WO2001097949A1

WO2001097949A1 - Filter assemblies

Info

Publication number: WO2001097949A1
Application number: PCT/GB2001/002738
Authority: WO
Inventors: Nicholas Llyod Yoward; Alan Collins; Charles Nicholas Rothwell
Original assignee: Pall Corporation
Priority date: 2000-06-23
Filing date: 2001-06-21
Publication date: 2001-12-27
Also published as: AU2001274291A1

Abstract

A filter assembly comprises a tubular fitler medium (10) with first and second ends, and two end caps (11, 12) that close and seal against respective ones of the ends. Each end cap carries a knife edge wall (21, 22, 34, 35) that penetrates into the associated end of the filter medium (10) so as to create the seal. The end caps are fixable to one another by a snap-fit mechanism (13, 29) that can comprise members integral with the end caps (11, 12). Another filter assembly has generally segmental shape filter media (84) arranged around an axis and fitting into a cylindrical housing. The shape of the media (84) allows a greater packing density of filter material to be achieved in the housing than would be the case with cylindrical shaped filter media. Other shapes of media are contemplated also providing increased packing densities. The filter media may be formed from depth filter media.

Description

FILTER ASSEMBLIES

The invention relates to filter assemblies.

A known type of filter assembly comprises a tubular filter medium with two ends and

two end caps that are fϊxable in sealing contact with respective ones of the ends so as

to close the ends. The end caps are made of plastics material and this allows each end

cap to be sealed to the corresponding end of the filter medium by welding techniques

in which an appropriate region of the end cap is softened by heating and the end of the

filter medium is then inserted into the softened region. On cooling, the end cap is

sealed to the end of the filter medium. One of the end caps (or optionally both) is

provided with a port that allows fluid to pass across the end cap to or from the interior

of the tubular filter medium. Fluid is filtered by passing the fluid across the filter

medium - either from the outside to the inside of the filter medium, or from the inside

to the outside of the filter medium. Hence, each end cap directs fluid through the filter

medium.

In accordance with a first aspect of the invention, there is provided a filter assembly

comprising a filter medium, a member and a snap-fit mechanism engaged or

engagable to fix the member in sealing contact with the filter medium so that the

member directs flow of fluid through the filter medium during filtration, the member

having a wall with a free edge, the wall penetrating into the filter medium so as to

form said seal. Many known filter assemblies include a housing containing two or more filter media.

The filter media are cylindrical and may, for example, be formed of depth filter

material. For stress resistance purposes, the housing is often of circular cross-section,

although other cross-sections are sometimes used. In order to obtain efficient

filtration and fluid flow, there is usually a minimum diameter for a particular

cylindrical filter medium. Likewise, manufacturing constraints provide a limit on the

maximum diameter of the filter media. Accordingly, for a particular fluid flow, it may

be necessary to insert two or more cylindrical filter media into a housing.

The insertion of cylindrical filter media into a cylindrical housing is inefficient since

the cross-sectional area of the filter media compared to the cross-sectional area of the

housing needed to accommodate the filter media is comparatively low. This means

that for a particular flow volume and filtration performance, a comparatively large

volume housing must be used with a comparatively large number of filter media.

According to a second aspect of the invention, there is provided a filter assembly

comprising a housing and at least two filter elements within the housing, each filter

element comprising a non-circular tube of depth filter media having at least one side,

the at least two filter elements being arranged side-by-side in the housing with said

sides adjacent.

According to a third aspect of the invention, there is provided a filter assembly comprising a housing having a curved cross-sectional shape and at least two filter

media within the housing, each filter medium having first and second sides, the first

side of each filter medium having a curved shape similar to the shape of a portion of

the cross-section of the housing and being adjacent said portion and the second side

of each filter medium extends away from the housing and being adjacent the second

side of another filter medium.

According to a fourth aspect of the invention, there is provided a filter assembly

comprising a housing and a plurality of filter media arranged side-by-side within the

housing, each filter medium being formed of depth filter material and having a non-

circular cross-section so as to achieve a packing density within the housing greater

than a corresponding plurality of filter media of circular cross-section.

By using filter elements that are non-circular, higher packing densities can be

achieved.

The following is a more detailed description of embodiments of the invention, by

means of example, reference being made to the appended schematic drawings in

which:

Figure 1 is a cross-sectional representation of an assembled filter assembly in

accordance with the invention; Figure 2 is a perspective view of a first end cap of the filter assembly of Figure 1;

Figure 3 is a perspective view of a second end cap of the filter assembly of Figure 1;

Figure 4 is a perspective view of the first and second end caps assembled together (the

filter medium being omitted for clarity);

Figure 5 is an enlarged view showing a part of the filter assembly of Figure 1 at a first

stage during the assembly process;

Figure 6 is a similar view to Figure 5 showing the filter assembly of Figure 1 at a

second, subsequent, stage of the assembly process;

Figure 7 is a cross-sectional view of a second filter assembly;

Figure 8 is a cross-sectional view of a third filter assembly;

Figure 9 is a representation of a fourth filter assembly;

Figure 10 is a cross-sectional view of the fourth filter assembly;

Figure 11 is a plan view of an inner face of a closed end cap of the fourth filter assembly;

Figures 12 to 14 are cross-sectional views, respectively on lines XII, XIII and XIV of

Figure 11, of the closed end cap;

Figure 15 is a plan view of an inner face of an open end cap of the fourth filter

assembly;

Figure 16 is a side view of a tie rod of the fourth filter assembly;

Figure 17 is a cross-section taken on the line XVII of Figure 16; and

Figure 18 is an enlarged view of an end of the tie rod of Figures 16 and 17.

As shown in Figure 1, the filter assembly comprises a tubular filter medium 10 having

first and second ends, and first and second end caps 8, 9, which, when the filter

assembly is assembled, close respective ones of the first and second ends.

