GB2492640B

GB2492640B - Filter unit

Info

Publication number: GB2492640B
Application number: GB1211583.8A
Authority: GB
Inventors: Sutherland Doug
Original assignee: PARKLAND ENGINEERING Ltd
Current assignee: PARKLAND ENGINEERING Ltd
Priority date: 2011-06-30
Filing date: 2012-06-29
Publication date: 2019-07-17
Anticipated expiration: 2032-06-29
Also published as: GB201111188D0; GB2492640A; GB201211583D0

Description

FILTER UNIT

Field of the Invention

The invention relates to filter units and, in particular, to filter units for filtering or screening coarse debris from fluid sources. More especially, the invention relates to filter units for filtering or screening coarse debris from water sources such as rivers, ponds and lakes.

Background of the Invention

When extracting raw water from sources such as rivers, ponds and lakes or reservoirs for use in for example fire fighting, irrigation etc, problems arise from coarse debris being sucked up with the water when pump vacuum is applied to the hose, pipe or other fixture used for extracting the water from the source. Providing a filter or screening unit on the end of the hose before it is thrown into the water source reduces the problems associated with such coarse debris.

One prior proposal for a filter or strainer unit used a perforated metal sheet located within a wicker basket. However, it was found that, in use, the metal sheet was relatively easily damaged owing the rough treatment the filter unit received. Additionally, with such filters odour was a significant problem arising from decaying organic detritus trapped at the intersections of the woven strands forming the wicker basket, the removal of such detritus during cleaning of the wicker basket being very difficult to achieve. Repeated wetting of both the wicker basket and the metal filter causes these two components to rot. Where the wicker basket is not cleaned effectively, it may be the source of disease.

An alternative prior proposal as exemplified in US 6978900 B2 consists of providing an annular cage framework that supports braided filter strands. As will be apparent from the construction shown in US 6978900 B2, the assembly/disassembly of such a filter unit is relatively complex and the odour problem arising from trapped decaying organic detritus would appear not to have been eliminated owing to the woven nature of the braided filter strands. To clean such a filter unit effectively, it would appear to be necessary to disassemble it and particularly clean the contact areas of the individual braids.

It is desirable, therefore, to provide a filter unit that is of simple construction, is easy to assemble/disassemble, reduces the trapping of organic detritus and is easy to clean.

Summary of the Invention

According to the present invention, a raw water filter unit comprises at least two tubular members mounted concentrically one within another between two end caps to define an annular space therebetween, each tubular member formed by a wall having a plurality of perforations thereon, the end caps and the innermost tubular member defining an interior space within the unit, at least one end cap having an opening therein in communication with the interior space and being adapted to receive a coupling for a hose, or a pipe. The inner tubular member, in relation to the outer adjacent tubular member, has annular end flanges extending radially outwardly therefrom; and each end flange is provided with at least one through, threaded aperture, the end caps each being provided with at least one corresponding plain through aperture through which is located a bolt screwed into respective said threaded aperture in the flange to lock the tubular members and the end caps together.

The at least one tubular member and end caps of the filter unit may be made of suitable metal, plastics or plastics-coated metal. If desired, mixtures of materials may be used; for example, the tubular members may be made of plastics and the end caps may be made of metal.

In a preferred embodiment of the invention, the at least one tubular member and end caps of the filter unit are made of plastics. Preferably, the plastics are low wetting plastics. The plastics may have a surface energy of not more than 40 dynes/cm, more preferably not more than 38 dynes/cm.

Suitable plastics from which the tubular members and end caps of the filter unit according to the invention are made include polyhydrocarbons such as polypropylene and polyethylene and copolymers thereof, polyfluorocarbons such as polytetrafluoroethylene, fluorinated ethylene and propylene copolymers and poly vinyl fluoride, polyamides, polyimides, polyacetals and polyphenylene sulphide. Preferred polymers for use in the invention are polyhydrocarbons and copolymers thereof. In particular, polypropylene and polyethylene, and copolymers thereof, are preferred polymers for use in the invention; polypropylene and copolymers thereof are particularly preferred.

The tubular members may be perforated by holes selected from a variety of shapes and sizes. For example, the shapes of the holes may include circular, non-circular, elongate, ie slots, holes or mixtures thereof. Preferably, the sizes of the holes may be the same, at least within each tubular member, ie they may differ between tubular members; or they may differ, at least within one tubular member.

