Patent Description:
The <CIT> describes a filtering unit comprising at least two filtering elements, each filtering elements having an internal face, an external face, a filtering mesh, two concentric circular edges, respectively an inner edge and an outer edge between which said filtering mesh extends, and radial ribs provided at least on the internal face, said radial ribs extending between said concentric edges and being distributed circumferentially in order to form distinct sectors on said internal face. Said filtering elements are configured to be assembled against each other so that their respective internal faces face each other so as to define a space between them, wherein said radial ribs delimiting the sectors form circumferential compartments in said space. At least one of said inner edge and outer edge has passages respectively communicating with corresponding ones of the sectors. The filtering elements are stacked along an axial direction between a upper cover and a lower cover.

By stacking a selected number of filtering elements pairs, a desired filter area is obtained for an intended application. Typically, the fluid to be filtered penetrates into the stack via inner passages of the inner edge, passes through the filtering mesh, and, once purified, exits via outer passages defined in the outer edge. Naturally, the flow of fluid through the filtering mesh could be reversed or arranged in some other way.

The filter described in that publication further comprises a divider arranged coaxially with the filtering elements, the divider having distinct distribution columns, and a rotary backwashing distributor provided at the first cover. The rotary backwashing distributor has a shutter provided with a discharge opening and is mounted to rotate so that said discharge opening is periodically and selectively put into communication with each distribution column, whereby each distribution column periodically and selectively establishes communication between the discharge opening and respective ones of the inner passages.

In this way, periodically, the fluid flow is reversed in the sectors corresponding to inner passages in fluid communication with the discharge opening, which enables backwashing to be performed in these sectors due to the pressure gradient across the filtering mesh, i.e. the pressure gradient between the external face side and the internal face side. The fluid used for backwashing is then discharged through the discharge opening.

In some applications, typically applications having a high rate of pollution, the pressure gradient may not be sufficient to ensure a high enough backflush flow and therefore a complete backwashing of the filtering mesh. Increasing the overall backflush flow is not desired as it represents a loss of cleaned flow. This loss may be compensated by an increase of the inlet flow, but this would imply oversizing upstream devices such as pumps, heat exchangers and other ancillaries.

Document <CIT> discloses a sleeve, wherein the apertures are organized in several circumferential rows, each circumferential row extending over a whole circumference of the sleeve.

The inventor have proposed a first solution to that problem in the<CIT>. Indeed, this application describes another backwashing system comprising a sleeve around which the filtering elements are stacked and a rotating distributor extending along the whole height of the sleeve and configured to selectively isolate apertures of the sleeve which face the inner passages of the filtering elements to enable backwashing in the corresponding sectors. In order to minimize the number of sectors which are backwashed simultaneously, and therefore optimize the pressure gradient so as to increase the backwashing efficiency, the filtering elements, together with the apertures of the sleeve, are circumferentially offset along the axial direction of the stack so as to increase the number of passage columns that can be individually isolated by the distributor.

In this document, a unique offset of half a sector is described. Of course, it would be desirable to increase the number of different offsets in order to increase the number of passage columns isolatable by the distributor. However, in practice, it is virtually impossible to provide additional offsets with the configuration disclosed in this document. Indeed, first, because of the size of each inner passage, the circumferential gap between two apertures of the sleeve is not enough to provide more than one offset aperture without overlapping at least some passage columns, which prevents the correct functioning of the backwashing. Second, such a staggered disposition of the apertures reduces the mechanical strength of the sleeve, said reduction in mechanical strength being all the more important that the number of offset apertures increases.

Thus, a need has arisen for still improving the efficiency of the backwashing. Therefore, there is a need for a new type of filtering units, or a new type of a part thereof.

The present disclosure relates to a sleeve for a filtering unit with backwashing, the sleeve being configured to be mounted coaxially inside a stack of annular filtering elements,.

Thanks to such a configuration, wherein the outer orifices of the apertures are elongated in the circumferential direction, that is to say in the same direction as the inner passages of the filtering element, a smooth flow is ensured at the interface with the filtering element, without a substantial pressure drop.

At least some of the apertures have an inner orifice elongated in the axial direction. In such a sleeve, the inner orifices of the apertures are elongated in the axial direction. Thanks to this special orientation, the inner orifices are better oriented with respect to the incoming flow of fluid to be filtered, the latter flowing indeed in the axial direction along the main direction of the sleeve. As a result, the pressure drop at the entrance of the inner orifice is reduced. However, since the outer orifices of the apertures are still elongated in the circumferential direction, a smooth flow is also ensured at the interface with the filtering element, without a substantial pressure drop.

Actually, the fact that the inner orifice is axial while the outer orifice is circumferential eases the direction transition of the flow of the fluid to be filtered from an axial flow within the sleeve to a radial flow within the filtering elements.

