Method of manufacturing a cartridge for a fluid treatment system

Abstract

A method of manufacturing a cartridge for a fluid treatment system, wherein the cartridge includes a housing defining at least one chamber for a fluid treatment medium, includes providing a cartridge housing part including at least one wall defining at least one opening closable by a filter element. The filter element includes a porous body for at least mechanically filtering fluid flowing into the filter element through at least one first surface area of the filter element, through the porous body and out through at least one second surface area of the filter element. The filter element includes a rim, covering at least a peripheral face of the porous body so as to frame the first and second surface areas. The filter element is combined with the cartridge housing part so as to close at least one of the at least one openings by bonding the rim to the cartridge housing part.

Claims

1. A method of manufacturing a cartridge for a fluid treatment system, wherein the cartridge includes a housing defining at least one chamber, including: providing a cartridge housing part including at least one wall defining at least one opening closable by a filter element; providing the filter element, wherein the filter element includes a porous body for at least mechanically filtering fluid flowing into the filter element through at least one first surface area of the filter element, through the porous body and out through at least one second surface area of the filter element, wherein the porous body is a sintered body comprising at least a binder, and wherein the filter element includes a rim, attached to the porous body and covering at least a peripheral face of the porous body so as to frame the first and second surface areas; and combining the filter element with the cartridge housing part so as to close the at least one opening by bonding the rim to the cartridge housing part by welding, soldering or adhesive bonding via an adhesive or filler material.

2. The method according to claim 1, wherein the cartridge housing is made of thermoplastic material and the rim is ultrasonically welded to the cartridge housing part.

3. The method according to claim 1, wherein the porous body is planar, and wherein the first and second surface areas are essentially parallel to a plane of the porous body and face in opposite directions.

4. The method according to claim 1, wherein the porous body is self-supporting.

5. The method according to claim 1, wherein the step of providing the filter element includes: providing an amount of loose material including a binder in a mould; and causing the loose material to be bound in the mould.

6. The method according to claim 1, wherein the rim is over-moulded.

7. The method according to claim 1, wherein the binder is a thermoplastic binder.

8. The method according to claim 1, wherein the porous body comprises a material for treatment of the fluid by sorption.

9. The method according to claim 1, wherein a fluid treatment medium is inserted into the cartridge housing part prior to combining the filter element with the cartridge housing part.

10. The method according to claim 1, wherein the chamber contains a granular fluid treatment medium.

11. The method according to claim 4, wherein the cartridge housing part includes an outer side wall, laterally enclosing the at least one chamber, wherein inward-facing surfaces of the side wall terminate at one end in an edge defining the at least one opening and lying essentially in a plane at an angle to the inward-facing surfaces of the side wall, and wherein the outer side wall flares outwards along its circumference, so that only the edge defines the at least one opening.

12. A cartridge for a fluid treatment system, including: a housing defining at least one chamber, the housing including a cartridge housing part including at least one wall defining at least one opening; at least one filter element, the filter element closing the at least one opening, wherein the filter element includes a porous body for at least mechanically filtering fluid flowing into the filter element through at least one first surface area of the filter element, through the porous body and out through at least one second surface area of the filter element, wherein the porous body is a sintered body comprising at least a binder, wherein the filter element includes a rim, attached to the porous body and covering at least a peripheral face of the porous body so as to frame the first and second surface areas, and wherein the rim is welded, soldered or adhesively bonded via an adhesive or filler material to the cartridge housing part.

13. The cartridge according to claim 12, having a body axis defining first and second opposite ends of the cartridge, wherein the at least one filter element is provided at the first end and at least one mechanism for attaching the cartridge to an outlet of a reservoir for accommodating untreated fluid is provided at the second end.

