GB2504198A

GB2504198A - System and method for filtering a flow of water

Info

Publication number: GB2504198A
Application number: GB1309414.9A
Authority: GB
Inventors: Philip Jackson
Original assignee: E Beaudrey et Cie SA
Current assignee: E Beaudrey et Cie SA
Priority date: 2012-05-24
Filing date: 2013-05-24
Publication date: 2014-01-22
Anticipated expiration: 2033-05-24
Also published as: FR2990877A1; FR2990877B1; GB2504198B; GB201309414D0

Abstract

A system for filtering a flow of water comprises a movable filter strainer 11 comprising a plurality of filtering elements 18 arranged in succession to form a closed filtering surface which can be set in movement such that each element can be displaced between a low point (P1) and a high point (P2) along a first path. A plurality of lifting scoops 30 are arranged on the upstream side of the filtering surface; each scoop having, in a plane perpendicular to that of said filtering surface, a cross-section in the form of a cup. Each scoop is of a shape and a depth which make it possible to contain a sufficient store of water to transport live fish during the displacement of the scoop between the high and low points and is of a sufficiently flared shape at the opening thereof so as to be washable by supplying water tangentially from a washing device 23 to one of the two side walls 30b, 30c thereof.

Description

SYSTEM AND METHOD FOR FILTERING A FLOW OF WATER

The invention relates to the recovery of the living fish which are stopped by the filtering elements of a fHter strainer such as a filter drum.

A filter drum generally comprises a porous rotating cylinder having a horizontal axis, which rotates between two vertical walls. The water to he strained either arrives outside the cylinder, passes through the filter cylinder and exits, having been strained, via one or more openings formed in the vertical side waRs, or arrives inside the filter cylinder and exits, having been strained, to the outside of the drum. In any case, the drum is of a sufficient diameter to ensure, 1.0 on the one hand, sufficient immersion when the water level is lowest and, on the other hand, a sufficient height to make counter-current washing possible using jets and to make it possible to collect the stopped bodies above the highest water level. The resulting diameter may for example be over twenty metres. The fish and some pieces of debris which are stopped on a filtering element (usuauy formed of a metal screen cr a perforated plate) tend to slide along it when it exits the water to ascend towards the washing zone.

So as to prevent said fish and debris from failing back down, horizontal recovery scoops are arranged at regular intervals on the upstream face of the filter cylinder. The fish and debris are thus collected and stored there until the arrival at the top part of the washing station. Most of the time, the peripheral speed of the filter cylinder is low (a few metres per minute), and the transit time of the fish outside the water is several minutes long, and this is found to be very unfavourable to the survival of the fish.

The present invention thus aims to improve the survival of the fish during the filtration of a flow of water using a filter strainer.

The present invention relates to a filtration system for a flow of water, characterised in that it comprises: a filter strainer comprising a plurality of filtering elements arranged in succession so as to form a filtering surface which is closed in on itself and which can be set in movement, the strainer being able to be arranged vertically in such a way that, during the movement thereof, each filtering element can be displaced from a low point to a high point along a first path and return to the low point along a second path, -a plurality of lifting scoops, arranged facing a first of the two opposite sides of the filtering surface and so as to be spaced apart from one another in the direction in which the filtering elements are arranged in succession, said scoops being able to be displaced simu!taneously with the filtering elements, each scoop having, in a plane perpendicular to that of said filtering surface, a crosssection in the form of a cup comprising a dished base, two flared side walls and an opening opposite the base, the cup being of a shape and a depth which make it possible to contain a sufficient store of water to transport fish while keeping them alive during the displacement of the scoop from the low point to the high point along the first path, the scoop being of a sufficiently flared shape at the opening thereof so as to be washable (at the top part) by supplying water tangentiahy to one of the two side walk thereof, -a device for washing the lifting scoops, which is arranged facing the filtering surface, on the second, opposite side thereof and close to the high point of the first path.

