Gravel fall prevention device and filtering device

Abstract

To provide a gravel fall prevention device which suppresses deterioration of a support member and has excellent gravel fall prevention performance for a long term and to provide a filtration apparatus which is provided with the device.SOLUTION: A gravel fall prevention device 10 prevents fall of gravel in a filtration apparatus 1, the filtration apparatus 1 includes a gravel layer 5 and a support member 6 which supports gravel of the gravel layer 5 from the lower side, the support member 6 is provided with a groove of a V-shaped cross section having a slit part which is elongated in one direction and is penetrated through the lower side, on the lowermost part, and the gravel fall prevention device 10 is a V-shaped cross section metallic member which is arranged so as to be brought into surface-contact along the groove of the support member 6 and has a slit-shaped water passage hole which is elongated in one direction, on the lowermost part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gravel fall prevention device and a filtering device. [Background technology]

[0002] Gravity filtration systems such as sand filters and activated carbon adsorption tanks used in water supply and sewerage purification systems use a water purification system in which sand or activated carbon is placed on a layer of gravel at the bottom of the tank as filter media, and water is passed through the media to remove pollutants. In such water purification systems, backflow cleaning (backwashing) is performed to clean the filter media by flowing air or other gases from below, in the opposite direction to the flow of water during filtration.

[0003] The gravel placed below the filter media supports the granular filter media, such as sand or activated carbon, and prevents the filter media from flowing into the under-drain device or collection chamber, which are placed further below the gravel layer. The gravel also plays a role in dispersing gas so that it flows evenly throughout the filter media during backwashing. By layering gravel of different particle sizes in sequence, it is possible to suppress the uneven flow of water during filtration and the uneven flow of gas during backwashing.

[0004] As an example of the above-mentioned water purification system, Patent Document 1 discloses an Enbico-type underdrain system (filter). This filter includes a concrete slit plate (gravel support member) that supports the gravel in the gravel layer from below, and an air mixing means that mixes air into the backwash water that flows from below to above the slit plate. The filter described in Patent Document 1 has a coil-shaped gravel receiving member, the outer diameter of which is larger than the width of the slit at the groove bottom, disposed at the bottom of each of the multiple grooves with a V-shaped cross section in the slit plate. Here, the gravel receiving member prevents the gravel from falling downward, and can therefore also be called a gravel fall prevention device.

[0005] Patent Document 1 describes the following effects: For example, even if the gravel in the gravel layer moves violently in the backwash water during cleaning, the provision of a coil-shaped gravel receiving member with an outer diameter larger than the width of the slit prevents not only the filter material but also small gravel from passing through the slit and falling into the water collection chamber below the lower drainage device, and because the flow resistance to the backwash water is relatively small, the gravel receiving member is able to separate the slit and the dispersed gravel layer without being lifted up by the force of the backwash water during cleaning. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 3741698 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when a coil-shaped gravel receiving element with an outer diameter larger than the width of the slit at the bottom of the groove is used as described in Patent Document 1, the gravel receiving element is relatively easily deformed when subjected to external forces due to its coil shape. Therefore, in situations where the gravel receiving element is subject to fluctuating external forces, such as during backwashing, depending on the material and shape of the coil, the coil shape may deform, causing gravel to fall through the slit and into the water collection chamber. Furthermore, during backwashing, the flow of gas, such as air, from below to above causes the slit plate and the gravel on it to vibrate, generating vibrations that can cause wear and chipping at the contact points between the slit plate and the gravel (the slopes and openings of the groove). In this case, concrete powder generated by wear may be mixed into the filtered water. Furthermore, deterioration of the slit plate openings may enlarge their size, making it more likely for gravel to fall into the water collection chamber.

