Liquid purification or separation – Diverse distinct separators – Including a filter
Reexamination Certificate
2000-02-03
2004-03-30
Savage, Matthew O. (Department: 1723)
Liquid purification or separation
Diverse distinct separators
Including a filter
C210S486000, C210S489000, C210S500270, C210S502100, C210S505000
Reexamination Certificate
active
06712966
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a composite filter medium having two or more filtration zones or layers of different particle-retention capability (“PRC”) with respect to the fluid suspension which is filtered under ambient filtration conditions (“composite filter medium”) wherein the zones or layers are positioned with respect to one another such that the contaminant-holding capacity (“CHC”) per unit area of the composite filter medium is greater than the CHC per unit area of the upstream filtration zone or layer of the composite filter medium when such is extrapolated to the depth of the composite filter medium. More particularly, an embodiment of the present invention relates to a cell-type filter unit employing such composite filter medium. More particularly, an embodiment of the present invention relates to a cell-type filter unit having upper and lower composite filter medium separated by a separator layer wherein the zones or layers of each composite filter medium are positioned with respect to one another such that the CHC per unit area of the composite filter medium is greater than the CHC per unit area of the upstream filtration zone or layer of the composite filter medium when such is extrapolated to the depth of the composite filter medium. More specifically, an embodiment of the present invention relates to a cell-type filter unit having an upper composite filter medium and a lower composite filter medium separated by a non-filtering separator layer, wherein each of the composite filter medium is comprised of two or more zones or layers of filter material of the same or different composition and/or fabrication, each layer being positioned with respect to one another such that the more distal the zone or layer from the separator layer the lesser the PRC with respect to the fluid suspension which is to be filtered under attendant filtration conditions. And yet another embodiment of the present invention relates to a lenticular filter unit having an upper composite filter medium and a lower composite filter medium, separated by a non-filtering separator layer, wherein each composite filter medium is fashioned to have a graded PRC in the direction of flow such that, as positioned on the non-filtering separator layer, the lenticular filter unit is capable of more efficiently retaining smaller and smaller particles as the fluid moves from the surface of the filter medium towards the non-filtering separator layer.
2. Background of the Related Art
Cell-type filter units are well known in the art, and comprise two overlying similarly-shaped filter media separated from one another along the majority of their opposing surface areas by a non-filtering separator element, and affixed to one another along their perimeter edges. Conventionally, the filter media and the separator element each have a central void of about the same shape and dimension so as to form a uniform through bore in the filter unit when each void is aligned.
The separator element is conventionally composed of a material distinct from the composition of the media which abuts it, and generally has openings therein of such size that the separator is substantially non-filtering with respect to the material to be filtered given its position within the cell-type filter unit. In addition to separating the two filter media, and supporting the media under differential pressure, the separator element is generally fashioned to have a plurality of conduits formed therein, such conduits communicating with the central void of the separator and the through bore of the filter unit to allow flow to get from the outer-diameter or edge of the cell-type filter unit to a stacked common bore. Separators are conventionally fashioned from polymeric materials, in particular plastics, although they can also be fashioned from other materials, such as, for example, metals, ceramics and other material known in the art to be capable of separating the two layers effectively in a particular filter application environment.
A separator element may be manufactured to include upper and lower ribs of varying thickness to maintain the media in a disk-shape. Lenticular cell-type filter units, comprising two disk-shaped filter media separated by a closed-curve non-filtering separator element, are particularly common place in the art. Separators used in lenticular filters generally have a plurality of ribs extending radially outward from a central aperture in a spoke-like fashion. An example of a lenticular cell-type filter unit is found in U.S. Pat. No. 4,783,262 to Ostreicher et al., the disclosure of which is herein incorporated by reference.
Generally the outer circumference of the two media discs of a lenticular filter unit are held together by an insert molding process which encapsulates the circumferences in plastic. U.S. Pat. No. 4,347,208 to Southhall, the disclosure of which is herein incorporated by reference, discloses a method of making a filtration cell having a sealed periphery which includes the steps of placing two media discs, and interposed separator, into a mold and injecting a thermoplastic polymer into the mold to form a seal around the two media discs. The Southhall patent discloses polypropylene, polyethylene, nylon, and polysulfone as the preferred thermoplastic polymers for molding the edge seal.
Cell-type filter units use a variety of materials for filtering fluids, including, without limitation, glass fibers, diatomaceous earth, perlite, cellulose, and binder resins. The filter media is typically produced by a wet laid papermaking operation. Media thickness generally ranges between about 0.130-0.218 inches depending on the material formulation. By filter medium it is meant a porous article or mass having a porosity, or carrying/producing a charge, or incorporating matter which binds matter in the suspension, such that it will separate out matter in suspension in the fluid, gas or liquid, which is to be filtered.
Cell-type filter units generally have a through bore and are generally employed in conventional practice by stacking one on another in seriatim to form a common bore, such common bore communicating with one or more separator conduits. The stacked cell-type filter unit assembly, or cell-type filter cartridge, is then enclosed in a housing having an inlet port and an outlet port, the common bore typically being positioned in the housing so as to communicate with the outlet port. Not infrequently, fluid is supplied to the housing at high temperature and/or high pressure. The fluid enters the gaps between the adjacent filter units and then passes through the filter media covering the separator. As the fluid passes through the filter media, undesirable materials such as aggregates and particulates are removed from the fluid. The filtered fluid then flows along the conduits of the separator to the common bore and exits the housing via the outlet tube.
A significant advantage of stacked cell-type filter cartridges is that the surface area of the filter material is quite large when compared to the total volume displaced by the stacked cell-type filter cartridge. This large surface area permits larger volumes of fluid to be filtered, as compared to cartridges displacing a similar volume but which have a lower surface area, over the same period of time. Conventional stacked cell type filter cartridges are useful in a variety of applications, including the filtration of fluids such as beverages, dielectric oils, chemicals, etc. Cell-type filter cartridges find use as both primary filters and pre-filters.
When used as pre-filters, stacked cell-type filter cartridges may be located upstream from another stacked cell-type filter cartridge, or from a filter cartridge of dissimilar construction, e.g. a pleated membrane filter. Owing to their large available surface areas cell-type filter cartridges are frequently used to remove particulates from a fluid stream prior to microfiltration by a membrane filter. The pre-filter is designed to remove particulates which wo
Artinyan Art
Larsen William A.
Paul Charles Thomas
Pulek John L.
Schorr Clifford L.
Cuno Incorporated
Payne R. Thomas
Savage Matthew O.
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