Each scoop thus has a sufficient water height (for example approximately a few cm), during the ascent thereof to the upper discharge position (high point), to keep the fl.sh in the water and thus alive. The depth of the scoop and the inclination of the side walls thereof make it possible to prevent said fish from Palling back down during the ascent thereof towards the discharge. The inclination of the side walls is such that, even when the scoop is tilted on one side from one or other of the walls thereof during the ascending movement (when the strainer is a drum), the fish remain within the container. Further, the side walls are sufficiently flared (that is to say, the distance between the two walls increases from the base towards the opening) for a jet of pressurised water from the washing device, in the discharge position, to penetrate inside the scoop tangentially to one of the walls so as to wash it and push the fish out without injuring them. It will be noted that, by placing the device for washing the scoops on the side of the filtration surface opposite the side where the scoops are positioned, the jet of water for washing the scoops can be attenuated by crossing the filtration surface. This reduces the risk of injuring the fish which are present in the scoops. This risk can also be reduced further with a moderate jet pressure (low water pressure). The first side of the filtration surface is for example arranged on the upstream side of the flow of water and each of the scoops has the opening orientated upwards when said scoops are arranged facing the filtering elements, which can be displaced from the low point to the high point along the first path, this opening being orientated downwards when said scoops are arranged facing the filtering elements, which can return from the high point to the low point along the second path.

In accordance with other features, which are possible in isolation or in S combination: -the device for washing the lifting scoops can, initially, generate a jet of washing water in such a way that it passes substantially perpendicularly through the filtering surface (making it possible to obtain a high washing effectiveness of the filtering elements) and, subsequently, direct it in such a way that It penetrates inside a scoop arranged close to the high point of the first path, in a direction tangential to one of the two lateral wails and so as to run along said wail; -the device for washing the lifting scoops comprises at least one member for generating a jet of washing water, arranged on the second, opposite side of the filtering surface and close to the high point of the first path; -the device for washing the lifting scoops is a low-water-pressure washing device; -the system comprises at least one deflector element (separate from the device for washing the lifting scoops) arranged on the first side of the filtering surface and facing the opening of each scoop so as to deflect the jet of washing water which has passed through the filtering surface towards the base of the scoop; this arrangement makes it possible to maintain the effectiveness of the direction of the jet perpendicular to the filtration surface for passing through said surface, and only to alter the direction thereof afterwards so as to introduce it tangentially to one of the side walls and along said wall; the jet is deflected in such a way as to recover as much as possible of the kinetic energy of the jet; -the one of the two side walls of each scoop which Is closer to the filtering surface extends from the base in a first direction, so as to extend said base as far as the opening of the scoop, and subsequently extends In a second direction, so as to extend the opening so as to form a ledge substantially perpendicular to the adjacent filtering surface; -said at least one deflector element comprises a face arranged facing the scoop, said face comprising, in cross-section, on the one hand a first part, arranged opposite the ledge and extending at an inclination thereto so as to form together therewith a passage of a shape converging towards the opening, and on the other hand a second part, arranged facing the opening and angled towards the base of the lifting scoop with respect to the direction of extension of the first part; -the other side wail of each scoop has a free edge, which is located close to the opening and which is provided with teeth arranged longitudinally in a direction perpendicular to the plane of the cross-section of the scoop; this toothed edge makes it possible, during the ascent of the scoop and the inclination thereof on one or other side (when the filter strainer is a drum), to let any excess water pass over the edge between the teeth but to hold back the fish by virtue of the teeth (retaining members); -the number of scoops depends in particular on the distance or height between the low point and the high point of the first path followed by the filtering elements and on the number of fish to be collected; -the system comprises a high-pressure washing device for the filtering surface, said device being arranged facing the filtering surface on the second, opposite side thereof and downstream from the device for washing the lifting scoops In terms of the direction of displacement of the filtering elements; by arranged the two washing devices on the same side of the filtration surface, the design of the system (arrival of water, pipes etc.) Is simplified; -the filter strainer Is a filter drum or a chain filter.The invention further relates to an installation comprising: -a duct having a longitudinal direction along which the water flows, -a system for filtering the flow of water as disclosed in brief above, which is arranged in the duct, the low point and the high point of the first path, which can be followed by the filtering elements during the movement thereof, being arranged along the height of the duct, which is perpendicular to the longitudinal direction thereof.

The Invention further relates to a method for filtering a flow of water, using a filtering system comprising: -a filter strainercomprising a plurality of filtering elements arranged In succession so as to form a filtering surface which is closed In on itself, -a plurality of lifting scoops arranged, on the one hand, facing a first of the two opposite sIdes of the filtering surface which Is arranged on the upstream side of the flow of water and, on the other hand, so as to be spaced apart from one another In the directIon In which the filtering elements are arranged in successon, each scoop having, in a plane perpendicular to that of said strainer, a cross-section in the form of a cup comprising a dished base, two flared side walls and an opening opposite the base.