As best seen in Figure 2, the first end cap 8 has a planar wall 12 that has a generally

triangular outer perimeter. A tubular wall 13, that is generally triangular in cross-

section, extends from the centre of the planar wall 12 in a direction normal to the

planar wall 12. As seen in Figures 1 and 2, the tubular wall 13 has a plurality of holes 14 extending therethrough. As seen in Figure 2, the tubular wall 13 is provided with

four thickened regions 15 that extend in the direction of the length of the tubular wall

13, and that are spaced from one another around the tubular wall 13. The thickening

is achieved by material that extends to the inside of the tubular wall 13. Each

thickened region 15 has two of the holes 14 passing thereacross.

The tubular wall 13 is also provided with four inwardly directed projections 16 - each projection 16 being located axially in line with a respective one of the thickened regions 15 and towards the free end 17 of the tubular wall 13. Each projection 16 is spaced from the corresponding thickened region 15 so as to provide a respective groove 18 therebetween. Each projection 16 has a surface 19 that is closest to the free end 17 of the tubular wall 13 and that slopes inwardly from the tubular wall 13 towards the planar wall 12.

As seen in Figures 1 and 2, the perimeter of the first end cap 8 is provided with a flange 20 that extends normally to the planar wall 12 in the same direction as the

tubular wall 13.

The planar wall 12 of the first end cap 8 is also provided with inner and outer sealing walls 21, 22 - each of which extends outwardly of and around the tubular wall 13 and within the flange 20. The outer sealing wall 22 helps to hold the filter medium in the

required shape (triangular in cross-section). The inner sealing wall 21 is seen best in Figures 5 and 6 (from which the outer sealing wall 22 is omitted for clarity). In these Figures, it can be seen that the inner sealing wall 21 has an outer surface 23 that extends normally to the planar wall 12 and an inner surface 24 that extends obliquely to the planar wall 12 so that the inner and outer surfaces 23, 24 meet at an edge 25 referred to as the knife edge.

The outer sealing wall 22 can have the same configuration.

As seen best in Figure 1, the first end cap 8 is provided with a port 26 that extends across the planar wall 12 opening within the tubular wall 13.

Referring now to Figures 1 and 3, the second end cap 9 has a planar wall 27 that also

has a generally triangular outer perimeter.

An inner flange 28, generally triangular in cross-section, extends normally to the

planar wall 27 from the centre of the planar wall 27. Four arms 29, spaced from one

another around the inner flange 28, extend from the inner flange 28 in a direction

normal to the planar wall 27. Each arm 29 is resilient and is provided at its free end

with a respective, outwardly directed projection 30. Each projection 30 has a sloping

surface 31 that extends outwardly and towards the planar wall 27.

An outer flange 32 extends around the outer perimeter of the planar wall 27, in a direction normal to the planar wall 27, and to the same side of the planar wall 27 as

the inner flange 28.

As best seen in Figure 3, three resilient fingers 33 are spaced around the outer flange

32 and extend away from the planar wall 27 in a direction normal to the planar wall

27.

Located between the inner and outer flanges 28, 32 are inner and outer sealing walls

34, 35 that are of a similar configuration to the inner and outer sealing walls 21, 22 of

the first end cap 8.

The second end cap 9 is also provided with a port 36 (which is optional) that extends

across the planar wall 27 and that opens within the inner flange 28.

The filter medium 10 is a coreless filter medium of known type. The filter medium

is composed of a plurality of fibres with spaces between the fibres through which fluid

flows during filtration. The filter medium 10 has an inner region 37 in which the

fibres are more tightly packed and an outer region 38 in which the fibres are more

loosely packed. (A filter medium having a constant packing throughout may be used.)

In this way, when fluid is being filtered from the outside of the filter medium 10 to the

inside of the filter medium 10, larger particles are trapped in the outer region 38

whereas smaller particles are trapped within the inner region 37. The filter medium 10 is also generally triangular in cross-section.

In order to assemble the filter assembly, the first end cap 8 is laid on a working

surface with the tubular wall 13 extending upwardly. The filter medium 10 is then slid

onto the tubular wall 13 so that the inner surface of the filter medium 10 contacts the

outer surface of the tubular wall 13. At this stage, the knife edges 25 of the inner and

outer sealing walls 21, 22 contact the lower end of the filter medium 10.

The second end cap 9 is then fitted to the assembly. During fitting of the second end

cap 9, the resilient arms 29 are inserted within the tubular wall 13 and the resilient

fingers 33 are held outward of the outer surface of the filter medium 10. Each arm 29

lies axially in line with a respective one of the projections 16 provided on the inside

of the tubular wall 13. As the second end cap 9 is fitted to the first end cap 8 each

sloping surface 31 of the arms 29 contacts the inclined surface 19 of the corresponding

projection 16 on the inner side of the tubular wall 13. As the first and second end caps

are pushed together, the contact between the surfaces 19, 31 causes the arms 29 to flex

inwardly and ride over the projections 16.

The second end cap 9 is then pushed hard against the first end cap 8 so that the free

end 17 of the tubular wall 13 comes to rest against the planar wall 27 of the second

end cap 12 and so that the projections 30 on the arms 29 snap into the grooves 18.

This interlocking of the projections 30 with the grooves 18 fixes the first and second end caps 8, 9 together (as seen in Figure 1). Hence, the tubular wall 13 and the arms

29 form a snap-fit mechanism for fixing the first and second end caps 8, 9 together.

The contact between the free end 17 of the tubular wall 13 and the planar wall 27 of

the second end cap 9 (and the lengths of the arms 29 together with the positions of the

grooves 18) ensures that the first and second end caps 8, 9 are fixed in a

predetermined spatial relationship relative to one another. This relationship is such

that the distance between the planar walls 12, 27 corresponds to the length of the filter

medium 10.

