Filter element and filter device

Abstract

A filter element (3, 3a, 3b) having a tubular shape with openings at opposite ends in a longitudinal direction thereof and configured to filter fluid by allowing the fluid to flow through the filter element from the inside to the outside, and to be backwashed by allowing the fluid to flow through the filter element from the outside to the inside, the filter element comprising: a filter member (31) extending over a predetermined length and having openings at opposite ends; a first end portion (32) connected to a first end of the filter portion (31) to support the filter portion (31) and having an opening (37) allowing fluid to flow therethrough; a second end portion (33) connected to a second end of the filter portion (31) so as to support the filter portion (31) and having an opening (37) allowing the fluid to flow therethrough; and a trapped object removing device (34) provided in an interior of the filter part (31) and configured to be movable by a flow of the fluid in an axial direction of the filter part (31) generated during filtration or backwashing in the interior of the filter part (31) between the first and second end parts (32, 33) along a guide shaft (35) whose opposite ends are fixed to the first end part (32) and the second end part (33), while an outer periphery of the trapped object removing device (34) slides into contact with an inner periphery of the filter part (31) so as to remove an object trapped by the filter part (31), wherein a first stop (38b) stopping a movement of the retained object removal device (34) toward the first end part (32) is mounted on one side of the first end part (32), and a second stop (38a) stopping a movement of the retained object removal device (34) toward the second end part (33) is mounted on one side of the second end part (33), wherein a flow rate limiting means for limiting a flow rate of the fluid through the second end part (33) is provided at the second end of the filter part (31), and wherein the opening (37) of the second end part (33) and a mounting part (34a) of the trapped object remover (34) form the flow rate limiting means, and when the trapped object remover (34) abuts the second stopper (38a) and an end face (34c) of the mounting part (34a) of the trapped object remover (34) is located near the openings (37), the fluid flow through the openings (37) of the second end part (33) is limited to a flow rate corresponding to a size of a gap (39) between the openings (37) of the second end part (33) and the end face (34c) of the mounting part (34a) of the trapped object remover (34).

Description

Technical area

[0001] The present invention relates to a filter device including tubular filter elements for inside-outside filtration, each having openings at opposite ends in its longitudinal direction, and which can be backwashed by causing a fluid to flow through the filter elements in directions reverse to those for filtration to remove objects that have been trapped and adhered to the filter elements.More particularly, the present invention relates to a filter element that filters a fluid and is backwashable by a fluid supplied thereto from the opposite end openings of the filter element, wherein trapped objects are removed by trapped object removing means provided in the filter element and reliably movable in the axial direction thereof by the fluid flow in the axial direction generated during filtration or backwashing, and to a filter device using such filter elements. Background of the technology

[0002] Conventionally, various filter devices are used for filtering water such as seawater, lake water, river water, drinking water, or wastewater, for filtering liquids widely used in industries such as cooling water or process fluids for any various equipment, and for filtering feed gases or the like used in chemical plants or the like to trap and remove substances such as microparticles and dust contained in such a fluid to be filtered.

[0003] When the filter device performs filtration for long periods of time, solids and / or gel-like substances such as dust that have been trapped by the filter elements accumulate in the filter elements. This increases the resistance of the filter media to the flow of the fluid and ultimately results in the filter device being barely able to filter the fluid. To address this problem, the filtration performance of the filter elements is restored, for example, by regularly performing a process called "backwashing," which is a process that causes a fluid to flow through the filter elements in directions opposite to those used for filtration to remove objects that have been trapped and adhered to the filter elements.

[0004] This backwashing process is effective, but sometimes fails to completely remove the objects trapped and adhering to the filter elements, so some objects may remain trapped in the filter elements after backwashing. Even repeating the backwashing process may not prevent an increase in the resistance of the filter media to fluid flow, which ultimately results in the filter device being barely able to filter the fluid.Particularly when gel-like substances such as dust and / or dust coated with highly adhesive materials are strongly adhered to the surfaces of the filter elements, as is the case with industrial fluid filtration, it is difficult to restore the filtering performance of the filter elements simply by backwashing, which causes a fluid to flow through the filter elements in directions opposite to those used for filtration. This is especially true for a filter device that includes filter elements with a mesh size of less than 200 µm.

[0005] The same largely applies to filtration performed in a situation where substances such as fibrous dust have become trapped in the filter elements. Such a filtration situation is particularly likely to occur when the fluid to be filtered contains microorganisms, such as when filtering water such as seawater, lake water, river water, drinking water, or wastewater. When filtering ballast water (seawater) in a ship's ballast tank, for example, the filter device traps a large amount of algae contained in the seawater. As a result, fibrous substances, including filamentous algae and / or cellulose substances, become trapped in the filter elements and cannot be easily removed.

[0006] To address the above, a filter device capable of restoring the filtering performance of the filter elements has been proposed. Examples of filter devices of this type include an inlet channel for the flow to be filtered, an outlet channel for the filtered flow, a number of parallel filter elements, and at least one flushing mechanism. The filter elements are open at both ends, into which the flow to be filtered can be directed, allowing infiltration through the element from the element. The flushing mechanism is alternately connected to the different ends of the elements at both ends of the filter elements and forms a discharge channel for backwashing the elements, which is generated by the pressure of the filtered flow.Each of the filter elements is divided between its ends so that the flushing mechanism connected to the end of the element only produces backwash for a part of the length of the element (see, for example, Patent Document 1).

[0007] In order to address the above problems, the present inventors have further proposed a filter device including, inside the filter element, a trapped object removing device configured to be movable in the axial direction of the filter element by the fluid flow generated during filtration or backwashing while sliding its outer peripheral part into contact with the inner periphery of the filter element so as to remove trapped objects (see Patent Document 2).

[0008] Further examples relating to filter devices are described in the documents DE 20 2005 018 853 U1, DE 40 30 084 A1, DE 41 28 210 C2, DE 10 2011 007 003 A1, DE 11 2013 000 673 T5, WO 2005 / 023 394A2, JP S49 - 17 566 A, JP S63 - 185 411 U, JP S61 - 146 312 A, JP 3 090 022 U, JP H02 - 307 503 A, US 3 623 607 A, US 2008 / 0282 905 A1, US 3 850 802 A and EP 1 225 963 B1 disclosed. List of reference documentsPatent specifications Patent document 1: JP 2003 - 509 200 A Patent document 2: JP 2013 - 91 046 A Overview of the inventionProblems to be solved by the invention

[0009] The filter device disclosed in Patent Document 1 performs backwashing to release objects trapped and adhered to the filter elements at different times from opposite end openings of each of the filter elements. However, these filter devices perform backwashing simply by using the pressure of the fluid flow. However, it is difficult to restore the filtering performance of the filter elements by backwashing simply by using the pressure of the fluid flow when fibrous substances such as dust are entangled in the filter elements or when such entangled fibrous substances are coated with highly sticky or adhesive materials.

[0010] In contrast, the filter device disclosed in Patent Document 2 includes the trapped object remover configured to be movable within the filter element in the axial direction thereof by the fluid flow generated during filtration or backwashing, while sliding its outer peripheral portion into contact with the inner periphery of the filter element, thereby removing trapped objects. However, since the filter element has a closed end opposite its inlet end, the axial flow rate near the closed end tends to be insufficient, and this axial flow may not be able to move the trapped object remover toward the closed end.

[0011] Furthermore, Patent Documents 1 and 2 disclose a backwashing method for backwashing the filter elements by connecting a backwash line to the filter elements. In the filter device employing this backwashing method, the backwash line remains connected to one or more of the filter elements even while the filter device performs filtration. This prevents unfiltered fluid from being introduced into the filter elements connected to the backwash line, thus preventing these filter elements from filtering the fluid.

