WO2006040670A2

WO2006040670A2 - A filter with a filter element and a method of manufacturing the filter element

Info

Publication number: WO2006040670A2
Application number: PCT/IB2005/003067
Authority: WO
Inventors: Henning Joubert; Henning Christoffel Joubert
Original assignee: Henning Joubert; Henning Christoffel Joubert
Priority date: 2004-10-14
Filing date: 2005-10-14
Publication date: 2006-04-20
Also published as: WO2006040670A3

Abstract

The invention provides a filter (10) for filtering petroleum oil or liquid petroleum-based fuel, typically diesel. The filter (10) includes a liquid flow path (26) along which liquid which is to be filtered is flowable, and a filter element (14) which is predominantly of a fibrous material, such as cotton. In use, diesel flows unidirectionally through the filter element (14) for at least 20 mm. Preferably, elongated fibres of the filter element (14) are more or less parallel, being aligned with the direction of diesel flow through the element. The invention also provides a method of manufacturing a diesel filter element (14) by compressing fibrous filter material radially inwardly relative to the direction of fluid flow through the resultant filter element (14).

Description

A FILTER AND A METHOD OF MANUFACTURING A FILTER ELEMENT

THIS INVENTION relates to a filter. In particular, the invention relates to a filter for filtering petroleum oil or a liquid petroleum-based fuel, such as diesel. The invention extends to a filter element. The invention extends further to a housing for a filter, and to a method of filtering diesel. The invention extends yet further to a method of manufacturing a filter element.

According to one aspect of the invention, there is provided a filter for filtering petroleum oil or liquid petroleum-based fuel, which filter includes: a liquid flow path along which liquid which is to be filtered is flowable; and a filter element located in the liquid flow path for filtering liquid which moves through the filter element in a liquid flow direction, the filter element being predominantly of a fibrous material, and a dimension of the filter element in the liquid flow direction being at least 20 mm.

By fibrous material is meant a material which contains fibers, i.e. long threadlike structures. Typically, the fibrous material is cellulosic, i.e. containing cellulose. The fibrous material may thus be a natural fibrous material, such as cotton, or it may be of a synthetic material, such as polyester. The dimension of the filter element in the liquid flow direction, i.e. the distance which liquid, in use, travels through the filter element, may be at least 40 mm, preferably being about 50 mm.

The filter element may comprise a solid mass of natural fibrous material, typically consisting of plant fibres. In one embodiment of the invention, the filter element is of compressed cotton wool.

The filter element may be of laminar construction, comprising a plurality of layers which are arranged face to face. The filter element is preferably arranged such that the liquid flow direction is more or less parallel to the layers of the filter element.

Typically, the filter element is cylindrical in shape, the liquid flow direction being more or less parallel to the longitudinal axis of the cylindrical filter element. In such case, the filter element may be formed of at least one sheet of spirally wound filter material, the layers of the spiral thus being more or less parallel to the longitudinal axis of the cylindrical element.

The filter material may comprise elongated fibers having a common orientation, so that the fibres of each layer of the filter material have the same orientation. Preferably, the common orientation of the filter element fibres is more or less parallel to the liquid flow direction.

The filter element preferably has a density of 250 - 350 kg/m³, more preferably having a density of 300 - 400 kg/m³, and most preferably having a density of about 360 kg/m³. The filter element may be located in a housing or casing, at least part of the housing being transparent to permit viewing of the filter element. In one embodiment of the invention, the housing is circular cylindrical in shape, . permitting viewing of the filter element 360° around the axis of the housing. The housing may in such case at least partially be made of a transparent polymeric plastics material.

The housing is preferably configured for facilitating unidirectional flow of liquid through the filter element. In a preferred embodiment of the invention, the housing comprises a pair of end pieces which a transparent cylindrical tube extending between them, the filter element being located in the tube, one of the end pieces providing an inlet port and the other end piece providing an outlet port, so that liquid, in use, flows from the inlet port to the outlet port, axially through the filter element. The tube may be of a transparent polymeric plastics material, such as PERSPEX, while the end pieces may either be metal pressings or moulded plastic members.