As the end caps 8, 9 are pushed together, as described above, the inner and outer sealing walls 21, 22 on the first end cap penetrate into the lower end of the filter medium 10 so as to seal the lower end against the first end cap, and the inner and outer sealing walls 34, 35 on the second end cap 9 penetrate into the upper end of the filter medium 10, so as to seal the upper end against the second end cap 9.

This sealing process is shown for the inner sealing wall 21 of the first end cap 8 in

Figures 5 and 6.

As shown in these Figures, the position of the outer surface 23 of the inner sealing wall 21 corresponds approximately to the interface between the inner and outer regions 37, 38 of the filter medium 10. As seen in Figure 6, as the inner sealing wall 21 penetrates into the lower end of the filter medium 10, the inclination of the inner

surface 24 of the inner sealing wall 21 causes the fibres of the inner region 37 of the filter medium 10 to be compressed together between the inner sealing wall 21 and the tubular wall 13. This compression reduces the volume of the spaces between the fibres and this, in turn, prevents or resists fluid flow between the fibres during filtration. This helps to ensure a good seal between the end cap and the filter medium.

Finally, the fingers 33 are released so that they bear against the outer surface of the filter medium 10 and push the filter medium 10 against the tubular wall 13. These

fingers 33 hold the filter medium 10 in the required shape - triangular in cross- section).

During filtration using the filter assembly, the fluid to be filtered is presented to the

outer surface of the filter medium 10. The fluid passes through the filter medium to

the tubular wall 13 and through the holes 14 in the tubular wall 13. Filtered fluid in

the space within the tubular wall 13 then passes out of the filter assembly through the

ports 26 and 36 (or through one of these ports if the other one is closed). The sealing

between the end caps 8, 9 and the filter medium 10 prevents fluid by-passing filter

medium 10 by passing between the filter medium 10 and the end caps 8, 9.

The tubular wall 13 acts as a "core" supporting the filter medium 10. It will be appreciated that a large number of modifications may be made to the filter

assembly described above.

The filter medium 10, and the end caps 8, 9, need not have the shapes described

above. For example, the filter medium 10, the tubular wall 13, and the perimeters of

the planar walls 12 and 27 may be generally circular, rather than triangular.

In the filter assembly described above, the tubular wall 13 and the arms 29 act as a

snap-fit mechanism allowing the end caps to be fixed to one another. However, other

snap-fit mechanisms may be provided.

In another embodiment, the tubular wall 13 is omitted from the first end cap 8.

Instead, a separate tubular member, similar to the tubular wall 13 is provided. The

separate member can be fixed to the inner surface of the filter medium thereby

carrying the medium. The first end cap 8 is provided with arms similar to the arms 29

of the second end cap 9. In this embodiment, the arms on the first end cap snap-fit

with holes in the tubular member. Similarly, the arms on the second end cap 9 snap-fit

with holes in the tubular member. The sealing walls 21, 22, 34, 35 seal with the ends

of the medium as described above.

A "double-sided" end cap might be used. Thus, for example, the first end cap 8 may

be provided with a further tubular wall, further sealing walls and a further flange that extend from the other side of the planar wall 27. In this way, a second filter medium

10 could be fitted over the further tubular wall, as described above, and a further

second end cap 9 could be fixed to the adapted first end cap 8 so as to hold the second

filter medium between the adapted first end cap and the further second end cap 9. In

this way, two filter media 10 are connected together with the internal spaces of the

filter media being in fluid communication by way of the port 26.

A similar "double-sided" end cap may be made by providing the second end cap 9

with arms, sealing walls, an outer flange and fingers on the other side of the planar

wall 27.

The end caps may be provided with grooves and 'O' rings for sealing the assembly

within suitable housings.

The end caps may be made of acetal resin for compatibility with fuel. Other materials,

e.g. plastics materials may be used. Suitable plastics are nylon, polyproplyene,

polyester.

In a second filter assembly shown in Figure 7, the assembly comprises first and

second end caps 39, 40, a filter medium 10 identical to the filter medium 10 described

above, and a separate tubular core 41. The first end cap 39 has a circular planar wall 42 provided with a cylindrical flange

43 extending from the perimeter of the planar wall 42. The cylindrical flange 43 is

provided with a plurality of holes 44 passing across the flange 43.

The planar wall 42 is also provided with inner and outer annular sealing walls 45, 46

that extend to the same side of the planar wall 42 as the cylindrical flange 43 and are

similar to the sealing walls 21, 22, 34, 35. A port 47 is provided in the planar wall 42.

The second end cap 40 has a circular, planar wall 48. A plurality of resilient arms 49

extend from the perimeter of the planar wall 48 and are spaced from one another

around the planar wall 48. Each arm 49 is provided with a respective inwardly

directed projection 50.

The second end cap 40 also has inner and outer sealing walls 51, 52 similar to the sealing walls 21, 22, 34, 35.

The tubular core 41 is cylindrical and is provided with a plurality of holes 53 through

its wall.

The filter assembly is assembled as follows. The filter medium 10 is placed within the cylindrical flange 43 of the first end cap 39 so that an end of the filter medium 10

lies against the knife edges of the sealing walls 45, 46. The tubular core 41 may be bound to the inner surface of the filter medium 10 (thereby carrying the filter medium) or it may be unconnected and inserted separately

into the inner space of the filter medium 10. The second end cap 40 is then positioned with the arms 49 outside the cylindrical flange 43 and the second end cap 40 is pushed towards the first end cap 39 until the cylindrical flange 43 contacts the planar wall 48 of the second end cap 40. At this stage, the projections 50 snap into respective ones of the holes 44 in the cylindrical flange 43.

Thus, the cylindrical flange 43 and the arms 49 act as a snap-fit mechanism.

As the first end cap 39 and the second end cap 40 are pushed together as described above, the sealing walls 45, 46, 51, 52 penetrate into the ends of the filter medium 10 so as to seal the ends of the filter medium 10 against the end caps 39, 40, as described

above.