[0012] To address the above problems, the present invention provides a filter element that filters a fluid and is backwashable by a fluid supplied thereto from opposite end openings of the filter element, wherein the trapped objects are removed by a trapped object removing device that is provided in the filter element and is reliably movable in the axial direction thereof by the fluid flow in the axial direction generated during filtration or backwashing, and a filter device using such filter elements. Means to solve the problems

[0013] The present invention solving the above problems is defined in independent claims 1, 6 and 7. Preferred embodiments are defined in the subclaims. Effects of the invention

[0014] The filter element according to the present invention includes a filter part, a first end part having an opening and connected to a first end of the filter part, a second end part having an opening and connected to a second end of the filter part, and a trapped object removing device provided inside the filter part. Here, a flow rate limiting means is provided at the second end of the filter part. Accordingly, the filter element is capable of limiting the flow rate of the fluid through the second end part. This allows the fluid to flow through the second end part in an appropriate amount and thus enables the trapped object removing device in the filter element to reliably move to an abutting position on the second end part side.When the filter element is used in the filter device according to the present invention, the trapped object removing means can be moved in the interior of the filter part between the first and second end parts by a flow of the fluid in an axial direction of the filter element, which is generated during filtration or backwashing, to reliably remove an object trapped by the filter part.

[0015] A filter device according to the present invention includes a housing, a first partition wall separating the interior of the housing into an unfiltered fluid chamber and a filtered fluid chamber, filter elements provided in parallel with each other in the filtered fluid chamber, with first ends communicating with the unfiltered fluid chamber, a second partition wall isolating a portion of the filtered fluid chamber from the rest thereof to define a communication chamber with which second ends of the filter elements communicate, a backwash line connected to one or more of the filter elements for backwashing the filter elements, and a backwash fluid discharge line that discharges a trapped object removed by backwashing to the outside. Here, each of the filter elements is the above-mentioned filter element according to the present invention.Accordingly, the filter device can allow the fluid to flow through the second ends while limiting the flow rate of the fluid through the second ends of the filter elements to an appropriate amount. This enables the trapped object removers in the filter elements to reliably move toward the second ends. In this way, the filter device allows each of the trapped object removers in the filter elements to be moved inside the corresponding filter part between the first and second ends by the fluid flow in an axial direction of the filter element generated during filtration or backwashing, so that objects trapped by the filter part are reliably removed, and can discharge the trapped and removed objects through the backwash line and the backwash fluid discharge line.This allows the filter device to provide improved backwashing efficiency. Furthermore, since the fluid can also flow through the connecting chamber into the filter element whose first end is connected to the backwash line, filtration can also be performed in such a filter element during the filtering process, which means that the utilization efficiency of the filter elements can be improved. Furthermore, the backwash line only needs to be provided at the first ends of the filter elements. This allows the filter device to have a simpler structure than the filter device equipped with two backwash lines at opposite ends of the filter elements, thus enabling it to be manufactured at a lower cost.

[0016] Another filter device according to the present invention includes a housing, a first partition wall separating the interior of the housing into an unfiltered fluid chamber and a filtered fluid chamber, filter elements provided in parallel with each other in the filtered fluid chamber, with first ends communicating with the unfiltered fluid chamber, a connecting line connected to second ends of the filter elements such that the second ends communicate with each other while being isolated from the filtered fluid chamber, a backwash line connected to one or more of the filter elements for backwashing the filter elements, and a backwash fluid discharge line for discharging a trapped object removed by backwashing to the outside. Here, each of the filter elements is the above-mentioned filter element according to the present invention.Accordingly, the filter device can allow the fluid to flow through the second ends of the filter elements while limiting the flow rate of the fluid through the second ends to an appropriate amount. This enables the trapped object removal devices in the filter elements to reliably move toward the second ends. In this way, the filter device allows each of the trapped object removal devices in the filter elements to be moved inside the corresponding filter part between the first and second ends while the filter part is backwashed, so that objects trapped by the filter part are reliably removed, and can discharge the trapped and removed objects through the backwash line and the backwash fluid discharge line. Thereby, the filter device can provide an improved backwash effect.Furthermore, since the fluid can flow through the connecting line into the filter element whose first end is connected to the backwash line, filtration can also be performed in such a filter element during the filtering process, which means that the utilization efficiency of the filter elements can be improved. Furthermore, the backwash line only needs to be provided at the first ends of the filter elements. This allows the filter device to have a simpler structure than the filter device equipped with two backwash lines at opposite ends of the filter elements, thus enabling it to be manufactured at a lower cost. Short description of the drawings Fig. 1 is a front cross-sectional view of a first embodiment of the filter device according to the present invention. Fig. 2 is a cross-sectional view taken along a line CC of Fig. 1. Fig. 3 is a front cross-sectional view of a first embodiment of the filter element according to the present invention. Fig. 4A and Fig. 4B are a top view and a bottom view of the Fig. 3 shown filter element. Fig. Figure 5 is a front cross-sectional view of the filter element not connected to the backwash line while the filter device performs filtration. Fig. 6 is a front cross-sectional view of the filter element connected to the backwash line while the filter device performs filtration. Fig. 7 is a front cross-sectional view of the filter element in Fig. 5, which has just been connected to the backwash line and for which backwashing has just begun. Fig. 8 is a front cross-sectional view of the filter element immediately after the Fig. 7 described situation. Fig. 9 is a front cross-sectional view of the filter element for which backwashing has just been completed and into which the fluid in the unfiltered fluid chamber begins to flow. Fig. Fig. 10 is a front cross-sectional view of the filter element 3 in which the trapped object removing device has its highest section after the Fig. The situation described in Figure 9 is reached. Fig. 11A and Fig. 11B are cross-sectional views of essential parts of a second embodiment of the filter element according to the present invention, illustrating an upper end portion during filtration and a lower end portion during backwashing, respectively. Fig. 12 is a cross-sectional view of an essential part of a third embodiment of the filter element according to the present invention. Fig. 13 is a front cross-sectional view of the filter device performing filtration. Fig. 14 is a front cross-sectional view of the filter device performing backwashing. Fig. 15 is a front cross-sectional view of a second embodiment of the filter device according to the present invention. Fig. 16 is a cross-sectional view taken along a line DD of Fig. 15. Method for carrying out the invention

[0017] Embodiments of the present invention will now be described with reference to the accompanying drawings.

[0018] Fig. 1 is a front cross-sectional view of a first embodiment of the filter device according to the present invention. Fig. 2 is a cross-sectional view taken along a line CC of Fig. 1. The filter device is used for filtering water such as seawater (such as ballast water in a ship), seawater, river water, drinking water, or wastewater, for filtering liquids commonly used in industries, such as cooling water or process fluids for any of a variety of devices, and also for filtering feed gases or the like used in chemical plants or the like. The filter device traps and removes substances such as microparticles and dust contained in such a fluid to be filtered. The filter device includes a housing 1, a first partition 2, filter elements 3, a second partition 4, a backwash line 5, and a backwash fluid discharge line 6, as shown in Fig. 1 shown.