Preferably, the filter includes a spacer arrangement at each end piece for spacing the filter element from the inlet port and the outlet port respectively, to permit the accumulation of liquid at both ends of the filter element, and to prevent blockage of the inlet port or the outlet port by the filter element. Each spacer arrangement may comprise a perforated end plate which is located in the housing at an end of the filter element, the respective end piece being shaped to engaged the end plate to space the end plate from the inlet port or the outlet port, as the case may be, the end plate, in turn, abutting the filter element to space it from the end piece. According to another aspect of the invention, there is provided a filter for filtering petroleum oil or liquid petroleum-based fuel, which filter includes: a liquid flow path along which liquid which is to be filtered is flowable; and a filter element located in the liquid flow path for filtering liquid which moves through the filter element in a liquid flow direction, the filter element being provided by a mass of filter material which is predominantly of cotton.

According to a further aspect of the invention, there is provided a filter for petroleum oil or liquid petroleum-based fuel, which filter includes: a liquid flow path along which liquid which is to be filtered is flowable; and a filter element located in the flow path for filtering liquid which moves through the filter element in a liquid flow direction, the filter element being of a fibrous filter material comprising a plurality of layers which are arranged face to face, the layers being more or less parallel to the liquid flow direction.

The invention also provides a housing for a diesel filter, at least a part of the housing being transparent to permit viewing of a filter element, in use, located in the housing.

The invention extends to a filter element for forming part of a filter as defined above.

According to another aspect of the invention, there is provided a method of filtering diesel, which method includes passing diesel through a filter material which consists predominantly of a fibrous material, the diesel traveling at least 20 mm through the filter material.

The method may include passing the diesel through a filter as defined above.

The invention extends yet further to a method of manufacturing a filter element for use in a liquid filter, which method includes compressing a mass of fibrous filter material, and inserting the compressed material into a filter housing such that the housing resists resilient expansion of the compressed material.

The method may include compressing the filter material in a direction transverse to the direction of liquid flow through the resultant filter element, in use. The method may include compressing the filter material into a circular cylindrical shape, the material being compressed more or less radially inwardly, normal to the longitudinal axis of the resultant cylindrical filter element.

The method may include includes the prior step of packing a plurality of separate pieces of fibrous material in a die cavity, filling the cavity, and thereafter compressing the fibrous material to form the cylindrical filter element. Each piece of fibrous material is preferably elongated and flattened, having height and length dimensions which are large relative to its thickness dimension, each piece being placed in the die cavity such that its height dimension extends more or less parallel to the longitudinal axis of the eventual cylindrical filter element. In one embodiment of the invention, the die cavity is formed by two opposed and spaced apart die halves which are semi-circular or semi-annular in shape, so that the die cavity is separated into three distinct sub-cavities, namely a quadrangular central cavity and two semi-circular end cavities, the method including filling the respective cavities with pieces of fibrous material, removing any division between the sub-cavities, and forcing the die halves towards each other, thus compressing the filter material inwardly to form the cylindrical filter element.

The die halves may be slidably moved towards each other along a rectilinear path during compression of the filter material, the die halves being guided along their path by a pair of parallel end rails which extend tangentially between the die halves on opposite sides thereof.

The method may include packing pieces of filter material in the central cavity such that they are parallel to each other and side by side, the lengths of the pieces of material being more or less parallel to the direction of movement of the die halves towards each other. In addition, the method may include packing pieces of filter material into the end cavities such that the lengthwise direction of the pieces in the end cavities is transverse to the lengthwise direction of pieces in the central cavity. The pieces of fibrous material in the central cavity may thus be perpendicular to the pieces of material in the end cavities.

Conveniently, the method includes dividing the die cavity into the respective sub-cavities by placing a pair of divider plates to extend diametrically between the ends of each semi-annular die half, the method further including removing the divider plates from the die cavity after the sub-cavities have been filled with filter material.

The method may include forming each piece of fibrous material such that its fibres are predominantly oriented more or less parallel to the height dimension of the element. Each piece of fibrous material may be formed by winding an elongated strand of fibrous material spirally around a spindle, thus forming a spiral coil of fibrous material, removing the coil from the spindle, and flattening the coil in a direction transverse to the longitudinal axis of the coil. The length dimension of the flattened coil will thus extend along its longitudinal axis, the height dimension being transverse thereto and more or less parallel to the flattened coils. The strand of fibrous material is preferably wound on the spindle such that a single layer of material is formed by successive side by side abutting revolutions of material.