In operation, fluid to be filtered is presented to the outside of the filter assembly and

passes through the holes 44 in the cylindrical flange 43. The fluid passes through the

filter medium 10 and through the holes 53 in the tubular core 41 to the inside of the

tubular core. The fluid then passes out of the filter assembly through the port 47.

By choosing an appropriate filter medium, inside to outside flow can also be used.

A third embodiment of a filter assembly is shown in Figure 8. The filter assembly of Figure 8 comprises first and second parts of a housing 54, 55, an end cap 56, a filter

medium 10 that is identical to the filter medium 10 described above and a tubular core

41 that is identical to the tubular core 41 described above.

The first part 54 of the housing has a circular, generally planar end region 57 and a

generally cylindrical flange 58 that extends around an outer perimeter of the end

region 57.

At the free end of the flange 58 is provided a lip 59 that extends radially outwardly

from the flange 58.

The end region 57 is provided with a central port 61 that passes across the end region

57. An annular sealing wall 60 extends around the port 61 to the same side of the end

region 57 as the flange 58.

The second part 55 of the housing has a circular, generally planar end region 63 and

a generally cylindrical flange 64 that extends around an outer perimeter of the end

region 63.

An annular locking formation 65 extends around the free end of the flange 64.

Starting from the end of the flange 64, the locking formation 65 has a first portion 66

that extends radially outwardly from the flange 64 to a second portion 67 that extends in an axial direction away from the end region 63. The free end of the second portion

67 of the locking formation 65 is provided with a lip 68 that projects radially inwardly.

The lip 68 has an inclined surface 69 that extends radially inwardly and towards the

end region 63 of the second part 55.

The end region 63 of the second part 55 is provided with a central port 70 that extends

across the end region 63. Additionally, the end region 63 is provided with raised

"pips" or projections that extend to the same side of the end region 63 as the flange

64.

The end cap 56 consists of a circular, planar wall 71 and an annular sealing wall 72

that extends around the planar wall 71 adjacent an outer perimeter of the planar wall

71.

The sealing walls 60, 72 have similar configurations to those of the sealing walls 21,

22, 34, 35 described above.

In order to assemble the third filter assembly, the filter medium 10 together with the

tubular core 41 located within and contacting the inner surface of the filter medium

10 are placed so that an end of the filter medium 10 lies against the sealing wall 60 of

the first part 54 of the housing. The end cap 56 is then placed so that the sealing wall

72 of the end cap 56 lies against the other end of the filter medium 10. The second part 55 of the housing is then placed over the end cap 56 and the associated end of the

filter medium 10 so that the inclined surface 69 of the locking formation 65 contacts

the lip 59 of the first part 54. The first and second parts 54, 55 of the housing are then

pushed together so that the locking formation 65 flexes outwardly and rides over the

lip 59 until the lip 68 snaps into position adjacent the lip 59 as shown in Figure 8.

The projections or pips bear against the end cap 56.

During this assembly, the sealing walls 60, 72 penetrate into the respective ends of the

filter medium 10, as described above, so as to seal the first part 54 against one end of

the filter medium 10 and the end cap 56 against the other end of the filter medium 10.

Suitable means (not shown) are provided to give a fluid tight seal between the two

parts 54, 55 of the housing.

In operation, fluid is passed into the housing via the port 70 and passes around the

outside of the filter medium 10. The fluid then passes through the filter medium 10

and through the holes 53 in the core 41 to the interior of the core 41. Fluid in the

interior of the core 41 passes out from the housing via the port 61.

The components of the third filter assembly can be assembled in a different manner,

as follows. Firstly, the end cap 56 is sealed against an end of the filter medium 10 by pushing the sealing wall 72 into the end of the filter medium 10. The planar end

region 57 of the first housing part 57 is then sealed against the other end of the filter

medium by pushing the sealing wall 60 into the other end. Finally, in order to fix the

end cap 56 and the first housing part 54 in their respective sealing positions relative

to the filter medium 10, the second housing part 55 is snapped onto the first housing

part 54 so that the pips bear against the end cap 56.

A fourth filter assembly is shown in Figures 9 to 18. As best seen in Figures 9 and 10,

the fourth filter assembly comprises four separate filter elements 80a,80b,80c,80d, an

open generally disc-shaped end cap 81, a closed generally disc-shaped end cap 82 and

four tie rods 83a,83b,83c,83d.

The four filter elements 80a to 80d are identical and only one of these, 80a, will be

described in detail. The same reference numerals will be used to indicate

corresponding features of the four filter elements 80a,80b,80c,80d.

Referring to Figures 9 and 10, the filter element 80a comprises a tubular filter medium

84 (not shown in Figure 10), a tubular inner core 85 and a tubular outer cage 86. The

filter medium 84 has an outer surface which, in cross-section, has a shape

corresponding generally to a quadrant of a circle. That is to say the outer surface of

the filter medium has two mutually perpendicular planar regions or sides

(corresponding to radii of a circle) and an arcuate region or side (corresponding to the circumference of the circle). Each region (or side) is connected to the other regions

(or sides) by a curved comer. The filter medium has an inner surface that has a similar

shape to the outer surface but that is, of course, smaller. Accordingly, the terms

"tube" and "tubular" as used in this specification include tubes having cross-sections

other than circular cross-sections.

The inner core 85 is a relatively rigid tubular wall that lies against, and has the same

shape as, the inner surface of the filter medium 84. The outer cage 86 is a thin,

relatively rigid tubular wall that lies against, and has the same shape as, the outer

surface of the filter medium 84. Hence the inner core 85 has first and second planar

regions 87,88 and an arcuate region 89. The first and second planar regions 87,88 are

joined by a first rounded comer 90. The first planar region 87 is joined to the arcuate

region 89 by a second rounded comer 91, and the second planar region 88 is joined

to the arcuate region 89 by a third rounded comer 92.

