Filter drain with floater assembly for lowering groundwater level

Abstract

The invention relates to a filter drain (20) for draining fluid from a subsoil, wherein the filter drain comprises: an outer pipe (21) for insertion into the subsoil, wherein the outer pipe comprises an outer pipe circumferential wall (22) with a filter drain inlet (25) for receiving the fluid from the subsoil; an inner pipe (31) inside the outer pipe, wherein the inner pipe and the outer pipe together bound a fluid receiving channel (35) that is in fluid communication with the filter drain inlet, and wherein the inner pipe internally bounds a drainage channel (36) for evacuation of the received fluid; and a floater assembly (50) inside the outer pipe, wherein the floater assembly comprises a fluid passage device (51) with a fluid inlet opening (59) between the fluid receiving channel and the drainage channel, and a floater (70) that is moveable in a moving direction with respect to the fluid passage device between a draining position and a closing position, wherein in the draining position a fluid passage is present from the fluid receiving channel to the drainage channel via the fluid inlet opening, and wherein in the closing position said fluid passage is blocked.

Description

[0001] P143419PC00

[0002] Filter drain with floater assembly

[0003] BACKGROUND

[0004] The invention relates to a filter drain for draining fluid from a subsoil .

[0005] A known the filter drain comprises a pipe with a plurality of filter drain inlets that bounds a drainage channel . The known filter drain may form part of a drainage system for draining ground water from a subsoil , wherein multiple filter drains are vertically inserted into the subsoil are brought in fluid communication with a fluid pump via a horizontally arranged collecting drain .

[0006] SUMMARY OF THE INVENTION

[0007] A disadvantage of the known filter drain is that the drainage system may become less effective or instable when air enters the collecting drain via one or more of the filter drains .

[0008] It is an obj ect of the present invention to provide a filter drain that provides a solution for this .

[0009] According to a first aspect , the invention provides a filter drain for draining fluid from a subsoil , wherein the filter drain comprises : an outer pipe for insertion into the subsoil , wherein the outer pipe comprises an outer pipe circumferential wall with a filter drain inlet for receiving the fluid from the subsoil ; an inner pipe inside the outer pipe, wherein the inner pipe and the outer pipe together bound a fluid receiving channel that is in fluid communication with the filter drain inlet, and wherein the inner pipe internally bounds a drainage channel for evacuation of the received fluid; and a floater assembly inside the outer pipe, wherein the floater assembly comprises a fluid passage device with a fluid inlet opening between the fluid receiving channel and the drainage channel , and a floater that is moveable in a moving direction with respect to the fluid passage device between a draining position and a closing position, wherein in the draining position a fluid passage is present from the fluid receiving channel to the drainage channel via the fluid inlet opening, and wherein in the closing position said fluid passage is blocked .

[0010] The filter drain according to the invention comprises an outer pipe and an inner pipe that divides the inside of the outer pipe into a fluid receiving channel and a drainage channel . The filter drain comprises a floater assembly inside the outer pipe , having a floater that is movable between a draining position in which a fluid passage is present between the fluid receiving channel and the drainage channel , and a closing position in which said fluid passage is blocked . When a water level inside the fluid receiving channel is lowered to a height at which the floater is moved to its closing position, it is prevented that the water level is lowered further to a height at which air may enter the drainage channel . In a drainage system having multiple of these filter drains in fluid communication with a collecting drain, the floater assembly prevents that air enters the collecting drain . This keeps a drainage system effective and stable .

[0011] In an embodiment the floater extends along the fluid passage device and is moveable along the fluid passage device between the draining position and the closing position, whereby the fluid passage device forms a guide for the movement of the floater .

[0012] In an embodiment the fluid passage device comprises a fluid passage device outer wall that defines a fluid passage channel therein, wherein the fluid inlet opening is provided in the fluid passage device outer wall , and wherein the fluid passage channel is in fluid communication with the drainage channel via the fluid inlet opening, wherein the floater extends around the fluid passage device outer wall .

[0013] In an embodiment the floater comprises a floater guiding wall around the fluid passage device .

[0014] In an embodiment the floater comprises a conical floater outer wall having a floater outer wall top end and a floater outer wall bottom end, wherein the floater outer wall has a floater outer wall diameter that increases in the moving direction from the floater outer wall top end towards the floater outer wall bottom end . The conical floater outer wall causes a fluid flow between the floater and the outer pipe circumferential wall to accelerate towards the outer wall bottom end . This may cause turbulations that wobbles the floater with respect to the fluid passage device . This may prevent that soil particles clog between the floater and the fluid passage device , whereby the floater remains movable with respect to the fluid passage device .