14. A fluid treatment system, including: a cartridge comprising; a housing defining at least one chamber, the housing including a cartridge housing part including at least one wall defining at least one opening; at least one filter element, the filter element closing the at least one opening, wherein the filter element includes a porous body for at least mechanically filtering fluid flowing into the filter element through at least one first surface area of the filter element, through the porous body and out through at least one second surface area of the filter element, wherein the porous body is a sintered body comprising at least a binder and wherein the filter element includes a rim, attached to the porous body and covering at least a peripheral face of the porous body so as to frame the first and second surface areas, and wherein the rim is welded, soldered or adhesively bonded via an adhesive or filler material to the cartridge housing part; a mechanical interface for connecting the cartridge to a supply of untreated fluid so as to establish a fluid-tight connection with an inlet of the cartridge; and a device for collecting fluid treated in the cartridge.

15. The method according to claim 1, wherein the rim has a lower permeability to fluid than the porous body.

16. The cartridge according to claim 12, wherein the rim has a lower permeability to fluid than the porous body.

17. The fluid treatment system according to claim 14, wherein the rim has a lower permeability to fluid than the porous body.

18. The method according to claim 1, wherein the binder comprises point-bonded particles.

19. The method according to claim 1, wherein the porous body is formed of loose material bound by the binder.

20. The method according to claim 1, wherein the porous body is planar and one or both surfaces of the porous body parallel to a plane of the porous body are covered by a sheet of permeable textile.

21. The method according to claim 1, wherein the filter element is arranged in an outlet of the chamber and a retainer with a larger mesh size is arranged in an inlet of the chamber.

22. The method according to claim 4, wherein the cartridge housing part includes an outer side wall, laterally enclosing the at least one chamber, and transitioning at an axial end into an end wall, wherein the end wall extends radially inwards over a distance large enough to provide a flange defining an opening, and wherein the opening is closed by the filter element by bonding the rim to the flange.

23. The cartridge according to claim 12, wherein the porous body is self-supporting, wherein the cartridge housing part includes an outer side wall, laterally enclosing the at least one chamber, and transitioning at an axial end into an end wall, wherein the end wall extends radially inwards over a distance large enough to provide a flange defining an opening, and wherein the rim is bonded to the flange so that the filter element closes the opening.

24. The cartridge according to claim 12, wherein the porous body is self-supporting, wherein the cartridge housing part includes an outer side wall, laterally enclosing the at least one chamber, terminate at one end in an edge defining the at least one opening and lying in a plane at an angle to inward-facing surfaces of the side wall, and, wherein the outer side wall flares outwards along its circumference, so that only the edge defines the at least one opening.

25. The cartridge according to claim 12, wherein the binder is a thermoplastic binder.

26. The cartridge according to claim 12, wherein the binder comprises point-bonded particles.

27. The cartridge according to claim 12, wherein the porous body is formed of loose material bound by the binder.

28. The cartridge according to claim 12, wherein the porous body is planar and one or both surfaces of the porous body parallel to a plane of the porous body are covered by a sheet of permeable textile.

29. The cartridge according to claim 12, wherein the filter element is arranged in an outlet of the chamber and a retainer with a larger mesh size is arranged in an inlet of the chamber.

30. The fluid treatment system according to claim 14, wherein the porous body is self-supporting, wherein the cartridge housing part includes an outer side wall, laterally enclosing the at least one chamber, and transitioning at an axial end into an end wall, wherein the end wall extends radially inwards over a distance large enough to provide a flange defining an opening, and wherein the rim is bonded to the flange so that the filter element closes the opening.

31. The fluid treatment system according to claim 14, wherein the porous body is self-supporting, wherein the cartridge housing part includes an outer side wall, laterally enclosing the at least one chamber, terminate at one end in an edge defining the at least one opening and lying in a plane at an angle to inward-facing surfaces of the side wall, and, wherein the outer side wall flares outwards along its circumference, so that only the edge defines the at least one opening.

32. The fluid treatment system according to claim 14, wherein the binder is a thermoplastic binder.

33. The fluid treatment system according to claim 14, wherein the binder comprises point-bonded particles.

34. The fluid treatment system according to claim 14, wherein the porous body is formed of loose material bound by the binder.