The filter medium 84 may be formed from a fibrous, depth filter material, such as that

sold by Pall Corporation under the Trade Mark PROFILE. Each of the inner core 85

and the outer cage 86 is provided with a plurality of openings so as to allow fluids to

pass freely through. The inner core 85 and the outer cage 86 serve to maintain the

filter medium 84 in the quadrant-like shape described above and prevent compression

of the filter medium 84 in an axial direction. If desired one of the inner core 85 and

the outer cage 86 can be omitted. The closed end cap 82 is shown in Figures 11 to 14. As seen in these Figures, the

closed end cap 82 comprises a planar wall 93 having an inner face 94 and an outer

face 95.

As best seen in Figure 11, four filter element receiving formations 96a,96b,96c,96d

are provided on the inner face 94 of the planar wall 93. The filter element receiving

formations 96a to 96d are identical and only one of these, 96a, will be described in

detail. The same reference numerals are used to indicate corresponding features of

the filter element receiving formations 96a,96b,96c,96d.

As best seen in Figures 11, 13 and 14, the filter element receiving formation 96a has

an outer tubular wall 97 that extends from the inner face 94 of the planar wall 93 in

a direction normal to the planar wall 93. The outer tubular wall 97 has, in cross-

section, the generally quadrant-like shape described above - the inner surface of the

outer tubular wall 97 corresponding generally in shape and size to the outer surface

of the outer cage 86.

The filter element receiving formation 96a also comprises four posts 98,99,100,101,

each of which extends from the inner face 94 of the planar wall 93 in a direction

normal to the planar wall 93. The posts 98,99,100,101 lie within the outer tubular

wall 97 and are positioned around a notional quadrant, the notional sides of which

lying parallel to the corresponding sides of the outer tubular wall 97. The notional quadrant on which the four posts 98 to 101 lie is slightly smaller than the cross-

sectional shape of the inner core 85.

Additionally, the filter element receiving formation 96a comprises a tubular sealing

wall 102 that extends from the inner face 94 of the planar wall 93 in a direction

normal to the planar wall 93. As shown in Figure 11, the sealing wall 102 has the

generally quadrant-like shape described above. As shown in Figures 13 and 14, the

sealing wall 102 has an outer surface 103 that extends normally to the inner face 94

and an inner surface 104 that is inclined so that it extends outwardly as it extends

away from the inner face 94. The outer and inner surfaces 103, 104 meet at an edge

105 that is known in the art as a knife-edge.

As seen in Figure 11 , the four filter element receiving formations 96a,96b,96c,96d are

angularly spaced around the inner face 94 of the closed end cap 82 such that the

arcuate regions of the outer tubular walls 97 lie at the outer perimeter of the planar

wall 93.

As best seen in Figures 11 and 12, the closed end cap 82 also has four tie rod

receiving sockets 106a,106b,106c,106d. Each of the four sockets 106a to 106d serves

to receive, in a snap-fit manner, an end of a respective one of the four tie rods 83 a to

83d. The sockets 106a to 106d are annularly spaced around the planar wall 93 and lie

near the outer perimeter of the planar wall 93. The sockets 106a to 106d are identical

and only one of the sockets, 106a, is described in detail. The same reference numerals are used to describe corresponding features of the four sockets 106a to 106d.

The socket 106a comprises a generally cylindrical formation 107 that extends from the

inner face 94 of the planar wall 93 in a direction normal to the planar wall 93. The

cylindrical formation 107 is continuous with an aperture 108 that extends through the

planar wall 93. As best seen in Figure 12, an annular ridge 109 extends from the

planar wall 93 around and into the aperture 108. The annular ridge 109 comprises a

rear surface 111 that extends from the outer face 95 of the planar wall 93, co-planar

with the outer face 95, to an annular edge 112 of the annular ridge 109. An inclined

surface 110 extends from the annular edge 112 outwardly and towards the inner face

94 of the planar wall 93.

As seen in Figures 11 to 13, a hole 113 extends across the planar wall 93 at the centre

of the planar wall 93.

As seen in Figure 15, the open end cap 81 is similar to the closed end cap 82. Features

of the open end cap 81 that are common to the closed end cap 82 are given the same

reference numerals and are not described in detail. The open end cap 81 differs from

the closed end cap 82 in two aspects. Firstly, the open end cap 81 has four polygonal

holes 116a, 116b,l 16c,l 16d that extend across the planar wall 93. Each polygonal

hole 116a to 116d is positioned within a respective one of the filter element receiving

formations 96a to 96d - so that each polygonal hole 116a to 116d lies within the

notional quadrant formed by the four posts 98 to 101 of the corresponding filter element receiving formation 96a to 96d. Secondly, the open end cap 81 has no central

hole 113.

The four tie rods 83 a to 83 d are identical and only one of the tie rods, 83 a, will be

described in detail. The same reference numerals are used to indicate the

corresponding features of the tie rods 83a to 83d.

As seen from Figures 16 to 18, the tie rod 83a has two end portions 118,119 that are

connected by a central portion 117. The central portion 117 is cross-shaped in cross-

section. The two end portions 118,119 are identical and only one of the end portions,

118, is described in detail. The same reference numerals are used to describe the

corresponding features of the end portions 118,119. Starting from the central portion

117, the end portion 118 has a first cylindrical surface 120 which extends to a first

frustro-conical surface 121. The first frustro-conical surface 121 narrows to a second

cylindrical surface 122 which is very short in the axial direction. From an outer end

of the second cylindrical surface 122 a radially extending surface 123 extends

outwardly to a third cylindrical surface 124 which, in turn, extends to a second frustro-

conical surface 125 which narrows to an end surface 126.

The fourth filter assembly is assembled as follows.

The closed end cap 82 is placed on a working surface with the inner face 94 upwards. Each of the filter elements 80a to 80d is then located into a respective one of the filter

element receiving formations 96a to 96d. Each filter element 80a to 80d is received

into the corresponding filter element receiving formation 96a to 96d in an identical

manner and the receipt of one filter element, 80a, into the corresponding filter element

receiving formation 96a, is described in detail.