The method comprises the following steps: -setting the filtering surface in movement so as to displace each filtering element and each scoop in succession from a low point located below the water to a high point located above the water along a first path and, subsequently, from the high point to the low point along a second path, the cup of each scoop being of a shape and a depth which make it possible to contain a sufficient store of water to transport fish while keeping them alive during the displacement of the scoop from the low point to the high point along the first path, generating and supplying a jet of washing water inside each scoop which is located close to the high point, the jet of water being generated close to the high point of the first path and on the second, opposite side of the filtering is surface which is located on the downstream side of the flow of water, the jet of water being introduced via the flared opening, tangentially to one of the two side walls of the cup and along said wall as far as the base of the scoop, thus making it possible to push the store or water and the fish, on the side of the opposite side wall, towards and beyond the free edge thereof which is located close to the opening.

In accordance with further features, which are possible in isolation or in combination: -the step of generating and supplying a jet of washing water inside each scoop comprises the following sub-steps: -generating a jet of washing water so as to pass substantially perpendicularly through the filtering surface so as to reach the scoop located on the first side of the filtering surface, -deflecting the jet of washing water which has passed through the filtering surface towards the base of the scoop; -the method comprises a step of recovering the fish which are collected by the scoop which is thus washed into a gutter arranged in line with said scoop, said scoop following the displacement thereof along the second path so as to return to the low point at collect water and fish again.

The advantages of the invention wifl become clearer from the non-limiting embodiment disclosed in the following with reference to the appended drawings, in which: -Fig. 1 is a schematic sectional view in the vertical plane of an installation comprising a filter drum according to the invention; Fig. 2 is a schematic view iii a horizontal section along the sectional s plane AA of the installation of Fig. 1; Fig. 3 is an enlarged schematic view of the detail zone C of the instahation of Fig. 1; Fig. 4 is an enlarged schematic view of the detail zone D of the installation of Fig. 1; to -Fig. 5 is a schematic perspective view of a lifting container of the installation of Fig. 1; Fig. 6 is an enlarged schematic view of part of the toothed free edge 48 of the inside of a scoop; Fig. 7a and 7b are schematic views in a longitudinal section and cross-section respectively of an installation comprising a chain filter according to the invention.

As shown in Fig. I and 2, an installation 1 comprises a duct 2 which conveys a flow of water in a longitudinal flow direction fi and which is for example subdivided into two parallel ducts 2a and 2b. The installation comprises a fiitering system 10 arranged in an opening 3, generally concreted, which is arranged between the two ducts and, more particularly, between two side walls 3a and 3b, which are for example parallel, of the opening. The two walls are each provided with an opening 4a, 4b, making it possible for the untreated water which arrives via the ducts 2a and 2b to return laterally into the filtering system 10 along the arrows f2, The system comprises a filter strainer 11 such as a vertically arranged drum or cylinder which comprises a shaft 12 carried by two bearings 13, a central hub 14, regularly distributed spokes 15 which are fixed, at one of the two opposite ends thereof, to the hub 14 and, at the other end, to a circular rim 16. This peripheral rim 16 supports axial struts 17, parallel to the shaft 12, to which for example a plurality of filtering elemenLs 18 are fixed, which are generally woven metal screens or perforated plates, or else of some other type. The filtering elements are arranged in succession so as to form a filtering surface which is closed in on itself, the untreated water passes through each immersed filtering element 18 along the arrows f3 and the debris and the various bodies which it contains are stopped on the upstream face ISa of the filtering element 18 (first side of the filtering surface, located on the side of the upstream flow). The water which has thus been strained exits from the opening via an outlet pipe 19 along the arrow f4 (Fig. 1), The drum 11 is driven in rotation, in the direction shown by the arrow R, S by a motor reducer (not shown) which engages with a pinion 20 which drives a circular rack 21 carried on the drum. During the rotational movement of the drum, each filtering element 18 passes frorri a low point P1 toa high point P2 via a first ascending path (right-hand semicircle in Fig. 1) and returns to the low point via a second path (lefthand semicircle).