35. The fluid treatment system according to claim 14, wherein the porous body is planar and one or both surfaces of the porous body parallel to a plane of the porous body are covered by a sheet of permeable textile.

36. The fluid treatment system according to claim 14, wherein the filter element is arranged in an outlet of the chamber and a retainer with a larger mesh size is arranged in an inlet of the chamber.

37. The method according to claim 5, further comprising: providing the rim; and using the rim as at least part of the mould, wherein the step of causing the loose material to be bound to the mould includes causing the porous body to bind to the rim.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in further detail with reference to the accompanying drawings, in which:

(2) FIG. 1 is a very schematic side view of a gravity-driven liquid treatment system (not to scale);

(3) FIG. 2 is a very schematic exploded cross-sectional view of a first cartridge for use in the system of FIG. 1 (not to scale);

(4) FIG. 3 is a very schematic exploded cross-sectional view of a second cartridge for use in the system of FIG. 1 (not to scale);

(5) FIG. 4 is a very schematic side view of a second gravity-driven liquid treatment system (not to scale);

(6) FIG. 5 is a very schematic exploded cross-sectional view (not to scale) of a cartridge for use in the system of FIG. 4 (not to scale);

(7) FIG. 6 is a very schematic exploded cross-sectional view (not to scale) of a second cartridge for use in the system of FIG. 4 (not to scale);

(8) FIG. 7 is a very schematic exploded cross-sectional view (not to scale) of a third cartridge for use in the system of FIG. 4;

(9) FIG. 8 is a very schematic exploded cross-sectional view (not to scale) of a modified version of the cartridge of FIG. 7; and

(10) FIG. 9 is a schematic cross-sectional view of an apparatus for manufacturing a filter element for any of the cartridges of FIGS. 1-8.

DETAILED DESCRIPTION

(11) In the following, examples of gravity-driven liquid treatment systems will be used to explain the principles of construction of a fluid treatment cartridge. These can be adapted to pressure-driven liquid treatment systems and indeed to gas treatment systems.

(12) Any liquid can be treated, but the example used herein will be that of water. The treatment is primarily for removing substances suspended or dissolved in the water, but the water may additionally be enriched through the addition of certain substances.

(13) A liquid treatment system 101 as shown in FIG. 1 includes a jug 102 of which the lower part forms a reservoir 103 for collecting water treated by a cartridge 104. A removable funnel 105 is suspended in the jug 102 in a manner known per se. The funnel 105 forms a reservoir 106 for water to be treated.

(14) The funnel 105 is provided with a mechanical interface in the form of a seat in the region of the outlet of the funnel 105, in which the cartridge 104 can be inserted from the direction of the reservoir 106. The seat is adapted to the cartridge 104 so that, upon proper insertion of the latter, an essentially liquid-tight seal is provided between the cartridge 104 and the seat around the circumference of the cartridge 104. As a result, the outlet of the funnel 105 is essentially closed. The seat can comprise a ledge against which a flange of the cartridge 104 is pressed due to the weight of the cartridge 104 and of the water in the reservoir 106 or it can include a device for locking and/or clamping the cartridge 104 to the seat, e.g. a screw thread, bayonet fitting or the like.

(15) The water in the reservoir 106 of untreated water is forced to flow through inlet openings 107 of the cartridge 104, through the cartridge 104, and out into the lower reservoir 103. The inlet openings 107 are located to one side of the seal between the cartridge 104 and the cartridge seat, this side corresponding to the reservoir 106 of untreated water. An outlet (not shown in FIG. 1) is located on the other side of the level of the seal, i.e. nearer to the reservoir 103 of treated water.

(16) In a manner known per se (e.g. from WO 2005/092155 A1), the jug 102 is provided with a lid 108 with a fill opening closed by a pivotable closure 109. Similarly, a separate pivotable closure 1010 is provided to prevent contamination of the water in the lower reservoir 103 through an opening of a pouring spout 1011 of the jug 102.