Preferably, within the filter unit, the holes in one tubular member are not in direct registry with the holes in an adjacent tubular member.

Preferably, the perforations in each tubular member occupy at least 20%, more especially at least 30% of the surface area of the member. Preferably, the perforations in each tubular member occupy not more than 60%, more especially at least 50% of the surface area of the member. It is preferred the perforations in each tubular member occupy between 20% and 60%, more especially occupy between 30% and 50%, of the surface area of the member.

In a preferred embodiment of the invention, the tubular members are perforated by circular holes. Preferably, the holes each have the same diameter, at least within each tubular member, i.e. the diameters of the holes in one tubular member may be different to the diameters of the holes in another tubular member. In yet another preferred embodiment of the invention, the tubular members are each perforated by circular holes each having the same diameter. It is preferred the diameters of the holes are not less than 2 mm, more especially are not less than 2.5 mm. It is also preferred the diameters of the holes are not more than 6 mm, more especially not are more than 4 mm. It is preferred the holes have a diameter in the range 2 mm to 6 mm, more especially a diameter in the range 2.5 mm to 4 mm.

In yet another preferred embodiment of the invention, the tubular members are perforated by circular holes each having the same diameter, said diameter being as defined in the preceding paragraph and wherein the holes are arranged in rows. Preferably, within a row, the centre-to-centre spacing of adjacent holes is equal to at least twice the diameter of the holes. Preferably, within a row, the centre-to-centre spacing of adjacent holes is equal to not more than six times the diameter of the holes, more especially is equal to not more than four times the diameter of the holes. Typically, within a row, the centre-to-centre spacing of adjacent holes is in the range between twice and four times the diameters of adjacent holes.

Preferably, the spacing between alternate rows of holes, which may be offset in relation to one another, is equal to at least 1.4 times, more especially at least twice, the diameter of the holes. When adjacent rows of holes are offset from one another, preferably the centres of holes in one row are equidistant from the centres of holes in an adjacent row of holes.

When the tubular members have alternate rows of holes that are offset in relation to adjacent rows of holes as described in the preceding paragraph, in a preferred embodiment of the invention the rows in one tubular member run perpendicularly to the rows in an adjacent tubular member. It is particularly preferred that the rows in one tubular member lie in radial planes and the rows in an adjacent tubular member lie in axial planes.

As will be appreciated, the size of the holes, the centre-to-centre spacing and the spacing between adjacent rows of holes will be selected to suit the application for which the filter unit is intended, for example based on the potential amount of debris to be filtered and the flow rate of fluid required.

Conveniently, the tubular members of the filter unit of the invention are made from perforated, planar sheet material formed into a tubular shape around a suitably shaped and sized device. One suitable device comprises a frame that is square in cross-section and has elongate members extending from each comer of the frame. The sheet material is cut to size then rolled up in the frame to engage oppositely located sides of the sheet with one another, the engaging sides then being attached together for example by welding to form a cylinder. Alternatively, the device may be a mandrel, eg a cylindrical mandrel, to engage oppositely located sides of the sheet with one another and securing the sides together. The sheet material may be provided as a large sheet from which sections of suitable size are cut for use in making the tubular members. Typically, the sheet is at least 2 mm thick and, more preferably, is 3 mm thick. However, in some applications, heavier gauge sheet may be used, if desirable.

If necessary, heat may be applied to the sheet to aid in the shaping of the sheet into a substantially cylindrical shape whilst it is in the device or immediately prior to its introduction into the device, or whilst the sheet is located around the mandrel. The engaging sides of the sheet may be secured by being welded together. When the tubular members are made of plastics material, eg polypropylene, typically the heat applied to the sheet and the welding together of the engaged sides of the sheet may be accomplished using a suitable hot air gun.

Although the filter unit may have more than two tubular members, in a preferred embodiment of the invention the filter unit has only two tubular members. Whilst the tubular members may be other than cylindrical, in a preferred embodiment of the invention the tubular members are cylindrical.

The inner tubular member, in relation to an outer adjacent tubular member, has annular end flanges extending radially outwardly therefrom. The flanges may function as strengthened for the tubular member from which they depend. If required, for example in a filter unit which has a length that is greater than that normally used for filter units for filtering or screening coarse debris, an additional flange or additional flanges may be provided intermediate the end flanges on the inner tubular member.

In one embodiment of the invention, said flanges may have a radial extent sufficient to contact and support the outer adjacent tubular member.