[0019] The housing 1 is an outer shell of the filter device and is formed in a shape such as a tubular shape (such as a cylindrical shape) with a top cover and a closed bottom, or a rectangular parallelepiped shape. The housing 1 has, for example, a fluid inlet 7 at the lower end portion of the side wall of the housing 1 and a fluid outlet 8 in an upper portion of the side wall. The fluid inlet 7 allows fluid to flow in from the outside to the inside, as indicated by an arrow A. The fluid outlet 8 allows fluid that has been filtered in the filter device to flow out, as indicated by an arrow B.The housing 1 is formed of a material such as a metal or a synthetic resin and may have any shape and size that are appropriately determined in accordance with conditions such as the intended use of the filter device, the type and volume of the liquid, gas or the like to be filtered, and the installation location.

[0020] The first partition wall 2 is provided horizontally at a lower position in the housing 1. The first partition wall 2 separates the interior of the housing 1 into an unfiltered fluid chamber 9 and a filtered fluid chamber 10. The unfiltered fluid chamber 9 is filled with unfiltered fluid and communicates with the fluid inlet 7. The filtered fluid chamber 10 is filled with a filtered fluid and communicates with the fluid outlet 8. A plurality of through holes 11 are formed in the first partition wall 2, each for fitting and holding a first end (lower end) of the corresponding filter element 3.

[0021] The plurality of filter elements 3 are provided vertically parallel to each other on the upper side of the first partition wall 2 in the filtered fluid chamber 10. The lower end of each of the filter elements 3 is fitted and held by the corresponding through-hole 11, with the interior of the filter element 3 communicating with the unfiltered fluid chamber 9. Each filter element 3 is formed in a tubular shape, for example, cylindrical, which allows fluid to be filtered to flow therethrough from the inside to the outside to trap and filter out solids and / or gel-like substances such as dust contained in the fluid, and which is backwashed by allowing the fluid to flow therethrough from the outside to the inside. Fig. Figure 2 shows an example in which eight filter elements 3 are arranged in a single circle. However, the number of filter elements 3 is not limited to eight, but can be any number. Furthermore, the filter elements 3 can be arranged in two or more concentric circles.

[0022] The second partition wall 4 is provided horizontally parallel to the first partition wall 2 so as to be located on the second end (upper end) side of the filter elements 3. The second partition wall 4 isolates an upper portion of the filtered fluid chamber 10 from the rest thereof to define a communication chamber 13. The communication chamber 13 allows fluid to flow between the filter elements 3. The second partition wall 4 has a plurality of through-holes 12 each for fitting and holding the second end (upper end) of the corresponding filter element 3.

[0023] The connecting chamber 13 is formed between the top cover of the housing 1 and the second partition wall 4. The connecting chamber 13, through which the filter elements 3 communicate with each other at their upper ends, allows the fluid to flow between the filter elements 3. The connecting chamber 13 is isolated from the unfiltered fluid chamber 9, the filtered fluid chamber 10, and the backwash line 5. The connecting chamber 13 does not need to have a particularly large capacity, but only needs to have a capacity large enough to allow the fluid to flow smoothly therethrough.

[0024] The backwash line 5 is arranged under the first partition wall 2. The backwash line 5 has a base end section 14 and extends radially from there to the left in Fig. 1 to be connected to any one of the filter elements 3 through the corresponding through hole 11 formed in the first partition wall 2. Fig. 1 illustrates an example in which the filter device includes a single backwash line 5. However, the filter device may alternatively include two or more backwash lines 5 to connect two or more filter elements 3 simultaneously.

[0025] A shaft 15 is attached to the base end portion 14 of the backwash line 5. The shaft 15 extends upward along the center axis of the base end portion 14 so as to protrude outward from the housing 1. A gear motor 16 is provided at the protruding end of the shaft 15 to drive the shaft 15 for rotation. When driven for rotation, the gear motor 16 rotates the shaft 15, for example, in the clockwise direction indicated by an arrow P, as shown in FIG. Fig. 2. The backwash line 5 is connected successively to the lower end openings of the plurality of filter elements 3, which are arranged, for example, in a circle.

[0026] As in Fig. 1, the backwash fluid discharge line 6 is connected to the discharge side of the backwash line 5, that is, to the base end portion 14 of the backwash line 5. The backwash fluid discharge line 6 is formed as a straight pipe extending in a radial direction of the housing 1. The backwash fluid discharge line 6 discharges trapped objects, which are removed while backwashing the filter elements 3, to the outside of the housing 1. At a base end portion 17 of the backwash fluid discharge line 6, a coupling port portion 18 is provided so as to open upward. The base end portion 14 of the backwash line 5 is rotatably connected to the coupling port portion 18. A discharge port 20 at the distal end of the backwash fluid discharge line 6 protrudes out of the housing 1.

[0027] The backwash fluid discharge line 6 is fixed to the housing 1. A bearing mechanism and a sealing mechanism are provided at the connection interface between the coupling connection portion 18 of the base end portion 17 and the base end portion 14 of the backwash line 5. The bearing mechanism, such as a bearing, supports the backwash line 5, and the sealing mechanism prevents discharged objects from mixing with the unfiltered fluid. When rotationally driven, the gear motor 16 rotates the backwash line 5 using the coupling connection portion 18 as a rotation support, thereby maintaining a seal between the coupling connection portion 18 and the base end portion 14 of the backwash line 5.

[0028] A valve (not shown) is connected to the discharge side of the discharge port 20 of the backwash fluid discharge line 6. The valve opens or closes the backwash fluid discharge system, which includes the backwash line 5 and the backwash fluid discharge line 6. The valve is open while the filter device is backwashing and closed while the filter device is filtration. The pressure on the discharge side of the valve is lower than that in the fluid outlet 8, for example, atmospheric pressure.

[0029] The filter elements 3 according to the present invention are each designed as follows.

[0030] Fig. 3, Fig. 4A and Fig. 4B are a front cross-sectional view, a top view, and a bottom view, respectively, of a first embodiment of the filter element 3 according to the present invention. The filter element 3 is used to filter the fluid to be filtered. The filter element 3 includes a filter part 31, a first end part 32, a second end part 33, and a trapped object remover 34. In the filter device according to the present invention, the first end part 32 is arranged at the first end (lower end) of the filter element 3, whereas the second end part 33 is arranged at the second end (upper end) of the filter element 3.

[0031] The filter part 31, i.e., a part for filtering the fluid, is tubular, for example, cylindrical. The filter part 31 can be any type as long as it includes multi-layer filter media in which the filter media with the finest mesh is located in the innermost layer. Examples of the filter part 31 include a cylindrical sintered mesh filter, a cylindrical notched wire filter, and a cylindrical profiled wire filter. The cylindrical sintered mesh filter can be one formed by sintering multiple metal mesh layers to increase their dimensional stability and then forming these sintered mesh layers into a cylindrical shape.When the sintered fabric filter is used, the mesh size of the innermost layer can be appropriately selected from the range of 10 to 200 µm, and the mesh size of the other outer layers only needs to be coarser than that of the innermost layer and can be appropriately selected from the range of 200 to 5,000 µm. In this case, the properties of a reinforcing fabric and a protective fabric in the layers other than the innermost layer affect the strength of the filter part 31. Accordingly, the number, mesh size, and wire diameter of these outer layers are appropriately selected so that the filter element 31 can provide the required strength. The fabric of the filter part 31 can have a plain weave, a twill weave, a satin weave, a dutch weave, a twill weave, and / or the like.Alternatively, the filter member 31 may be formed by first arranging cylindrical perforated tubes having numerous square holes or a reinforcing member comprising multiple axially extending thin rods arranged side by side around a metal mesh in the innermost layer, and then sintering the resulting layers.