Also, thanks to this special orientation, it is possible to substantially reduce the circumferential width of the inner orifices without substantially reducing the total flow cross section of the inner orifice and, thus, without substantially increasing the pressure drop at the entrance of the apertures. Consequently, when desirable, it is possible to provide a greater number of columns of inner orifices which can be selectively isolated by a rotating distributor without overlap. As a result, the number of sectors simultaneously backwashed can be reduced.

Particularly, because of this special configuration of the apertures, and of the resulting organization of the inner and outer orifices within the sleeve, it is possible, when desirable, to increase the number of aperture columns without substantially impacting the mechanical strength of the sleeve.

In some embodiments, most of the apertures and preferably all of the apertures have an inner orifice elongated in the axial direction and an outer orifice elongated in the circumferential direction.

In some embodiments, the apertures are regularly spaced apart in each circumferential row.

In some embodiments, each row comprises the same number of apertures.

In some embodiments, each row comprises between <NUM> and <NUM> apertures, preferably between <NUM> and <NUM> apertures.

In some embodiments, the interval between each circumferential row is constant.

In some embodiments, the sleeve comprises at least <NUM>, preferably at least <NUM> circumferential rows.

In some embodiments, the apertures are offset circumferentially along an axial direction of the sleeve. As explained above, such an offset enables to increase the number of columns which can be individually isolated by the distributor and, thus, to decrease the number of sectors which are backwashed simultaneously.

In some embodiments, the outer orifices of the apertures are organized in j sets such that, in each set of outer orifices of a first j set, the outer orifices of each row are aligned in the axial direction with the outer orifices of one row of a second j set, j being an integer greater or equal to <NUM>, preferably equal to <NUM> or <NUM>. As explained above, thanks to the special configuration of the apertures, it is possible to provide more than two sets of apertures whose outer orifices are offset the ones with respect to the others. Consequently, an improved backwashing can be obtained.

In some embodiments, the circumferential offset θ(<NUM>) between the outer orifices belonging to different sets of outer orifices is a multiple of a pitch θ<NUM> = <NUM>°/n. j, where n is the number of apertures within each row and j is an integer greater or equal to <NUM>, preferably greater or equal to <NUM>, for instance equal to <NUM> or <NUM>. Preferably, n is also equal to the number of sectors in each filtering elements. Preferably, j is the number of sets of outer orifices as mentioned above. Put another way, the pitch θ<NUM> is equal to the sector width multiplied by <NUM>/j. Therefore, it can be noted that offsetting j times a given aperture leads to transform this aperture into an adjacent aperture of the row. Thus, due to the offset being an offset by a pitch which is a non-integer multiple of a sector, the offset of the outer orifices is precisely and uniformly controlled.

In some embodiments, the rows of each set of outer orifices come one after another alternately along the axial direction of the sleeve. The alternation between the rows having different offsets is therefore regular.

In some embodiments, the circumferential offset θ(<NUM>) between the outer orifices of any row and the outer orifices of the preceding row in the axial direction of the sleeve is equal to θ<NUM> = <NUM>°/n. j, where n is the number of apertures within each row and j is an integer greater or equal to <NUM>, preferably greater or equal to <NUM>, for instance equal to <NUM> or <NUM>. Each row is therefore regularly offset by the pitch θ<NUM> with respect to the proceeding row.

In some embodiments, the inner orifice of at least some apertures is circumferentially offset with respect to the center of the outer orifice of said apertures in the circumferential direction. This is preferably the case of most, or even all, of the apertures. This enables to decorrelate the position of the inner orifice from the position of the outer orifice, thereby increasing the design freedom of the sleeve. Particularly, for any aperture, it is possible to optimize the position of the inner orifice irrespective of the position of the outer orifice.

In some embodiments, the position of the inner orifice of an aperture with respect to the position of the outer orifice thereof is variable among the plurality of apertures. This enables to artificially increase the number of columns of inner orifices with respect to the number of columns of outer orifices. As a result, it is possible to increase the number of columns which can be individually isolated by the distributor and, thus, to decrease the number of sectors which are backwashed simultaneously.

In some embodiments, the sleeve comprises k types of apertures such that the circumferential offset φ(<NUM>) of the inner orifice with respect to the center of the outer orifice is equal for every aperture of a given type, k being an integer greater or equal to <NUM>.

In some embodiments, all the apertures of a given row are of a same type.

In some embodiments, k is equal to <NUM> and the circumferential offset φ(<NUM>) of the inner orifice of any aperture with respect to the center of the outer orifice thereof is equal to + φ(<NUM>)λ' or - φ(<NUM>)', where φ(<NUM>)' is an angle value strictly greater than <NUM>°, preferably greater than <NUM>°. Preferably, this value φ(<NUM>)' is lower than <NUM>° or <NUM>°. Particularly, this value is preferably lower or equal to θ<NUM>/<NUM>.