The filter element 80a is located such that the outer surface of the outer cage 86 fits

closely within the inner surface of the outer tubular wall 97. The posts 98 to 101 lie

against the inner surface of the inner core 85. The post 98 is located at the first

rounded comer 90. The post 99 is located at the second rounded comer 91. The post

100 is located at the third rounded comer 92. Finally, the post 101 is located mid-way

along the arcuate region 89.

The filter elements 80a to 80d are located in the corresponding filter element receiving

formations 96a to 96d in this manner, but they are not yet pushed fully into the filter

element receiving formations 96a to 96d. Instead, they are located such that the edges

105 of the sealing walls 102 contact lower ends of the respective filter media 84.

Each one of the tie rods 83a to 83d is then inserted into a respective one of the sockets

106a to 106d of the closed end cap 82 so that, for each tie rod 83a to 83d, the second

frustro-conical surface 125 of one of the end portions 118,119 lies against the inclined

surface 110 of the corresponding socket 106a to 106d. The open end cap 81 is then positioned so that each one of the filter elements 80a to

80d locates, in the manner described above, into a respective one of the filter element

receiving formations 96a to 96d of the open end cap 81. Simultaneously, the upper

end portions 118, 119 of the four tie rods 83 a to 83 d locate, in the manner described

above, in respective ones of the sockets 106a to 106d of the open end cap 81.

The open end cap 81 is then pushed towards the closed end cap 82. This performs two

functions.

Firstly, each end of each filter element 80a to 80d is pushed fully into the

corresponding filter element receiving formation 96a to 96d. During this process,

each sealing wall 102 penetrates into the corresponding filter medium end so as to seal

the filter medium end to the planar wall 93 of the adjacent end cap 81,82. The

inclined inner surfaces 104 of the sealing walls 102 act to compress fibres of the filter

media 84 against the corresponding inner cores 85, in a similar way to that described

above in respect of the first filter assembly and shown in Figures 5 and 6. Secondly,

and simultaneously, each end portion 118,119 of each tie rod 83 a to 83 d locates fully

into the corresponding socket 106a to 106d. This involves each annular ridge 109

riding over the second frustro-conical surface 125 and the third cylindrical surface 124

of the corresponding tie rod end portion 118,119. Each annular ridge 109 (which is

resilient) then snaps into the groove formed by the first frustro-conical surface 121,

the second cylindrical surface 122 and the radially extending surface 123 of the corresponding tie rod end portion 118,119. Hence the tie rods 83a to 83d serve to lock

the open and closed end caps 81,82 in a predetermined spacing relative to one another,

by a snap-fit mechanism. The spacing is such that the ends of the inner and outer

cages 85,86 and the ends of the filter media 84 contact the corresponding inner faces

94 of the open and closed end caps 81,82.

The inner cores 85 and the outer cages 86 prevent the filter media 84 from bending,

or compressing in an axial direction, and this in turn ensures that the sealing walls 102

penetrate fully into the filter media 84, thereby forming effective seals between the

media 84 and the end caps 81,82.

In use, the fourth filter assembly is inserted into a housing (not shown). The housing,

which may be of metal, is cylindrical with one end open and the other end closed. The

housing has a circular cross-sectional shape that has an axis co-axial with the axis of

the filter assembly, when it is inserted into the housing. The arcuate sides of each

filter element 80a,80b,80c,80d have a curvature similar to the curvature of the housing

and the planar sides extend generally radially away from the housing. The arcuate

sides are closely adjacent the housing. Fluid to be filtered is passed to the outsides of

the filter elements 80a to 80d (and as shown in Figure 9 can pass between adjacent

sides of the filter elements). Fluid becomes filtered as it passes across the filter

elements 80a to 80d to the insides of the filter elements 80a to 80d. Filtered fluid

lying inside the filter elements 80a to 80d drains through the polygonal holes 116. It will be appreciated that the filter media 84 of the fourth filter assembly, as a result

of being provided with curved sides adjacent the housing and adjacent planar sides,

achieve a packing density of filter material within the volume defined between the end

caps 81,82 that is greater than would be occupied by cylindrical filter media having

the same wall thickness as the wall thickness of the filter media 84. Thus, within that

volume, the filter media 84 can handle a greater throughput of fluid to be filtered and

also have a greater dirt capacity and thus a greater life.

The use of cylindrical filter media of the same wall thickness as the filter media 84,

and whose perimeter tangentially intersects the three sides of that media will produce

a circle (in cross-section) whose perimeter is 13% smaller than the perimeter of one

of the filter media 84. Put another way, each filter media 84 has a surface area that

is 15% greater than a circular cross-section medium occupying the same position.

Thus, the four filter media 84 described above achieve a 60% increase in surface area

over such circular media.

It will be appreciated that this is only one example of a number of configurations that

achieve greater packing densities than cylindrical filter media. For example, instead

of four generally quadrant shaped media 84, there could be two media of generally D-

shaped cross-section or three similar media each subtending an angle of about 120°,

or five or more media. In addition, the filter unit described above with reference to Figures 9 to 18 is, as

described above, intended to be mounted in a housing of circular cross-section.

However, housings of other cross-sections may be used with suitably shaped filter

media having adjacent sides achieving packing densities within those housings greater

than can be achieved with filter media of circular cross section. For example, in an

elongate rectangular housing, a plurality of filter media 84 of the kind described above

with reference to Figures 9 to 18 could be located side-by-side with the media 84

arranged in alternately oppositely facing directions and with the comers between the

planar sides directed in respective opposite directions. In this case, the arcuate sides

could be replaced by straight sides. Plainly different end caps would be required.

The filter media need not all be the same shape. They could be of different shapes.