[0032] For example, when used for filtering ballast seawater, the filter part 31 preferably includes a fine mesh and a coarse metal mesh joined together. The fine mesh determines the filtration fineness of the filter part 31. The coarse metal mesh imparts strength to the filter part 31 against an inside-out force generated during filtration and an outside-in force generated during backwashing. More preferably, the filter part for filtering ballast seawater should further include a metal mesh having an intermediate mesh size between the coarse metal mesh and the fine mesh, and be formed by sintering the layers in which the intermediate metal mesh is disposed between the coarse metal mesh and the fine mesh.The suitable mesh size for the fine mesh is 400 to 100 mesh (63.5 to 254 µm), the suitable mesh size for the medium metal mesh is 100 to 20 mesh (254 to 1,270 µm), and the suitable mesh size for the strength metal mesh is 50 to 5 mesh (508 to 5,080 µm).

[0033] The characteristics such as the shape and size of the filter parts 31 can be appropriately determined in accordance with conditions such as the intended use and filtering performance of the filter device, the size of the housing 1, and the type of fluid to be filtered. For example, when the filter part 31 is formed in a cylindrical shape, it may have an outer diameter appropriately selected from the range of 300 to 1,000 µm and a length appropriately selected from the range of 5,000 mm or less.

[0034] The first end portion 32 is connected to the first end (lower end) of the filter portion 31. The first end portion 32 is cylindrical and reinforces the first end opening of the filter portion 31 and prevents the corresponding trapped object removal device 34 from falling off. The first end portion 32 also forms an end portion at the unfiltered fluid inlet of the filter element 3. As shown in Fig. 4B, in this embodiment, a web 36 is attached to the first end portion 32 so as to span the circular opening of the first end portion 32 and extend through the center thereof. The web 36 has a center hole to allow a guide shaft 35, described below, to be inserted therethrough.

[0035] The second end part 33 is connected to the second end (upper end), which is an end opposite the first end located at the unfiltered fluid inlet of the filter part 31. The second end part 33 is in the form of a cylindrical cover with predetermined openings. The second end part 33 reinforces the second end opening of the filter part 31 and prevents the corresponding trapped object removal device 34 from falling off. In a plan view, the second end part 33 is a closed circular cover, as shown in Fig. 4A, and it has a center hole and four openings 37 surrounding the center hole. The center hole allows the guide shaft 35, described below, to be inserted therethrough. The openings 37 form the flow-rate limiting means, which will be described below.

[0036] The trapped object remover 34 is provided inside the filter part 31. When an axial fluid flow is generated in any of the filter parts 31 during filtration or backwashing, the fluid flow moves the trapped object remover 34 between the first and second end parts 32 and 33 in the filter part 31. Thereby, the outer periphery of each trapped object remover 4 slides into contact with the inner periphery of the corresponding filter part 31 and removes trapped objects from the filter part 31. With a view to stabilizing the movement of the trapped object remover 34, it is desirable to make the trapped object remover 34 movable in the axial direction of the filter part 31.To achieve this, it is desirable that the trapped object removing device 34 has a through hole at its central axis and that the guide shaft 35, the opposite ends of which are fixed to the first and second end portions 32 and 33, is inserted through the through hole.

[0037] The removal device 34 for captured objects is a removal brush, such as in Fig. 3 shown.

[0038] The removal brush 34 is formed by inserting bristles 34b onto the outer periphery of a brush main body 34a and moves up and down in the corresponding filter element 3 along its guide shaft 35. A hole is formed in the center of the brush main body 34a through which the guide shaft 35 is inserted. The brush main body 34a is formed as an annular disk having a predetermined thickness and an outer diameter smaller than the inner diameter of the filter part 31. The bristles 34b are inserted in an annular pattern onto the outer periphery of the brush main body 34a so that their tips slide into contact with the inner periphery of the corresponding filter part 31. The bristles 34b must be at least long enough to allow their tips to come into contact with the inner periphery of the filter part 31 with a certain pressure.

[0039] The bristles 34b can be formed from any material commonly used as brush bristles, for example, natural or synthetic fibers or metal wires such as steel, copper, or brass wires. The bristles 34b are flexible enough to be bent by the pressure of the fluid flow in the filter elements 3. When the bristles 34b are bent by the fluid pressure, the bending creates a gap between the tips of the bristles 34b and the inner periphery of the filter part 31, allowing the fluid to flow through the gap.

[0040] As in Fig. 3, in each of the filter elements 3, stoppers 38a and 38b are mounted at the upper and lower ends of the guide shaft 35. The stoppers 38a and 38b stop the movement of the corresponding trapped object removing device 34 (removal brush) at the upper and lower ends of the filter element 3 when the trapped object removing device 34 moves up and down in the filter element 3 along the guide shaft 35. The stoppers 38a and 38b are preferably each formed of a shock-absorbing material such as rubber or a spring.

[0041] In the present invention, the flow rate limiting means is provided at the second end (upper end) of each of the filter parts 31. The flow rate limiting means limits the flow rate of a fluid flowing through the second end part 33. Allowing a certain amount of fluid to flow through the second end part 33 offers the following advantages. a) At the start of backwashing of the filter element 3, the trapped object removing device 34 is allowed to move smoothly from the abutting position on the second end part 33 side to the first end part 32. b) At the end of backwashing the filter element 3, the trapped object removing device 34 is allowed to move smoothly to the abutting position on the second end part 33 side. c) During filtration, the filter element 3, which is connected to the backwash line 5 and thus not supplied with fluid from the unfiltered fluid chamber 9, is enabled to filter the fluid by allowing the fluid to flow thereinto through the connecting chamber 13.

[0042] In contrast, limiting the flow rate by the second end part 33 offers the following advantages.

[0043] d) The decrease in backwash efficiency due to excessive inflow is prevented. If the fluid were to flow through the connecting chamber 13 at an excessively large flow rate into the filter element 3 being backwashed, a backpressure difference between the inside of the filter part 31 and the outside would be reduced, so that backwash efficiency would decrease.

[0044] The openings 37 formed in the second end part 33, together with the mounting part 34a of the retained object removal device 34, form Fig. 3 shows the flow rate limiting means according to this embodiment. When moved to remain at the abutting position on the second end part 33 side, the mounting part 34a of the trapped object removing device 34 limits the fluid flow channels through the openings 37. In the Fig. 3, the trapped object remover 34 does not close the openings 37 with the end face 34c of its mounting portion 34a when it is located away from the stopper 38a on the second end portion 33 side. In this way, the openings 37 allow fluid to flow therethrough in an amount corresponding to the opening area of the openings 37. In contrast, when the trapped object remover 34 abuts the stopper 38a on the second end portion 33 side, the end face 34c of the mounting portion 34a of the trapped object remover 34 is located near the openings 37 and thus limits the fluid flow through the second end portion 33 to an amount corresponding to the size of a gap 39 between the openings 37 and the end face 34c.

[0045] In the above description, while the trapped object remover 34 abuts against the stopper 38a, the fluid flow through the second end portion 33 is limited to a flow rate corresponding to the size of the gap 39 between the openings 37 and the end surface 34c of the mounting portion 34a located near the openings 37. However, the first embodiment of the present invention is not limited to this. Alternatively, the end surface 34c of the mounting portion 34a may not completely seal the openings 37 but may leave some gaps therebetween while the trapped object remover 34 abuts against the stopper 38a. In this case, the fluid flow through the second end portion 33 is limited to a flow rate corresponding to the size of the gaps.Further alternatively, the end face 34c may seal only some of the openings 37 while the trapped object remover 34 abuts the stop 38a. In this case, the fluid flow through the second end portion 33 is limited to a flow rate corresponding to the size of the opening area of the unsealed openings 37. The statement in claim 7, "when moved to an abutment position on the second end portion side, the trapped object remover mounting portion defines a flow channel for the fluid through the opening," includes these configurations.

