IMPROVED SEPARATOR FOR CELL TYPE FITER CARTRIDGES

Abstract: Cell type filter cartridge (10) in which the individual cells (20,30,40) contain a separator disc (50) having stiffening members (70,72) formed at the central aperture of the cell and connected to a plurality of the separating ribs (52,68) in spaced relation to each other. The coaction of the two or more discs with the separator ribs provides for a rigid, box-like structure of the ribs to impart a substantial cantilevered strength to the ribs. Additionally, at least one of the stiffening discs is positioned at or near the ends of the separator ribs to act as a load-bearing surface to prevent media intrusion of the filtering medium (42,44) and thereby maintain the area of the flow path of the filtered liquid as it passes through the central aperture of the disc.

Description: Background of the Invention Field of the Invention The present invention relates to a spacer member for a filter cell comprising a plurality of space ribs extending from a central aperture and a plurality of arcuate ribs connecting said extending spacer ribs to form a continuous web. Description of the Prior Art Cell type filter cartridges typically are fabricated from individual cells which generally have two layers of filter medium separated from each other so that liquid flows from the outside of the filter medium into the space between the layers of filter medium towards the central portion of the cell. Often the separators that keep the layers of filter medium apart are formed in the shape of discs with ribs radially extending from the central aperture in a spoke-like pattern. The ribs are widest near the central aperture of the cell. The typical construction of the separator discs poses two problems. First is the loss of filtering area. Though the discs do separate the upper and lower medium layers of the cell, they do not provide rigidity or stiffness to the cells. Therefore, in cartridges having a plurality of cells, the cells tend to droop onto each other so that the adjoining media surfaces will contact each other thereby reducing the effective filtering area of the cartridge. In order to compensate for the lack of stiffness or rigidity in the filter elements, external spacers have been put into the cartridge type filters to separate the cells and maintain them in their proper position for maximum filter area. The second problem is the loss of fluid flow area through the cell. The ribs of the separator discs within each cell have the narrowest spacing at the ends which form the central aperture of the disc, i.e., the minimum flow area occurs at the point of maximum flow. Therefore, the velocity of the fluid must be greatest at this point of minimum flow area and this high velocity of the fluid flow tends to abrade the filter media. The rib ends extend above any connecting member and contact the inner surface of the media. The media is forced down upon the rib ends by several different forces. First, the swelling of the media during use. Second, the axial forces exerted on the cartridge to force the cells together or sealing means therebetween to prevent seepage of unfiltered liquid between the cells. Third, the hydraulic pressure of the liquid to be filtered forces the filter media against the disc. The forcing of the media down on the ends of the separating ribs has serious consequences. It forces the filter media down between the separating ribs at the central aperture. This further restricts the passages formed by the separating ribs between the layers of filter medium on each disc. This produces increased resistance to flow as well as increased media abrasion and migration resulting from the high fluid flow velocity in contact with the distorted and damaged filter media at that point. The attempts to maintain the separation of the cells and other examples of attempts to avoid the problem of media intrusion are shown in several patents, though none have satisfactorily addressed these concerns. For example, US-A-3,666,107 discloses a filter cartridge comprising a plurality of filter elements each consisting of two dished diaphragm sections of filter material, each section having attached thereto one or more circumferential or radial stiffening members or ribs. Such construction is believed to be difficult to manufacture and would impair to some extent the usable surface area of the filter elements. A prior art filter cartridge having wafer-like elements but with no additional support therefor is seen in US-A-2,966,269. This patent discloses a filter assembly including filter cartridges, each constituting a stack of wafers, each wafer being formed from a pair of opposed dished annular discs of filter paper or the like. The discs are secured around their outer peripheral edges, for example by an adhesive, and are spaced apart at their inner peripheral edges by annular spacers between the discs, i.e. within the wafers. The annular spacers have apertures opening into the interior of the wafer. The wafers are stacked together in generally cylindrical form and held together between end plates by tie rods. Other filter cartridge structures are disclosed in US-A-3,165,471; US-A-4,094,793; US-A-1,102,685; US-A-1,742,919; US-A-2,411,341; US-A-3,178,028; and US-A-4,048,073. GB-A-2185695 discloses a filter element of hollow disc form comprising filter discs joined by an edge seal with a spacer element which is held in a fixed position between the filter disc by connection of its outer periphery to the edge seal. The spacer element comprises radial ribs connected by concentric rings and a flat outer ring. In other constructions the outer ring has tabs, or the ribs extend beyond the outer ring, said tabs or ribs being incorporated in the edge seal. Another example of an improved separator for a cell type filter is shown in the co-pending application, serial no. 06/803,819, filed December 2, 1985, for a filter cartridge including external cell separators, assigned