In these alternative arrangements of the fourth filter assembly, a filter assembly is

provided with a plurality of filter media arranged side-by-side in the housing with

each filter medium having a non-circular cross-section so as to achieve a packing

density within the housing greater than a corresponding plurality of filter media of

circular cross-section. In a housing having a cross-sectional shape that is curved, the

provision of filter media with a correspondingly curved outer side adjacent the

housing and a second side extending away from the housing adjacent the associated

side of a second filter medium, provides increased packing densities. The filter assemblies described above can be assembled more quickly and with the

expenditure of less energy than conventional filter assemblies in which the end caps

are sealed to the medium by welding. Moreover welding apparatus is not necessary.

It will be appreciated that the snap-fit mechanisms used in the filter assemblies of the

first aspect of the invention may either be irreversible, or they may be of a type in

which the fixing achieved is reversible, for example to allow a filter element or filter

medium to be changed.

It will be appreciated that the various aspects of the invention are independent of one

another. Thus, a filter assembly according to the first aspect of the invention may

have only a single filter medium or it may have a plurality of filter media. Where a

plurality of media are provided, the media may or may not be shaped to maximise

packing density as described above. Additionally filter assemblies that are in

accordance with one or more of the second, third or fourth aspects of the invention

may or may not be provided with snap-fit mechanisms and/or sealing walls as

described above.

Claims

1. A filter assembly comprising a filter medium, a member and a snap-fit

mechanism engaged or engagable to fix the member in sealing contact with the filter

medium so that the member directs flow of fluid through the filter medium during

filtration, the member having a wall with a free edge, the wall penetrating into the

filter medium so as to form said seal.

2. A filter assembly according to claim 1, wherein the filter medium comprises

fibres with spaces therebetween through which fluid to be filtered flows during

filtration, the member being formed so as to cause fibres of the filter medium located

adjacent the member to move together so as to reduce the volume of the spaces

therebetween whereby to effect or assist said sealing.

3. A filter assembly according to claim 2, wherein the member has a further wall,

said moved fibres being compressed together between said walls.

4. A filter assembly according to claim 2, wherein the wall has a surface that is

inclined to the direction of penetration of the wall into the filter medium so that,

during penetration of the wall into the filter medium, the inclined surface causes said

movement together of said fibres.

5. A filter assembly according to any one of claims 1 to 4, wherein the filter medium is hollow and has an open end, the member being an end cap that closes and

seals against said end.

6. A filter assembly according to claim 5, wherein the filter medium is tubular so

as to define an internal passage.

7. A filter assembly according to claim 6, wherein the filter medium has a

predefined length in a direction parallel to the passage, the filter medium being

provided with a support to resist bending or compression of the filter medium tending

to shorten said length.

8. A filter assembly according to any one of claims 1 to 7, when the member

includes a part of the snap-fit mechanism.

9. A filter assembly according to claim 6 or claim 7, wherein the filter medium

has a further end, and including a further end cap, the end caps being fixable relative

to one another by said snap-fit mechanism with each end cap closing and sealing

against a respective one of the ends of the filter medium.

10. A filter assembly according to claim 9, wherein the snap-fit mechanism

comprises first and second members carried respectively by the first-mentioned and

further end caps, said fixing of the end caps comprising interlocking of the members with one another.

11. A filter assembly according to claim 10, wherein the first member is a tubular

wall having a plurality of holes therethrough and lying within the tubular filter

medium when the end caps are so fixed, the second member being a resilient arm

bearing a projection, said interlocking consisting of receipt of the projection within

one of the holes.

12. A filter assembly according to claim 11, wherein the first-mentioned end cap

comprises a planar wall, the tubular wall extending normally from the planar wall and

having a free end spaced from the planar wall, the further end cap comprising a planar

wall, the free end of the tubular wall lying against the planar wall of the further end

cap when the end caps are so fixed.

13. A filter assembly according to claim 11 or claim 12, wherein the tubular wall

and the tubular filter medium are generally triangular in cross-section.

14. A filter assembly according to claim 11 or claim 12, wherein the tubular wall

and the tubular filter medium are generally circular in cross-section.

15. A filter assembly according to claim 9, including a tubular member having first

and second ends and being separate from both end caps, the tubular member having a plurality of holes through the wall thereof and lying within the filter medium when

the end caps are so fixed, the snap fit mechanism comprising first and second

members carried respectively by the first-mentioned and. further end caps and the

tubular member, said fixing of the end caps comprising interlocking of the first

member with the tubular member and interlocking of the second member with the

tubular member.

16. A filter assembly according to claim 15, wherein the first and second members

are each resilient arms having respective projections, said interlocking consisting of

receipt of the projections within respective ones of the holes of the tubular member.

17. A filter assembly according to claim 15 or claim 16, wherein each end cap has

a respective planar wall, the first and second ends of the tubular member lying against

respective ones of the planar walls when the end caps are so fixed.

18. A filter assembly according to any one of claims 15 to 17, wherein the tubular

member and the tubular filter medium are generally triangular in cross-section.

19. A filter assembly according to any one of claims 15 to 17, wherein the tubular

member and the tubular wall are generally circular in cross-section.

20. A filter assembly according to any one of claims 11 to 19, wherein one of the end caps carries a resilient finger that bears against the outside of the filter medium

urging the filter medium against the tubular wall or the tubular member.

21. A filter assembly according to claim 20, when claim 20 is dependent on claim

12, wherein the finger extends from an outer edge of the planar wall of the further

end cap, the planar wall of the first-mentioned end cap having an outer edge provided

with a flange that extends around the outside of the filter medium.

22. A filter assembly in accordance with any one of claims 1 to 5, wherein the

member is part of a housing for the filter medium.

23. A filter assembly in accordance with claim 22, wherein the filter medium is

hollow and has an open end and the housing part closes and seals against the open

end.

24. A filter assembly according to claim 22 or claim 23, wherein the part of the

housing includes a part of the snap-fit mechanism.