[0015] In a combined embodiment the conical floater outer wall is arranged around the floater guiding wall .

[0016] In an embodiment the floater comprises a closing wall that closes of f between the floater outer wall and the floater guiding wall to define a buoyancy chamber between the floater guiding wall and the floater outer wall that gives the floater buoyancy on water .

[0017] In an embodiment the floater outer wall extends from the floater guiding wall as from the floater outer wall top end .

[0018] In an embodiment the floater comprises a plurality of grooves or undulations in the floater outer wall that extend between the floater outer wall top end and the floater outer wall bottom end, and that are arranged adj acent to each other in a circumferential direction of the floater outer wall . The grooves or undulations may split and divide abovementioned fluid flow between the floater and the outer pipe circumferential wall around the floater .

[0019] In an embodiment thereof the grooves or undulations have tops with a straight top line and bottoms with a straight bottom line, wherein the top lines and the bottom lines are inclined under an orientation angle with respect to the moving direction when seen in a direction transverse to the moving direction . The inclined grooves or undulations may provide a tangential thrust on the outer wall of the floater caused by abovementioned fluid flow . The tangential thrust may rotate the floater around the fluid passage device to prevent that soil particles clog between the outer pipe circumferential wall and the floater .

[0020] In an embodiment thereof the orientation angle is in the range of 3-15 ° .

[0021] In an embodiment the outer pipe circumferential wall has an outer pipe inner diameter, wherein the floater has a largest floater outer diameter at the floater outer wall bottom end, wherein the largest floater outer diameter is smaller than the outer pipe inner diameter .

[0022] In an embodiment the fluid passage device comprises a fluid passage device outer wall with a guiding section for guiding the floater along the fluid passage device, and an inlet section adj acent the guiding section with the fluid inlet opening for receiving fluid from the fluid receiving channel , wherein the guiding section has a constant guiding section outer diameter, and wherein the inlet section has a decreasing outer diameter as from the guiding section . The decreasing outer diameter may enhance the fluid passage through the fluid inlet opening .

[0023] In an embodiment the fluid passage device comprises a fluid passage device outer wall that defines a fluid passage channel therein, wherein the fluid passage channel is in fluid communication with the drainage channel , wherein the fluid passage device comprises a confining flange and a closure flange at the fluid passage device outer wall , wherein the fluid inlet opening is provided in the fluid passage device outer wall between the confining flange and the closure flange , wherein the floater extends around the fluid passage device outer wall and is enclosed between the confining flange and the closure flange .

[0024] In an embodiment the confining flange has a confining flange outer diameter, wherein the closure flange has a closure flange outer diameter, wherein the confining flange outer diameter and the closure flange outer diameter are larger than the guiding section outer diameter, wherein the floater abuts the confining flange in the draining position, and wherein the floater abuts the closure flange in the closing position .

[0025] In an embodiment the outer pipe has a first length and extends between an outer pipe bottom end and an outer pipe top end, wherein the inner pipe has a second length smaller than the first length and extends between an inner pipe bottom end and an inner pipe top end, wherein the inner pipe top end is provided inside the outer pipe spaced from the outer pipe top end, wherein the filter drain comprises a seal at the inner pipe top end between the inner pipe and the outer pipe that seals of f the fluid receiving channel . The outer pipe may be of any length as from the seal to the collecting drain, wherein the inside volume of the outer pipe forms a continuation of the drainage channel as from the seal .

[0026] In an embodiment the outer pipe and the inner pipe are concentric .

[0027] In an embodiment the floater is moveable between the draining position and the closing position in dependence of a level of fluid inside the filter drain .

[0028] According to a second aspect, the invention provides a drainage system for draining ground water from a subsoil of a drainage site, wherein the drainage system comprises a plurality of filter drains according to the invention, a collecting drain arranged on the subsoil , and a fluid pump, wherein the filter drains are in fluid communication with the collecting drain, and wherein the fluid pump is in fluid communication with the collecting drain for pumping ground water from the subsoil through the filter drains and the collecting drain .

[0029] The various aspects and features described and shown in the specification can be applied, individually, wherever possible . These individual aspects , in particular the aspects and features described in the attached dependent claims , can be made subj ect of divisional patent applications .