to the assignee of the present invention. Summary of the invention In order to over come the difficulties encountered in the prior art, the present invention sets forth an improved spacer member for a filter cell comprising: a plurality of spacer ribs extending from a central aperture and a plurality of arcuate ribs connecting said extending spacer ribs to form a continuous web characterized by two or more stiffening members in vertical spaced relation connected with said plurality of extending spacer ribs at the central aperture, wherein said stiffening members comprise two or more circular discs, at least two or more stiffening members in vertical spaced relation connected with said plurality of extending spacer ribs at the central aperture, wherein said stiffening members comprise two or more circular discs, at least two of the circular discs are disposed to form continuous surfaces on the upper and under side of said extending spacer ribs. Accordingly it is an object of the present invention to provide a spacer member for a filter cell which ensures accurate positioning of the cells for maxium filter efficiency. It is still another object of the present invention to provide a spacer member for a filter cell which is relatively more rigid and is therefore more efficient. Another object of the present invention is to provide a space member for a filter cell which is resistant to media intrusion and maintains the flow passage for filtered liquid within the cell at an optimum rate. A further object of the present invention is to provide a spacer member for a filter cell which is relatively lighter and stronger. Yet another object of the present invention is to provide a spacer member for a filter cell which is relatively durable and reliable and improves the efficiency of the filter. It is a further object of the present invention to provide a spacer member for a filter cell which is able to be subjected to a greater amount of axial sealing pressure along the cartridge without restricting the flow of the filtered liquid due to media intrustion at the core of the spacer member. The foregoing and further objects of the invention will be apparent from the following description of the invention. However, although the invention will be described in connection with a preferred embodiment, other variations and modifications will be apparent to those skilled in the art. The invention is defined therfor in the claims following this specification. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of the upper portion of a cell type filter cartridge, with the top cell partially broken away; Figure 2 is a sectional view taken along line 2-2 of Figure 1; Figure 2A is a partial view of another embodiment of the invention shown in Figure 2: Figure 3 is a sectional view taken along line 3-3 of Figure 2; Figure 4 is a perspective view of a portion of the separated discs shown in Figures 2 and 3; Figure 5 is a fragmentary view in perspective of a portion of a separate disc known in the prior art; Figure 6 is a sectional view of a portion of a cell type filter element using the separator disc shown in Figure 5. DETAILED DESCRIPTION OF THE INVENTION Referring to the figures, Fig. 1 shows the upper portion of a cell type filter cartridge generally indicated at 10 in which several cells 20, 30, and 40 are stacked together and held in relation to each other by three securing bands 14, 16, and 18. The bands extend from the top of the top cell 40 down the inner elongated central core of the cartridge formed by the central apertures in the individual cells. A gasket retainer 12 prevents the securing bands from crushing the top of the top filter cell 40. Referring to Fig. 2, the top filter cell 40 consists of an upper filter media layer 42, having an inner surface 43, and a lower media layer 44, having an inner surface 45. The upper and lower media are circular in shape and are joined by a circular edge seal 46 which grips the upper and lower media on either side of a circular distal rib 48 to form a liquid tight seal at the circumference of the cell. Each of the cells has a separator member generally indicated at 50 having a plurality of ribs 52 extending the full radius, or major ribs, and other ribs of partial radius extension or minor ribs 68. Each major or full length rib 52 has an upper shoulder 54 and a lower shoulder 56 which form a section 58 adjacent the central aperture, which can also be referred to as a juncture section. Juncture section 58 of major rib 52 has an axial end surface 62 and a top portion 64. As seen in Figs. 1 and 2, the major ribs 52 and minor ribs 68 are joined by a plurality of arcuate connecting ribs such as concentrically disposed circular ribs 66. As seen best in Figs. 2, 3, and 4, upper stiffening disc 70 fits into the top of juncture section 58 of major rib 52, and is positioned against the shoulder 54 on the upper surface of each of the ribs. Upper stiffening disk 70 coacts with lower stiffening disc 72, which may be integrally formed with the major ribs at the time of molding the separator disc. The coaction of the upper stiffening disc 70 and the lower stiffening disc 72 form a spaced box-like structure of high strength and rigidity which insures the dimensional stability of the flow passages 90 formed between the sides of juncture portion 58 and the inner surface 76 of stiffening disc 70 and the inner surface 82 of stiffening disc 72. As seen in Figs. 2 and 3, the outer surfaces 74 and 84 of stiffening discs 70 and 72, respectively, form a continuous surface on which media adjacent the central aperture of the cell can rest and be pressed without the filter media being deformed by the major ribs and/or the stiffening discs. Fig. 2A shows an alternate embodiment of the invention in which the stiffening discs 170 and 172 are positioned on top of the major or full radius separating ribs 152. This will raise the upper and lower media levels 142 and 144 respectively, somewhat off the