.Preferably, the second filter is arranged interchangeably on the supporting body.Further objectives, features, advantages and possible applications of the present invention will become apparent from the following description of exemplary embodiments with reference to the drawings. All features described and / or graphically depicted form the subject matter of the invention by themselves or in any meaningful combination, also independently of the summary in individual claims or their relations.The following are shown: FIG. 1 is a side view of a filter device; FIG. 2 : a perspective illustration of the filter device from FIG. 1, illustrated without a second filter; FIG. 3 : shows a schematic illustration of the supporting body of the filter device from FIG. 1, wherein the second filter is partially illustrated; FIG. 4 a : shows a perspective illustration of the second filter of the filter device from FIG. 1 ; FIG. 4 b : a side view of the second filter from FIG. 4 a; FIG. 4 c : a cross section along the line A-A through the second filter from FIG. 4 b; FIG. 4 d : shows an enlarged detail X of the second filter from FIG. 4 c; FIG. 5 : measurements for determining the bubble point on different porous bodies for the second filter; FIG. 6 : Measurements for determining the roughness on different porous bodies for the second filter; FIG. 6a shows a comparison of the quantity of treated water and the pore size, which results from the measurements; FIG. 7 shows a schematic illustration of a section of the first filter; FIG. 8 shows a section through the support body with the first and the second filter.FIG. 1 shows a filter device 1 for a liquid medium, in particular for water. The filter device 1 has a feed line 2 and a discharge line 3 for the liquid medium. The liquid medium enters the filter device 1 through the feed line 2, while the filtered liquid medium leaves the filter device through the discharge line 3. In the embodiment shown, the feed line 2 and the discharge line 3 are arranged coaxially in a combined connection element, wherein the discharge line 3 is arranged annularly around the feed line 2. However, feed line 2 and discharge line 3 can also be provided-unlike shown-in separate connections.The filter device 1 has a head 4. On its underside, a housing 5 is arranged, in which a supporting body 6 is arranged. The liquid-tight housing 5 has a control window 7 which makes the interior of the housing 5 visible.The first filter 8 and the second filter 9 are arranged on the support body 6 in the manner described in more detail below. In order to better illustrate the supporting body 6, the second filter 9 is not shown in FIG. 1.The filter device 1 has a back flushing device 11 which is arranged in the head 4. With the backwash device 11, the flow direction in the filter can be reversed in order to remove contaminants retained by the first and / or second filters 8, 9. The liquid with the impurities can then exit from the filter device 1 through the outlet 10.In the exemplary embodiment shown, the back-flushing device 11 has a solenoid valve 20 which opens a flow channel in order to carry out the back-flushing. The solenoid valve 20 has electrical connections 21, via which the solenoid valve 20 can be activated by the controller.The support body 6 has passages 14 for the liquid medium, which connect the interior of the support body 6 to the outside of the support body 6. In the exemplary embodiment shown, these are designed as elongate slots. In this case, a maximum length of the passages 14 formed as slots is in each case more than twice the shortest width of the respective slot. The elongated slots each have a longitudinal direction extending in the circumferential direction of the cylindrical portion 13.The support body 6 has a cylindrical section 13 in which the passages 14 are arranged.The first filter 8 described in more detail below is arranged on the inner side of the cylindrical section 13. The second filter 9 is disposed on the outside of the cylindrical portion 13. The first filter 8 abuts the inner side of the cylindrical section. In operation, the liquid medium first passes through the first filter 8, then through the passages 14 in the support body 6 and then through the second filter 9.The passages 14 are arranged in rows extending in the axial direction of the cylindrical portion 13. As shown, each of the rows 15 comprises more than ten elongated slots.Longitudinal webs 16 are formed between the rows 15, each separating two rows 15 of passages 14.The filter device 1 can have a controller which automatically actuates the backwash device.For this purpose, the controller can comprise a sensor device, not shown, which detects the differential pressure at the first filter 8 and / or at the second filter 9 and initiates a back flushing process if the measured differential pressure is above a setpoint value.FIG. 2 shows the filter device 1 from the side. While the filter device 1 has been shown in FIG. 1 without the second filter 9, the filter device 1 with the second filter 9 is shown in FIG. 2. The second filter 9 is disposed on the outside of the support body 6.FIG. 3 shows the support body 6 with the first filter 8 and the second filter 9. the second filter 9 encloses the cylindrical section 13 and is illustrated in the lower half of FIG. 3. In the upper half of Fig. 3, the second filter 2 is only partially shown to show the cylindrical portion 13 with the passages 14. The first filter 8 is disposed on the inner side of the cylindrical portion 13. The first filter 8 and the second filter 9 are flowed through from the inside to the outside during operation. As a result, the first filter 8 arranged on the inner side of the cylindrical section 13 can be supported on the supporting body 6.In operation, the flow passes through the first filter 8 before the second filter in the embodiment shown. In the filter device shown, the flow through the supporting body 6 is from the inside to the outside. The first filter 8 is arranged on the inner side of the supporting body 6.The first filter 8 has filter openings whose opening width is greater than the filter openings of the second filter. In this way, it can be achieved that the first filter 8 is designed for coarse filtration and the second filter 9 is designed for fine filtration of particles.In particular, the first filter can have filter openings whose opening width is between 20 and 50 μm, preferably 30 