In some embodiments, with the possible exception of the first bottom rows and/or the last top rows, the rows of apertures are grouped in groups of k successive rows, all the apertures of a given group being of the same type. Consequently, a succession of one row of each set, but of the same type of apertures, can be provided before changing the type of apertures. The succession of the rows is therefore regular, so as the columns of the inner orifices. The first group at the bottom and/or the last group at the top may be incomplete, notably if the total number of rows is not a multiple of k.

In some embodiments, the inner orifices of the apertures are organized in N series such that, in each series of inner orifices, the inner orifices of any row are aligned in the axial direction with the inner orifices of the other rows, m being an integer greater or equal to <NUM>, preferably greater or equal to <NUM> or <NUM>. Thus, the number of columns which can be individually isolated by the distributor is increased and the number of sectors which are backwashed simultaneously is decreased, which improves the backwashing efficiency.

In some embodiments, some apertures comprise an inner funnel portion opening at the inner orifice and narrowing toward the outer direction. This is preferably the case of most, or even all, the apertures. This funnel portion guides the flow from the axial direction toward the radial direction and, therefore, helps to reduce the pressure drop at the entrance of the aperture.

In some embodiments, only the axial height of the inner funnel portion reduces while its circumferential width remains substantially constant.

In some embodiments, some apertures comprise an outer funnel portion opening at the outer orifice and narrowing toward the inner direction. This is preferably the case of most, or even all, the apertures. This funnel portion helps to distribute the flow over the whole width of the inner passage of the filtering element and, therefrom, over the whole width of the sector thereof.

In some embodiments, only the circumferential width of the outer funnel portion reduces while its axial height remains substantially constant.

In some embodiments, the inner and the outer funnel portions intersect. This eases the integration of both the inner and the outer funnel portions within the thickness of the sleeve. This also enables to limit the reduction in flow cross section at the junction between the inner and the outer funnel portions.

In some embodiments, the minimal flow cross section of some apertures is no less than <NUM>%, preferably <NUM>, preferably <NUM>% of the flow cross section of the inner orifice thereof. This is preferably the case of most, or even all, the apertures. This limits the pressure drop within the apertures.

In some embodiments, the diameter of the sleeve is comprised between <NUM> and <NUM>.

In some embodiments, the height of the sleeve is lower than <NUM> meters, preferably lower than <NUM> meters.

In some embodiments, the sleeve is produced by addition manufacturing.

In other embodiments, the sleeve is produced by lost-wax casting.

The present disclosure also relates to a filtering assembly for a filtering unit with backwashing, comprising a sleeve according to any one of the preceding embodiments, and a plurality of filtering elements stacked with one another, wherein each filtering element has a filtering medium and a plurality of inner passages for conducting fluid to be filtered to the filtering medium, the inner passages opening out on compartmented sectors.

In some embodiments, the filtering elements are keyed with respect to the sleeve so that the inner passages of one of the filtering elements are offset with respect to the inner passages of an adjacent one of the filtering elements.

In some embodiments, each filtering element comprises an inner edge, an outer edge and a filtering medium extending between the inner edge and the outer edge, the filtering element having an internal face and an external face on either side of the filtering medium, wherein, on the internal face, main ribs extending between the inner edge and the outer edge are circumferentially distributed to form sectors, wherein the filtering element is adapted to be assembled against a first identical filtering element so that their facing respective internal faces define a space that is circumferentially compartmented by the contacting respective main ribs of said internal faces, wherein the inner edge has inner passages communicating with each of the sectors on the internal face.

The filtering medium may extend over part or all of the distance between the inner edge and the outer edge. One side of the filtering medium defines the internal face of the filtering element, while the opposite side of the filtering medium defines the external face of the filtering element. The filtering element may be generally flat.

The ribs defined on the internal face enable isolating a sector for backwashing. The external face needs not be compartmented. At least one outer passage may be provided on the external face on the outer edge, for purified fluid outlet and backflush inlet. Conversely, on the internal face, the outer edge may be devoid of passages, so that the fluid entering one sector via a passage must cross the filtering medium to exit that sector.

In some embodiments, the external face of the filtering element has a key for pairing the filtering element in a given position with respect to a second identical filtering element, the key being arranged such that the inner passages of the second identical filtering element are offset with respect to the passages of the filtering element.

A key is an element providing a keyed connection between the respective external faces of the reference filtering element and of the second identical filtering element. Therefore, the key predetermines the relative position of the second identical filtering element with respect to the reference filtering element, e.g. angularly. The key may include a physical element providing physical cooperation.

The key may be located between the inner edge and the outer edge, in order to reduce the bulk of the filtering element.

Particularly, this keying system can be configured in accordance with the teaching of the <CIT>.

Note that the filtering elements need not be keyed with respect to one another, insofar as they are keyed with respect to a common element, here the sleeve. Hybrid solutions, where some filtering elements are keyed with respect to one another and some filtering elements are keyed to the sleeve, are also envisaged.