hub of the disc, leaving a small space which will be of no significance to the operation of the filter cell. The placing of the stiffening discs 170 and 172 above the ends of the major separating ribs provides for a larger surface area of the flow passages 190. Fig. 4 shows one manner in which the separator disc used in the filter cell of the present invention can be manufactured. In this case, the entire separating disc, in the absence of upper stiffening disc 70, can be injection molded, from a suitable material such as polypropylene, to form a continuous web, and then the upper stiffening disc can be ultrasonically welded or otherwise suitably fastened to the upper surfaces of the juncture portions of the separating ribs. As can readily be seen, the stiffening discs provide large bearing surfaces, for example, 74 and 84 near the central aperture of the separating disc. These bearing surfaces are capable of supporting relatively large axial forces exerted by the filter housing in which the cartridge is mounted. These axial forces prevent the hydraulic forces acting on the outside of the cells from tending to force the separate cells apart, which would allow unfiltered liquid to enter the elongated central column of the filter cartridge and contaminate the filtered liquid. The stiffening effect of the entire separating disc results from the box-like structure at the central aperture of the disc produced by the spaced displacement of the stiffening discs in coaction with the separator ribs. The box-like structure produces a torsional rigidity that maintains the major separator ribs in an upright and parallel relationship. The major separator ribs coact with the minor separator ribs via arcuate concentrically disposed connecting ribs 66 so that all of the separator ribs, which are relatively high with respect to their width, are positioned for maximum resistance to bending loads exerted on the separator disc. Therefore, the greater stiffness of the separator discs tends to hold the peripheral portions of the individual cells in the proper position in relation to the central portion of the cell, thereby producing maximum filtering efficiency for each cell. It should be noted that while the embodiments show a plurality of arcuate ribs positioning the separator ribs, any continuous sheet or other connecting means would also be suitable. The major function of the secondary connector is to radially position the separator ribs which when coacting with the stiffeners provide the resistance to bending. The prior art discs shown in Figs. 5 and 6 have only a single disc 270 to connect separator ribs 252 from each other. The ribs are free to twist and this twisting motion will tend to allow the entire disc to bend or deflect with relatively little resistance. Therefore, the individual cells will tend to contact each other when deflected, reducing the effective surface area of the filtering media. Additionally, because of the protruding ends 264 and 265 of the separator ribs which contact the inner surfaces 243 and 245 of the upper and lower media layers 240 and 244, the flow passages 290 are constricted, restricting the flow of filtered fluid into the central aperture of the cartridge. Also, as can be seen, the more axial pressure that is applied on the media near the central aperture of the cell, the greater will be the media intrusion into the flow channels. This media intrusion is not present near the central aperture of the cells of the present invention because of the presence of the stiffening discs. It should be noted that it is possible to have more than the two stiffening discs as shown in Fig. 2, or Fig. 2A. incorporated in a separating disc. Nor must the stiffening discs be located only on the top portions of the separator ribs. There could, for example, be a combination of the separator disc shown in Fig. 2A with an intermediate connecting disc used to join the spacing ribs prior to the positioning separate stiffening discs 170 and 172. Additionally, while not shown, it is conceivable that the separator ribs adjacent the stiffening discs may protrude slightly above the stiffening discs or disc in order to position the spacer disc with respect to the filter media. As will be readily apparent to those skilled in the art, the invention may be used in other specific forms or for other purposes without departing from its spirit or central characteristics. The present embodiments are therefore to be considered as illustrative and not restrictive, the scope of the invention being indicated by the claims rather than by the foregoing description, and all embodiments which come within the range of equivalence of the claims are intended to be embraced.

Claims: A spacer member for a filter cell comprising: a plurality of spacer ribs (52;152) extending from a central aperture and a plurality of arcuate ribs (66;166) connecting said extending spacer ribs to form a continuous web; characterized by two or more stiffening members (70,72;170,172) in vertical spaced relation connected with said plurality of extending spacer ribs at the central aperture, wherein said stiffening members comprise two or more circular discs, at least two of the circular discs are disposed to form continuous surfaces (74;84) on the upper and the under side of said extending spacer ribs. A spacer member for a filter cell according to claims 1, further comprising a plurality of minor ribs (68) disposed between said extending spacer ribs (52;152) and connected to said arcuate connecting ribs (66;166). A spacer member according to claim 1 or 2, wherein said plurality of extending spacer ribs (52;152) are radially disposed. A spacer member as in one of claims 1 to 3, wherein said arcuate connecting ribs (66;166) comprise a series of concentrically disposed circular ribs.

Inventors: ARTINYAN, ARTO, BARNES, ROBERT G., OSTREICHER, EUGENE A.
Applicants: CUNO INCORPORATED
Application year: 1988
Main classification: B01D29
IPC codes: B01D29