Preferably, the fibres of each strand of fibrous material extend lengthwise along the strand, so that the fibres of the resultant flattened coil are predominantly oriented parallel to the height dimension of the coil.

The circumference of the spindle is selected such that each revolution of fibrous material around the spindle is 80 - 120 mm long, so that the height of the resultant flattened coil is 40 - 60 mm.

The fibrous material is preferably combed cotton wool whose fibres are more or less aligned. The method may include aligning a cylindrical housing or housing element with the die cavity after compression of the filter material, the housing element being tubular and of substantially equal diameter to that of the die cavity, the housing element being positioned co-axial and in end-to-end abutment with the die cavity, the method including thereafter forcing or ramming the compressed filter element axially out of the die cavity in into the housing element.

According to yet a further aspect of the invention, there is provided an apparatus for manufacturing a filter element for liquid petroleum-based fuel, which apparatus includes: a die which defines a die cavity in which a compressible fibrous material is receivable, the die including two semi-circular die members which are relatively displaceable to vary the size of the die cavity defined between them; and an actuating means for forcing the die members towards each other, to reduce the size of the die cavity and to compress fibrous material in the die cavity, thus forming a circular cylindrical filter element of fibrous material.

The die members may be linearly slidable relative to each other. The die members are preferably opposed, so that the open ends of the semi-circular die members face each other, the apparatus including a pair of parallel side rails which extend tangentially between the die members, thus bordering opposite sides of the die cavity. The apparatus may include a pair of dividers for removable insertion in the die cavity to divide the die cavity into separate sub-cavities, which may optionally comprise: a more or less quadrangular central cavity bordered by the side rails and by dividers which extend diametrically across the open ends of the respective semi-circular die members; and a pair of semi-circular end cavity bordered by the respective dividers and their associated die members.

The invention will now be further described by way of example, with reference to the accompanying diagrammatic drawings, in which:

Figure 1 is a schematic axial section of a filter in accordance with the invention;

Figure 2 is a schematic end view of the filter of Figure 1 ;

Figure 3 is an isolated schematic three-dimensional view of a filter element forming part of the filter of Figure 1 ;

Figure 4 is a schematic three-dimensional view which shows a strand of cotton being wound on a pipe during a first step of forming a filter element in accordance with another embodiment of the invention;

Figure 5 is a schematic three-dimensional view of a number of cotton coils formed during the step shown in Figure 4, the strands having been flattened and placed in a central rectangular space in a press cavity;

Figure 6 is a view corresponding to Figure 5, showing the central rectangular space and a pair of semi-circular end spaces having been filled with flattened cotton coils; Figure 7 is a view corresponding to Figure 6, showing a filter element which is formed by compressing the packed cotton coils of Figure 6 radially inwardly; and

Figure 8 is a schematic three-dimensional view of a filter which comprises the filter of Figure 7 inserted in a transparent cylindrical housing which is closed off by perforated end plates.

In the drawings, reference numeral 10 generally indicates a diesel filter in accordance with the invention. The filter 10 includes a casing or housing 12 which houses a filter element 14 through which diesel is, in use, passed for filtering.

The housing 12 comprises a pair of identical, oppositely oriented co-axial end pieces 16 which are generally disc-shaped, as can be seen in Figure 2. The end pieces 16 are steel pressings, but in other embodiments of the invention, the end pieces can be moulded of a polymeric plastics material. Each end piece 16 defines a central fluid flow aperture for in-line connection of the housing 12 to a diesel flow line, so that one of the apertures provides an inlet port 18 leading into the interior of the housing 12, while the other aperture provides an outlet port 20 leading out of the housing 12.

The housing 12 is completed by a cylindrical sheath or tube 22 which is co¬ axial with the aligned end pieces 16 and extends axially between them. The tube 22 is of a transparent material, in this example being of Perspex, although the tube 22 can, in other embodiments of the invention, be of glass. It will be appreciated that the tube 22 is completely of a transparent material, so that viewing of the filter element 14 is permitted 360° around the housing 12. The filter element 14 consists substantially exclusively of cotton wool. The filter element 14 was formed by winding a sheet of cotton in spiral shape, a central axis 24 of the wound filter element 14 being aligned with the longitudinal axis of the housing 12. The filter element 14 is thus a laminar unit, providing a plurality of layers which are arranged face to face, the layers being more or less parallel to a direction in which liquid, in use, flows through the housing, as indicated by arrows 26 in Figure 1 of the drawings.