[0008] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a gravel fall prevention device that suppresses deterioration of the support member and has excellent gravel fall prevention performance over the long term. It also aims to provide a filtration device that is less likely to cause gravel to fall into the water collection chamber over the long term, thereby reducing the maintenance burden and providing a long-life filtration device. [Means for solving the problem]

[0009] The gravel fall prevention device of the present invention is a gravel fall prevention device for a filtration device, characterized in that the filtration device comprises a gravel layer and a support member that supports the gravel in the gravel layer from below, the support member having a V-shaped cross-sectional groove at its bottom that has a slit portion that extends downward in one direction, and the gravel fall prevention device is a metal member that is arranged face-to-face along the groove of the support member and has a V-shaped cross-sectional groove at its bottom that has a slit-shaped water passage hole that also extends in one direction.

[0010] The gravel fall prevention device has two plate-shaped members and a connecting member that connects the two plate-shaped members, and the plate-shaped members have a plurality of through holes.

[0011] The plurality of through holes are slit-shaped through holes, and are arranged in parallel in the longitudinal direction of the water passage hole, facing in a direction other than the longitudinal direction of the water passage hole.

[0012] At least one of the plurality of through holes is disposed adjacent to the connecting member in the minor axis direction of the water passage hole.

[0013] The filtering device of the present invention is characterized by comprising the gravel fall prevention device described above. [Effects of the Invention]

[0014] In the gravel fall prevention device of the present invention, the support member is provided with a V-shaped cross-sectional groove having a slit portion penetrating downward in one direction at its lowermost portion, and the gravel fall prevention device is a metal member having a V-shaped cross-sectional shape that is disposed flush with the groove of the support member and has a slit-shaped water passage hole that also extends in one direction at its lowermost portion, so that the slope of the support member and the slit portion are well protected. As a result, the gravel fall prevention device suppresses deterioration of the support member and has excellent gravel fall prevention performance over the long term.

[0015] The gravel fall prevention device has two plate-shaped members and a connecting member that connects the two plate-shaped members. The plate-shaped members have multiple through-holes, so even if gas gets between the gravel fall prevention device and the support member during backwashing, the gas can escape through the through-holes. This makes it difficult for the gravel fall prevention device to float up (low flow resistance), and gravel is less likely to get between the support member and the gravel fall prevention device. As a result, the slope and slit portions of the support member are better protected.

[0016] The multiple through holes are slit-shaped through holes that face in a direction other than the longitudinal direction of the water passage holes and are arranged in parallel in the longitudinal direction of the water passage holes, so that the gas rising during backwashing is more likely to come into contact with the through holes for a long period of time, and the gas is more likely to pass through the through holes.

[0017] At least one of the multiple through holes is arranged adjacent to the connecting member in the minor axis direction of the water passage hole, so even if the connecting member prevents rising gas from passing through the water passage hole and it gets between the gravel fall prevention device and the support member, the gas can still pass through the through hole arranged adjacent to the connecting member. This further reduces the upward pressure on the gravel fall prevention device, making it even less likely to float up.

[0018] The filtering device of the present invention is equipped with the gravel fall prevention device described above, so that the gravel in the gravel layer is less likely to come into contact with the two slopes that form the grooves of the support member, and the slopes of the support member are less likely to deteriorate. As a result, the gravel fall prevention device prevents gravel from falling into the water collection chamber for a long period of time, reducing the maintenance burden of the filtering device and extending its lifespan. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a cross-sectional schematic view of a filtration device of the present invention. [Figure 2] FIG. 10 is a perspective view of a support member equipped with a gravel fall prevention device. [Figure 3] FIG. [Figure 4] FIG. [Figure 5] FIG. 10 is a plan view of a support member equipped with a gravel fall prevention device. [Figure 6] FIG. 10 is a cross-sectional view of a support member equipped with a gravel fall prevention member. [Figure 7] FIG. 2 is an exploded plan view of the gravel fall prevention device according to the first to third embodiments. [Figure 8] FIG. 10 is an exploded plan view of the gravel fall prevention device of the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0020] The gravel fall prevention device and filtration device of the present invention will be described with reference to Fig. 1. Fig. 1 is a cross-sectional schematic diagram of one embodiment of the filtration device of the present invention. As shown in Fig. 1, the filtration device 1 has a filtration tank 2, and inside the filtration tank, from top to bottom, a filter media layer 3, a porous concrete layer 4, and a gravel layer 5 are arranged.