Each end flange is provided with at least one through, threaded aperture; preferably a plurality of through, threaded apertures, for example typically four to eight but six being preferred. The aperture or apertures may accept a cylindrical metal sleeve threaded on its internal surface. The end caps are provided with at least one corresponding plain through aperture, preferably countersunk at its external end whereby when the end caps and tubular members are assembled together a bolt or bolts passing through the plain apertures in the end caps and engaging with the threaded apertures in the flanged tubular member lock the components together.

The end caps each have a first annular shoulder for receiving and locating an end of an inner tubular member and a second annular shoulder, located radially outwardly of the first shoulder, for receiving and locating an end of an outer tubular member. When the inner tubular member has end flanges as previously described, the first annular shoulder of each end cap abuts a flange thereby to locate the inner tubular member through the flanges.

In a preferred embodiment of the invention, the opening of said at least one end cap having an opening therein in communication with the interior space and being adapted to receive a coupling for a hose, pipe or other fixture is provided over at least part of its axial length with a screw thread for receiving said coupling during use of the filter unit. Preferably, the screw thread extends only partially along the opening in the end cap and terminates at an inwardly-extending annular collar that forms an end stop to prevent a coupling engaging with the screw thread in use of the filter unit from penetrating into the interior space.

It will be appreciated, however, that, in other embodiments, other means for attaching the coupling for a hose, pipe or other fixture may be used as are well known in the art, the end cap or caps being adapted to accommodate the particular fitting selected.

In an alternative embodiment, both end caps are provided with an opening therein in communication with the interior space and being adapted to receive a coupling for a hose, pipe or other fixture. In this instance, couplings may be engaged with a respective end cap whereby fluid is extracted from the filter unit at both ends thereof.

As will be appreciated, couplings suitable for connection may be available in different sizes. For example, screw-threaded couplings are typically available in 4" (101.6 mm) and 5.5" (139.7 mm) sizes. One option to accommodate such variation in size, is to provide two separate filter units, which units each being capable of connecting with one of the coupling units.

Alternatively, in accordance with the invention, the filter unit may accommodate couplings of different sizes in a variety of ways.

In accordance with one embodiment, a filter unit according to the invention may be supplied with alternative end caps each having an opening to accommodate a specific coupling size. For example, referring to the screw-threaded couplings described above, the filter unit would be supplied with two interchangeable end caps, one having an opening capable of receiving the 4" (101.6 mm) coupling and the other having an opening capable of receiving the 5.5" (139.7 mm) coupling.

In accordance with another embodiment, in a filter unit according to the invention, both end caps may have an opening to accommodate a specific coupling size. Such a filter unit would be provided with closure plugs, for example threaded plugs, for plugging the end cap not connected to the coupling being used. Alternatively, in use of the filter unit, couplings of different sizes could be simultaneously connected to the unit.

In accordance with yet another embodiment, in a filter unit according to the invention, one end cap may have an opening to accommodate a specific coupling size, preferably the larger or largest coupling size, and would be provided with at least one adapter having a corresponding opening and being capable of being connected with the opening and with a coupling of a different size to the coupling connectable with the end cap.

Such embodiments may be used in combination with one another.

In another embodiment of the invention, the filter unit comprises an end flange, the end flange having a peripheral wall and walls located inwardly of the peripheral wall, the inner tubular member engaging with said inner walls. Preferably, the filter unit comprises two such end flanges, one engaging each end of the inner tubular member.

Preferably, the inner walls form a shoulder, which may be a right angle.

Advantageously, the filter unit further includes an end cap, the end cap including a base and walls extending from the base, the walls configured to engage with the outer tubular member.

Preferably, the end cap is configured to engage the end flange. The wall extending from the base engages with the peripheral wall of the flange.

Advantageously, the wall extending from the base includes a rebate, and the outer tubular member sits in the rebate. Preferably, the peripheral wall of the flange extends beyond the lower edge of the rebate and forms a recess having a substantially U shaped cross section with the walls of the recess, the outer tubular member sitting in the recess.

The filter unit preferably includes a fitting including two bores, each of a different diameter and configured to receive and engage with a corresponding coupling, such as a hose fitting. Preferably, each bore is internally threaded. Advantageously, the fitting includes an inwardly-extending annular wall elements that each form an end stop for the respective bores.

The end cap may mount lugs and may include bores configured to receive such lugs.