It will be appreciated that the cotton sheet from which the filter element is formed comprises elongated cotton fibres which are oriented along the length of the sheet. When the filter is thus formed by spiral winding of the cotton sheet, the fibres are also oriented spirally and are thus transverse to the direction of fuel flow through the filter. In other embodiments of the invention, the laminar filter element can be formed by different methods, such that the fibres are oriented parallel to the direction of flow fuel flow through the housing 12. Such an embodiment is described below with reference to Figures 4 - 8.

The axial length of the filter element 14, i.e. the minimum dimension of the filter element in the direction of fuel flow through the filter element 14, is 50 mm. The diameter of the filter element 14 is 110 mm. It will be appreciated that the filter element 14 can have different dimensions in other embodiments of the invention, preferably being longer than 50 mm and having a diameter greater than 100 mm.

The filter element 14 is arranged in the housing 12 such that the radially outer surface of the filter element 14 bears tightly against the radially inner periphery of the housing 12, which is provided by the tube 22. An axially extending disc-shaped gap is formed between the filter element 14 and the respective end pieces 16, upstream and downstream of the filter element 14.

In use, the filter 10 is connected in-line in the diesel supply line of a diesel engine, so that diesel, in use, flows from the inlet port 18 to the outlet port 20 in the diesel flow direction 26, passing axially through the filter element 14. Particles of dirt and grime are filtered from the diesel during its passage through the filter element 14.

It will be appreciated that the filter element 14 progressively becomes stained by the filtered particles, until the filter element 14 is occluded and requires replacement. The transparent tube 22 effectively provides a viewing window for permitting visual inspection of the filter element 14. A user can thus readily check whether or not the filter element 14 is due for replacement.

As the filter element 14 is of simple construction and inexpensive material, it can be disposed of after use, and replaced by another filter element 14.

Another embodiment of a filter in accordance with the invention, as well as a method of making the filter, will now be described with reference to Figures 4 - 8. Like reference numerals indicate like parts in Figures 1 - 3 and in Figures 4 - 8, unless otherwise indicated. In this embodiment, a filter element 30 is formed by packing a plurality of cotton pieces in a die, and compressing the cotton pieces. Each cotton piece is in the form of a coil 32 made of cotton strand.

First, as is shown in Figure 4, cut lengths of cotton strand 34 are wound spirally on a cylindrical spindle or pipe 36. The cotton strand 34 is wound such that successive revolutions of the coil thus formed abut one another side by side, so that a single layer of cotton wool extends circumferentially around the pipe 36. It will be appreciated that the cotton strand 34 is formed of elongated cotton fibres which extend lengthwise along the strand 34. When the cotton strand 34 is thus wound on the pipe 36, the elongated cotton fibres also extend circumferentially around the pipe 36.

The pipe 36 is dimensioned such that each revolution of the cotton strand 34 on the pipe 36 comprises more or less 100 mm of the cotton strand 34. The strand 34 is wound in lengths of 140 mm on the pipe 36.

Each coil 32 which is formed in the manner described above is removed from the pipe 36 and is flattened in a direction radially inwards, transverse to the longitudinal axis of the coil 32. Each coil 32 is thus a flattened element having a length of about 140 mm and a height of about 50 mm. The cotton fibres comprising the coil 32 extend predominantly in a direction more or less parallel to the height of the coil 32.

The coils 32 are hereafter placed in a press or die 38 for compression of the coils 32, to form a filter element 30 in accordance with the invention. The die 38 comprises two semi-circular or semi-annular die halves 40 which are opposed face to face and are spaced apart. The die halves 40 are relatively slidably towards and away from each other, being connected by side rails 42 which extend tangentially between the die halves 40. One of the halves 40 can thus slide towards the other along a rectilinear path guided by the side rails 42, maintaining a constant orientation relative to the other half 42, until the halves 42 meet to form a circular die cavity 44.