The filtration system 10 comprises a washing apparatus 22 arranged facing the filtering surface and comprising at least one member for generating a (pressurised) jet of washing water, arranged at the top part of the drum (close to the high point P2) and facing the downstream face 18b of the filtering surface (second opposite side of the surface, located on the side of the downstream flow). The washing apparatus 22 comprises a device 23 for washing the lifting scoops comprising for example, outside the drum, at least one manifold each formed of a plurality of members for generating a jet of water. A couection gutter 24 is arranged facing the upstream face 18a of the filtering surface, at the top part of the drum and facing said at least one washing manifold (washing station) so as to coliect the debris and bodies separated from the upstream face of the filtering surface by the jet or jets.

The opening 3 and the drum 11 are designed in such a way that, on the one hand, the drum provides a sufficient wetted surface when the untreated water is at the lowest level (BE) thereof and, on the other hand, the counter-current washing device and the collection gutter are located above the highest possible water level (HE).

So as to reduce the overall cost, it is attempted to reduce the diameter of the drum and, therefore, the volume of the opening. This results in having a small immersed height when the water level is low, and in the gutter assembly 24 and washing apparatus 22 being installed very high up. This design is not satisfactory in terms of the ascent and the collection of the debris, since, above the axis 12. of the drum, the debris is not supported against the filtering elements 18 by gravity and can fall back down into the untreated water, thus reducing the effectiveness of the drum. The greater the angle between the horizontal at the axis 12 and a radial line L passing through the manifold 23, the

S

more debris fafls back down into the untreated water. So as to overcome this drawback, lifting scoops or containers 30, the concavity of which is orientated upwards on the ascending side of the drum and downwards on the descending side of the drum, are instaDed at regular intervals (for example a few tens of centimetres apart) facing the upstream face 18a of the fiftering surface, for examp!e at the support cross-beams 17, and fixed to said cross--beams in a manner known per se. The scoops are for example installed in the cross-beams 17, although any other attachment arrangement is conceivable. The debris which faNs from the fNtering elements during the ascent thereof out of the water is collected by the scoops 30. The number of lifting scoops depends in particular on the distance or height between the low point and the high point of the first path followed by the filtering elements and on the number of fish to be collected.

It will be noted that the filtering surface of the drum comprises, at the width or depth thereof shown in Fig. 2, two filtering elements, one for each half-is drum (the two half-drums are separated from one another by the spokes 15), and one cross-beam for each filtering element as well as one scoop for each cross-beam.

The fish which are held back along with the debris on the upstream face of the filtering elerTlents are alive, and nowadays it is compulsory to do everything possible to keep them safe. The fish survives better ii it is not exposed to the air at any moment. Also, it should not be subjected to any vioLent water jet impact.

The co!lection scoops thus each comprise a sufficient store of water for the fish which is/are collected in the scoop not to be exposed to the air at any moment, irrespective of the position of the scoop in the ascent thereof towards the washing station (first path between points P1 and P2). By contrast, the scoop has to be emptied of the fish which it contains very rapidly at the top part, above the gutter 24.

Each scoop 30 has, in a piane (plane of Fig. 1, 3 and 4) perpendicular to that of the filtration surface, a cross-section in the form of a cup, and extends axia!ly (parallel to the shaft 12) along a filtering element in a longitudinal direction as shown in perspective in Fig. 5. The inside of the scoop has for example the form of a trench or channel. The cup shape (Fig. 3) comprises a concave, dished base 30a, from which two side walls 30b, 30c extend, away from said base, in a form flared towards the opening 30 of the scoop which is opposite the base. The scoop is closed at the two opposite ends by end walls or partitions 30e, 30f. The side waRs are at a large incUnation to a straight line N normal to the surface of the fiftering elements 18 (the angle of inclination of these waRs is substantiaRy greater than the angle a in Fig. 1 between the horizontal straight line passing through the axis 12 of the drum and the radius L passing through the central axis of the washing manifold 23; this angle is for example at least 45°), and are long enough to give the cup a shape and depth which allow it to create a store of water 31 of an appropriate volume for accommodating the fish which it is desired to keep safe. The store of water is created when the eye is located at the low water eve! (Fig. 3) and is displaced inside the cup while remaining trapped when the scoop ascends (Fig. 4). This makes it possible to keep the fish collected in the scoop alive both when the store of water is created and during the ascent and fall of the scoop, in which the fish are stopped by the filtration surface. It should be noted that if the level of untreated water is higher than the low water level, the volume of the store of water 31 is greater.