In some embodiments, the filtering medium comprises a mesh. In some embodiments, the mesh is sloped from one end of the inner edge to the opposite end of the outer edge, which helps increasing the filtering surface and decreasing pressure losses.

In some embodiments, the filtering assembly further comprises a rotary backwashing distributor configured to selectively isolate the inner orifices of the sleeve to enable backwashing in the corresponding sectors.

In some embodiments, the rotary backwashing distributor has an opening, said opening being periodically and selectively put into communication with at least one of the inner orifices of the sleeve.

The present disclosure also relates to a filtering unit comprising a filtering assembly according to any one of the preceding embodiments.

The above mentioned features and advantages, and others, will become apparent when reading the following detailed description of exemplary embodiments of the presented sleeve, filtering assembly and filtering unit. This detailed description refers to the accompanying drawings.

The invention and advantages thereof will be better understood upon reading the detailed description which follows, of embodiments of the invention given as non-limiting examples. This description refers to the appended drawings, wherein:.

A filter <NUM> is shown in cross-section in <FIG>. The filter <NUM> comprises a carter <NUM> and a filtering assembly <NUM>.

In the present example, the filter <NUM> comprises two inlet portions <NUM> and one outlet portion <NUM>, each arranged in the carter <NUM>. However, the filter <NUM> may comprise any number of inlet portions <NUM> and any number of outlet portions <NUM>. The filter <NUM> also comprises a backwashing motor <NUM> and a backwashing outlet <NUM> which will be presented afterwards.

The filtering assembly <NUM> comprises a plurality of filtering elements <NUM> stacked along the axial direction X of the filter <NUM> around a sleeve <NUM> and between an upper cover <NUM> and a lower cover <NUM>. The filtering assembly <NUM> also comprises a backwashing distributor <NUM>.

<FIG> depict an exemplary filtering element <NUM>. This filtering element <NUM> has an internal face <NUM>, an external face <NUM>, a filtering mesh <NUM>, two concentric circular edges, respectively an inner edge <NUM> and an outer edge <NUM> between which said filtering mesh <NUM> extends. The concentric circular edges <NUM>, <NUM> are circular about a central axis X, hereafter referred to as defining an axial direction. The inner edge <NUM> mainly extends in a plane which is perpendicular to the axial direction X, i.e. a radial plane. The outer edge <NUM> mainly extends in a plane which is perpendicular to the axial direction X, i.e. a radial plane.

In this embodiment, the diameter of the outer edge <NUM> is about <NUM>. Of course, other diameters are possible, including, for example diameters in the range from about <NUM> to about <NUM>.

The filtering element <NUM> comprises main ribs <NUM> provided at least on the internal face <NUM>. In this embodiment, as shown in <FIG>, the main ribs <NUM> are provided on the external face <NUM> too. Thus, if three similar filtering elements <NUM> are stacked, both faces of filtering element in the middle of the stack face the respective internal faces of the two other filtering elements, and the main ribs provided on these respective faces interact to form compartments.

The main ribs <NUM> extend between the inner edge <NUM> and the outer edge <NUM>, in the radial direction. The main ribs <NUM> are regularly distributed circumferentially in order to form n sectors on said internal face <NUM>, as shown in <FIG>. In this embodiment, the radial ribs <NUM> also form n sectors on said external face <NUM>, as shown in <FIG>. The main ribs <NUM> on the internal face <NUM> and on the external face <NUM> face one another on opposite sides of the filtering mesh <NUM>. In other words, the radial ribs <NUM> are in axial correspondence on the internal face <NUM> and on the external face <NUM>.

The inner edge <NUM> has inner passages <NUM> respectively communicating with corresponding ones of the sectors. The inner passages <NUM> are provided as notches or cutouts in the inner edge <NUM>. The inner passages <NUM> are provided between consecutive main ribs <NUM>. The inner passages <NUM> are provided on the internal face <NUM>. The inner passages <NUM> have therefore an opening angle ε(<NUM>) and a height a2.

As shown in <FIG>, the outer edge <NUM> has outer passages <NUM> respectively communicating with corresponding ones of the sectors. The outer passages <NUM> are provided as notches or cutouts in the outer edge <NUM>. The outer passages <NUM> are provided between consecutive main ribs <NUM>. The outer passages <NUM> are provided on the external face <NUM>.

Holes <NUM> for passing assembly rods or assembly keys are defined in the vicinity of the outer edge <NUM> of each filtering element, and they are formed by molding the same material that defines the circular edges <NUM>, <NUM> and the main ribs <NUM>. Male and female bushings <NUM> are arranged around these holes <NUM>, e.g. in a main rib <NUM>, for indexing two filtering elements <NUM> relative to each other.