The coils 32 are, however, placed in the die cavity 44 while the die halves 40 are spaced apart, the die cavity 44 being extended so that it is more or less rectangular in outline, with semi-circular ends. An end plate 46 is positioned at the open end of each die half 40, extending diametrically across the die half 40 and thus defining a semi-circular end cavity 48 which is enclosed by the half-annular die half 40 and the end plate 46. A rectangular central cavity 50 is defined between the opposed and parallel end plates 46, on the one hand, and the opposed and parallel side rails 42, on the other hand, the end plates 46 and the side rails 42 being perpendicular to each other.

As can be seen in Figure 5, coils 32 are first packed in the central cavity 50, each flattened coil 32 extending lengthwise between the end plates 46, with the height of the coil 32 oriented upwards. The length of each coil 32 is thus equal to the distance between the end plates 46. The coils 32 are parallel to each other and are packed tightly side by side, so that a series of packed coils 32 extend from one side rail 42 to the other, thus completely filling the central cavity 50. In this example, twenty seven cotton coils 32 are packed into the central cavity 50.

Thereafter, wound and flattened coils 32 are inserted side by side into each of the end cavities 48 (Figure 6). The first coils 32 in the end cavities 48 thus run perpendicularly to the coils 32 in the central cavity 50. In this example, five coils 32 are placed in each end cavity 48.

Once the central cavity 50 and the end cavities 48 have been fully packed, the end plates 46 are removed, and the die halves 40 are forced towards each other to compress the cotton coils 32 in the die cavity 44 (Figure 7). As the die halves 40 slide towards each other, the cotton coils 32 are effectively compressed radially inwardly along a single axis which extends diametrically across the eventual circular cylindrical filter element 30.

Compression of the coils 32 which have been stacked as described above thus results in a circular cylindrical filter element 30 which has a height or thickness of about 50 mm and a diameter of about 140 mm. The volume of the filter element 30 is thus about 3080 cm³. The total weight of cotton material which is wound on coils 32 and forms part of the filter element 30 is 250 g, so that the density of the resultant filter element 30 is 361 kg/m³.

It will also be appreciated that the method of manufacturing the filter element 30 as described above facilitates orientation of the cotton fibres along the axis 24 of the cylindrical filter element 30. Not only are the cotton strands 34 first wound such that their fibres are more or less parallel, but all the coils 32 are placed upright in the die cavity 44, so that their fibres also extend upwardly. Compression of the coils 32 in the way described further ensures that the respective coils 32 have an upright or axially aligned orientation. The compressed filter element 30 is then inserted into a cylindrical housing 12 of transparent plastics material. It is important to bear in mind that the cotton strands 34 from which the filter element 30 is formed has a significant amount of resilient resistance to compression. Removal of the filter element 30 from the die 38 without restraining it will thus cause decompression of the element 30.

To prevent this, the housing 12 is axially aligned with the die 38, so that the filter element 30 and the housing 12 are co-axial and are positioned in end to end abutment. The filter element 30 is then pressed with a ram (not shown) axially out of the die 38 and into the housing 12.

Because the filter element 30 has been compressed radially inwardly, its resilience causes it to bear radially outwardly in extremely tight abutment with the radially inner surface of the housing 12. However, there is no need to restrain the filter element 30 against axial expansion.

After such insertion of the filter element 30 into the housing 12, perforated cheek plates 52 are placed in the housing 12 at opposite ends of the filter element 30, the cheek plates 52 being normal to the axis 24 of the filter element 30 and housing 12. End pieces or end caps 54 are then connected to the respective ends of the cylindrical housing 12, to close off the ends of the housing 12.

Connection of the end caps 54 to the housing 12 is by screwing engagement of complementary screw threads 56 on the end caps 54 and the housing 12 respectively. It will be appreciated that the end caps 54 are sealingly connected to the housing 12, to prevent leakage of fuel or diesel, in use.

As can best be seen in Figure 8 of the drawings (in which one of the end caps 54 are shown in an inverted position, before connection thereof to the housing 12), the end cap 54 includes an annular spacer 58 which projects axially inwardly into the housing 12, in use, to bear against the associated cheek plate 52, spacing the cheek plate 52 from an axial end wall 60 of the end cap 54. This ensures proper spacing of the filter element 30 from the inlet port 18 provided in the end wall 60 of the end cap 54, to prevent blockage of the inlet port 18 (or the outlet port 20, as the case may be) by the filter element 30.