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The invention will be elucidated on the basis of an exemplary embodiment shown in the attached drawings , in which :

[0032] Figure 1 is a schematic overview of a drainage system with a plurality of filter drains at a drainage site ;

[0033] Figure 2 is a detail of a filter section of one of the filter drains of figure 1 ;

[0034] Figure 3A is a front view of one of the filter drains of figure 1 at a bottom section thereof ;

[0035] Figure 3B is a front view cross section of the bottom section of the filter drain of figure 3A, showing an internal floating assembly thereof in its draining position;

[0036] Figure 3C is a front view of the bottom section of the filter drain of figure 3A, wherein an outer pipe have been removed to show the floater assembly of figure 3B ;

[0037] Figure 4A is a front view of the floater assembly of figure 3C in its closing position;

[0038] Figure 4B is a front view cross section of the floater assembly of figure 4A;

[0039] Figure 5 is a front view of the floater assembly of figure 4A, wherein a floater thereof has been removed for illustrative purposes ;

[0040] Figure 6 is a front view cross section of a detail of a top section of one of the filter drains of figure 1 ; and Figure 7 is an isometric bottom view of the floater as shown in figure 4A. DETAILED DESCRIPTION OF THE INVENTION

[0041] Figure 1 is a schematic overview of a drainage system 1 at a drainage site 10 . The drainage system 1 is employed for draining ground water from a subsoil 11 at the drainage site 10 for locally and temporarily lowering the ground water level . The drainage system 1 comprises a horizontally or substantially hori zontal arranged collecting drain 2 on the subsoil 11 , a plurality of filter drains 20 that are each in fluid connection with the collecting drain 2 via a flexible connecting pipe 3 , and a fluid pump 4 that is in fluid connection with the collecting drain 2 for pumping ground water from the subsoil 11 through the filter drains 20 and the collecting drain 2 . The filter drains 20 are elongated in a longitudinal direction L and are inserted into the subsoil 11 in a vertical or substantially vertical direction, for example by flushing or by insertion into predrilled holes .

[0042] As best shown in figures 1 , 2 and 3B, the filter drain 20 comprises an outer pipe 21 having an outer pipe circumferential wall 22 that extends between a top end 23 and a bottom end 24 opposite the top end 23 . The outer pipe 21 has a first length LI between the top end 23 and the bottom end 24 , an inner diameter DI and an outer diameter D2 . In this example, the first length LI is about 6 meter, the outer diameter D2 is about 50 millimeter, and the inner diameter DI is about 45 millimeter .

[0043] The filter drain 20 has subsequently from the top end 23 of the outer pipe circumferential wall 22 towards the bottom end 24 thereof a top section 17 , a filter section 18 and a bottom section 19 . The outer pipe circumferential wall 22 comprises a plurality of elongated through slits 25 that form filter drain inlets at the filter section 18 of the filter drain 20 . As best shown in figure 2 , the through slits 25 extend in this example parallel to the longitudinal direction L of the outer pipe circumferential wall 22 . Multiple through slits 25 are arranged side by side both longitudinally and circumferentially at the outer pipe circumferential wall 22 to form rings . The through slits 25 are dimensioned to allow ground water to pass through, while holding back soil particles of the subsoil 11 .

[0044] As best shown in figures 3B and 3C, the filter drain 20 comprises a conical end cap 26 that closes off the bottom end 24 of the outer pipe circumferential wall 22 of the outer pipe 21 . The conical end cap 26 comprises a hollow cylindrical insertion portion 28 that is inserted in the outer pipe 21 at the bottom end 24 . The cylindrical insertion portion 28 merges into a conical tip portion 27 with a tip 29 that faces away from the outer pipe 21 . The cylindrical insertion portion 28 has a top inner diameter D3 and a bottom inner diameter D4 that is slightly smaller than the top inner diameter D3 . The cylindrical insertion portion 28 has an outer diameter D5 that is similar to or slightly smaller than the inner diameter DI of the outer pipe 21 so that the cylindrical insertion portion 28 is fitted inside the outer pipe 21 . The conical tip portion 27 has at the side closest to the top end 23 of the outer pipe circumferential wall 22 an outer diameter D6 that is similar to the outer diameter D2 of the outer pipe 21 , so that the conical tip portion 27 and the bottom end 24 of the outer pipe circumferential wall 22 are aligned .

