GB2375494A

GB2375494A - Filter assembly

Info

Publication number: GB2375494A
Application number: GB0111758A
Authority: GB
Inventors: Charles Nicholas Rothwell
Original assignee: Pall Corp
Current assignee: Pall Corp
Priority date: 2001-05-14
Filing date: 2001-05-14
Publication date: 2002-11-20
Also published as: GB0111758D0

Abstract

A filter assembly has a cylindrical housing including a plurality of generally segmental shape tubular filter elements (10a, 10b, 10c, 10d) arranged around an axis. The shape of the elements (10a, 10b, 10c, 10d) allows a greater packing of filter elements than would be possible with cylindrical filter elements.

Description

FILTER ASSEMBLIES The invention relates to filter assemblies. Many filter assemblies include a housing containing two or more filter elements. The filter elements are cylindrical and may, for example, be formed of depth filter media. 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.

Likewise, manufacturing constraints provide a limit on the maximum diameter of the filter elements. Accordingly, for a particular fluid flow, it may be necessary to insert two or more cylindrical filter elements into a housing.

The insertion of cylindrical filters into a cylindrical housing is inefficient since the cross-sectional area of filter material compared to the cross-sectional area of the housing needed to accommodate the filters 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 elements.

According to a first 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 being 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 second aspect of the invention, there is provided a filter assembly comprising a housing having a curved cross-sectional shape and at least two filter elements within the housing, each filter element having first and second sides, the first side of each filter element 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 element extends away from the housing and being adjacent the second side of another filter element.

According to a third aspect of the invention, there is provided a filter assembly comprising a housing and a plurality of filter elements arranged side-by-side within the housing, each filter element being formed of depth filter media and having a noncircular cross-section so as to achieve a packing density within the housing greater than a corresponding plurality of filter elements 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 an embodiment of the invention, by way of example, reference being made to the accompanying drawings in which-

Figure 1 is a plan view from above of a filter assembly, including four filter elements ; Figure 2 is a cross-sectional view of the filter assembly of Figures on the line II-II of Figure 1 ; Figure 3 is a plan view of an inner face of a closed end cap of the filter assembly of Figures 1 and 2; Figures 4 to 6 are cross-sectional views, respectively on lines IV-IV, V-V and VI-VI of Figure 3, of the closed end cap; Figure 7 is a plan view of an inner face of an open end cap of the filter assembly ; Figure 8 is a side view of a tie rod of the filter assembly; Figure 9 is a cross-section taken on the line IX-IX of Figure 8; and Figure 10 is an enlarged view of an end of the tie rod of Figures 8 and 9.

Referring first to Figures 1 and 2, the filter assembly comprises four separate filter elements 10a, 10b, 10c, 10d, an open generally disc-shaped end cap 11, a closed generally disc-shaped end cap 12 and four tie rods 13a, 13b, 13c, 13d.

The four filter elements 10a to 10d are identical and only one of these, 10a, will be described in detail. The same reference numerals will be used to indicate corresponding features of the four filter elements 10a, 1 Ob, 1 Oc, 10d.

Referring to Figures 1 and 2, the filter element 10a comprises a tubular filter medium 14 (not shown in Figure 2), a tubular inner core 15 and a tubular outer cage 16. The filter medium 14 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 sides (corresponding to radii of a circle) and an arcuate side (corresponding to the circumference of the circle).

Each side is connected to the other 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 cross-section other than circular cross-section.

The inner core 15 is a relatively rigid tubular wall that lies against, and has the same shape as, the inner surface of the filter medium 14. The outer cage 16 is a thin, relatively rigid tubular wall that lies against, and has the same shape as, the outer surface of the filter medium 14. Hence the inner core 15 has first and second planar regions 17,18 and an arcuate region 19. The first and second planar regions 17,18 are joined by a first rounded comer 20. The first planar region 17 is joined to the arcuate

region 19 by a second rounded comer 21, and the second planar region 18 is joined to the arcuate region 19 by a third rounded comer 22.

The filter medium 14 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 15 and the outer cage 16 is provided with a plurality of openings so as to allow fluids to pass freely through. The inner core 15 and the outer cage 16 serve to maintain the filter medium 14 in the quadrant-like shape described above and prevent compression of the filter medium 14 in an axial direction.

The closed end cap 12 is shown in Figures 3 to 6. As seen in these Figures, the closed end cap 12 comprises a planar wall 23 having an inner face 24 and an outer face 25.