The end cap may include a lanyard attachment means, which may comprise a bore extending through a part of the end cap.

It will be apparent from the foregoing description that the filter unit of the invention is easy to make and is simple to assemble and disassemble thus making it easy to clean debris and organic detritus from the components thereof. That the preferred materials from which the filter unit components are made are non-wetting plastics contributes to the ease with which the filter unit components may be cleaned. Additionally, as the tubular members do not have interstices such as those formed owing to the weave construction of some prior constructions of filters, detritus is not as readily trapped by the filter unit components in a manner such that it cannot be readily cleaned from the components.

Brief Description of the Drawings

The present invention will now be illustrated by way of example only with reference to the accompanying drawings in which:

Figure I is an elevation in the direction of Arrow C in Figure 2 of an end cap for a filter unit according to the invention;

Figure 2 is a section on Arrow A-A in Figure I;

Figure 3 is a section on Arrow B-B in Figure I;

Figure 4 is an elevation the same as that shown in Figure I but of an end cap at the opposite end of the filter;

Figure 5 is a photograph of an unassembled filter of the present invention without its end cap as shown in Figure I but with the outer tubular member located on the end cap as shown in

Figure 4;

Figure 6 illustrates an intermediate flange;

Figure 7a is a schematic representation of an alternative embodiment of a filter unit of the invention; Figure 7b is a side view of the filter unit illustrated in Figures 7a;

Figure 7c is a cross-sectional elevation on the axis A-A shown in Figure 7b;

Figure 7d is a plan view of the filter unit illustrated in Figures 7a to 7c; and

Figure 8 is a cross-sectional elevation of an alternative embodiment of an end cap for a filter unit according to the invention.

Detailed Description of the Preferred Embodiments

Referring now the drawings, a filter unit 10 according to the invention has two tubular, cylindrical perforate members 12, 14 mounted between concentrically one within the another between two end caps 16, 18 to define an annular space therebetween, the end caps 16, 18 and the inner tubular member 14 defining an interior space within the unit 10.

The tubular members 12, 14 (see Figure 5) are made of polypropylene copolymer (SG 0.91).

The tubular members 12, 14 were made from 3 mm gauge plastic sheet perforated with circular holes 24. The holes are arranged in rows 26 and are typically 3 mm diameter and have a centre-to-centre spacing of 8 mm, which results in approximately 37-40% of the surface area of the sheet being occupied by holes. In an alternative embodiment the holes are typically 3.5 mm diameter and have a centre-to-centre spacing of 9.5 mm

The spacing between alternate rows 26 of holes 24 is 6 mm, the holes 24 in one row 26 being offset from the holes 24 in an adjacent row 26 and the centres of holes 24 in one row 26 being equidistant from the centres of holes 24 in an adjacent row 26. The rows 26 in the outer tubular member 12 run perpendicularly to the rows 26 in the inner tubular member 14, the rows 26 in the tubular member 12 being located in radial planes and the rows 26 in the tubular member 14 being located in axial planes. The holes 24 in the outer tubular member 12 are not in direct registry with the holes 24 in the inner tubular member 14.

The tubular members 12, 14 of the filter unit 10 were made by cutting appropriately sized sections from the sheet material, which sections then being formed into a tubular shape around a suitably shaped and sized mandrel, eg a cylindrical mandrel, to engage oppositely located sides of the sheet with one another and securing the sides together. The sections of the sheet material were heated using a hot air gun to assist in the forming process, the hot air gun then being used to weld the engaging sides of the sections together, the weld lines being visible at 28 and 30, respectively, for the tubular members 12, 14.

The tubular member 14 has annular end flanges 32 extending radially outwardly therefrom. The flanges 32 are made from the same plastics material as the tubular members 12, 14 and, conveniently, are welded to the ends of the tubular member 14 using the hot air gun. The flanges 32 are each provided with six, equally spaced, through, threaded apertures 34 in the form of cylindrical metal sleeves threaded on their internal surfaces, the sleeves being moulded into the plastics of the flanges 32.

The end caps 16,18 are made from propylene homopolymer (SG 0.91).

The end cap 16 has an opening 36 therein in communication with the interior space and its inner peripheral wall 38, which defines the opening 36, is formed with a screw threaded section 40 for receiving a threaded coupling (not shown) for a hose, pipe or other fixture (not shown). The inner peripheral wall 38 has at its axially inner end an inwardly-extending annular collar 42 that terminates and forms an end stop for the screw threaded section 40 to prevent a coupling (not shown) engaging with the screw threaded section 40 in use of the filter unit 10 from penetrating through the opening 36 into the interior space.