[0045] As best shown in figures 3B, 3C and 6, the filter drain 20 comprises an inner pipe 31 that is arranged inside the outer pipe 21 . The inner pipe 31 has an inner pipe circumferential wall 32 that bounds a drainage channel 36 inside . The inner pipe circumferential wall 32 extends parallel or substantially parallel to the longitudinal direction L of the outer pipe 21 between a top end 33 and a bottom end 34 opposite the top end 33 . The inner pipe 31 has a second length L2 between the top end 33 and the bottom end 34 , an inner diameter D7 and an outer diameter D8 . The second length L2 is smaller than the first length LI , and the outer diameter D8 of the inner pipe 31 is smaller than the inner diameter DI of the outer pipe 21 . The inner pipe 31 is arranged inside the outer pipe 21 such that the top end 33 of the inner pipe 31 is located spaced from the top end 23 of the outer pipe circumferential wall 22 . The top end 33 of the inner pipe 31 is located at the top section 17 of the filter drain 20 near and above the filter section 18 thereof .

[0046] As best shown in figure 6, the filter drain 20 comprises at the top end 33 of the inner pipe 31 a seal 40 that extends between the inner circumference of the outer pipe circumferential wall 22 and the outer circumference of the inner pipe circumferential wall 32 . The seal 40 comprises a cylindrical holder 41 with an external ring groove 42 and a sealing ring 43 inside the ring groove 42 . The cylindrical holder 41 comprises an insert opening 44 having an abutment edge 49 . The inner pipe 31 is inserted into the insert opening 44 , and the top end 33 abuts the abutment edge 49. The cylindrical holder 41 is provided around the inner pipe 31 and has an outer diameter D9 that is similar to or slightly smaller than the inner diameter DI of the outer pipe 21 . The sealing ring 43 is in sealing contact with both the inner circumference of the outer pipe circumferential wall 22 and the cylindrical holder 41 . As best shown in figure 6 , the filter drain 20 comprises a annular fluid receiving channel 35 between the inner circumference of the outer pipe circumferential wall 22 and the outer circumference of the inner pipe circumferential wall 32 that is sealed off by the seal 40 .

[0047] As best shown in figure 3B, the filter drain 20 comprises a floater assembly 50 provided inside the outer pipe 21 and that comprises a fluid passage device 51 and a floater 70 around the fluid passage device 51 . The floater 70 has buoyancy on water . As best shown in figure 5, the fluid passage device 51 is elongated and extends in a longitudinal direction P between an open top end 53 and a closed bottom end 54 opposite the top end 53 . The longitudinal direction P of the fluid passage device 51 is parallel or substantially parallel to the longitudinal direction L of the outer pipe 21 . The fluid passage device 51 has subsequently from the top end 53 towards the bottom end 54 thereof a mounting section 45 with a constant mounting section outer diameter DI O , a guiding section 46 with a constant guiding section outer diameter Dl l that is larger than the mounting section outer diameter DI O , an inlet section 47 having an inlet section outer diameter that decreases as from the guiding section 46, and a bottom section 48 with a constant bottom section outer diameter D12 similar to the guiding section outer diameter Dl l .

[0048] The fluid passage device 51 comprises in this example a removable confining flange ring 61 at the mounting section 45 having a flange ring outer diameter D13 that is larger than the guiding section outer diameter Dl l . The flange ring 61 abuts against the guiding section 46 of the fluid passage device 51 . The fluid passage device 51 comprises an inlet closure flange 62 at the bottom section 48 near the inlet section 47 . The inlet closure flange 62 has an inlet closure flange outer diameter D14 similar to the flange ring outer diameter D13 .

[0049] As best shown in figure 4B, the fluid passage device 51 comprises a circumferential wall 52 that defines a fluid passage channel 58 therein that extends into the longitudinal direction P through the mounting section 45 , the guiding section 46 , the inlet section 47 , and partly into the bottom section 48 . The circumferential wall 52 comprises two opposite fluid inlet openings 59 to the fluid passage channel 58 .