[0021] The filtration device 1 has a support member 6 that supports the gravel in the gravel layer 5 from below. The support member 6 has slits, which are slit-shaped holes that penetrate downward and allow water (such as filtered water) to pass through. The support member 6 is supported by beams 7, forming a water collection chamber 8 at the bottom of the filtration device 1. The filtration device 1 also has a gas discharger 9 that discharges gas, such as air, into the filter tank 2. The gas discharger generates a gas-liquid mixture fluid consisting of gas and water, thereby cleaning the filter media layer 3, the porous concrete layer 4, the gravel layer 5, and the like. A gravel fall prevention device 10 is provided between the support member 6 and the gravel layer 5 to prevent the gravel from falling downward. Note that the support member 6 does not necessarily have to be supported from the bottom of the filtration tank 2 via the beams 7. In that case, the beams 7 may be installed horizontally to connect opposing side walls of the filtration tank 2 and support the support member 6 from below.

[0022] Here, we will explain filtration during water purification in the filtration device 1 and backwashing during cleaning. During water purification, inflow water is introduced from the top of the filter tank 2, and the water passes from the filter media layer 3, through the porous concrete layer 4, and then through the gravel layer 5, from top to bottom, whereby fine pollutants are removed by the filtering action of the filter media, etc. After filtration, the treated water passes through the slits in the support member 6, collects in the water collection chamber 8, and is discharged from the bottom of the filter tank 2.

[0023] Backwashing is performed by introducing gas from the gas discharge device 9 from below the support member 6. For example, when gas is discharged from the gas discharge device 9 into the water collection chamber, the gas passes through the slits at the bottom of the support member 6, rises upward, and permeates the gravel layer 5, the porous concrete layer 4, and the filter media layer 3. In this way, the gas applies upward pressure and vibration to the support member 6 and each layer, thereby peeling off and removing contaminants trapped in the filter media, etc. By passing the gas through each layer in this way, water containing contaminants peeled off and removed from the filter media, etc. is discharged from above the filter media layer 3, and the filtration device 1 is cleaned.

[0024] The support member will be described with reference to Figs. 2 to 4. Fig. 2 is a perspective view of the support member equipped with the gravel fall prevention device, viewed obliquely from above, with the filter media layer, porous concrete layer, and gravel layer removed from the filtration device. As shown in Fig. 2, multiple support members 6 are arranged so as to be spread out inside the filtration tank 2. The movement of the gravel fall devices 10, 16 is restricted by being inserted into grooves in the support members 6 without using fasteners such as screws.

[0025] FIG. 3 is a plan view of the support member 6 as seen from above (the gravel layer side). As shown in FIG. 3, the support member 6 is a rectangular plate-like member having a predetermined thickness. The length of the long side of the support member 6 can be, for example, approximately 35 cm to 65 cm. The length of the short side of the support member 6 can be, for example, approximately 25 cm to 45 cm. The material of the support member 6 can be selected from various materials, and can be made of, for example, concrete, resin, or metal. From the viewpoints of durability, strength, cost, etc., it is preferable that the material of the support member be concrete.

[0026] The support member 6 has seven grooves 11 of the same shape on the gravel layer side, and the grooves are arranged in parallel in the direction of their short axes. The grooves 11 penetrate from the gravel layer side (near the paper) to the water collection chamber side (farther from the paper), with the opening on the gravel layer side being larger than the opening on the water collection chamber side. The length of the long side of the outer edge 12 of the opening on the gravel layer side of the groove 11 can be, for example, approximately 20 cm to 40 cm. The length of the short side of the outer edge 12 can be, for example, approximately 3.0 cm to 7.0 cm. Here, the outer edge 12 of the opening on the gravel layer side is the part of the groove 11 that contacts the upper surface 13 of the support member 6.