As best seen in Figure 3, four filter element receiving formations 26a, 26b, 26c, 26d are provided on the inner face 24 of the planar wall 23. The filter element receiving formations 26a to 26d are identical and only one of these, 26a, will be described in detail. The same reference numerals are used to indicate corresponding features of the filter element receiving formations 26a, 26b, 26c, 26d.

As best seen in Figures 3,5 and 6, the filter element receiving formation 26a has an outer tubular wall 27 that extends from the inner face 24 of the planar wall 23 in a direction normal to the planar wall 23. The outer tubular wall 27 has, in cross-section,

the generally quadrant-like shape described above-the inner surface of the outer tubular wall 27 corresponding generally in shape and size to the outer surface of the outer cage 16.

The filter element receiving formation 26a also comprises four posts 28,29, 30, 31, each of which extends from the inner face 24 of the planar wall 23 in a direction normal to the planar wall 23. The posts 28,29, 30,31 lie within the outer tubular wall 27 and are positioned around a notional quadrant, the notional sides of which lying parallel to the corresponding sides of the outer tubular wall 27. The notional quadrant on which the four posts 28 to 31 lie is slightly smaller than the cross-sectional shape of the inner core 15.

Additionally, the filter element receiving formation 26a comprises a tubular sealing wall 32 that extends from the inner face 24 of the planar wall 23 in a direction normal to the planar wall 23. As shown in Figure 3, the sealing wall 32 has the generally quadrant-like shape described above. As shown in Figures 5 and 6, the sealing wall 32 has an outer surface 33 that extends normally to the inner face 24 and an inner surface 34 that is inclined so that it extends outwardly as it extends away from the inner face 24. The outer and inner surfaces 33,34 meet at an edge 35 that is known in the art as a knife-edge.

As seen in Figure 3, the four filter element receiving formations 26a, 26b, 26c, 26d are angularly spaced around the inner face 24 of the closed end cap 12 such that the arcuate regions of the outer tubular walls 27 lie at the outer perimeter of the planar wall 23.

As best seen in Figures 3 and 4, the closed end cap 12 also has four tie rod receiving sockets 36a, 36b, 36c, 36d. Each of the four sockets 36a to 36d serves to receive, in a snap-fit manner, an end of a respective one of the four tie rods 13 a to 13d. The sockets 36a to 36d are annularly spaced around the planar wall 23 and lie near the outer perimeter of the planar wall 23. The sockets 36a to 36d are identical and only one of the sockets, 36a, is described in detail. The same reference numerals are used to describe corresponding features of the four sockets 36a to 36d.

The socket 36a comprises a generally cylindrical formation 37 that extends from the inner face 24 of the planar wall 23 in a direction normal to the planar wall 23. The cylindrical formation 37 is continuous with an aperture 38 that extends through the planar wall 23. As best seen in Figure 4, an annular ridge 39 extends from the planar wall 23 around and into the aperture 38. The annular ridge 39 comprises a rear surface 41 that extends from the outer face 25 of the planar wall 23, co-planar with the outer face 25, to an annular edge 42 of the annular ridge 39. An inclined surface 40 extends from the annular edge 42 outwardly and towards the inner face 24 of the planar wall 23.

As seen in Figures 3 to 5, a hole 43 extends across the planar wall 23 at the centre of the planar wall 23.

As seen in Figure 7, the open end cap 11 is similar to the closed end cap 12. Features of the open end cap 11 that are common to the closed end cap 12 are given the same reference numerals and are not described in detail. The open end cap 11 differs from the closed end cap 12 in two aspects. Firstly, the open end cap 11 has four polygonal holes 46a, 46b, 46c, 46d that extend across the planar wall 23. Each polygonal hole 46a to 46d is positioned within a respective one of the filter element receiving formations 26a to 26d-so that each polygonal hole 46a to 46d lies within the notional quadrant formed by the four posts 28 to 31 of the corresponding filter element receiving formation 26a to 26d. Secondly, the open end cap 11 has no central hole 43.

The four tie rods 13a to 13d are identical and only one of the tie rods, 13a, will be described in detail. The same reference numerals are used to indicate the corresponding features of the tie rods 13a to 13d.

As seen from Figures 8 to 10, the tie rod 13a has two end portions 48,49 that are connected by a central portion 47. The central portion 47 is cross-shaped in crosssection. The two end portions 48,49 are identical and only one of the end portions, 48, is described in detail. The same reference numerals are used to describe the corresponding features of the end portions 48,49. Starting from the central portion 47,

the end portion 48 has a first cylindrical surface 50 which extends to a first frustroconical surface 51. The first frustro-conical surface 51 narrows to a second cylindrical surface 52 which is very short in the axial direction. From an outer end of the second cylindrical surface 52 a radially extending surface 53 extends outwardly to a third cylindrical surface 54 which, in turn, extends to a second frustro-conical surface 55 which narrows to an end surface 56.