[0050] As best shown in figure 3B, the mounting section 45 of the fluid passage device 51 is inserted into the inner pipe 31 through the bottom end 34 thereof so that the bottom end 34 of the inner pipe 31 and the flange ring 61 abut each other . The bottom section 48 of the fluid passage device 51 is partly inserted into the cylindrical insertion portion 28 of the conical end cap 26, and abuts against the portion of the cylindrical insertion portion 28 having the smaller bottom inner diameter D4 . The outer pipe 21 , the conical end cap 26, and the fluid passage device 51 are mutually locked to each other by means of a fastener 30 that passes through the outer pipe circumferential wall 22 , the cylindrical insertion portion 28 , and into the bottom section 48 of the fluid passage device 51 transverse to the longitudinal direction L of the outer pipe circumferential wall 22 .

[0051] As best shown in figures 4A, 4B and 7 , the floater 70 is shaped as a hollow generally conical frustum having a floater centerline F . The floater 70 is made of rigid plastic and comprises at its inside a cylindrical guiding wall 71 that extends between a guiding wall top end 73 and a guiding wall bottom end 74 , and that defines a floater channel 75 therein having a constant inner diameter D15. The constant inner diameter D15 is slightly larger than the guiding section outer diameter Dl l of the fluid passage device 51 , larger than the inlet section outer diameter of the fluid passage device 51 at the inlet section 47 thereof , and smaller than the flange ring outer diameter D13 and the inlet closure flange outer diameter D14 . The floater 70 comprises a conical outer wall 72 that extends between an outer wall top end 81 and an outer wall bottom end 82 and that extends around the guiding wall 71 . The outer wall top end 81 is connected to the guiding wall 71 near the guiding wall top end 73 .

[0052] The floater 70 comprises a closing wall 77 between the guiding wall 71 and the outer wall 72 that extends from the guiding wall 71 at the guiding wall bottom end 74 transverse to the floater centerline F . The closing wall 77 is connected to the outer wall 72 near the outer wall bottom end 82 . The closing wall 77 closes off the outer wall 72 against the guiding wall 71 to define a closed-off air-filled buoyancy chamber 78 between the guiding wall 71 and the outer wall 72 that gives the floater 70 buoyancy on water .

[0053] As best shown in figures 3C, 4A and 7 , the outer wall 72 of the floater 70 comprises at the outer circumference thereof a plurality of fluent grooves or undulations 76 . Each groove or undulation 76 extends between the outer wall top end 81 and the outer wall bottom end 82 . Multiple grooves or undulations 76 are arranged at the outer circumference of the outer wall 72 adj acent to each other in the circumferential direction of the outer wall 72 . The grooves or undulations

[0054] 76 have tops 79 with a straight top line T and bottoms 80 with a straight bottom line B in the outer wall 72 . The top lines T and the bottom lines B are inclined with respect to the floater centerline F when seen in a direction transverse to the floater centerline F . The top lines T and bottom lines B are inclined under an orientation angle a that is approximately 3- 15 ° . Each groove or undulation 76 bounds a flow chamber 90 between its two subsequent tops 79 and the outer pipe circumferential wall 22 .

[0055] The floater 70 has a smaller outer diameter D16 at the guiding wall top end 73 , and a larger outer diameter D17 at the outer wall bottom end 82 . The larger outer diameter D17 is defined by the tops 79 of the grooves or undulations 76. The larger outer diameter D17 is larger than the inlet closure flange outer diameter D14 , and slightly smaller than the inner diameter DI of the outer pipe 21 . The conical outer wall 72 is inclined with respect to the floater centerline F by a cone inclination angle p that is approximately 2- 6 ° .

[0056] As best shown in figure 4A, the floater 70 is arranged around the fluid passage device 51 and is enclosed between the confining flange ring 61 and the inlet closure flange 62 . The floater 70 is moveable in a moving direction M parallel to the longitudinal direction P of the fluid passage device 51 and parallel to the floater centerline F between a draining position as shown in figures 3B and 3C and a closing position as shown in figures 4A and 4B .

[0057] When the floater 70 is in the draining position as shown in figures 3A and 3B, the guiding wall top end 73 of the floater 70 abuts the flange ring 61 , and the closing wall

[0058] 77 and the guiding wall bottom end 74 are spaced from the inlet closure flange 62 , thereby providing a fluid passage T from the fluid receiving channel 35 to the fluid passage channel 58 via the fluid inlet openings 59. The floater 70 moves into the draining position when a level of fluid in the filter drain 20 is such that the floater 70 experiences suf ficient buoyancy to float . When the floater 70 is in de closing position as shown in figures 4A and 4B, the closing wall 77 and the guiding wall bottom end 74 of the floater 70 abut the inlet closure flange 62 under the own weight of the floater 70 , and the guiding wall top end 73 is spaced from the flange ring 61 , thereby blocking said fluid passage T from the fluid receiving channel 35 to the fluid passage channel 58 via the fluid inlet openings 59. The floater 70 moves into the closing position when a level of fluid in the filter drain 20 is such that the floater 70 does not experience sufficient buoyancy to float .