[0027] The opposing slopes on the outer periphery of each of the adjacent support members 6, 6 form a groove 17. Like groove 11, groove 17 also penetrates from the gravel layer side (the front side of the paper) to the water collection chamber side (the back side of the paper), and the opening on the gravel layer side is larger than the opening on the water collection chamber side.

[0028] Fig. 4 is a cross-sectional view of the support member. Fig. 4(a) is a cross-sectional view taken along line A-A' in Fig. 3, and Fig. 4(b) is a cross-sectional view taken along line B-B' in Fig. 3. As shown in Fig. 4, groove 11 has a V-shaped cross section and a slit-like slit portion 14 at its bottom that extends in one direction. The V-shaped cross section of groove 11 is formed by two trapezoidal slopes that extend in the same direction as the long axis direction of slit portion 14. Groove 17 also has a V-shaped cross section and a slit-like slit portion 18 at its bottom that extends in one direction.

[0029] The width of the slit portions 14, 18 in the minor axis direction is, for example, approximately 1 mm to 20 mm. From the viewpoints of preventing gravel from falling, ensuring the strength of the support member, and water permeability, the width of the slit portions 14, 18 in the minor axis direction is preferably approximately 2 mm to 10 mm. The width of the slit portions 14, 18 in the major axis direction is, for example, approximately 10 cm to 40 cm. From the viewpoints of strength and water permeability, the width of the slit portions 14, 18 in the major axis direction is preferably approximately 20 cm to 30 cm. The support member 6 is not limited to the configuration shown in FIGS. 3 and 4 . As long as the bottom portion is provided with grooves having unidirectional slit-shaped slit portions, the size, shape, and number of grooves can be freely selected. The grooves may have different shapes and sizes. The grooves may be arranged in either the long or short side direction of the support member, or they may be arranged in different directions. A plurality of support members may be combined, or a single support member having multiple grooves may support a gravel layer or the like.

[0030] The gravel fall prevention device will be described with reference to Figs. 5 to 8. Fig. 5 is a plan view of a support member equipped with a gravel fall prevention device, seen from above. As shown in Fig. 5, the gravel fall prevention device 10 is provided on a groove 11 of the support member 6. The gravel fall prevention device 10 is a metal member with a V-shaped cross section (see Fig. 6) and a slit-shaped water passage hole 15 extending in one direction at its bottom. The water passage hole 15 of the gravel fall prevention device 10 is disposed at a position corresponding to the slit portion 14 of the support member 6. The width of the water passage hole 15 in the minor axis direction is, for example, the same as the width of the slit portion 14 in the minor axis direction. Note that the width of the water passage hole 15 in the minor axis direction may be smaller than the width of the slit portion 14 in the minor axis direction.

[0031] The gravel fall prevention device is not limited to being provided in the groove of one support member, but may also be provided in a groove formed between adjacent support members. In FIG. 5, a gravel fall prevention device 16 is provided between adjacent support members 6, 6. The gravel fall prevention device 16 is provided on a groove 17 formed by opposing slopes on the outer peripheries of adjacent support members 6, 6. Like the gravel fall prevention device 10, the gravel fall prevention device 16 has a V-shaped cross section (see FIG. 6) and a slit-shaped water passage hole 19 extending in one direction is provided at the bottom. The water passage hole 19 of the gravel fall prevention device 16 is disposed at a position corresponding to the slit portion 18 formed by the adjacent support members 6, 6. The width of the water passage hole 19 in the minor axis direction is, for example, the same as the width of the slit portion 18 in the minor axis direction. Note that the width of the water passage hole 19 in the minor axis direction may be smaller than the width of the slit portion 18 in the minor axis direction.

[0032] The shape and size of the water passage hole are preferably approximately the same as the shape and size of the slit portion located directly below. From the viewpoints of preventing deterioration of the support member and allowing filtered water and gas to pass through easily, the ratio W1 / W2 of the width W1 of the water passage hole in the short axis direction to the width W2 of the slit portion in the short axis direction is preferably 0.8 to 1.2, more preferably 0.8 to 1.0, and even more preferably 1.0. If the width W2 of the slit portion in the short axis direction of the support member expands due to long-term use, the width W2 is likely to be larger than the width W1 of the water passage hole in the short axis direction of the newly installed gravel fall prevention device.