Although a filter 70 formed by the method described above can be used as a stand alone filter, the inventor has found that the filter 70 functions particularly well when retro-fitted to existing diesel filtering systems as an additional, final filter.

It is an advantage of a filter 10, 70 as described with reference to the drawings that the filter element 14 is considerably less expensive to manufacture than prior art filter elements, and can thus be distributed as a disposable article. Thus is partly due to the fact that the filter element 14 is made from a raw, unrefined natural product. Furthermore, the transparent tube 22 facilitates quick and easy visual inspection of the state of the filter element 14. In addition, the Applicant has found that a filter in accordance with the invention filters diesel more effectively than more expensive prior art filters. The method of manufacturing the filter element 30 described with reference to Figures 4 - 8 ensures that the cotton fibres are more or less parallel to the direction of liquid flow through the filter 70. It will be appreciated that cotton in the filter element 30 should optimally be equally compressed throughout. This is achieved by the described method.

Furthermore, radially inward compression of the cotton ensures tight sealing of the filter element 30 against the cylindrical wall of the housing 12, to prevent liquid which is to be filtered from seeping unfiltered through gaps between the filter element 30 and the housing 12.

Claims

CLAIMS:

1. A filter for filtering petroleum oil or liquid petroleum-based fuel, which filter includes: a liquid flow path along which liquid which is to be filtered is flowable; and a filter element located in the liquid flow path for filtering liquid which moves through the filter element in a liquid flow direction, the filter element being predominantly of a fibrous material, and a dimension of the filter element in the liquid flow direction being at least 20 mm.

2. A filter as claimed in 1 , in which the dimension of the filter element in the liquid flow direction is at least 40 mm.

3. A filter as claimed in claim 1 or claim 2, in which the filter element comprises a solid mass of natural fibrous material.

4. A filter as claimed in claim 3, in which the filter element is of cotton.

5. A filter as claimed in claim 4, in which the filter element is of compressed cotton wool.

6. A filter as claimed in any one of the preceding claims, in which the filter element is of laminar construction, comprising a plurality of layers which are arranged face to face.

7. A filter as claimed in claim 6, in which the filter element is arranged such that the liquid flow direction is more or less parallel to the layers of the filter element.

8. A filter as claimed in claim 7, in which the filter element is cylindrical in shape, the liquid flow direction being more or less parallel to the longitudinal axis of the cylindrical filter element.

9. A filter as claimed in claim 8, in which the filter element is formed of at least one sheet of spirally wound filter material.

10. A filter as claimed in any one of the preceding claims, in which the filter material comprises elongated fibers having a common orientation, so that the fibres of each layer of the filter material have the same orientation.

11. A filter as claimed in claim 10, in which the common orientation of the filter element fibres is more or less parallel to the liquid flow direction.

12. A filter as claimed in any one of the preceding claims, in which the filter element has a density of 250 - 350 kg/m³.

13. A filter as claimed in any one of the preceding claims, in which the filter element has a density of 300 - 400 kg/m³.

14. A filter as claimed in any one of the preceding claims, in which the filter element has a density of about 360 kg/m³.

15. A filter as claimed in any one of the preceding claims, in which the filter element is located in a housing, at least part of the housing being transparent to permit viewing of the filter element.

16. A filter as claimed in 15, in which the housing is circular cylindrical in shape, permitting viewing of the filter element 360° around the axis of the housing.

17. A filter as claimed in 15 or claim 16, in which the housing is at least partially made of a transparent polymeric plastics material.

18. A filter as claimed in any one of claim 15 to 17 inclusive, in which the housing is configured for facilitating unidirectional flow of liquid through the filter element.

19. A filter as claimed in claim 18, in which the housing comprises a pair of end pieces which a transparent cylindrical tube extending between them, the filter element being located in the tube, one of the end pieces providing an inlet port and the other end piece providing an outlet port, so that liquid, in use, flows from the inlet port to the outlet port, axially through the filter element.

20. A filter as claimed in claim 19, which includes a spacer arrangement at each end piece for spacing the filter element from the inlet port and the outlet port respectively, to permit the accumulation of liquid at both ends of the filter element.