[0059] During drainage of the ground water from the subsoil 11 , fluid enters the fluid receiving channel 35 in the filter drain 20 at the filter section 18 thereof via the through slits 25. Fluid flows downwards through the fluid receiving channel 35, along the floater 70 , and towards the bottom end 24 of the outer pipe circumferential wall 22 . The bottom section 19 of the filter drain 20 is filled with fluid thereby causing the floater 70 to float due to its buoyance . This moves the floater 70 from the closing position into the draining position .

[0060] In the draining position the fluid passage T between the fluid receiving channel 35 and the fluid passage channel 58 is present . As the fluid pump 4 is in fluid communication with the top end 23 of the outer pipe 21 via the connecting pipe 3 and the collecting drain 2 , the fluid pump 4 pumps fluid subsequently through the fluid passage channel 58 , the inner pipe 31 , the outer pipe 21 at the portion thereof extending between the seal 40 and the top end 23 , the connecting pipe 3 , and into the collecting drain 2 .

[0061] When fluid flows along the floater 70 , the fluid flows through the flow chambers 90 that are defined by the grooves or undulations 76. As the outer wall 72 of the floater 70 is conical , the flow chambers 90 have a decreasing cross section towards the outer wall bottom end 82 . The decreasing cross section combined with the inclined grooves or undulations 76 provide a tangential thrust on the outer wall 72 of the floater 70 caused by the flow of fluid along the floater 70 . The tangential thrust rotates the floater 70 around its floater centerline F in a rotation direction R opposite the direction of the grooves or undulations 76 when seen from the outer wall top end 81 towards the outer wall bottom end 82 . During draining, while fluid enters the filter drain 20 via the through slits 25 , the floater 70 keeps rotating in the rotating direction R to prevent that soil particles clog between the outer pipe circumferential wall 22 and the floater 70 , and between the floater 70 and the fluid passage device 51 .

[0062] When substantially all fluid has been drained from the subsoil 11 , the level of fluid in the bottom section 19 of the filter drain 20 decreases , thereby moving the floater 70 from the draining position into the closing position . The fluid passage T between the fluid receiving channel 35 and the fluid passage channel 58 is blocked so that it is prevented that the fluid pump 4 draws air from the respective filter drain 20 into the collecting drain 2 . As the respective the filter drain 20 is closed of f from the drainage system 1 , the remaining filter drains of the drainage system 1 keep draining fluid from the subsoil 11 .

[0063] It is to be understood that the above description is included to illustrate the operation of the preferred embodiments and is not meant to limit the scope of the invention . From the above discussion, many variations will be apparent to one skilled in the art that would yet be encompassed by the scope of the present invention .

Claims

C L A I M S1 . A filter drain for draining fluid from a subsoil , wherein the filter drain comprises : an outer pipe for insertion into the subsoil , wherein the outer pipe comprises an outer pipe circumferential wall with a filter drain inlet for receiving the fluid from the subsoil ; an inner pipe inside the outer pipe, wherein the inner pipe and the outer pipe together bound a fluid receiving channel that is in fluid communication with the filter drain inlet, and wherein the inner pipe internally bounds a drainage channel for evacuation of the received fluid; and a floater assembly inside the outer pipe, wherein the floater assembly comprises a fluid passage device with a fluid inlet opening between the fluid receiving channel and the drainage channel , and a floater that is moveable in a moving direction with respect to the fluid passage device between a draining position and a closing position, wherein in the draining position a fluid passage is present from the fluid receiving channel to the drainage channel via the fluid inlet opening, and wherein in the closing position said fluid passage is blocked .2 . Filter drain according to claims 1 , wherein the floater extends along the fluid passage device and is moveable along the fluid passage device between the draining position and the closing position .3 . Filter drain according to any one of the preceding claims , wherein the fluid passage device comprises a fluid passage device outer wall that defines a fluid passage channel therein, wherein the fluid inlet opening is provided in the fluid passage device outer wall , and wherein the fluid passage channel is in fluid communication with the drainage channel via the fluid inlet opening, wherein the floater extends around the fluid passage device outer wall .4 . Filter drain according to any one of the preceding claims , wherein the floater comprises a floater guiding wall around the fluid passage device .