[0046] Next, with reference to Fig. 5 to 10, the operations of the filter elements 3 according to the first embodiment configured as above will be described.

[0047] Fig. 5 is a front cross-sectional view of one of the filter elements 3 which are not connected to the backwash line 5 (see Fig. 1) while the filter device performs filtration. In this state, the unfiltered fluid flows upward into the filter element 3 through the first end part 32, that is, through the lower end. As a result, the fluid is filtered by flowing from the inside out through the filter part 31 so that it enters the filtered fluid chamber 10. At the same time, this upward flow of the unfiltered fluid moves the trapped object remover 34 upward until the trapped object remover 34 abuts the stopper 38a on the second end part 33 side. At the same time, the end surface 34c of the mounting part 34a of the trapped object remover 34 approaches the openings 37 but does not abut them, leaving the narrow gap 39 therebetween. The gap 39 communicates with the communication chamber 13 of the filter device.Since the fluid in the connecting chamber 13 flows into the filter element 3, which is connected to the backwash line 5, the pressure in the connecting chamber 13 is lower than that in the filter elements 3 that filter the fluid. Accordingly, the fluid in these filter elements 3, which filter the fluid, flows partially through the gaps 39 into the connecting chamber 13.

[0048] Fig. 6 is a front cross-sectional view of the filter element 3 connected to the backwash line 5 while the filter device performs filtration. During filtration, the fluid in the unfiltered fluid chamber 9 cannot flow into the filter element 3 connected to the backwash line 5 even though the valve for the backwash fluid discharge system is closed. However, the fluid in the filter elements 3 not connected to the backwash line 5 flows through the connecting chamber 13 and the openings 37 of the second end part 33 into the filter element 3 connected to the backwash line 5. Accordingly, the pressure in this filter element 3 rises higher than that in the filtered fluid chamber 10. As a result, the fluid in this filter element 3 flows from the inside to the outside through its filtering part 31, being filtered thereby, and enters the filtered fluid chamber 10.At this time, the downward flow of the flow entering from the connecting chamber 13 moves the trapped object removing device 34 downward until the trapped object removing device 34 abuts against the stopper 38b on the first end part 32 side at the lower end of the filter part 31.

[0049] Fig. Figure 7 is a front cross-sectional view of the filter element 3 when the filter device has just started backwashing and the backwash line 5 has rotated so that it is just connected to the filter element 3, which performs the filtration in Fig. 5. The fluid in the filter element 3 flows out through the backwash line 5 and the backwash fluid discharge line 6 connected thereto, and is ultimately introduced into a region with a pressure lower than that in the filtered fluid chamber 10 (hereinafter, the situation is referred to as "the backwash line 5 sucks out the fluid"). This lowers the pressure in this filter element 3 and consequently causes the fluid in the filtered fluid chamber 10 to flow back into the filter element 3 to begin backwashing. At this time, the trapped object remover 34 is still at its highest position.In this way, the fluid in the filtered fluid chamber 10 hardly flows into the interior of the filter part 31 in the area above the trapped object remover 34 and is less likely to move the trapped object remover 34 downward. However, the second end part 33 of each of the filter elements 3 according to the present invention has the openings 37 and communicates with the communication chamber 13 through the openings 37. Moreover, the communication chamber 13, although limited, is shared by all of the filter elements 3 (see ). Fig. 10) which are not connected to the backwash line 5. Accordingly, the fluid in the connecting chamber 13 also flows through the openings 37 into the Fig. 7. By this fluid flow, the pressure in the space above the trapped object removing device 34 is further increased than in the area below the trapped object removing device 34, and thus the trapped object removing device 34 is reliably pressed down.

[0050] Fig. 8 is a front cross-sectional view of the filter element 3 immediately after the Fig. 7. The trapped object removal device 34 is moved away from the second end part 33, so that a certain space is created therebetween. The pressure in the space is higher than in the area below the trapped object removal device 34. However, the pressure in the space is lower than in the filtered fluid chamber 10 surrounding the space, since the flow rate of fluid from other filter elements 3 that filter the fluid into the connecting chamber 13 is limited by the spaces 39 of these filter elements 3, and furthermore, the flow rate of fluid from the connecting chamber 13 into the Fig. 8 shown filter element 3 through the openings 37 of the Fig. 8. Accordingly, the fluid in the filtered fluid chamber 10 also flows into the space and then pushes down the trapped object removing device 34 until the trapped object removing device 34 abuts the lower end of the filter part 31 on the side of the first end part 32. As a result, the trapped object removing device 34 scrapes the trapped objects from the inner circumference of the filter part 31. These objects are then introduced into the backwash line 5 together with the backwash fluid and discharged.

[0051] It should be noted that when the trapped object remover 34 abuts the stopper 38b on the first end portion 32 side at the lower end of the filter portion 31, the outer peripheral portion (such as the bristles 34b) of the trapped object remover 34 is bent downward by the fluid flow. As a result, a gap is created between the trapped object remover 34 and the filter portion 31, allowing the fluid to flow therethrough into the backwash line 5.

[0052] Fig. Figure 9 is a front cross-sectional view of the filter element 3 when the backwash line 5 has rotated further and is now connected to another of the filter elements 3, not shown, which is located next to the one shown in Fig. 9 shown filter element 3. Since the connection of the Fig. 9 is now separated from the backwash line 5, the fluid in the unfiltered fluid chamber 9 continues to flow into this filter element 3. As a result, the fluid is filtered by flowing through the filter part 31 from the inside to the outside so that it enters the filtered fluid chamber 10, and at the same time, this upward flow of the unfiltered fluid moves the trapped object remover 34 upward. When the upper end of each of the filter elements 3 is completely closed and the trapped object remover 34 moves closer to this closed end, the fluid trapped therebetween could not easily escape, thus sometimes preventing the trapped object remover 34 from being sufficiently moved upward. In fact, however, the second end part 33 of each of the filter elements 3 according to the present invention has the openings 37.Accordingly, the fluid above the removal device 34 for retained objects of the type shown in . Fig. 9 through the openings 37 and the connecting chamber 13 into another of the filter elements 3, which is then backwashed. This allows the trapped object removal device 34 to move smoothly upwards to its highest position.

[0053] Specifically, in this embodiment, the mounting portion 34a of the trapped object remover 34 restricts the fluid flow passages through the openings 37 when moved so as to remain at the abutting position on the second end portion 33 side. In other words, the restriction of the flow rate by the second end portion 33 remains reduced unless the trapped object remover 34 comes closest to the second end portion 33. Accordingly, even if the filtering and backwashing operations are frequently and alternately repeated in each of the filter elements 3 while the filter device performs backwashing, the corresponding trapped object remover 34 can reliably move upward to its highest position.