The side of the end cap 16 contacting the tubular members 12, 14 has a first annular shoulder 44 for receiving and locating an end of the inner tubular member 14, the periphery of the flange 32 thereof engaging with the shoulder 44, and a second annular shoulder 46, located radially outwardly of the first shoulder 44, for receiving and locating an end of the outer tubular member 12. The end cap 16 also has six equally spaced, plain through apertures 48, countersunk at their external ends, for receiving bolts that engage the threaded apertures 34 in the flange 32 on the inner tubular member 14.

The end cap 16 further includes bores 43 configured to receive a lug element that protrudes beyond the outer surface of the end cap. Also, the end cap 16 further includes a bore 41 to receive a rope so that the filter may be retrieved in the event that it becomes detached from the hose to which it is connected.

The end cap 18, located at the opposite end of the filter unit 10 from the end cap 16, closes that end of the filter unit 10. The side of the end cap 18 contacting the tubular members 12, 14 has a first annular shoulder 50 for receiving and locating an end of the inner tubular member 14, the periphery of the flange 32 thereof engaging with the shoulder 50, and a second annular shoulder 52, located radially outwardly of the first shoulder 50, for receiving and locating an end of the outer tubular member 12. Similarly to the end cap 16, the end cap 18 has six equally spaced plain through apertures 54, countersunk at their external ends, for receiving bolts that engage the threaded apertures 34 in the flange 32 on the inner tubular member 14.

Typically, the filter unit 10 may be assembled as follows: • The inner tubular member 14 is engaged with the end cap 18, the flange 32 on the member 14 engaging with the first annular shoulder 50 on the end cap 18, the apertures 54 in the end cap 18 being located in registry with the threaded apertures 34 in the flange 32. Bolts (not shown) are passed through the apertures 54 to engage the threaded apertures 34 and tightened to retain the inner tubular member 14 relative to the end cap 18. • The outer tubular member 12 is then passed over the inner tubular member 14 to engage with the end cap 18 and abut the second annular shoulder 52. • The end cap 16 is then located on to the other ends of the tubular members 12, 14, the flange 32 on the inner member 14 engaging with the first annular shoulder 44 thereon and the end of the outer member 12 engaging with the second annular shoulder 46 thereon, the apertures 48 in the end cap 16 being located in registry with the threaded apertures 34 in the flange 32. Bolts (not shown) are passed through the apertures 48 to engage the threaded apertures 34 and tightened to retain the inner tubular member 14 relative to the end cap 16.

The outer tubular member 12 is retained relative to the end caps 16, 18 by virtue of its engagement at each end of the filter unit 10 with the respective annular shoulders 46, 52 on the end caps 16, 18.

Figure 6 illustrates an intermediate flange 60. The filter unit 10 may be strengthened by the inclusion of one or more of such flanges mounted within the unit. The flange 60 includes an opening 61 through which the inner tubular member 14 passes, the opening 61 having a diameter that substantially corresponds to the external diameter of the inner tubular member 14. The external diameter of the flange 60 corresponds substantially to the internal diameter of the outer tubular member 12. The flange 60 may be attached to the filter unit 10 simply by being a push fit on to the inner tubular member 14, and/or a push fit in to the outer tubular member 12. Alternatively, the flange 60 may be fixed to one or both of the inner and outer tubular members 12, 14, for example by welding or adhesive.

It will be apparent that disassembly of the filter unit 10 for cleaning etc is as easy as the assembly of the components and may be done repeatedly.

Referring now to Figures 7a to 7d, there is shown an alternative embodiment of the filter unit 10, which includes strengthening rods 70. The rods 70 are threaded and engage with threaded apertures 34 in the flanges 32’. The filter unit 10 includes an intermediate flange 60, which includes apertures 61 through which the rods 70 pass. The apertures may be threaded to engage with the threads of the rods 70. The rods 70 also pass through apertures in the end cap 18’ which are aligned with the apertures 34. Whilst an end cap is shown only attached to the base of the filter unit 10, in this embodiment, an end cap 18’ is also attached to the top of the filter unit.