μm.In particular, the first filter 8 can comprise a sheet material with fibers, wherein passages are formed between the fibers. A preferred embodiment provides that the fibers of the sheet material are arranged in a fiber fabric. In this way, the first filter 8 can be designed as a surface filter, in which the particles are separated as impurities on the surface of the filter material of the first filter 8.The second filter 9 is formed as a depth filter and has a porous body made of a sintered plastic material. The porous body comprises filter channels through which the liquid medium can pass through the porous body. At the same time, particles larger than the filter channels are retained by the second filter 9. The second filter is designed as a depth filter, wherein the particles can be retained in the cross section of the filter material of the second filter 9. Due to the three-dimensional structure of the porous body 17, a good filtering effect is achieved with long service lives.The porous body 17 is made of sintered thermoplastic material and may in particular comprise polyethylene.The average pore width of the porous body 17 is preferably smaller than the average opening width of the first filter 8.FIGS. 4 ato d show an exemplary embodiment of the second filter 9 of the filter device 1; FIGS. 4 aand c show that the second filter 9 with the porous body 17 is cylindrical and has a cylindrical surface 18. The second filter 9 is configured to be flowed through by the liquid medium in a direction perpendicular to the cylinder surface. As illustrated, the second filter 9 may be tubular.The cylinder surface 18 of the second filter 9 has a material thickness S, which can be in particular between 1 mm and 3 mm.The porosity of the porous body 17 can be in particular between 40% and 60%. This means that between 40% and 60% of the porous body are voids, while the remaining volume is occupied by the plastic material.It has been found that a particularly good filtering effect is achieved with long service lives if the porous body 17 of the second filter 9 has pores which are designed such that certain values are achieved in the so-called bubble point test.FIG. 5 shows measurements according to the bubble point test on different porous bodies 17, which are each cylindrical and have a material thickness S of 2 mm. The measurements were carried out in accordance with DIN EN 13443-2:2007-10.The measurement results for three different filter materials are shown. On the left, the filter material L1 is shown, in the middle, the filter material L2 and on the right, the filter material L3. The respective bubble point is marked with B1, B2 and B3.The associated measurement results are shown in Table 1 below. Table 1 Table 1L1Δp [bar]D [μm]0,015217Bubble Point0,046Open Bubble PointL2Δp [bar]D [μm]0,007535Bubble Point0,03148Open Bubble PointL3Δp [bar]D [μm]0,00465Bubble Point0,0125Open Bubble PointFrom the bubble point or open bubble point determined, the associated pore size D (in micrometers) can be determined by the following formula:The aforementioned formula is also referred to as Poiseuille's law. "σ" is the surface tension of the liquid and is 7.3×10 -2 N / m for water at 15° Celsius. "θ" denotes the contact angle that the surface of a liquid drop forms with the surface of the filter material. "P" is the pressure (in Pascal).Good filter properties with a long service life are achieved in particular even when the average pore size is between 20 and 30 μm. The mean pore size can be determined from the pressure at the open bubble point.Furthermore, it has been shown that the roughness of the porous body 17 reliably gives indications as to whether a good filtering effect can be achieved with a long service life.FIG. 6 shows the measurement of the pressure loss on different filter materials, through which 2000 liters / h each containing 5 mg / l of an impurity have been passed. The measurements show that the filter materials initially have a quite constant pressure loss after a short running-in time. This increases sharply when the filter material of the second filter 9 is fully loaded. This is the time at which replacement of the filter material becomes necessary. In the case of the filter material L1, this point is reached already after somewhat more than half an hour. In the case of the filter materials V1, L2 and V2, an increase in the pressure loss takes place only after somewhat more than one hour. In the case of filter material V3, the increase takes place only after just two hours, while filter material L3 has a particularly long service life, the pressure loss only increasing after clearly over two hours.The roughness values of the various filter materials are shown in Table 2 below:Table 2 Table 2Filter material L111,90Filter material L213,78Filter material L319,07Filter material V9,42Filter material V28,15Filter material V332,75The above-mentioned measured values demonstrate that a particularly good filtering effect is achieved with long service lives if the mean roughness Ra of the surface of the porous body 17 is more than 15 μm, in particular more than 17 μm. It has thus been shown that somewhat higher values for the average roughness value Ra are more favorable than average roughness values Ra which are below the values mentioned.Fig. 6a shows an amount of treated water (Y axis) and a pore size of bubble point (X axis) obtained from the measurements. The amount of water treated is the total amount of water filtered by the respective filters L 1, L 2, and L 3 until the pressure loss limit is reached. The illustration shows that a pore size contributes to improving the service life of the filter material. On the other hand, however, the pore size cannot be increased arbitrarily without impairing the filtering effect.FIG. 7 schematically shows a section of the first filter 8, which comprises a sheet material 80 made of fibers 81, 82, between which filter openings 83 are formed. The fibers 81, 82 are arranged crosswise in a fiber fabric. The first filter constitutes a surface filter in which particles are deposited on the surface of the first filter 8 as contaminants.The filter openings 83 can have an opening width that is between 20 and 50 μm, preferably 30 μm.FIG. 8 shows a cross section through the supporting body 6. On the outside of the support body 6, the second support body 9 is arranged.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedUS 2005 / 0115886 A1