(17) A first variant (FIG. 2) of a cartridge 204 for use in the system 101 of FIG. 1 comprises a housing defining a chamber for a liquid treatment medium. A first housing part 212 is essentially beaker-shaped. It comprises a side wall 213 for forming a boundary of the chamber in radial direction with respect to a main axis 214 corresponding to a body axis of the first housing part 212 (all directions are with reference to the main axis, which is parallel to the main direction of flow through the chamber for housing the liquid treatment medium). In the illustrated embodiment, the first housing part 212 is rotationally symmetric with respect to the main axis 214, but the cross-section of the first housing part 212 can be oval, in particular elliptic, or polygonal in other embodiments. In the illustrated embodiment, the side wall 213 tapers toward one axial end, facilitating production of the first housing part 212 by injection moulding, in particular its ejection from mould. In another embodiment, the side wall 213 is cylindrical.

(18) The first housing part 212 is completely open at one axial end, thus defining a first opening 215 It is provided with a protruding flange 216 at this end, the function of which will be explained in more detail below.

(19) At the opposite axial end, the side wall 213 transitions into an approximately annular end wall 217 extending radially inwards from the side wall 213 over a distance just large enough to provide a stepped flange. Otherwise, the end wall 217 defines an opening 218 of the chamber that is closable by a filter element 219.

(20) The filter element 219 includes a porous body 220 that is essentially planar, having a face directed towards the chamber for housing the liquid treatment medium and a face directed away from the cartridge 204 when the filter element 219 is in position in the opening 218.

(21) To manufacture the filter element 219, first the porous body 220, which is self-supporting, is manufactured. One way of manufacturing the porous body is to provide a binder in granular or powder form that undergoes a heat treatment at relatively low pressure such that the binder particles are point-bonded together. The binder in this case can be a thermoplastic or thermosetting resin, e.g. polyethylene. A typical mass-mean diameter d.sub.50 of the particles will be in the range of 10 to 300 m, more particularly 90 to 150 m. In one embodiment, the porous body 220 is cut, e.g. punched, from a larger porous sheet. Such a sheet can be formed by extrusion, by spreading the particles on a belt of a heated double-belt press or by passing the particles through the nip of a pair of heated rollers. In the case of a thermoplastic resin, the chosen temperature will a temperature sufficient for the resin to soften and become tacky, but it need not be at or above the melting temperature of the resin.

(22) In an embodiment, the porous body 220 further includes a material for treatment of the liquid by sorption. This embodiment is obtainable by mixing the binder particles with particles of the treatment material. Examples of suitable treatment materials include activated carbon, ion exchange resins, chelating resins etc. In an embodiment, the porous body 220 is further configured to add one or more substances to fluid passing through it. In particular, water can be enriched through the addition of certain minerals. In a further embodiment, one or more materials with biocidal or bacterial growth-retarding properties can be comprised in the porous body. One simple embodiment is obtainable by mixing thermoplastic binder particles of the type described above with silver-coated particles or fibres of activated carbon.

(23) It is observed that the porous body can be a laminated porous body. In such an embodiment, at least one of the average pore size, porosity, and material composition can be different for different layers of the laminated porous body. It is further observed that one or both of the axial end faces (with reference to the main axis 214, which is perpendicular to the plane of the porous body 220) can be covered by a sheet of woven or non-woven (including felted) textile. This helps retain small particles without having to decrease the average pore size of the porous body to such an extent that its resistance to flow would be unacceptably high. Such a sheet can be attached to a face of the porous body using adhesives, but it is simpler to attach it by heating the binder in the porous body 220 and applying a small amount of pressure.

(24) In a final manufacturing step, the filter element 219 is provided with a rim 221 of material that is impervious to liquid. The rim 221 covers the radial end face of the porous body 220 and the edges of this end face, as well as a small area at the radially outer edges of the axial end faces. It thus provides a frame surrounding permeable surface areas on opposite sides of the filter element 219, which surface areas correspond to regions of the axial end faces of the porous body in embodiments in which these are not covered by a sheet of woven or non-woven textile.