In the non-limiting example shown, each filtering element <NUM> is divided into sixteen sectors (n=<NUM>). Depending in particular on its diametrical size, the filtering element can have less or more sectors. For example, a filtering element having an outer diameter of <NUM> to <NUM> may have <NUM> to <NUM> sectors, and a filtering element having an outer diameter of <NUM> to <NUM> may have <NUM> to <NUM> sectors.

The filtering elements <NUM> may be manufactured by molding around the filtering mesh <NUM>. In other words, they may be manufactured by injection molding or similar, wherein the filtering mesh <NUM> forms an insert in the mold. The molded portions may be made of metal (e.g. an aluminum alloy) or of plastics material, especially polymers. The main ribs <NUM> and the inner and outer edges <NUM>, <NUM> may be coated in elastomer in order to avoid leaks between filtering elements <NUM>.

Each one of the sectors is provided with at least one reinforcing rib <NUM> connecting a main rib <NUM> to the outer edge <NUM>. In the present example, each reinforcing rib <NUM> has a portion that is inclined, when viewed in the radial plane in which the outer edge <NUM> extends, with respect to the main rib <NUM> and to the outer edge <NUM>. However, other configurations are possible.

As shown in <FIG>, the reinforcing ribs <NUM> are also provided on the external face <NUM>. The reinforcing ribs <NUM> on the internal face <NUM> and on the external face <NUM> face one another on opposite sides of the filtering mesh <NUM> so as to decrease pressure losses.

As illustrated in <FIG>, the filtering elements <NUM> are configured to be assembled against each other so that their respective internal faces <NUM> face each other so as to define a space between them. Said space is circumferentially compartmented by the contacting main ribs <NUM> of said internal faces. On the other hand, the main ribs <NUM> provided on the external face <NUM> do not have to contact one another. Two filtering elements <NUM> assembled in such a way form a filtering part <NUM>.

Then, when the filtering elements <NUM> are stacked so as to form the filtering assembly <NUM>, a circumferential offset α is introduced between each successive filtering part <NUM>. As a result, when introducing such a circumferential offset α, the main ribs <NUM> on the external sides <NUM> of two successive filtering elements <NUM> may not extend in correspondence; similarly, the outer passages <NUM> of these successive filtering elements <NUM> may not extend in correspondence: however, such an offset is of no consequence for the functioning of the filter.

A keying mechanism may be provided on some or all the filtering elements <NUM> in order to ensure that the proper circumferential offset is introduced between each filtering part <NUM>. An exemplary keying system is for instance described in the <CIT>.

The upper cover <NUM> rests against the casing <NUM> in a stacking direction of the filtering elements, here in the direction of the central axis X. Specifically, the upper cover <NUM> may rest against a shoulder of the casing <NUM>, the shoulder forming a stop against axial and optionally radial movements of the upper cover <NUM>.

The upper cover <NUM> may be a generally annular part. The upper cover <NUM> may have a central opening for insertion of the sleeve <NUM>, as shown in <FIG>. The first cover <NUM> may extend radially from the sleeve <NUM> and outwards at least to the outer edge <NUM> of the filtering elements <NUM>. The first cover <NUM> and the sleeve <NUM> may be in sealing contact with each other, e.g. due to tight clearance between them. If needed, a gasket may be provided.

Likewise but independently, the lower cover <NUM> may be a generally annular part. The lower cover <NUM> may have a central opening for insertion of the sleeve <NUM>, as shown in <FIG>. The lower cover <NUM> may extend radially from the sleeve <NUM> and outwards at least to the outer edge <NUM> of the filtering element <NUM>. The lower cover <NUM> and the sleeve <NUM> may be in sealing contact with each other, e.g. due to tight clearance between them. Sealing is however not required because both the sleeve <NUM> and the lower cover <NUM> are in the dirty zone 2a.

Thus, the sleeve <NUM> extends at least from the upper <NUM> to the lower cover <NUM>.

As better shown on <FIG>, the sleeve <NUM> comprises apertures <NUM> configured to face and communicate with the inner passages <NUM> of the filtering elements <NUM>. Each aperture <NUM> has an inner orifice <NUM> provided on the inner surface of the sleeve <NUM> and an outer orifice <NUM> provided on the outer surface thereof. In order to ensure proper alignment of the outer orifices <NUM> of the apertures <NUM> with the inner passages <NUM> of the filtering elements <NUM>, the sleeve <NUM> may have a keyed connection with at least one of the first cover <NUM> and the second cover <NUM>.

Besides, at least one of the first cover <NUM> and the second cover <NUM> may comprise a key for mounting one of the plurality of filtering elements in a given position with respect to said at least one of the first cover <NUM> and the second cover <NUM>. Therefore, the filter <NUM> presents a keyed connection between the sleeve <NUM> and the filtering elements <NUM>, here through at least one of the first cover <NUM> and the second cover <NUM>.