The filter assembly is assembled as follows.

The closed end cap 12 is placed on a working surface with the inner face 24 upwards.

Each of the filter elements 10a to 10d is then located into a respective one of the filter element receiving formations 26a to 26d. Each filter element lOa to 10d is received into the corresponding filter element receiving formation 26a to 26d in an identical manner and the receipt of one filter element, 10a, into the corresponding filter element receiving formation 26a, is described in detail.

The filter element 10a is located such that the outer surface of the outer cage 16 fits closely within the inner surface of the outer tubular wall 27. The posts 28 to 31 lie against the inner surface of the inner core 15. The post 28 is located at the first rounded comer 20. The post 29 is located at the second rounded comer 21. The post 30 is located at the third rounded comer 22. Finally, the post 31 is located mid-way along the arcuate region 19.

The filter elements 10a to 10d are located in the corresponding filter element receiving formations 26a to 26d in this manner, but they are not yet pushed fully into the filter element receiving formations 26a to 26d. Instead, they are located such that the edges 35 of the sealing walls 32 contact lower ends of the respective filter media 14.

Each one of the tie rods 13a to 13d is then inserted into a respective one of the sockets 36a to 36d of the closed end cap 12 so that, for each tie rod 13a to 13d, the second frustro-conical surface 55 of one of the end portions 48,49 lies against the inclined surface 50 of the corresponding socket 46a to 46d.

The open end cap 11 is then positioned so that each one of the filter elements 10a to 10d locates, in the manner described above, into a respective one of the filter element receiving formations 26a to 26d of the open end cap 11. Simultaneously, the upper end portions 48, 49 of the four tie rods 13a to 13d locate, in the manner described above, in respective ones of the sockets 36a to 36d of the open end cap 11.

The open end cap 11 is then pushed towards the closed end cap 12. This performs two functions.

Firstly, each end of each filter element 10a to 10d is pushed fully into the corresponding filter element receiving formation 26a to 26d. During this process, each sealing wall 32 penetrates into the corresponding filter medium end so as to seal

the filter medium end to the planar wall 23 of the adjacent end cap 11,12. The inclined inner surfaces 34 of the sealing walls 32 act to compress fibres of the filter media 14 against the corresponding inner cores 15. Secondly, and simultaneously, each end portion 48,49 of each tie rod 13a to 13d locates fully into the corresponding socket 36a to 36d. This involves each annular ridge 39 riding over the second frustro- conical surface 55 and the third cylindrical surface 54 of the corresponding tie rod end portion 48,49. Each annular ridge 39 (which is resilient) then snaps into the groove formed by the first frustro-conical surface 51, the second cylindrical surface 52 and the radially extending surface 53 of the corresponding tie rod end portion 48,49.

Hence the tie rods 13a to 13d serve to lock the open and closed end caps 11,12 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 15,16 and the ends of the filter media 14 contact the corresponding inner faces 24 of the open and closed end caps 11, 12.

The inner cores 15 and the outer cages 16 prevent the filter media 14 from bending, or compressing in an axial direction, and this in turn ensures that the sealing walls 32 penetrate fully into the filter media 14, thereby forming effective seals between the media 14 and the end caps 11, 12.

In use, the filter assembly described above with reference to the drawings 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 10a, 10b, 10c, 10d has 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 10a to 10d (and as shown in Figure 1 can pass between adjacent sides of the filter elements). Fluid becomes filtered as it passes across the filter elements lOa to lOd to the insides of the filter elements 10a to lord. Filtered fluid lying inside the filter elements 10a to lOd drains through the polygonal holes 46.

It will be appreciated that the filter elements lOa, 1 Ob, 1 Oc, 10d, 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 11,12 that is greater than would be occupied by cylindrical filter elements with filter material having the same thickness as the thickness of the filter element 1 Oa, 1 Ob, 10c, 10d. Thus, within that volume, the filter elements 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 circular elements with filter media of the same thickness as the media in the filter elements 10a, 1 Ob, 10c, 10d and whose perimeter tangentially intersects the three sides of that media will produce a circle whose perimeter is 13% smaller than

the perimeter of one of the filter elements 10a, 10b, 10c, 10d. Put another way, each filter element 10a, 10b, 10c, 10d has a surface area that is 15% greater than a circular cross-section element occupying the same position. Thus, the four filter elements 1 Oa, 1 Ob, 10c, 10d described above achieve a 60% increase in surface area over such circular elements.