The angle of inclination of the side wails should not be too close to 90° (US-shape), that is to say the opening 30d should be sufficiently flared (V-shape of the walls) to make it possible to wash the scoop in the high position (Fig. 4) by way of an arrival of water tangential to the wall 3Db adjacent to the fi!tration surface. It wi!l be noted that the wa!ls JOb and 30c are not necessary symmetrical with one another about the central plane of the cup, perpendicular to the plane of Fig. 3. The wall 30b closer to the filtering element 18 extends from the opening 30d, away from said opening, in a different direction from the direction of extension of the wall 30b between the base and the opening. The extension of the wall 30b towards the adjacent filtering element 18 thus forms a ledge JOg which is substantially perpendicular to said element and which may or may not be fixed thereto. This edge has a smooth, planar upper face.

The aforementioned manifold 23 is equipped with members for generating a jet of water, which are sprayers 37 which generate fanned jets. The jets which are thus generated are regularly spaced and are designed to produce a high speed layer of water 40. This manifold is a low-pressure manifold having a sufficiently low impact so as not to injure the fish (pressure obtained by experimental biological determination and generally less than or equal to I bar).

The different jets of water, and therefore the layer of water resulting therefrom, are directed substantially perpendicular to the filtration surface so as to reach it with the maximum effectiveness for washing and for removing the bodies stopped and fixed thereto! The device for washing the lifting scoops also comprises, separately from the washing manifold, on the side of the upstream face of the filtering elements, a deflector element 42 for each scoop 30. The element 42 is arranged both facing the opening 30d of the scoop and adjacent to a filtering element 18, so as to deflect the washing water of the layer 40, which has passed through the filtering element, towards the base of the scoop. More specifically, the element 42 is in the form of an plate which is laid out in the longitudinal direction of the scoop and which comprises two parts 42a and 42b which are angled with respect to one another as shown in cross-section in Fig. 3 and 4: a first part 42a (adjacent to the filtering element 18) has a smooth internal face 42c arranged facing the ledge 30g and extending at an inclination thereto so as to form together therewith a space or passage 44 of a shape converging towards the opening 30d, and a second part 4Th, arranged facing the opening 30d and penetrating therethrough towards the base 30a of the scoop, in a direction parallel to the side wall 3Db. This second part 42b has a smooth internal face 42d arranged facing the side wall 3Db, forming together therewith a duct 46 which extends the converging passage 44. The second part 42b penetrates slightly into the inside of the scoop, by a sufficient distance (a few centimetres) to give the deflected jet the appropriate orientation, It will be noted that the element 42 may cover other shapes which allow it to deflect the arrival of water from the filtration surface. The opposite side wall 30c of the scoop has a free edge 48 which, for example, projects beyond the plane of the opening 30d defined by the free edges of the end walls 30e and 30f and by the plane of the upper face of the ledge 30g. This free edge 48 thus extends the length or extension of the side wall 30c, making it possible to increase the volume of the store of water contained in the scoop. Further, the free edge 48 is provided with teeth or slots 49 arranged over the length thereof (Fig. 5) or over part of said length.

When the scoop 30 passes above the level of the shaft 12, the maximum volume of water which the scoop can store decreases until the configuration of Fig. 4, showing detail D of the washing of the scoop at the top part, is reached.

When the scoop ascends, any excess water escapes by being poured out over the free edge 48. This toothed free edge 48 makes it possible to retain the small bodies or fish contained in the scoop 30 and to prevent them from fafling back down into the water during this slow pouring, as shown in Hg. 6. The jet (layer 40) initiafly deans the filtering elements 18 arranged above the scoop 30 as they are travelled past, in front of the jet along the arrow R, and throws the debris which has accumulated on the upstream face iSa into the gutter 21.