[0003] RU 174 088 U1

[0004] US 2006 / 0049096 A1

[0004] Cited Non-Patent LiteratureDIN EN 13443-2:2007-10

[0019] DIN EN ISO 21920-2:2021-12

[0020]

Claims

A filter device for a liquid medium, in particular for water, comprising a hollow support body (6) with passages (14) for the liquid medium, wherein a first filter (8) is associated with the hollow support body (6), wherein the first filter (8) is formed as a surface filter, wherein the filter device has a back flushing device (11) for removing contaminants from the first filter (8), characterized in that a second filter (9) is associated with the support body (6), wherein the second filter (9) is formed as a depth filter and wherein the second filter has a porous body (17) made of a sintered plastic material.A filter device according to claim 1, characterized in that one of the first and second filters (8, 9) is arranged on the inside of the hollow support body (6) and the other of the first and second filters (9, 8) is arranged on the outside of the hollow support body (6).Filter device according to claim 1 or 2, characterised in that an average pore width of the porous body (17) is between 10 μm and 30 μm.Filter device according to one of Claims 1 to 3, characterized in that the porosity of the porous body (17) is between 40% and 60%.Filter device according to one of claims 1 to 4, characterised in that the bubble pressure test is reached at a pressure difference on the porous body between 0.003 bar and 0.005 bar.Filter device according to one of Claims 1 to 5, characterized in that the porous body (17) has a surface which has a mean roughness Ra of more than 15 μm in at least part of the surface.Filter device according to one of Claims 1 to 6, characterized in that the second filter (9) is cylindrical and has a cylinder jacket surface.Filter device according to claim 7, characterised in that the cylinder surface of the second filter has a material thickness which is between 1 mm and 5 mm.Filter device according to one of Claims 1 to 8, characterized in that the filter unit is designed such that, during operation, the flow passes through the first filter (8) upstream of the second filter (9).Filter device according to one of Claims 1 to 9, characterized in that the first filter (8) has filter openings (83), the opening width of which is greater than 20 μm.Filter device according to one of Claims 1 to 10, characterized in that the first filter (8) comprises a sheet material with fibres (81, 82), passages being formed between the fibres, said passages forming the filter openings (83).Filter device according to one of Claims 1 to 11, characterized in that the first filter (8) is designed for coarse filtration and the second filter is designed for fine filtration (9).A filter device according to any one of claims 1 to 12, characterized in that the support body (6) comprises a cylindrical portion, the passages (14) in the cylindrical portion being arranged in rows.Filter device according to claim 13, characterised in that the first filter (8) is arranged on the inside of the cylindrical section and that the second filter (9) is arranged on the outside of the cylindrical section.Filter device according to one of Claims 1 to 14, characterized in that the filter unit has a pressure reducer.The filter device according to any one of claims 1 to 15, characterized in that the filter device has a control which automatically actuates the backwash device.Filter device according to claim 16, characterised in that the controller comprises a sensor device which detects the differential pressure at the first filter and / or at the second filter and initiates a back flushing process if the measured differential pressure is above a setpoint value for a differential pressure stored in the controller.

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