[0033] The gravel fall prevention device 10 has two plate-shaped members 10a, 10a and a connecting member 10b that connects them. Both the plate-shaped member 10a and the connecting member 10b are made of metal. The connecting member 10b connects both ends and the center of the top sides of the two trapezoidal plate-shaped members 10a, 10a. The gravel fall prevention device 16 also has two plate-shaped members 16a, 16a and a connecting member 16b that connects them. Both the plate-shaped member 16a and the connecting member 16b are made of metal. The connecting member 16b connects both ends and the center of the bottom sides of the two trapezoidal plate-shaped members 16a, 16a.

[0034] The gravel fall prevention device may be formed, for example, by punching out a metal plate and then performing press processing or the like, or by connecting a pre-prepared plate-shaped member and a connecting member by welding or the like.

[0035] Fig. 6 is a cross-sectional view of a gravel fall prevention device. Fig. 6(a) is a cross-sectional view taken along line CC' in Fig. 5, and Fig. 6(b) is a cross-sectional view taken along line DD' in Fig. 5. As shown in Fig. 6, gravel fall prevention devices 10 are provided along opposing slopes that form groove 11 of support member 6, so as to be in contact with groove 11. Gravel fall prevention devices 16 are also provided along opposing slopes on the outer periphery of adjacent support members 6, 6, so as to be in contact with groove 17. Note that gravel fall prevention devices 10 may also have metal plate-like members on slopes that face each other in the longitudinal direction of groove 11.

[0036] The angle θ1 formed by the two plate-like members 10a, 10a of the gravel fall prevention device 10 is approximately the same as the angle formed by the two slopes that form one groove 11 (see FIG. 6(a)). θ1 can be set to, for example, approximately 20° to 70°. From the viewpoint of water collection, θ1 is preferably approximately 30° to 60°, and more preferably approximately 40° to 50°. The angles of the two slopes relative to the vertical direction may be the same or different. Note that, from the viewpoint of water collection, the angle formed by the two plate-like members 16a, 16a of the gravel fall prevention device 16 is also preferably approximately 30° to 60°, and more preferably approximately 40° to 50°.

[0037] The gravel fall prevention device of the present invention has the above-mentioned configuration, which makes it difficult for the gravel in the gravel layer to come into contact with the two slopes of the support member, thereby providing excellent protection for the slopes and slits of the support member. As a result, the gravel fall prevention device suppresses deterioration of the support member and provides excellent gravel fall prevention performance for a long period of time.

[0038] The thickness (plate thickness) of the plate-shaped member of the gravel fall prevention device can be, for example, approximately 0.1 mm to 1.5 mm. From the viewpoints of workability, cost, and durability, the thickness of the plate-shaped member is preferably approximately 0.3 mm to 1.0 mm. The material of the plate-shaped member can be freely selected as long as it is made of metal, and for example, any stainless steel plate can be used. As the stainless steel plate, for example, SUS304 or the like can be used.

[0039] The following describes the specific configuration of the gravel fall prevention device of the present invention. Figures 7 and 8 are developed plan views of various embodiments of the gravel fall prevention device. Figure 7(a) is a developed plan view of the first embodiment of the gravel fall prevention device shown in Figures 5 and 6. Figure 7(b) is a developed plan view of the second embodiment, and Figure 7(c) is a developed plan view of the third embodiment. Figures 8(a) and 8(b) are developed plan views of the fourth embodiment.

[0040] (First embodiment) A first embodiment will be described. As shown in FIG. 7(a), the gravel fall prevention device 10 of the first embodiment has two slit-shaped water passage holes 15, 15 along the longitudinal direction of the device. As described above, the two plate-shaped members 10a, 10a are connected by three connecting members 10b, 10b, 10b. The number of connecting members 10b is not limited to three. From the viewpoints of strength and cost, it is preferable to provide two to four connecting members 10b. Furthermore, from the viewpoints of strength and water permeability, the length of the water passage hole 15 in the longitudinal direction of the connecting member 10b is preferably, for example, 5 cm to 30 cm, and more preferably 7 cm to 15 cm. Because the gravel fall prevention device 10 has no holes other than the water passage hole 15, some of the gas that does not pass through the water passage hole 15 during backwashing may exert upward pressure on the plate-shaped member 10a of the gravel fall prevention device 10.