The flanges 32’ and end cap 18’ differ in some respects to corresponding components in the embodiment of the filter unit 10 illustrated in Figures 1 to 5. The flanges 32’ include a shoulder 32’ formed by an annular rebate in the flange 32’. Each end of the inner tubular member 14 sits against the shoulder of a respective flange, with its end face abutting the surface of the rebate 32” that extends radially. The inner tubular member 14 is therefore constrained against movement with respect to the flanges 32’.

In the illustrated example, each flange 32’ includes an opening 32a. Whilst the flange 32’ at the lower end of the filter unit could be closed, it is preferred to use the same component at each end of the filter unit for ease of manufacture.

An end cap 18’ is attached to each flange 32’, the end caps being configured to engage with outer tubular member 12. The end cap 18’ includes a base 18a’ and a wall portion 18b’ extending perpendicular to the base 18a’. The free end of the wall portion 18b’ includes a rebate 18c’ forming a shoulder. The inner surface of the wall portion below the rebate engages with the peripheral surface of the flange 32’. As can be seen from Figure 7c in particular, the peripheral surface of the flange 32’ and the rebate 18c’ together form a recess which receives the end of the outer tubular member 12.

As is best appreciated from Figures 7b and 7c, the lower end of each rod 70 is secured in position by a nut 71. The upper end of each rod 70 may also be secured by a nut 71 (not shown) to thereby exert a compressive force on the elements of the filter unit 10.

The upper end of the filter unit 10 receives an end cap, for example of the type illustrated in Figure 8. A fitting 80 has an opening therein for communication with the interior space of the filter unit 10. The fitting 80 includes two screw threaded sections 82, 83, each defining a different diameter and each configured to receive one of a standard size of hose coupling. The fitting 80 includes bores 81 which receive rods 70. The fitting 80 provides an inwardly-extending annular wall 82’, 83’ that each form an end stop for the respective screw threaded section 82, 83 to prevent a coupling (not shown) engaging with the screw threaded section 40 in use of the filter unit 10 from penetrating through the opening therein into the interior space.

The fitting 80 further includes lug elements 84 and may include a bore for receiving a rope so that the filter may be retrieved in the event that it becomes detached from the hose to which it is connected.

When the end cap is mounted on the rods 70 and nuts 71 are attached to the rods 70, the components of the whole filter unit 10 are compressed so as to form a strong assembly.

The filter unit 10 can be configured to operate with two different sizes of hose. All that is required is for the fitting 80 to be removed, inverted and re-attached.

Whilst the fitting 80 illustrated provides threaded sections 82, 83 to receive two different sizes of coupling, the fitting may only include one threaded section in the manner illustrated in Figures 1 to 5, with alternate sizes of coupling being accommodated by different fittings each with a single opening for receiving a coupling, such as a hose coupling.

The fitting 80 is described as having threaded sections for receiving hose couplings. Of course the fitting may be provided with alternate means of attaching a hose coupling thereto and is not restricted to screw threads for this purpose.

Where the filter unit 10 is to be used in bodies of water that are shallower than the height of the filter unit it is necessary to blank off the holes in the outer tubular member. The invention therefore provides a sleeve made of a flexible material, such as rubber, which may be used to cover some of the holes. The sleeve may be located at the upper end of the filter unit and rolled down as far as is required to cover the holes to below the level of the body of water in which the filter unit is situated. Such a sleeve 90 is shown in Figure 7b, indicated in its rolled up state in broken lines, and in its fully extended state in solid lines. The sleeve when fully extended does not fully cover the outer tubular member, since to do so would seal the filter unit completely.

The sleeve may be attached to the upper end of the outermost tubular member, or to the end cap situated at the upper end of the filter unit, for example by means of adhesive.

Although a preferred embodiment has been described with reference to the drawings, as previously described the filter unit of the invention may be realised in a number of embodiments and it will be understood the description of the preferred embodiment is not intended to limit the invention to that embodiment but that the scope of the invention is as expressed in the claims hereto.

Claims

1. A raw water filter unit comprising at least two tubular members mounted concentrically one within another between two end caps to define an annular space therebetween, each tubular member formed by a wall having a plurality of perforations thereon, the end caps and the innermost tubular member defining an interior space within the unit, at least one end cap having an opening therein in communication with the interior space and being adapted to receive a coupling for a hose- or a pipe; wherein the inner tubular member, in relation to the outer adjacent tubular member, has annular end flanges extending radially outwardly therefrom; and wherein each end flange is provided with at least one through, threaded aperture, the end caps each being provided with at least one corresponding plain through aperture through which is located a bolt screwed into respective said threaded aperture in the flange to lock the tubular members and the end caps together.