When the scoop reaches the washing station (high position of Fig. 4), the volume of the store of water 31 containing the fish has to be discharged into the gutter 24. It will be appreciated that it the wall 30c were at a smaller indination to the normal N to the surface, the stock of water would have been emptied before reaching the discharge position (Fig. 4) and the fish would have been trapped in the scoop without any water. The jet layer 40 passing through the filtration surface strikes the facing internal face 42c of the deflector substantially tangentially (maximum recovery of kinetic energy), and thus follows the profile of the internal faces 42c and 42d thereof. The jet layer or sheet of water is thus is guided into the converging passage 44 with a small loss of kinetic energy, and subsequently into the duct 45 via which it penetrates into the scoop, tangentially to the side wall 3Db and flowing along said wall as far as the base 30a. The kinetic energy of the high-energy sheet of water (a few mis) thus carries the water and the fish contained in the store 31 towards the free edge 48 and throws them beyond it in such a way that they are poured out into the gutter 24 without being subjected to a significant shock or to any drying out. The teeth 49 and the gaps thereof are also swept and cleaned. The filtering elements 18 and the associated scoops 30 are thus relieved of all aquatic life.

The washing apparatus 22 further comprises a device 50 for washing the filtering elements, such as a second higherpressure washing manifold 50 (for example several bars). This second washing manifold is located above the low-pressure manifold 23 (Fig. 1) and washes each filtering element 18 with a counter-current, to finish relieving it of stickier non-biological bodies. Each scoop is cleaned violently in turn when it passes in front of the high-pressure manifold.

The system of scoops having a permanent water store, which can be cleaned by sweeping, may beneficially be used for all types of chain filter, in particular those with flow from the outside to the inside as shown in Fig. 7a and lb. The filter strainer 60 is installed in a duct 70 upstream from an outlet pipe 72 for filtered flow. The strainer comprises a filtration surface which is closed in on itself, having a general oblong shape in longitudinal section (Fig. 7a), having two large vertical walk 60a (ascending side), 60b (descending side) which are interconnected at the top and bottom parts by two rounded waRs 60c, 60d. The surface formed of ffltering elements 61 which are arranged in succession and articulated rotates on itseft in the direction of rotation R, in such a way that each S filtering element is displaced from a low point P1 to a high point P2 along a first, ascending path and returns to the low point along a second, descending path.

The filtration surface is equipped, on the upstream side, with scoops 62 which are identical to the scoops 30 and which are mounted on the cross-beams 17.

Two washing devices 74, 76 (for example manifolds) are arranged facing the downstream side of the strainer and two recovery gutters 78, 80 are arranged facing the devices 74, 76 respectively on the upstream side of the strainer, at the top part. The device 74 is of a low pressure so as to recover the fish in the gutter 78 (like the device 23), and the device 80 is of a high pressure, like the device 50. The filtration system of Fig. 7a and 7b has the same features and operates in the same manner as that of the preceding drawings, apart from the fact that in this case the scoops 62 maintain the orientation thereof during the ascent thereof to the first washing position (74, 78), and subsequently during the descent thereof from the second washing position (76, 80) thereof to the bottom part.

The system of scoops may also be used in drums for circulating water from the outside to the inside when the low-pressure washing is carried out on the ascending side of the drum.

Any other system for sweeping the store of water of a scoop so as to throw it towards a collection tray is an application of the present invention. By way of non-limiting example, this may be a washing manifold arranged on the side of the untreated water and sweeping a shell-shaped scoop.

Claims

1. System for filtering a flow of water, characterised in that it comprises: -a filter strainer (11; 60) comprising a plurality of filtering elements (18; 61) arranged in succession so as to form a filtering surface which is closed in on S itself and which can be set in movement, the strainer being able to be arranged vertically In such a way that, during the movement thereof, each filtering element can be displaced from a low point (P1) to a high point (P2) along a first path and return to the low point along a second path, -a plurality of lifting scoops (30; 62), arranged facing the first of the two opposite sides of the filtering surface and so as to be spaced apart from one another In the direction in which the filtering elements are arranged in succession, said scoops being able to be displaced simultaneously with the filtering elements, each scoop having, in a plane perpendicular to that of said filtering surface, a cross-section in the form of a cup comprising a dished base (30a), two flared side walls (30b, 30c) and an opening (30d) opposite the base, the cup being of a shape and a depth which make it possible to contain a sufficient store of water to transport fish while keeping them alive during the displacement of the scoop from the low point to the high point along the first path, the scoop being of a sufficiently flared shape at the opening thereof so as to be washable by supplying water tangentially to one of the two side wails thereof, -a device for washing the lifting scoops, which is arranged facing the filtering surface, on the second, opposite side thereof and close to the high point of the first path.