[0041] (Second embodiment) A second embodiment will now be described. As shown in Fig. 7(b), the gravel fall prevention device 20 of the second embodiment differs from the configuration described in the first embodiment in that two plate-like members 20a, 20a are provided with a plurality of through holes 21. The through holes 21 are slit-shaped, and from the viewpoints of protecting the slopes of the support members and allowing gas to pass through easily, as will be described later, the width in the minor axis direction is preferably, for example, about 1 mm to 20 mm, and more preferably about 3 mm to 10 mm. The width in the major axis direction of the through holes 21 is preferably, for example, about 20 mm to 60 mm, and more preferably about 30 mm to 50 mm.

[0042] The through holes 21 are oriented in a direction perpendicular to the longitudinal direction of the water passage hole 25 and are arranged in parallel in the longitudinal direction of the water passage hole 25. The interval between adjacent through holes 21 is, for example, preferably about 15 mm to 35 mm, and more preferably about 20 mm to 30 mm. Furthermore, the intervals between adjacent through holes 21 are preferably equal.

[0043] Because the gravel fall prevention device 20 has the above configuration, even if gas gets between the gravel fall prevention device 20 and the support member during backwashing without passing through the water passage hole 25, the rising gas can pass through the through hole 21. In particular, because the through hole 21 is disposed in the above manner relative to the water passage hole 25, the rising gas is more likely to come into contact with the through hole for a long period of time, making it easier for the gas to pass through the through hole 21. This makes it less likely for the gravel fall prevention device 20 to float up, and gravel is less likely to get between the support member and the gravel fall prevention device 20. As a result, the slope and slit portions of the support member are better protected.

[0044] The shape of the plurality of through holes is not limited to a slit shape and may be any shape. The plurality of through holes may face in different directions and be arranged at different intervals and in different positional relationships.

[0045] (Third embodiment) A third embodiment will now be described. As shown in Fig. 7(c), the gravel fall prevention device 30 of the third embodiment differs from the configuration described in the second embodiment in that the two plate-like members 30a, 30a are provided with slit-shaped through holes 32 that are arranged adjacent to the connecting member 30b in the minor axis direction of the water passage hole 35 of the gravel fall prevention device 30. The through holes 32 are arranged in parallel with the adjacent through holes 31.

[0046] With the gravel fall prevention device 30 having the above-described configuration, even if gas rising from below during backwashing is prevented from passing through the water passage hole 35 by the connecting member 30b, it can pass through the through-hole 32 arranged adjacent to the connecting member 30b. This further reduces the upward pressure acting on the gravel fall prevention device 30, making it even less likely to float up.

[0047] (Fourth embodiment) A fourth embodiment will now be described. Fig. 8(a) is an expanded plan view of a gravel fall prevention device provided in the groove of one support member, and Fig. 8(b) is an expanded plan view of a gravel fall prevention device provided in the groove between two adjacent support members. As shown in Fig. 8(a), a gravel fall prevention device 40 of the fourth embodiment differs from the configuration described in the third embodiment in that a plurality of slit-shaped through holes 41 are arranged in parallel and inclined with respect to the longitudinal direction of the water passage hole 45. Also, as shown in Fig. 8(b), a gravel fall prevention device 46 has a plurality of slit-shaped through holes 47 arranged in parallel and inclined with respect to the longitudinal direction of the water passage hole 49.