21. A filter as claimed in claim 20, in which each spacer arrangement comprises a perforated end plate which is located in the housing at an end of the filter element, the respective end piece being shaped to engaged the end plate to space the end plate from the inlet port or the outlet port, as the case may be, the end plate, in turn, abutting the filter element to space it from the end piece.

22. A method of filtering diesel, which method includes passing diesel through a filter material which consists predominantly of a fibrous material, the diesel traveling at least 20 mm through the filter material.

23. A method as claimed in claim 22, in which the diesel is passed at least 40 mm through the filter material.

24. A method as claimed in claim 22 or claim 23, in which the diesel is passed though a filter element of the fibrous filter material, elongated fibres in the filter element being oriented more or less parallel to the direction of travel of diesel through the filter element.

25. A method of manufacturing a filter element for use in a liquid filter, which method includes compressing a mass of fibrous filter material, and inserting the compressed material into a filter housing such that the housing resists resilient expansion of the compressed material.

26. A method as claimed in claim 25, which includes compressing the filter material in a direction transverse to the direction of liquid flow through the resultant filter element, in use.

27. A method as claimed in claim 26, which includes compressing the filter material into a circular cylindrical shape, the material being compressed more or less radially inwardly, normal to the longitudinal axis of the resultant cylindrical filter element.

28. A method as claimed in claim 27, which includes the prior step of packing a plurality of separate pieces of fibrous material in a die cavity, filling the cavity, and thereafter compressing the fibrous material to form the cylindrical filter element.

29. A method as claimed in claim 28, in which each piece of fibrous material is elongated and flattened, having height and length dimensions which are large relative to its thickness dimension, each piece being placed in the die cavity such that its height dimension extends more or less parallel to the longitudinal axis of the eventual cylindrical filter element.

30. A method as claimed in claim 29, in which the die cavity is formed by two opposed and spaced apart die halves which are semi-annular in shape, so that the die cavity is separated into three distinct sub-cavities, namely a quadrangular central cavity and two semi-circular end cavities, the method including filling the respective cavities with pieces of fibrous material, removing any division between the sub-cavities, and forcing the die halves towards each other, thus compressing the filter material inwardly to form the cylindrical filter element.

31. A method as claimed in claim 30, in which the die halves are slidably moved towards each other along a rectilinear path during compression of the filter material, the die halves being guided along their path by a pair of parallel end rails which extend tangentially between the die halves on opposite sides thereof.

32. A method as claimed in claim 30, which includes packing pieces of filter material in the central cavity such that they are parallel to each other and side by side, the lengths of the pieces of material being more or less parallel to the direction of movement of the die halves towards each other.

33. A method as claimed in claim 32, which includes packing pieces of filter material into the end cavities such that the lengthwise direction of the pieces in the end cavities are transverse to the lengthwise direction of pieces in the central cavity.

34. A method as claimed in any one of claims 30 to 33, which includes dividing the die cavity into the respective sub-cavities by placing a pair of divider plates to extend diametrically between the ends of each semi-annular die half, the method further including removing the divider plates from the die cavity after the sub-cavities have been filled with filter material.

35. A method as claimed in any one of claims 29 to 34 inclusive, which includes forming each piece of fibrous material such that its fibres are predominantly oriented more or less parallel to the height dimension of the element.

36. A method as claimed in claim 35, which includes forming each piece of fibrous material by winding an elongated strand of fibrous material spirally around a spindle, thus forming a spiral coil of fibrous material, removing the coil from the spindle, and flattening the coil in a direction transverse to the longitudinal axis of the coil.

37. A method as claimed in claim 36, in which the strand of fibrous material is wound on the spindle such that a single layer of material is formed by successive side by side abutting revolutions of material.

38. A method as claimed in claim 36 or claim 37, in which the fibres of each strand of fibrous material extend lengthwise along the strand.

39. A method as claimed in claim 36, claim 37, or claim 38, in which the diameter of the spindle is selected such that each revolution of fibrous material around the spindle is 80 - 120 mm long.

40. A method as claimed in any one of claims 25 to 39 inclusive, in which the fibrous material is combed cotton wool whose fibres are more or less aligned.