(25) The rim 221 can be formed by injection moulding with the porous body 220 provided as an insert. It is also possible to provide it as two halves that are inserted over the edges of the porous body 220 and bonded together, e.g. by welding or using adhesives. The rim 221 protects the filter element 219, enabling it to be manufactured at a different location to that at which the cartridge 204 is assembled.

(26) In the process of assembling the cartridge 204, the filter element 219 is combined with the first housing part 212 by bonding the rim 221 to the flange defined by the end wall 217. It is possible to use adhesive bonding, but in the context of a cartridge for the treatment of a potable liquid, this would require the use of a food-grade adhesive, of which there aren't very many. Alternatively, the rim 221 can be welded to the end wall 217, the flange increasing the contact area and providing a surface against which to place a welding tool (not shown in FIG. 2). Thus, in the process of manufacturing the cartridge 204, the filter element 219 is placed in the opening 218 from the inside of the first housing part 212, a welding tool is inserted through the opening 215 at the opposite axial end of the first housing part 212 and a further tool is held against the flange defined by the end wall 217. The tools can be a sonotrode and anvil in the case of ultrasonic welding, for example.

(27) After the filter element 219 has been combined with the first housing part 212 in this way, the liquid treatment medium (not shown) is inserted into the chamber such as to be retained by the filter element 219. The liquid treatment medium can be a granular medium, e.g. comprising particles of ion exchange resin, activated carbon and the like.

(28) Subsequently, the chamber is closed by combining the first housing part 212 with a cap 222. The cap 222 is provided with a flange 223 that is joined to the protruding flange 216 of the first housing part 212, e.g. by welding.

(29) Optionally, a mesh, e.g. as described in WO 01/32560 A2, is joined to the cap 222 prior to its attachment to the first housing part 212.

(30) In use, water flows into the cartridge 204 through inlet openings 207 in the cap 222. In the illustrated embodiment, optional venting openings 224 are also provided to allow air to escape from the cartridge 204. The filter element 219, in particular the outward facing permeable surface area framed by the rim 221 forms a relatively large outlet aperture for discharging treated water from the cartridge 204.

(31) FIG. 3 shows a cartridge 304 that is a variant of the cartridge 204 of FIG. 2, but with fewer cartridge housing parts. The way in which it is assembled also differs.

(32) A first housing part 312 includes not only a side wall 313 corresponding to the side wall 213 of the cartridge 204 of FIG. 2 but also an integral cap 322, such that the side wall 313 and the cap 322 form one monolithic part, obtainable by moulding, in particular injection moulding. The first housing part 3012 is thus essentially beaker-shaped.

(33) The illustrated cap 322 is provided with inlet openings 307 and venting openings 324. A mesh 325 is bonded to the inside of the first housing part 312 between an axial section surrounded by the side wall 313, configured to form the chamber for housing the liquid treatment medium, and the inlet openings 307 and venting openings 324. A different kind of retaining device, liquid-permeable but arranged to block the passage of the liquid treatment medium, can be used.

(34) It is observed that the first housing part 312 is also provided with a flange 316, which in this case serves only to form a seal with the cartridge seat in the outlet of the funnel 105. Compared to the cartridge 204 of FIG. 2, the cartridge 304 can be manufactured with one less welding step.

(35) In the illustrated embodiment, the side wall 313 is essentially cylindrical, but it may also taper towards the closed axial end, i.e. away from an opening 318 closable by a filter element 319. The side wall 313 flares radially outwards all around its circumference at the opening 318. In an alternative embodiment, it may flare outwards along sections of its circumference only. There is thus defined a surface 326 for a tool to be used in joining the filter element 319 to the first housing part 312.

(36) The filter element 319 is essentially the same as the filter element 219 of the cartridge 204 of FIG. 2. It is provided with a rim 321 that is bonded to the first housing part 312, in particular by welding. Thus, one of a sonotrode and anvil can be placed against the surface 326 and the other of the sonotrode and anvil placed against the rim 321, where the filter element 319 is ultrasonically welded to the first housing part 312.