[0054] Fig. 10 is a front cross-sectional view of the filter element 3 according to the Fig. 9, in which the distance device 34 for captured objects reaches its highest position. The Fig. The situation shown in Figure 10 is similar to that in Fig. 5 apart from the fact that a further filter element 3, which is connected to the filter element 3 of Fig. 10 through the connecting chamber 13, is backwashed and consequently has a low pressure. Accordingly, the pressure in the connecting chamber 13 is also reduced, thereby allowing the fluid in the filter element 3 to Fig. 10 flows into the connecting chamber 13 in a higher quantity than in the Fig. 5. However, in this embodiment, the mounting part 34a of the trapped object removing device 34 limits the fluid flow channels through the openings 37 while remaining at the abutting position on the side of the second end part 33, as shown in Fig. 10. In this way, it is possible to prevent the fluid in the filter element 3 from Fig. 10 flows in an excessively large flow rate through the connecting chamber 13 into another filter element 3, which is backwashed, and causes a reduction in the back pressure difference between the inside and outside of the filter part 31, so that the backwash efficiency is reduced. In other words, this configuration limits the flow of fluid into the connecting chamber 13 from the filter element 3 in the situation of Fig. 10, while the design allows a flow of fluid from the Fig. 9, in which the trapped object removal device 34 moves upwards, into the connecting chamber 13. This allows the trapped object removal device 34 to move upwards sufficiently without reducing the backwashing effect.

[0055] Subsequently, the backwash line 5 is rotated so that it is connected to the filter elements 3 one after the other. This allows each of the trapped object removing devices 34 to reliably scrape the trapped objects while moving up and down in the corresponding filter element 3, as shown in Fig. 7 to 10.

[0056] The opening areas of the openings 37 and the size of the abutment gap 39 are set as follows. Specifically, the wider the abutment gap 39, the greater the flow rate of fluid allowed to enter the connecting chamber 13 from the filter elements 3, which filter the fluid supplied from the unfiltered fluid chamber 9, and consequently, the greater the flow rate of fluid allowed to enter the filter element 3 connected to the backwash line 5. This means that the wider gap 39 makes it easier to achieve advantages a) and c) in

[0041] , but makes it more difficult to achieve advantage d). Therefore, the size of the abutment gap 39 should be set to a value that has been proven by experiments and the like to be optimal for achieving advantages a), c), and d).

[0057] Meanwhile, the larger opening area of the openings 37 allows a larger amount of fluid in the filter element 3 to flow out into the connecting chamber 13 while the trapped object remover 34 is located away from the abutment position on the second end portion 33 side. This means that a larger opening area of the openings 37 makes it easier to achieve advantage b). On the other hand, if, for some reason, the corresponding trapped object remover 34 in any of the filter elements 3 not connected to the backwash line 5 is unable to reach the abutment position on the second end portion 33 side while the filter device is performing backwashing, the openings 37 alone are unable to sufficiently restrict the flow rate into the connecting chamber 13.Furthermore, the openings 37 with a large opening area are unable to sufficiently limit the flow rate from the connecting chamber 13 into the filter element 3 being backwashed. This means that the large opening area of the openings 37 makes it difficult to achieve advantage d). Therefore, the opening area of the openings 37 should be set as small as possible, provided that advantage b) can be achieved.

[0058] In order to achieve the advantage d), it is desirable to adjust the size of the gap 39 and the opening area of the openings 37 of each of the filter elements 3 so that the flow rate from the connecting chamber 13 into the filter element 3 being backwashed reaches 5 to 20% of the flow rate of the fluid flowing from the filtered fluid chamber 10 through the corresponding filter part 31 into this filter element 3.

[0059] Next, a second embodiment of each of the filter elements 3 according to the present invention will be described.

[0060] Fig. 11A and Fig. 11B are each a front cross-sectional view of the second embodiment of the filter element 3 according to the present invention. The second embodiment differs from the first embodiment in that the openings 37 formed in the second end portion 33, together with the bristles 34b of the removal brush 34, constitute the flow rate restricting means, and that when the removal brush 34 is located at the abutting position on the second end portion 33 side, the bristles 34b restrict the fluid flow channels through the openings 37. Specifically, a removal brush is used as the trapped object removing means 34. Meanwhile, the second end portion 33 has the openings 37.When the removal brush 34 abuts the stopper 38a on the second end portion 33 side, the bristles 34b fill the space between the outer periphery of the brush main body 34a and the inner periphery of the filter portion 31, since no space remains between the bristles 34b of the removal brush 34 and the inner periphery of the filter portion 31. With this configuration, the fluid must flow through the spaces between the bristles 34b before flowing through the openings 37. In other words, the bristles 34b of the removal brush 34 limit the flow rate through the second end part 33. Note that when the removal brush 34 abuts against the stopper 38b on the first end part 32 side, the bristles 34b are bent sufficiently to create a gap between the bristles 34b and the inner periphery of the filter parts 31, and allow the fluid to flow through the gap, as shown in FIG. Fig. 11B.

[0061] The operation of the filter element 3 according to the second embodiment configured as above is basically identical to that according to the first embodiment. While the second end portion 33 is located at the abutting position on the openings 37 side, the flow rate through the openings 37 depends on conditions such as the density and flexibility of the bristles 34b and the distance between the outer periphery of the brush main body 34a and the inner periphery of the filter portion 31. Accordingly, these conditions are set to achieve the advantages a), c), and d). The opening area of the openings 37 of the second end portion 33 is set to achieve the advantage b), as in the first embodiment.

[0062] Next, a third embodiment of the filter element 3 according to the present invention will be described.

[0063] Fig. 12 is a front cross-sectional view of the third embodiment of the filter element 3 according to the present invention. The third embodiment differs from the first and second embodiments in that the openings 37 of the second end portion 33 are passages that constitute the flow rate limiting means. Specifically, the passages 37 limit the flow rate through the second end portion 33. Even while the trapped object remover 34 abuts against the stopper 38a on the second end portion 33 side, the mounting portion 34a and the bristles 34b do not limit the fluid flow channels through the passages 37, or limit these fluid flow channels to a lesser extent than that caused by the passages 37 themselves.Unlike the second embodiment, when the trapped object removing device 34 is, for example, a removing brush, the bristles 34b are bent sufficiently to create a gap between the bristles 34b and the filter part 31, and thus do not obstruct the fluid flow through the second end part 33 even while remaining at the abutting position on the side of the second end part 33.

[0064] The operation of the filter element 3 according to the third embodiment, configured as above, is basically identical to that according to the first and second embodiments. However, in this embodiment, the opening area of the passages 37 is the sole factor limiting the flow rate through the second end portion 33. The opening area of the passages 37 must be set so that the advantages a) to d) are achieved.

[0065] In the above description, each of the trapped object removing devices 34 is a removing brush as an example. However, the present invention is not limited to this. The trapped object removing device 34 may be any unit as long as it can be moved in the axial direction of the corresponding filter element 3 by the fluid flow generated during filtration or backwashing, and it has a part on the outer circumference capable of sliding into contact with the inner circumference of the filter element 3 and removing trapped objects from the inner circumference. The trapped object removing device 34 may alternatively be, for example, a blade-shaped or spatula-shaped scraper made of a metal, a resin, or rubber, or the like.

[0066] Next, with reference to Fig. 13 and Fig. 14 describes the operations of the first embodiment of the filter device configured as above. Since they have been described in detail in the above description for the first embodiment of the filter element 3, the behavior of the fluid flow in each of the filter elements 3 and the movements of their trapped object removal device 34 during the operations of the filter device will be described only in outline.

[0067] Fig. Figure 13 is a front cross-sectional view of the filter device performing filtration. During filtration, the valve for the backwash fluid discharge system is closed, no suction is performed through the backwash line 5, and the backwash line 5 stops rotating.