2. A filter unit according to Claim 1, wherein the tubular members and end caps of the filter unit are made of plastics.

3. A filter unit according to Claim 2 wherein the plastics are selected from the group comprising polyhydrocarbons and copolymers thereof, polyfluorocarbons, fluorinated ethylene and propylene copolymers and poly vinyl fluoride, polyamides, polyimides, polyacetals and polyphenylene sulphide.

4. A filter unit according to Claim 3, wherein the plastics are polyhydrocarbons and copolymers thereof.

5. A filter unit according to any preceding claim, wherein the tubular members are perforated by circular holes each having the same diameter, at least within each tubular member.

6. A filter unit according to any preceding claim, wherein the tubular members are perforated by circular holes each having the same diameter, at least within each tubular member, the holes in one tubular member not being in direct alignment with the holes in an adjacent tubular member.

7. A filter unit according to any preceding claim, wherein the perforations in the tubular members occupy between 20% and 60% of the surface area of the member.

8. A filter unit according to any preceding claim, wherein the tubular members are perforated by circular holes each having the same diameter, at least within each tubular member, the holes having a diameter in the range 2 mm to 6 mm.

9. A filter unit according to any preceding claim, wherein the tubular members are perforated by circular holes each having the same diameter, at least within each tubular member, and wherein the holes are arranged in rows.

10. A filter unit according to any preceding claim, wherein the end caps each have a first annular shoulder for receiving and locating an end of an inner tubular member and a second annular shoulder, located radially outwardly of the first shoulder, for receiving and locating an end of an outer tubular member.

11. A filter unit according to any preceding claim, further including at least one flange mounted between the inner and the outer tubular members and between the end caps.

12. A filter unit according to any preceding claim, wherein, to accommodate coupling units of different sizes, said unit further comprises: alternative end caps each having an opening to accommodate a specific coupling size; and/or both end caps having an opening to accommodate a specific coupling size and, optionally, closure plugs for plugging said openings; and/or an adapter for a coupling which engages with the opening in said end.

13. A filter unit according to any preceding claim, wherein each end flange has a peripheral wall and walls located inwardly of the peripheral wall, the inner tubular member engaging with said inner walls.

14. A filter unit according to Claim 13, wherein the inner walls form a shoulder.

15. A filter unit according to Claim 14, wherein the shoulder is a right angle.

16. A filter unit according to any of Claims 13 to 15, wherein at least one of the flanges includes an opening therein.

17. A filter unit according to any of Claims 13 to 16, wherein the at least one end cap includes a base and walls extending from the base, the walls configured to engage with the outer tubular member.

18. A filter unit according to Claim 17, wherein the wall extending from the base engages with the peripheral wall of the flange.

19. A filter unit according to Claim 17 or 18, wherein the wall extending from the base includes a rebate, and the outer tubular member sits in the rebate.

20. A filter unit according to Claim 19, wherein the peripheral wall of the flange extends beyond the lower edge of the rebate and forms a recess having a substantially U shaped cross section with the walls of the recess, the outer tubular member sitting in the recess.

21. A filter unit according to any preceding claims, further comprising a fitting including at least one bore configured to engage with a corresponding hose or pipe coupling.

22. A filter unit according to any preceding claim, further comprising a fitting that includes two bores, each of a different diameter and configured to receive and engage with a corresponding hose or pipe coupling.

23. A filter unit according to Claim 21 or 22, wherein the or each bore is internally threaded.

24. A filter unit according to Claim 23, wherein the fitting includes at least one inwardly-extending annular wall element forming an end stop for a respective bore.

25. A filter unit according to any preceding claim, further including at least one rod, the or each rod configured to pass through bores in end caps and/or flanges and/or fitting.

26. A filter unit according to Claim 23, wherein at least one rod includes a threaded portion.

27. A filter unit according to Claim 24, further including at least one nut, the nut engaging the threaded portion of the rod.

28. A filter unit according to any of Claims 24 to 27, wherein at least one of the bores is threaded.

29. A filter unit according to any preceding claim, further including a sleeve of flexible material configured to cover a part of the outermost perforated tubular member.

30. A filter unit according to Claim 29, wherein the sleeve is moveable between extended and retracted configurations to cover more or fewer of the perforations of the outermost perforated tubular member.