(37) The joining of the filter element 319 to the first housing part 312 takes place after the chamber formed by the first housing part 312 and closable by the filter element 319 has been filled with a liquid treatment medium. The first housing part 312 is held with the opening 318 facing upwards during the filling operation, whereupon the filter element 319 is joined to the first housing part 312.

(38) It is observed that the side wall 313 terminates at an edge defining the opening 318, so that the opening is defined only by the edge of the side wall 313. There is no end wall extending radially inwards. In combination with the radially outwardly flaring side wall 313 and an appropriately sized rim 321 of the filter element 319, this maximizes the area of the outlet formed by the porous body 320. The relatively large surface area causes a decrease in the flow resistance of the filter element 319. Where the porous body 320 includes active substances that are effective in removing substances from the liquid by sorption and/or active substances that are effective to add substances to the liquid, the resistance to flow per unit area can be increased to increase the effectiveness of the liquid treatment by the filter element 319 without increasing the pour-through time of the cartridge 304 to an unacceptable level, as a consequence.

(39) The description of the filter element 219 of FIG. 2 applies equally to the filter element 319 of FIG. 3.

(40) FIG. 4 shows an alternative liquid treatment system 401. It again includes a jug 402 with a pouring spout 411 and a lid 408 with pivotable closures 409,410. Again, a funnel 405 forming a reservoir 406 for liquid to be treated is suspended in the jug 402 in a manner known per se. The cartridge 404 is connected to a mechanical interface 427 of the funnel 405 in a different manner, in that the mechanical interface 427 is provided downstream of an outlet opening of the funnel 405 with respect to the reservoir 406 of untreated liquid defined by the funnel 405. Thus, in use, the replaceable cartridge 404 is suspended in the jug 402 over a reservoir 403 of treated water.

(41) FIG. 5 shows a suitable cartridge 504 for the system 401 of FIG. 4. The liquid treatment medium is not shown for reasons of clarity. The cartridge 504 comprises a cartridge housing including a first housing part 512 that includes a mainly cylindrical side wall 513. In other embodiments, the side wall 513 can have an oval or polygonal cross-section. The first housing part 512 is provided with a radially outwardly extending flange 516 at one axial end (with respect to a main axis 514 corresponding to a body axis essentially aligned with the main direction of flow through the cartridge 504). The flange 516 is provided to facilitate the joining of the first housing part 512 to a cap 522, with the joint being formed by bonding, in particular by welding.

(42) The cap 522 includes a cap flange 523 arranged to cooperate with the flange 516 of the first housing part 512. It further includes lugs 528 forming a mechanism for attaching the cartridge 504 to the reservoir 506 of untreated liquid. The lugs 528 are part of a bayonet fitting, and are arranged to be inserted into guides (not shown) forming part of the mechanical interface 527 in a manner known per se. These guides will generally be provided with a slight speed, so that the cartridge 504 is forced towards the reservoir 506 as the lugs 528 are moved along the guides. In the process, one or more sealing elements 529 on a top surface of the cap 522 are compressed against a sealing surface provided in the mechanical interface 527, so that a sealed fluid connection between an outlet of the reservoir 506 and inlet openings 507 in the cap 522 is provided. The inlet openings 507 are defined by bars 530 of a lattice in the top of the cap 522. Optionally (not shown here), venting openings can be provided in a section of the cap 522 lying radially outside the confines of the part sealed against the funnel 505. Optionally, a mesh similar to the mesh 525 of the cartridge 304 can be provided to prevent back-flow of liquid treatment medium, but the inlet openings 507 will generally be of sufficiently small size relative to the liquid treatment granules to take on this role.

(43) At the opposite axial end to the end for connection to the cap 522, the first housing part 512 an end wall 517 that extends radially inwards only slightly defines an opening 518 closable by a filter element 519. The filter element 519 is essentially identical to the filter elements 219,319 of FIGS. 2 and 3, so that reference is made to the description provided above in connection with the filter element 219 of FIG. 2.