[0068] First, the fluid to be filtered flows through the fluid inlet 7 into the unfiltered fluid chamber 9 of the housing 1, as indicated by arrow A. Then, the fluid flows into the filter element 3a, which communicates with the unfiltered fluid chamber 9, and is filtered by flowing from the inside out through the filter elements 3a to enter the filtered fluid chamber 10. The fluid that has entered the filtered fluid chamber 10 is discharged to the outside through the fluid outlet 8, as indicated by arrow B. During filtration, the fluid pushes the trapped object remover 34 in the filter element 3a to its uppermost position.It should be noted that although the backwash line 5 prevents the fluid in the unfiltered fluid chamber 9 from flowing into the filter element 3b connected to the backwash line 5, the fluid in the other filter elements 3 flows into the filter element 3b through the connecting chamber 13. In this way, the filter element 3b also filters the fluid while the filter device performs filtration.

[0069] Fig. Figure 14 is a front cross-sectional view of the filter device performing backwashing. During backwashing, the valve for the backwash fluid discharge system is opened, and the backwash line 5 begins to suck out the fluid. The backwash line 5 is rotated by the gear motor 16 so that it is sequentially connected to the filter elements 3.

[0070] When rotated to connect to the filter element 3b, the backwash line 5 sucks out the fluid in the filter element 3b. This lowers the pressure in this filter element 3b, thus causing the fluid in the filtered fluid chamber 10 surrounding the filter element 3b to flow into the interior of the filter element 3b in the opposite direction to that for filtration. This backwashes the filter element 3b. At the same time, the downward fluid flow in the axial direction of the filter element 3b generated during backwashing moves the trapped object remover 34 in the filter element 3b from its highest position to its lowest position. As a result, the trapped object remover 34 scrapes the trapped objects from the inner periphery of the filter part 31.The trapped and removed objects are discharged along with the backwash fluid through the backwash line 5 and the backwash fluid discharge line 6. Meanwhile, the fluid in the unfiltered fluid chamber 9 continues to flow into the filter element 3a, which is not connected to the backwash line 5. Accordingly, the filter elements 3a continue to filter the fluid, similar to when the filter device performs filtration. The fluid that has entered the filter element 3a flows through the connecting chamber 13 into the filter element 3b, which is connected to the backwash line 5. This allows the trapped object remover 34, located at its highest portion in the filter element 3b, to smoothly descend to start the backwashing process for the filter element 3b.It should be noted that the fluid flow from the connecting chamber 13 into the filter element 3b is limited to a small amount by the flow rate limiting means in order not to impair the backwash efficiency.

[0071] In the filter element 3a, which has just been disconnected from the backwash line 5, the fluid flow from the unfiltered fluid chamber 9 into the filter element 3a moves the trapped object remover 34 upward. At this time, the trapped object remover 34 can move upward smoothly to its highest position because the fluid above the trapped object remover 34 is allowed to flow out through the connecting chamber 13 into another of the filter elements 3 to be backwashed. Thereafter, the backwash line 5 is rotated by the gear motor 16 so that it is sequentially connected to the filter elements 3. This causes each of the trapped object removers 34 to move up and down in the corresponding filter element 3, so that the filter elements 3 can be reliably backwashed.

[0072] For example, if the filter parts are used for ballast seawater, filtration and backwashing are performed under the following conditions. For example, filtration is performed with a primary pressure of 3.0 kg and a secondary pressure of 2.8 to 2.9 kg. Every one to ten hours of the filtering operation, backwashing is performed for two minutes at a rotational speed of 1 / min, with the outlet of the backwash fluid discharge line 6 open to atmospheric pressure.

[0073] Next, the configuration of a second embodiment of the filter device according to the present invention using the filter elements 3 will be described.

[0074] Fig. 15 is a front cross-sectional view of the second embodiment of the filter device according to the present invention. The filter device according to the second embodiment does not include the second partition wall 4 and the connecting chamber 13 defined by the second partition wall 4, which are included in the first embodiment. Instead, the filter device according to the second embodiment includes a connecting conduit 19 connected to the first ends of the filter elements 3 opposite the second ends connected to the unfiltered fluid chamber 9 so that they communicate with each other, while being isolated from the filtered fluid chamber 10.

[0075] The connecting line 19 allows the fluid to flow therethrough between the filter elements 3 while isolating the fluid from the environment. The connecting line 19 includes a line part 19a and joining parts 19b that join the line part 19a to the second end parts 33 of the filter elements 3. In the filter device according to the present invention, the line part 19a basically only needs to connect a filter element 3 connected to the backwash line 5 with a filter element 3 not connected to the backwash line 5. Accordingly, the line part 19a can have a shape capable of connecting any two of the filter elements 3 at a time. However, from the viewpoint of stable operation, the line part 19a should desirably have a shape that simultaneously connects all of the filter elements 3 to each other.In particular, the conduit part 19a may, for example, have a ring shape connecting all of the filter elements 3, as shown in . Fig. 16. The conduit part 19a can be formed from a known conduit material. For example, the conduit part 19a can be formed from a metal such as stainless steel, natural rubber, or a resin such as polyvinyl chloride resin. The conduit part 19a can be formed from any flexible material, as long as the material is strong enough to maintain its shape against any force due to a pressure difference inside and outside the conduit part 19a. Forming the conduit part 19a from a flexible material enables the conduit part 19a to be assembled or disassembled more efficiently. Any known fitting having a predetermined strength and reliable airtightness can be used as the joining parts 19b.

[0076] The operations of the filter device configured as above are basically similar to those of the first embodiment. Therefore, the operations related to the connecting line 19 will be described below.

[0077] During a filtration, as in Fig.15, the fluid to be filtered is supplied to the unfiltered fluid chamber 9 and then enters the filter elements 3a that communicate with the unfiltered fluid chamber 9. The fluid is filtered by flowing from the inside out through the filter elements 3a so that it enters the filtered fluid chamber 10 surrounding the filter elements 3a. It should be noted that although the backwash line 5 prevents the fluid in the unfiltered fluid chamber 9 from flowing into the filter element 3b connected to the backwash line 5, the fluid in another filter element 3a flows through the connecting line 19 into the filter element 3b. In this way, filtration is also performed in the filter element 3b.

[0078] In contrast, during backwashing, although not illustrated, the valve for the backwash fluid discharge system is opened, and the backwash line 5 sucks the fluid from the filter element 3b connected to the backwash line 5. This reduces the pressure in this filter element 3b, causing the fluid in the filtered fluid chamber 10 surrounding the filter element 3b to flow into the interior of the filter element 3b in the opposite direction to that for filtration. This backwashes the filter element 3b. Meanwhile, the fluid in the filter element 3a, which is not connected to the backwash line 5, flows through the connecting line 19 into the filter element 3b connected to the backwash line 5.This allows the trapped object remover 34, which is located at its highest portion in the filter element 3b at the start of the backwashing operation for the filter element 3b, to smoothly descend to remove the trapped objects. Note that the fluid flow into the filter element 3b is limited to a small amount by the flow rate limiting means so as not to impair the backwashing efficiency. In the filter element 3a whose backwashing has just been completed, the trapped object remover 34 is moved upward. At this time, the trapped object remover 34 can smoothly move upward to its highest position because the fluid between the upper end part 33 and the trapped object remover 34 is allowed to flow out through the connecting pipe 19 into another filter element 3 being backwashed.