5. Filter drain according to any one of the preceding claims , wherein the floater comprises a conical floater outer wall having a floater outer wall top end and a floater outer wall bottom end, wherein the floater outer wall has a floater outer wall diameter that increases in the moving direction from the floater outer wall top end towards the floater outer wall bottom end .

6. Filter drain according to claims 4 and 5 , wherein the conical floater outer wall is arranged around the floater guiding wall .7 . Filter drain according to claim 6 , wherein the floater comprises a closing wall that closes of f between the floater outer wall and the floater guiding wall to define a buoyancy chamber between the floater guiding wall and the floater outer wall that gives the floater buoyancy on water .8 . Filter drain according to claim 6 or 7 , wherein the floater outer wall extends from the floater guiding wall as from the floater outer wall top end .

9. Filter drain according to any one of the claims 5-8 , wherein the floater comprises a plurality of grooves or undulations in the floater outer wall that extend between the floater outer wall top end and the floater outer wall bottom end, and that are arranged adj acent to each other in a circumferential direction of the floater outer wall .10 . Filter drain according to claim 9 , wherein the grooves or undulations have tops with a straight top line and bottoms with a straight bottom line, wherein the top lines and the bottom lines are inclined under an orientation angle with respect to the moving direction when seen in a direction transverse to the moving direction .11 . Filter drain according to claim 10 , wherein the orientation angle is in the range of 3-15 ° .12 . Filter drain according to any one of the claims 5-11 , wherein the outer pipe circumferential wall has an outerpipe inner diameter, wherein the floater has a largest floater outer diameter at the floater outer wall bottom end, wherein the largest floater outer diameter is smaller than the outer pipe inner diameter .13 . Filter drain according to any one of the preceding claims , wherein the fluid passage device comprises a fluid passage device outer wall with a guiding section for guiding the floater along the fluid passage device, and an inlet section adj acent the guiding section with the fluid inlet opening for receiving fluid from the fluid receiving channel , wherein the guiding section has a constant guiding section outer diameter, and wherein the inlet section has a decreasing outer diameter as from the guiding section .14 . Filter drain according to any one of the preceding claims , wherein the fluid passage device comprises a fluid passage device outer wall that defines a fluid passage channel therein, wherein the fluid passage channel is in fluid communication with the drainage channel , wherein the fluid passage device comprises a confining flange and a closure flange at the fluid passage device outer wall , wherein the fluid inlet opening is provided in the fluid passage device outer wall between the confining flange and the closure flange , wherein the floater extends around the fluid passage device outer wall and is enclosed between the confining flange and the closure flange .

15. Filter drain according to claims 13 and 14 , wherein the confining flange has a confining flange outer diameter, wherein the closure flange has a closure flange outer diameter, wherein the confining flange outer diameter and the closure flange outer diameter are larger than the guiding section outer diameter, wherein the floater abuts the confining flange in the draining position, and wherein the floater abuts the closure flange in the closing position .

16. Filter drain according to any one of the preceding claims , wherein the outer pipe has a first length and extends between an outer pipe bottom end and an outer pipe top end, wherein the inner pipe has a second lengthsmaller than the first length and extends between an inner pipe bottom end and an inner pipe top end, wherein the inner pipe top end is provided inside the outer pipe spaced from the outer pipe top end, wherein the filter drain comprises a seal at the inner pipe top end between the inner pipe and the outer pipe that seals of f the fluid receiving channel .17 . Filter drain according to any one of the preceding claims , wherein the outer pipe and the inner pipe are concentric .18 . Filter drain according to any one of the preceding claims , wherein the floater is moveable between the draining position and the closing position in dependence of a level of fluid inside the filter drain .

19. Drainage system for draining ground water from a subsoil of a drainage site, wherein the drainage system comprises a plurality of filter drains according to any one of the preceding claims , a collecting drain arranged on the subsoil , and a fluid pump, wherein the filter drains are in fluid communication with the collecting drain, and wherein the fluid pump is in fluid communication with the collecting drain for pumping ground water from the subsoil through the filter drains and the collecting drain .-o-o-o-o-o- o-o-o-LO / FG

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