(44) The cartridge 504 is assembled by first joining the filter element 519 to the first housing part 512. The rim 521 of the filter element 519 is joined to the stepped flange defined by the end wall 517, in particular by bonding. A tool such as an anvil or sonotrode can be inserted into the space defined by the first housing part 512 to enable the filter element 519 to be combined with the first housing part 512.

(45) After the joint has been formed, the resulting beaker-shaped assembly is filled with the liquid treatment medium. The description of the liquid treatment medium provided above in connection with the cartridge 204 of FIG. 2 applies also to the liquid treatment medium for the cartridge 504 of FIG. 5.

(46) Thereupon the cap 522 is combined with the first housing part 512 to close the chamber accommodating the liquid treatment medium.

(47) FIG. 6 illustrates a cartridge 604 that is a variant of the cartridge 504 of FIG. 5. It has a cap 622 that is identical to the cap 522 of the cartridge 504 of FIG. 5, so that reference is made to the description given above in respect of that cap 522.

(48) The cartridge 604 further includes a filter element 619 which is identical to that of the cartridges 204,304,504 described above, so that the description given above with respect the filter element 219 of FIG. 2 applies equally to the filter element 619 of FIG. 6.

(49) The first housing part 612 of the cartridge 604 of FIG. 6 includes a side wall 613 for forming a boundary of a chamber for accommodating a liquid treatment medium in radial direction with respect to a main axis 614 corresponding to a body axis of the first housing part 612 (the main axis 614 is again aligned with the main direction of flow through the chamber for housing the liquid treatment medium). In the illustrated embodiment, the first housing part 612 is rotationally symmetric with respect to the main axis 614, but the cross-section of the first housing part 612 can be oval, in particular elliptic, or polygonal in other embodiments. It may also taper towards either axial end.

(50) One axial end of the side wall 613 is configured for joining to an annular wall 631 depending from the cap 622 and forming an integral part of the cap 622. The joint can be formed by bonding, in particular welding, more particularly ultrasonic welding. In the illustrated embodiment, neither the cap 622 nor the end of the first housing part 612 to be joined to the cap 622 is provided with a radially outwardly protruding flange. Instead, the radially outwardly facing surface of the side wall 613 is essentially flush with a side wall of the cap 622 when the latter has been joined to the first housing part 612. This gives the cartridge a smooth appearance and represents a materials saving.

(51) At the opposite axial end, an inner surface of the side wall 613 terminates in an edge defining an opening 618 closable by the filter element 619. At this end, the side wall 613 of the first housing part 612 also flares outwards to define a surface 626 for a tool.

(52) To assemble the cartridge 604, the cap 622 is first joined to the first housing part 612. The assembly is then held such that the opening 618 closable by the filter element 619 faces upwards, and the liquid treatment medium is then inserted into the assembly. Thereupon, the filter element 619 is combined with the first housing part 612. Again, this involves joining a rim 621 of the filter element 619 to the first housing part 612 by bonding, in particular by welding. A tool can be applied to the surface 626 to effect the bonding operation.

(53) FIG. 7 illustrates a cartridge 704 that is a variant of the cartridge 604 of FIG. 6, in which the first housing part 712 includes the cap 722 as an integral part that forms a monolithic whole with the side wall 713. The first housing part 712 is obtainable by moulding, in particular injection moulding. Compared to the cartridge 604 of FIG. 6, the cartridge 704 of FIG. 7 can be assembled with one less joining operation. However, the range of possible configurations of features of the cap 722 may be limited due to restrictions imposed by the injection moulding tools.

(54) FIG. 8 illustrates a cartridge 804 that is identical to the cartridge 704 of FIG. 7 except that it further includes a cover part 832. The cover part 832 illustrated in FIG. 8 is configured to be joined to the rim 821 of the filter element 819. In an alternative embodiment (not shown), it is joined to the first housing part 812.