[0079] The second embodiment has a large acceptable length range for the filter elements 3 since their length does not depend on the distance between the two partition walls. List of reference symbols 1 housing 2 first partition wall 3, 3a and 3b filter element 4 second partition wall 5 Backwash line 6 Backwash fluid drain line 7 Fluid inlet 8 Fluid outlet 9 Chamber for unfiltered fluid 10 chamber for filtered fluid 11 Through hole 12 through holes 13 Connecting chamber 14 Base end section of the backwash line 15 Wave 16 Gear motor 17 Base end section of the backwash fluid drain line 18 Coupling connection section 19 connecting line 19a line section 19b Joining part 20 discharge connection 31 Filter part 32 first end part 33 second end part 34 Removal device for trapped objects (removal brush) 34a Assembly part (brush main body) 34b bristles 34c frontal surface 35 Guide shaft 36 jetty 37 Opening (passage) 38, 38a, 38b stop 39 space A Inflow direction of the fluid B Outflow direction of the filtered fluid C Cutting line P Direction of rotation of the backwash line

Claims

[1] A filter element (3, 3a, 3b) having a tubular shape with openings at opposite ends in a longitudinal direction thereof and configured to filter fluid by allowing the fluid to flow through the filter element from the inside out and to be backwashed by allowing the fluid to flow through the filter element from the outside in, the filter element comprising: a filter member (31) extending over a predetermined length and having openings at opposite ends; a first end portion (32) connected to a first end of the filter portion (31) to support the filter portion (31) and having an opening (37) allowing fluid to flow therethrough; a second end portion (33) connected to a second end of the filter portion (31) so as to support the filter portion (31) and having an opening (37) allowing the fluid to flow therethrough; and a trapped object removing device (34) provided in an interior of the filter part (31) and configured to be movable by a flow of the fluid in an axial direction of the filter part (31) generated during filtration or backwashing in the interior of the filter part (31) between the first and second end parts (32, 33) along a guide shaft (35) whose opposite ends are fixed to the first end part (32) and the second end part (33), while an outer periphery of the trapped object removing device (34) slides into contact with an inner periphery of the filter part (31) so as to remove an object trapped by the filter part (31), wherein a first stop (38b) stopping a movement of the retained object removal device (34) toward the first end part (32) is mounted on one side of the first end part (32), and a second stop (38a) stopping a movement of the retained object removal device (34) toward the second end part (33) is mounted on one side of the second end part (33), wherein a flow rate limiting means for limiting a flow rate of the fluid through the second end part (33) is provided at the second end of the filter part (31), and wherein the opening (37) of the second end part (33) and a mounting part (34a) of the trapped object remover (34) form the flow rate limiting means, and when the trapped object remover (34) abuts the second stopper (38a) and an end face (34c) of the mounting part (34a) of the trapped object remover (34) is located near the openings (37), the fluid flow through the openings (37) of the second end part (33) is limited to a flow rate corresponding to a size of a gap (39) between the openings (37) of the second end part (33) and the end face (34c) of the mounting part (34a) of the trapped object remover (34). [2] Filter element (3, 3a, 3b) according to claim 1, further comprising a guide shaft (35) arranged on a central axis of the filter part (31), opposite ends of the guide shaft (35) being fixed to the first and second end parts (32, 33), wherein the retained object removing device (34) has a through hole on the central axis through which the guide shaft (35) is inserted so that the retained object removing device (34) is movable in the axial direction of the filter part (31). [3] The filter element (3, 3a, 3b) according to claim 1, wherein the trapped object removing means (34) is a removing brush having a brush main body (34a) and bristles (34b) inserted on the outer periphery of the brush main body (34a). [4] The filter element (3, 3a, 3b) according to claim 1, wherein the trapped object removing means (34) is a blade-shaped or spatula-shaped scraper made of a metal, a resin or rubber. [5] Filter element (3, 3a, 3b) according to one of claims 1 to 4, wherein the filter part (31) is a metal mesh filter comprising an innermost layer and one or more outer layers integrated by sintering. [6] Filter device comprising: a housing (1) having a fluid inlet that allows fluid to flow in from an outside of the housing and a fluid outlet that allows the fluid filtered in the filter device to flow out; a first partition wall (2) separating an interior of the housing (1) into an unfiltered fluid chamber (9) filled with unfiltered fluid and communicating with the fluid inlet, and a filtered fluid chamber (10) filled with a filtered fluid and communicating with the fluid outlet; a plurality of filter elements (3, 3a, 3b) according to one of claims 1 to 5, each of which is tubular and is provided parallel to one another in the filtered fluid chamber (10), wherein first ends are fitted and held by through-holes (11) formed in the first partition wall (2), and wherein interior spaces of the filter elements (3, 3a, 3b) communicate with the unfiltered fluid chamber (9), and each of which is designed to filter the fluid by allowing the fluid to flow through the filter element from the inside to the outside, and to be backwashed by allowing the fluid to flow through the filter element from the outside to the inside; a second partition wall (4) provided parallel to the first partition wall (2) so as to be located at a second end side of the filter elements (3, 3a, 3b), and having a plurality of through holes (12) each serving to fit and hold the second end of the corresponding one of the filter elements (3, 3a, 3b), so that a portion of the filtered fluid chamber (10) on the second end side of the filter elements (3, 3a, 3b) is isolated from the remaining filtered fluid chamber (10) so as to define a communication chamber (13) between the filter elements (3, 3a, 3b) through which the fluid can flow, a backwash line (5) connected to the first ends of one or more of the plurality of filter elements (3, 3a, 3b) for backwashing the filter elements (3, 3a, 3b) by allowing the fluid to flow through the filter elements (3, 3a, 3b) from the outside to the inside; and a backwash fluid discharge line (6) connected to a discharge side of the backwash line (5) and discharging a trapped object removed by backwashing the filter elements (3, 3a, 3b) to the outside of the housing (1), wherein each of the filter elements (3, 3a, 3b) is arranged such that the first and second end parts (32, 33) are located on the first and second end sides of the filter element, respectively. [7] Filter device comprising: a housing (1) having a fluid inlet that allows fluid to flow in from an outside of the housing and a fluid outlet that allows the fluid filtered in the filter device to flow out; a first partition wall (2) separating an interior of the housing (1) into an unfiltered fluid chamber (9) filled with unfiltered fluid and communicating with the fluid inlet, and a filtered fluid chamber (10) filled with a filtered fluid and communicating with the fluid outlet; a plurality of filter elements (3, 3a, 3b) according to one of claims 1 to 5, each of which is tubular and is provided parallel to one another in the filtered fluid chamber (10), wherein first ends are fitted and held by through-holes (11) formed in the first partition wall (2), and wherein interiors of the filter elements (3, 3a, 3b) communicate with the unfiltered fluid chamber (9), and each of which is designed to filter the fluid by allowing the fluid to flow through the filter element from the inside to the outside, and to be backwashed by allowing the fluid to flow through the filter element from the outside to the inside; a connecting line (19) connected to second ends of the filter elements (3, 3a, 3b) such that the second ends communicate with each other while being insulated from the filtered fluid chamber (10); a backwash line (5) connected to the first ends of one or more of the plurality of filter elements (3, 3a, 3b) for backwashing the filter elements (3, 3a, 3b) by allowing the fluid to flow through the filter elements (3, 3a, 3b) from the outside to the inside; and a backwash fluid discharge line (6) connected to a discharge side of the backwash line (5) and discharging a trapped object removed by backwashing the filter elements (3, 3a, 3b) to the outside of the housing, wherein each of the filter elements (3, 3a, 3b) is arranged such that the first and second end parts (32, 33) are located on the first and second end sides of the filter element, respectively. [8] The filter device according to claim 6 or 7, wherein, while the filter device performs filtration, the trapped object removing means (34) abuts against the second stopper (38a) in the state in which the filter elements (3, 3a, 3b) are not connected to the backwash line (5), and the trapped object removing means (34) abuts against the first stopper (38b) in the state in which the filter elements (3, 3a, 3b) are connected to the backwash line (5).

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