Note that in addition to or instead of being keyed with respect to one another, the filtering parts <NUM> could be keyed with respect to the sleeve <NUM> so that the passages of one of the filtering parts <NUM> are offset with respect to the inner passages <NUM> of an adjacent one of the filtering parts <NUM>. Any type of keyed connection, including those detailed above, is encompassed.

As shown schematically by arrows in <FIG>, the fluid to be filtered enters the filters through an inlet <NUM> of the casing <NUM> and penetrates into the central conduit <NUM> formed by the sleeve <NUM> and into the apertures <NUM> of the sleeve <NUM> that are not isolated by the backwashing distributor <NUM>. After filtering through the filtering parts <NUM>, the filtered fluid is delivered to the outside of the filtering parts <NUM> and is extracted at the outlet <NUM> of the casing <NUM>.

Thus, in the casing <NUM>, the lower cover <NUM> separates a zone 2b of the casing <NUM>, also called clean zone, adapted to receive the filtered fluid from a zone 2a of the casing, also called dirty zone, adapted to receive the fluid to be filtered. Thus, the pressure drop of the fluid between the dirty zone 2a and the clean zone 2b helps biasing the lower cover <NUM> towards the upper cover <NUM> and thus maintaining the filtering elements <NUM> in sealing contact with one another.

Besides, the filtering assembly <NUM> further comprises a cover backing <NUM>. The cover backing <NUM> is coupled to the second lower <NUM> by a return system configured to return the lower cover <NUM> towards the upper cover <NUM>. The cover backing <NUM> rests against the casing <NUM> in the stacking direction, for instance thanks to a shoulder of the casing 2a, the shoulder forming a stop against axial and optionally radial movements of the cover backing <NUM>. This shoulder may have a continuous annular shape or may be provided as a plurality of discrete supports.

The cover backing <NUM> may be a generally annular part. The cover backing <NUM> may have a central opening for insertion of the sleeve <NUM>, as shown in <FIG>. The cover backing <NUM> may extend radially from the sleeve <NUM> and outwards at least to the outer edge <NUM> of the filtering elements <NUM>.

The cover backing <NUM> is openwork. That is, the cover backing <NUM> has through openings enabling fluid to pass through, which helps maximizing the pressure difference across the second cover <NUM>. The openings may be angularly distributed along the circumference of the cover backing <NUM>.

<FIG> now illustrate the principle of backwashing the filtering elements <NUM>. As describes above, the sleeve <NUM> is arranged concentrically with the filtering elements <NUM>, radially inside the filtering elements <NUM>. The sleeve <NUM> has a sealing contact with the filtering elements <NUM>. As already explained, the inner passages <NUM> of the filtering elements <NUM> are offset circumferentially along the axial direction: as a result, the outer orifices <NUM> of the apertures <NUM> are circumferentially offset in correspondence with the inner passages <NUM>. Furthermore, as it will be explained in greater details further in the present disclosure, the inner orifice <NUM> of each aperture <NUM> may also be circumferentially offset with respect to its outer orifice <NUM>.

The distributor <NUM> is driven in rotation by the backwashing motor <NUM> and configured to selectively isolate inner orifices <NUM> of the apertures <NUM> of the sleeve <NUM> so as to isolate the corresponding sectors of the filtering elements <NUM>. For instance, in this embodiment, the distributor <NUM> has a shutter <NUM> provided with two shutter portions 82a flanking a discharge opening <NUM>, and is mounted to rotate, e.g. about the central axis X, so that said discharge opening <NUM> is periodically and selectively put into communication with each one of the inner orifices <NUM>.

As best shown in <FIG>, the discharge opening <NUM> may extend, continuously or not, axially over a plurality of filtering elements <NUM> so that all the inner orifices <NUM> which are in radial correspondence with the discharge opening <NUM>, e.g. all the inner orifices <NUM> which are aligned with it, are put into communication with the discharge opening <NUM> at the same time. For instance, the opening <NUM> may be rectilinear. The opening <NUM> may extend parallel to the central axis X. The discharge opening <NUM> has an opening angle δ(<NUM>) while each shutter portion 82a has a shutter angle δ(<NUM>). Preferably, the opening angle δ(<NUM>) of the discharge opening <NUM> of the distributor <NUM> is substantially equal to the opening angle φ(<NUM>) of the inner orifices <NUM>.

<FIG> show that the shutter angle δ(<NUM>) of the shutter potions 82a is large enough to ensure that an inner orifice <NUM> is not simultaneously put in communication with the discharge opening <NUM> and with the central conduit <NUM>.

Although the illustrated embodiment has a unique discharge opening <NUM>, a plurality of discharge openings <NUM> may be provided. The discharge openings may be circumferentially distributed, such that the frequency of backwashing a given sector is increased without increasing the speed of the backwashing distributor <NUM>. The plurality of discharge openings <NUM> may be such that when one sector is fully backwashed through one of the discharge openings <NUM>, the other discharge openings <NUM> do not face any passages; otherwise, the backflush specific flow would be reduced.