(55) Like the other illustrated filter elements 219,319,519,619,719, the filter element 819 has a first surface area framed by the rim 821 through which liquid flows into the porous body 820, which surface area faces the chamber accommodating the liquid treatment medium. The liquid flows out through an opposite second surface area framed by the rim 821. The cover part 832 is provided with at least one, in the illustrated embodiment exactly one, fluid-permeable aperture 833. Once it has been combined with the assembly of the first housing part 8012 and the filter element 819, the cover part 832 is situated with a wall facing the second surface area of the filter element 819. The cover part 832 thus shields the exposed part of the filter element 819 that is not covered by the rim 821. This exposed part will generally be the porous body or a sheet of woven or non-woven textile covering the porous body. The cover part 832 shields this relatively vulnerable part of the filter element 819.

(56) The wall facing the second surface area of the filter element is slightly concave, so that a cavity is defined between the filter element 819 and the cover part 832. As a result, the surface area framed by the rim 821 is not limited by the cover part 832. The flow resistance of the fluid-permeable aperture 833 is lower than that of the filter element 819, so that the cover part 832 has no negative impact on the overall pour-through time of the cartridge 804.

(57) An alternative way of manufacturing the filter elements 219,319,519,619,719,819 to the one described above in connection with the filter element 219 of FIG. 2 includes thermally binding loose material in a mould. In this method, a rim 921 is first placed in a heatable cavity-providing tool 934. The tool 934 surrounds an outward-facing surface of the rim 921.

(58) A first heatable die 935 supports the rim 921 from below.

(59) In an optional step, a first piece of fabric 936 is placed in a space surrounded and delimited laterally by the rim 921, on top of the first heatable die 935. The fabric 936 may be a non-woven fabric, for example.

(60) A quantity 937 of loose, in this example particulate, material is placed on top of the first piece of fabric 936 in the space surrounded and delimited laterally by the rim 921. The material includes a binder in granular or powder form, e.g. a thermoplastic or thermosetting resin. In an embodiment, the binder comprises ultra-high density polyethylene. The loose material further includes a material for the treatment of the liquid by sorption. This latter material will generally also be provided in granular form and is mixed with the binder before being placed in the space delimited laterally by the rim 921. Again, suitable treatment materials include activated carbon, ion exchange resins, chelating resins and the like. The particle sizes are as indicated for the embodiment explained with reference to FIG. 2.

(61) The quantity 937 of loose material is compacted by doctoring or by vibrating the assembly comprising the tool 934 and the first heatable die 935.

(62) In an optional step, a second piece of fabric 938 is placed on top of the quantity 937 of loose material. The second piece of fabric 938 has essentially the same properties as the first piece of fabric 936.

(63) Where the binder comprises a thermoplastic resin, the first heatable die 935, the tool 934 and a second heatable die 939 are heated to a temperature sufficient to make the binder become tacky (above the Vicat softening point but below the decomposition temperature). It is sufficient to place the first and second heatable dies 935,939 at positions corresponding to the desired position of the opposing end faces of the filter element and to provide enough material to allow these positions to be taken in without exerting excess pressure. The pressure needed to achieve point-bonds between the particles arises through the expansion of the binder under the influence of heat.

(64) In the process, the quantity 937 of loose material is formed into a porous body. It is also bonded to the first and second pieces 936,938 of fabric and the rim 921. Thereupon, one of the first and second heatable dies 935,939 is moved out of the way and the other is used to eject the filter element from the tool 934, whereupon it is left to cool. It can then be used to manufacture any of the cartridges 104,204,304,404,504,604,704,804 described above.

(65) The invention is not limited to the embodiments described above, which may be varied within the scope of the accompanying claims. Suitable materials for the cartridge housing include thermoplastics, in particular polypropylene. This allows both thermal and ultrasonic welding. The material of the rim of the filter element can be the same as that of the first housing part or it can be a different in terms of at least one of its material composition and physical properties. Variants of any of the cartridges 204,304,504,604,704 can be provided with a cover part such as the one illustrated in FIG. 8.