25. A filter assembly according to any one of claims 1 to 8, wherein the wall

having a free edge penetrates into the filter medium as the snap-fit mechanism is

brought into said fixing engagement.

26. A filter assembly according to any one of claims 1 to 4, wherein said filter

medium is one of a plurality of tubular filter media having respective ends, said wall

with a free edge being one of a corresponding number of such walls, each wall

penetrating into a respective one of the ends so as to form a seal between the

corresponding filter medium and the member.

27. A filter assembly according to claim 26, wherein the filter media extend side

by side, each filter medium having a further end, the assembly comprising a further

member having a plurality of walls with respective free edges, each wall of the further

member penetrating into a respective one of the further ends so as to form a seal

between the corresponding filter medium and the further member.

28. A filter assembly according to any one of claims 1 to 4, or claims 26 and 27,

wherein the snap-fit mechanism comprises a rod with an end and a socket on said

member or on one of said members, the end of the rod snap-fitting into said socket.

29. A filter assembly according to any one of claims 1 to 4, wherein the member

comprises a planar wall having first and second opposed faces, said wall with a free

edge being provided on the first face, the second face being provided with a further

wall with a free edge, and the assembly including a further filter medium, the snap-fit

mechanism fixing the further filter medium in sealing contact with the second face,

and the further wall with a free edge penetrating into the further filter medium to form said seal between the second face and the further filter medium.

30. A filter assembly according to claim 29, wherein the first-mentioned and

further filter media are tubular defining respective interiors.

31. A filter assembly according to claim 30, wherein the planar wall is provided

with an opening connecting the interiors of the filter media.

32. A filter assembly comprising a housing and at least two filter elements within

the housing, each filter element comprising a non-circular tube of depth filter media

having at least one side, the at least two filter elements being arranged side-by-side in

the housing with said sides adjacent.

33. A filter assembly according to claim 32, wherein said sides are planar.

34. A filter assembly according to claim 32, wherein said sides are curved.

35. A filter assembly according to claim 34, wherein said sides are convexly

curved.

36. A filter assembly according to any one of claims 32 to 35, wherein said

adjacent sides are spaced apart.

37. A filter assembly according to any one of claims 32 to 35, wherein said

adjacent sides are in contact.

38. A filter assembly according to any one of claims 32 to 37, wherein the housing

defines an interior wall, said at least two media tubes having respective further sides

adjacent said interior wall and having a shape such that each further side extends

generally parallel to said wall, said first-mentioned side extending generally away

from said wall.

39. A filter assembly according to claim 38, wherein said interior wall is of

generally circular cross-section, each said further side being arcuate in cross-section.

40. A filter assembly according to claim 39, wherein each first-mentioned side

extends generally radially relative to said wall.

41. A filter assembly according to claim 40, wherein said first-mentioned side and

said further side have respective first ends and second ends, the first end of the further

side being connected to the comer, and a third side being provided having a first end

and a second end, the first end of the third side being connected to the second end of

the first-mentioned side by a second comer and the second end of the third side being

connected to the second end of the further side by a third comer.

42. A filter assembly according to claim 41, wherein three or more filter elements

are provided the second comers of the filter elements being adjacent a central axis of

the housing.

43. A filter assembly according to claim 42, wherein four filter elements are

provided.

44. A filter assembly according to any one of claims 39 to 43, wherein said interior

wall is cylindrical.

45. A filter assembly comprising a housing having a curved cross-sectional shape

and at least two filter media within the housing, each filter medium having first and

second sides, the first side of each filter medium having a curved shape similar to the

shape of a portion of the cross-section of the housing and being adjacent said portion

and the second side of each filter medium extends away from the housing and being

adjacent the second side of another filter medium.

46. An assembly according to claim 45, wherein the housing is of circular cross-

section and each first side is arcuate.

47. An assembly according to claim 45 or claim 46, wherein the housing is of

circular cross-section, each second side extending in a generally radial direction relative to the axis of said housing cross-section.

48. An assembly according to claim 46 or claim 47, wherein each filter medium

has a cross-sectional shape similar to a segment of the cross-sectional shape of the

housing.

49. A filter assembly according to any one of claims 45 to 48, wherein the filter

medium is formed from depth filter material.

50. A filter assembly according to any one of claims 32 to 44 or claim 49, wherein

each media tube or filter medium is surrounded by a cage.

51. A filter assembly according to any one of claims 32 to 50, wherein said at least

two media tubes or filter media extend between first and second end caps.

52. A filter assembly according to claim 51, wherein the first end cap is in fluid

communication with interiors of the at least two media tubes or filter media and the

second end cap is in fluid communication with exteriors of the at least two media

tubes or filter media.

53. A filter assembly according to claim 51 or claim 52, wherein the first and

second end caps are interconnected.

54. A filter assembly according to any one of claims 51 to 53, wherein at least one

of said end caps is provided with formations for locating the associated ends of the at

least two media tubes or filter media relative to said end cap.

55. A filter assembly according to claim 54, wherein each formation comprises two

spaced walls defining a channel therebetween for receiving the end of the associated

media tube or filter medium.

56. A filter element according to claim 55, wherein said channel has the same

shape as the cross-section of the associated media tube or filter medium.

57. A filter assembly comprising a housing and a plurality of filter media arranged

side-by-side within the housing, each filter medium being formed of depth filter

material and having a non-circular cross-section such as to achieve a packing density

within the housing greater than a corresponding plurality of filter media of circular

cross-section.

58. A filter assembly according to claim 57, wherein the housing is of circular

cross-section, each filter medium extending generally parallel to the axis of said

circular cross-section and each filter medium having a cross-section generally the

shape of a segment of said circular cross-section of the housing.

59. A filter assembly substantially as hereinbefore described with reference to

Figures 1 to 6, Figure 7, Figure 8 or Figures 9 to 18.