Thanks to offset of the inner orifices <NUM> in adjacent filtering parts, the number of inner orifices <NUM> that are put at the same time in communication with the discharge opening <NUM> is reduced. Therefore, the backflush flow is divided between fewer sectors, and the specific backflush flow is increased.

Indeed, <FIG>, which is a view similar to <FIG> but relating to another filtering element <NUM>, here an adjacent filtering element <NUM>, shows that while the discharge opening <NUM> is not in contact with any inner orifice <NUM> in the plane of <FIG>, the discharge opening <NUM> communicates with an inner orifice <NUM> in the plane of <FIG>. Upon rotation of the backwashing distributor <NUM>, the shutter will shut the inner orifices <NUM> of <FIG> while the discharge opening <NUM> will come into contact with an inner orifice 73of another column. This configuration achieves a filter with continuous backwashing, i.e. wherein at least one sector is backwashed for every position of the backwashing distributor <NUM>. Continuous backwashing may be obtained in other ways, e.g. with a plurality of discharge openings <NUM>. Conversely, with an appropriate sizing of the discharge opening <NUM>, the filter may achieve discontinuous backwashing, i.e. there would exist positions of the backwashing distributor <NUM> in which no sector is backwashed.

In any case, the backwashing fluid is discharged at the top of the discharged opening <NUM> in a discharge room 6a which lead to the backwashing discharge outlet <NUM>. If desired, the backwashing fluid may itself be purified through another similar filtering unit.

<FIG> illustrates the sleeve <NUM> in greater details. As already explained, the sleeve <NUM> is cylindrical and define a central conduit <NUM>. The sleeve <NUM> comprises a main portion <NUM>, a upper rim <NUM> and a lower extension <NUM>.

The main portion <NUM> extends over the greatest part of the sleeve <NUM>: it is provided with the above-mentioned apertures <NUM>.

The upper rim <NUM> is intended to be keyed to the upper cover <NUM> thanks to flat sections 76a. As shown in <FIG>, the upper rim <NUM> is also configured to mount a ball bearing 85a intended to rotatably support the upper end <NUM> of the backwashing distributor <NUM>. The upper end <NUM> of the backwashing distributor therefore tightly close the upper end of the central conduit <NUM>.

The lower extension <NUM> extends along the lower cover <NUM> and the cover backing <NUM> and protrudes over the cover backing <NUM> into the dirty zone 2a. The lower extension <NUM> comprises a lower rim 77a, intended to rotatably support the lower end <NUM> of the backwashing distributor <NUM>. The lower end <NUM> of the backwashing distributor <NUM> is closed so that the discharge opening <NUM> does not communicate with the dirty zone 2a. In addition to the lower end of the sleeve <NUM> which is open, the lower extension <NUM> comprises openings 77b enabling the fluid to be filtered to enter into the central conduit <NUM>.

The organization of the apertures <NUM> will now be described with reference to <FIG>.

The sleeve <NUM> comprises a plurality of regularly spaced-apart rows <NUM> of apertures <NUM>, each row <NUM> extending circumferentially (ie. in a radial plane) and comprising the same number of regularly spaced-apart apertures <NUM>. In the present example, the sleeve <NUM> comprises <NUM> rows and each row comprises <NUM> apertures <NUM>.

As already explained, each aperture <NUM> comprises an inner orifice <NUM> and an outer orifice <NUM>. The outer orifices <NUM> are elongated in the circumferential direction. Every outer orifice <NUM> has the same opening angle φ(<NUM>) which is substantially equal to the opening angle ε(<NUM>) of the inner passages <NUM> (with a difference of e.g. <NUM>% or less). Every outer orifice <NUM> has also the same height f(<NUM>) which is substantially equal to the height a2 of the inner passage <NUM> (with a difference of e.g. <NUM>% or less). Conversely, the inner orifices <NUM> are elongated in the axial direction. Every inner orifice <NUM> has the same size. The height f(<NUM>) of the inner orifices <NUM> is preferably as large as possible while remaining inferior to the thickness a1 of the elements <NUM> in order to preserve the mechanical strength of the sleeve <NUM>.

As better visible on <FIG>, the position of the inner orifice <NUM> is not always the same with respect to the outer orifice <NUM>. Particularly, in the present example, two types of apertures are provided: the apertures of the first type <NUM>-<NUM> have their inner orifices <NUM> offset to the left with respect to their outer orifices <NUM> when looking at the apertures <NUM>-<NUM> from the outer side (<FIG>) while the apertures of the second type <NUM>-<NUM> have their inner orifices <NUM> offset to the right with respect to their outer orifices <NUM> when looking at the apertures <NUM>-<NUM> from the outer side (<FIG>). The type of aperture <NUM> is always the same in a given row <NUM>.