[0048] The gravel fall prevention devices 40, 46 have the above-described configuration. When gas gets between the gravel fall prevention device and the support member without passing through the water passage holes 45, 49 during backwashing, the gas easily passes through the through-holes 41, 47. Specifically, because the through-holes 41, 47 are inclined relative to the upward direction of the gas, the gas easily comes into contact with the through-holes 41, 47 as it rises along the back surface of the gravel fall prevention devices 40, 46 (the surface facing the support member), and easily passes through the through-holes 41, 47. Furthermore, when viewed perpendicularly to the longitudinal axis of the grooves in the support member, the gas that has passed through the through-holes 41, 47 escapes over the entire surface (the gas escapes evenly without partial unevenness). This finely disperses the gas, making it less likely to vibrate during backwashing. Furthermore, sand, filter media, gravel, etc. are less likely to get stuck or become clogged in the through-holes 41, 47, so the gravel fall prevention devices 40, 46 remain resistant to floating for a long period of time.

[0049] The filtering device of the present invention is equipped with the above-mentioned gravel fall prevention device, so that the gravel in the gravel layer is less likely to come into contact with the two slopes that form the grooves of the support member, and the slopes of the support member are less likely to deteriorate. As a result, the gravel fall prevention device prevents gravel from falling into the water collection chamber for a long period of time, reducing the maintenance burden of the filtering device and extending its lifespan.

[0050] Although the embodiments of the present invention have been described above using the drawings, the gravel fall prevention device and filtering device of the present invention are not limited to these. For example, the gravel fall prevention device may be provided on a support member to prevent gravel from falling and to protect the slope of the support member, and the shape of the plate-like member may be uneven rather than flat, and the slits of the water passage holes may be curved. [Industrial Applicability]

[0051] The gravel fall prevention device of the present invention suppresses deterioration of the support member and has excellent gravel fall prevention performance over the long term. Furthermore, the filtration device of the present invention has a long life and requires little maintenance because gravel is less likely to fall into the water collection chamber over the long term. As a result, it can be widely used in gravity filtration devices such as sand filtration basins and activated carbon adsorption basins used in water supply and sewerage purification systems. [Explanation of symbols]

[0052] 1. Filtration equipment 2 Filtration tank 3 Filter layer 4 Porous concrete layer 5 Gravel layer 6 Support member 7 Beam 8 Water Collection Chamber 9 Gas release device 10 Gravel fall prevention device 10a Plate-shaped member 10b Connecting member 11 Groove 12 outer edge 13 Top side 14 Slit section 15 Water vent 16 Gravel fall prevention device 16a Plate-shaped member 16b Connecting member 17 Groove 18 Slit section 19 Water vent 20 Gravel fall prevention device 20a Plate-shaped member 20b connecting member 21 Through hole 25 Water vent 30 Gravel fall prevention device 30a Plate-shaped member 30b connecting member 31 Through hole 32 Through hole 35 Water vent 40 Gravel fall prevention device 40a Plate-shaped member 40b connecting member 41 Through hole 45 Water vent 46 Gravel fall prevention device 46a Plate-shaped member 46b Connecting member 47 Through hole 49 Water vent

Claims

1. A gravel fall prevention device for a filtering device, The filtering device includes a gravel layer and a support member that supports the gravel in the gravel layer from below, the support member includes a groove having a V-shaped cross section and a slit portion at its bottom that extends in one direction and penetrates downward, The gravel fall prevention device is characterized in that it is a metal member with a V-shaped cross section that is placed flush along the groove of the support member and has a slit-shaped water passage hole at the bottom that extends in one direction.

2. The gravel fall prevention device has two plate-shaped members and a connecting member that connects the two plate-shaped members, 2. The gravel fall prevention device according to claim 1, wherein the plate-like member has a plurality of through holes.

3. The gravel fall prevention device according to claim 2, characterized in that the plurality of through holes are slit-shaped through holes that face in a direction other than the longitudinal direction of the water passage hole and are arranged in parallel in the longitudinal direction of the water passage hole.

4. 4. The gravel fall prevention device according to claim 2, wherein at least one of the plurality of through holes is disposed adjacent to the connecting member in the minor axis direction of the water passage hole.

5. A filtering device comprising the gravel fall prevention device according to any one of claims 1 to 4.

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