2. System according to claim 1, characterlsed in that the device for washing the lifting scoops can, initially, generate a jet of washing water in such a way that it passes substantially perpendicularly through the filtering surface and, subsequently, direct it in such a way that it penetrates inside a scoop (30) arranged close to the high point of the first path, in a direction tangential to one of the two lateral walls and so as to run along said wall.

3. System according to either claim 1 or claim 2, characterised in that the device for washing the lifting scoops comprises at least one member for generating a jet of washing water (23; 74), arranged on the second, opposite side of the ffltering surface and dose to the high point of the first path.

4. System according to daim 3, characterised in that the device for washing the lifting scoops is a ow-water-pressure washing device.

5. System according to any one of claims 2 to 4, characterised in that it comprises at east one deflector element (42) arranged on the first side of the fiftering surface and facing the opening of each scoop (30; 62) so as to deflect the jet of washing water which has passed through the ffltering surface towards the base of the scoop.

6. System according to any one of claims 1 to 5, characterised in that the one (30b) of the two side wails of each scoop which is closer to the filtering surface extends from the base in a first direction, so as to extend said base as far as the opening (30d) of the scoop, and subsequently extends in a second direction, so as to extend the opening by forming a edge (30g) substantially perpendicular to the adjacent filtering surface.

7. System according to claims S and 6, characterised in that at east one deflector element (42) comprises a face arranged facing the scoop, said face comprising, in cross-section, on the one hand a first part (42c), arranged over the ledge and extending at an inclination thereto so as to form together therewith a passage (44) of a shape converging towards the opening, and on the other hand a second part (42d), arranged facing the opening and angled towards the base (30a) of the lifting scoop with respect to the direction of extension of the first part.

8. System according to either claim 6 or claim 7, characterised in that the other side wafl (30c) of each scoop has a free edge (48), which is located close to the opening (30d) and which is provided with teeth (49) arranged longitudinally in a direction perpendicular to the plane of the cross-section of the scoop.

9. System according to any one of claims 1 to 8, characterised in that it comprises a high-pressure washing device for the fiftering surface, said device being arranged facing the filtering surface on the second, opposite side thereof and downstream from the device for washing the Ufting scoops with respect to S the direction of displacement of the filtering elements.

10. System according to any one of claims 1 to 9, characterised in that the filter strainer is a filter drum or a chain filter.

11. Method for filtering a flow of water, using a filtering system comprising: -a filter strainer (11; 60) comprising a plurality of filtering elements (18; 61) arranged in succession so as to form a filtering surface which is closed in on itself, Is -a piurality of lifting scoops (30; 62) arranged, on the one hand, facing the first of the two opposite sides of the filtering surface which is arranged on the upstream side of the flow of water and, on the other hand, so as to be spaced apart from one another in the direction in which the filtering elements are arranged in succession, each scoop having, in a plane perpendicular to that of said strainer, a cross-section in the form of a cup comprising a dished base (30a), two flared side walls (30b, 30c) and an opening (30d) opposite the base, the method comprising the following steps: -setting the filtering surface in movement so as to displace each filtering element (18, 61) and each scoop (30, 62) in succession from a ow point (P1) located below the water to a high point (P2) located above the water along a first path and, subsequently, from the high point to the low point along a second path, the cup of each scoop being of a shape and a depth which make it possible to contain a suffident store of water to transport fish while keeping them alive during the displacement of the scoop from the low point to the high point along the first path, -generating and supplying a jet of washing water inside each scoop which is located close to the high point, the jet of water being generated close to the high point of the first path and on the second, opposite side of the filtering surface which is located on the downstream side of the flow of water, the jet of water being introduced via the flared opening, tangentially to one of the two side waDs of the cup and along said waD as far as the base of the scoop, thus making it possible to push the store of water and the fish, on the side of the opposite side wafl, towards and beyond the free edge thereof which is located dose to the opening.

12. Filtering method according to claim 11, characterised in that the step of generating and supplying a jet of washing water inside each scoop (30; 62) comprises the foflowing sub-steps: -generating a jet of washing water so as to pass substantiafly perpendicularly through the fUtering surface so as to reach the scoop located on the first side of the filtering surface, -deflecting the jet of washing water which has passed through the filtering surface towards the base of the scoop (30a).

13. A system for filtering a flow of water substantiafly as any one embodiment herein described with reference to the accompanying drawings.

14. A method for filtering a flow of water substantially s any one embodiment herein described with reference to the accompanying drawings.