Most particularly, in the present example, the circumferential offset φ(<NUM>) between the center of the outer orifice <NUM> and the center of the inner orifice <NUM> is equal to <NUM>°.

Also, as visible on <FIG> and <FIG>, irrespective of their type, each aperture <NUM> comprises an inner funnel portion 73a, opening at its inner orifice <NUM> and narrowing toward the outer direction, and an outer funnel portion 74a, opening at its outer orifice <NUM> and narrowing toward the inner direction. In the present example, the depth of both the inner funnel portion 73a and the outer funnel portion 74a is greater than half the thickness of the wall of the sleeve <NUM>: consequently, the inner funnel portion 73a and the outer funnel portion 74a intersect the one with the other.

The outer orifices <NUM> of the apertures <NUM> are organized in j sets of rows <NUM> on the outer surface of the sleeve <NUM>. In the present example, j=<NUM>. In each set of rows <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, the outer orifices <NUM> of any row <NUM> are aligned in the axial direction with the outer orifices of the other rows <NUM> so as to form columns <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>.

The rows <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> of the three sets are provided in a regular alternation along the whole length of the main portion <NUM> of the sleeve <NUM>. Also, the circumferential offset θ(<NUM>) between the outer orifices <NUM> of two succeeding rows <NUM> is identical along the whole length of the main portion <NUM> of the sleeve <NUM>. In the present example, this circumferential offset θ(<NUM>) is equal to <NUM>°.

Also, for the sake of regularity, the apertures <NUM> are always of the same type within a group of three successive rows, that is to say within a group comprising exactly one row of each set <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>. The type <NUM>-<NUM>, <NUM>-<NUM> of the apertures <NUM> then changes for the next group of three rows <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, and so on so forth.

As a result, when observing the inner orifices <NUM> of the apertures <NUM>, the combination of the three sets of rows <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> and of the two types of apertures <NUM>-<NUM>, <NUM>-<NUM>, creates six different series of rows of inner orifices <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, circumferentially offset the ones with respect to the others. The rows of these six series regularly alternate along the length of the main portion <NUM> of the sleeve <NUM>. As a result, when scanning the sleeve from one end to the other, there is a pitch N of six rows before finding again an identical row.

Consequently, this organization provides p=<NUM> corresponding series of columns <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, each circumferentially spaced-part by a regular offset θ(<NUM>)=<NUM>°/n. N, therefore here equal to <NUM>°. Consequently, in the present example, the opening angle φ(<NUM>) of each inner orifice <NUM> is equal to said regular offset θ(<NUM>), while the opening angle δ(<NUM>) of the discharge opening <NUM> of the distributor <NUM> is also equal to said value. As a result, in the present example, the sleeve <NUM> comprises <NUM> columns which are individually isolatable by the backwashing distributor <NUM>.

Nevertheless, while the optimal value for the opening angle φ(<NUM>) of the inner orifices <NUM> is the value corresponding to the regular offset θ(<NUM>)=<NUM>°/n. N, the opening angle φ(<NUM>) of the inner orifices <NUM> can take other values in alternative example.

Particularly, in a first alternative example, the opening angle φ(<NUM>) of the inner orifices <NUM> can be greater than this regular offset θ(<NUM>)=<NUM>°/n. Nevertheless, in such a case, there are necessarily at least some inner orifices <NUM> of series of rows which overlap with inner orifices <NUM> of rows of another series. In such an alternative example, it is then preferable that the opening angle δ(<NUM>) of the discharge opening <NUM> of the distributor <NUM> be lower than the opening angle φ(<NUM>) of the inner orifices <NUM> so as to reduce the time period during which two adjacent sectors are in backflush at the same time. Most particularly, it is preferable that the opening angle δ(<NUM>) of the discharge opening <NUM> be lower than 2ε(<NUM>)/N- φ(<NUM>) in order to ensure that there are at least moments where each sector is effectively isolated from its adjacent sector. Therefore, such an alternative configuration may be useful to smoothen the transition between the backflush of adjacent sectors.

Claim 1:
A sleeve for a filtering unit with backwashing, the sleeve (<NUM>) being configured to be mounted coaxially inside a stack of annular filtering elements (<NUM>),
comprising apertures (<NUM>) each having an inner orifice (<NUM>) and an outer orifice (<NUM>), the outer orifice (<NUM>) of each aperture (<NUM>) being configured to face and communicate with an inner passage (<NUM>) of a filtering element (<NUM>),
wherein the apertures (<NUM>) are organized in several circumferential rows (<NUM>), each circumferential row (<NUM>) extending over a whole circumference of the sleeve (<NUM>),
wherein at least some of the apertures (<NUM>) have an outer orifice (<NUM>) elongated in the circumferential direction, and
wherein at least some of the apertures (<NUM>) have an inner orifice (<NUM>) elongated in the axial direction.