It will be appreciated that this is only one example of a number of configurations that achieve greater packing densities than cylindrical filter elements. For example, instead of four generally quadrant shaped elements 10a, 10b, 10c, 10d, there could be two elements of generally D-shaped cross-section or three similar elements each subtending an angle of about 120 or five or more elements.

In addition, the filter unit described above with reference to the drawings 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 elements having adjacent sides achieving packing densities within those housings greater than can be achieved with filter elements of circular cross section. For example, in an elongate rectangular housing, a plurality of filter elements 10a. 10b. 10c. 10d ofthe kind described above with reference to Figures 1 to 10 could be located side-by-side with the elements 10a, lOb, 10c, 10d 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 elements need not all be the same shape. They could be of different shapes.

In all these arrangements, a filter assembly is provided with a plurality of filter elements arranged side-by-side in the housing with each filter element having a noncircular cross-section so as to achieve a packing density within the housing greater than a corresponding plurality of filter elements of circular cross-section. In a housing having a cross-sectional shape that is curved, the provision of filter elements 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 element, provides increased packing densities.

Claims

1. A filter assembly comprising a housing and at least two filter elements within the housing, each filter element being 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.

2. A filter assembly according to claim 1, wherein said sides are planar.

3. A filter assembly according to claim 1, wherein said sides are curved.

4. A filter assembly according to claim 3, wherein said sides are convexly curved.

5. A filter assembly according to any one of claims 1 to 4, wherein said adjacent sides are spaced apart.

6. A filter assembly according to any one of claims 1 to 4, wherein said adjacent sides are in contact.

7. A filter assembly according to any one of claims 1 to 6, wherein the housing defines an interior wall, said at least two filter elements having respective second

surfaces adjacent said interior wall and having a shape such that each surface extends generally parallel to said wall, said first-mentioned surface extending generally away from said wall.

8. A filter assembly according to claim 7, wherein said interior wall is of generally circular cross-section, each said second surface being arcuate in crosssection.

9. A filter assembly according to claim 8, wherein each first-mentioned surface extends generally radially relative to said wall.

10. A filter assembly according to claim 9, 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.

11. A filter assembly according to claim 10, wherein three or more filter elements are provided the second comers of the filter elements being adjacent a central axis of the housing.

12. A filter assembly according to claim 11. wherein four filter elements are provided.

13. A filter assembly according to any one of claims 8 to 12, wherein said interior wall is cylindrical.

14. A filter asssembly comprising a housing having a curved cross-sectional shape and'at least two filter elements within the housing, each filter element having first and second sides, the first side of each filter element 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 element extends away from the housing and being adjacent the second side of another filter element.

15. An assembly according to claim 14, wherein the housing is of circular cross-section and each first side is arcuate.

16. An assembly according to claim 14 or claim 15, 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.

17. An assembly according to claim 15 or claim 16, wherein each filter element has a cross-sectional shape similar to a segment of the cross-sectional shape

of the housing.

18. A filter assembly according to any one of claims 14 to 17, wherein the filter element is formed from depth filter media.

19. A filter assembly according to any one of claims 1 to 13 or claim 18, wherein said depth filter media is surrounded by a cage.

20. A filter assembly according to any one of claims 1 to 19, wherein said at least two filter elements extend between first and second end caps.

21. A filter assembly according to claim 20, wherein the first end cap is in fluid communication with interiors of the at least two filter elements and the second end cap is in fluid communication with exteriors of the at least two filter elements.

22. A filter assembly according to claim 20 or claim 21, wherein the first and second end caps are interconnected.

23. A filter assembly according to any one of claims 20 to 22, wherein at least one of said end caps is provided with formations for locating the associated ends of the at least two filter elements relative to said end cap.

24. A filter assembly according to claim 23, wherein each formation comprises

two spaced walls defining a channel therebetween for receiving the end of the associated filter element.

25. A filter element according to claim 24, wherein said channel has the same shape as the cross-section of the associated filter element.

26. A filter assembly comprising a housing and a plurality of filter elements arranged side-by-side within the housing, each filter element being formed of depth filter media and having a non-circular cross-section such as to achieve a packing density within the housing greater than a corresponding plurality of filter elements of circular cross-section.

27. A filter assembly according to claim 26, wherein the housing is of circular cross-section, each filter element extending generally parallel to the axis of said circular cross-section and each filter element having a cross-section generally the shape of a segment of said circular cross-section of the housing.

28. A filter assembly substantially as hereinbefore described with reference to the accompanying drawings.