Liquid purification or separation – Plural distinct separators – Filters
Reexamination Certificate
1999-11-09
2002-03-12
Kim, John (Department: 1723)
Liquid purification or separation
Plural distinct separators
Filters
C210S346000, C210S483000, C210S486000, C210S487000, C210S497010
Reexamination Certificate
active
06355171
ABSTRACT:
FIELD OF THE INVENTION
This invention is related generally to liquid filtration apparatus of the type having filter socks and, more particularly, to filter socks for such apparatus.
BACKGROUND OF THE INVENTION
Tubular filters, sometimes referred to as filter socks or sleeves, are used in various liquid filtration applications involving the removal of particulates from a liquid stream. Such liquid filtration apparatus typically include a liquid vessel, a multiplicity of elongate sock supports which are suspended within the vessel, and a filter sock over and along each of the sock supports.
In such typical liquid filtration apparatus, each elongate sock support is a rigid tube structure with a hollow interior and an open end for fluid communication with a downstream flow channel leaving the vessel. Each such tube structure has a large number of closely-spaced perforations at all locations along its length to allow ingress of filtrate liquid all along the length of the tube structure—after the filtrate has passed through the filter sock which is mounted on such sock support. The elongate sock supports are typically suspended from above, with at least a majority of their lengths, or more accurately at least the majority of the lengths of the filter socks thereon, being submerged in the unfiltered liquid which is contained in the liquid vessel.
Liquid flows through the filter socks, through the sock-mount perforations and into the sock-mount tube structures, up the sock-mount tube structures, and through the open ends thereof into one or more downstream flow channels (typically overhead) which receive the filtrate (i.e., filtered liquid). This flow of liquid—through the filter socks (and related structure)—is caused when a sufficient pressure differential is established between the liquid vessel (i.e., outside the filter socks) and downstream of the filter socks.
Certain materials have been used as liquid filter socks, including woven materials, microporous membranes, membranes such as dirt-treated polypropylene, and certain laminates such as expanded polytetravfluoroethylene (PTFE) bonded to a felt or felt-like material. However, available liquid filter socks have significant drawbacks, disadvantages and problems related to the nature of their materials, particularly when used in certain applications, and liquid filter socks have particular problems and concerns.
Liquid filter socks of certain materials, such as the laminates referred to above, are prone to delamination of the PTFE layer from the felt or felt-like layer, particularly in repetitive use and depending on various conditions to which the laminate is exposed, such as the pressure differentials, the liquids and the high temperatures which may be involved, the nature of upset conditions from back-pulsing (to remove accumulated solids) and the like. Furthermore, the PTFE layer, which provides the primary filtering action, requires a felt or felt-like lamination with it because the PTFE layer alone does not have sufficient strength on its own to function as a filter sock, i.e., in a filter-sock environment.
Liquid filter socks of some materials present problems in that they are incapable of providing efficient filtering action; they allow passage of liquid at an insufficient pace or else fail to remove significant amounts of undesired particulates. Filter socks of some materials are weak and incapable of extended operation at significant pressure differentials. If they are thin, which may be desirable for reasons such as improved flow-through, they are prone to be unable to withstand desired pressure differentials without losses in integrity. Some liquid filter socks have problems in releasing particulate materials during back-pulsing (back-washing).
One significant problem with commercially-available liquid filter socks is the simple fact that they are quite costly and in many cases require replacement on a fairly frequent basis.
Other problems recognized in the art involve the nature of the distal end of the liquid filter sock. Filter socks are often cylindrical sleeves which are open at both ends and have end portions which engage imperforate annular wall portions near each of the ends of the sock support, by means of a wide elastic band, a cord, water-proof tape, a removable ring-clamp or the like. Such sealing operations at both ends may be prone to problems of inaccuracy of installation and failures, particularly for relatively thick sock materials; if liquid-tight seals are not made, particulates can seep past the filter and into the filtrate inside the sock supports. In fact, exposure of the edge of the filter sock, including any inner drainage layer, can offer a pathway for unintended seepage of particulates into the filtrate. With thick sock materials, such as the aforementioned PTFE-felt laminates, leakage proneness is exacerbated because of a tendency for the sock material to bunch and gather under a band or clamp. Furthermore, given the nature of such liquid-tight seals, removal of the filter sock for any reason would involve more steps than would be required if the sock had a closed distal end.
Some prior art liquid filter socks have closed distal ends, one purpose being to reduce sealing problems. In some, the distal end of the sock is closed by a pre-installed rigid end cap, typically made of a common rigid plastic material. Such an end cap provides a downwardly-extending, downwardly-facing center socket which can facilitate placement of the sock support in the right location vis-a-vis adjacent sock supports, and an upwardly-extending center hub to assure proper placement of the filter sock on the sock support. As set forth in U.S. Pat. Nos. 5,456,834 and 5,580,456 (Bowlsbey), which disclose such liquid filter socks, the filter material of the sock is permanently bonded to a side wall of the end cap by a bonding process such as sonic welding. Such method of manufacture of a liquid filter sock is costly, and even then leaves the distal edge of the filter sock material exposed to the unfiltered liquid.
Other pertinent background information which is useful in understanding this invention is also included in the detailed descriptions section of this document.
OBJECTS OF THE INVENTION
It is an object of this invention, in the field of liquid filtration apparatus of the type having filter socks, to provide an improved liquid filtration apparatus overcoming some of the problems and shortcomings of the prior art.
Another object of this invention is to provide a liquid filter sock which has excellent qualities and provides excellent performance, but is less expensive than the present commercially-available liquid filter socks.
Another object is to provide an improved liquid filter sock which avoids any delamination problems.
Still another object of the invention is to provide an improved liquid filter sock which provides excellent flow-through and filtering properties together, yet provides good strength in difficult filter-sock environments.
Another object of this invention is to provide an improved liquid filter sock which readily releases captured particulates in back-pulsing operations.
Another object of this invention is to provide an improved liquid filter sock which can be contacted in handling without risk of any degradation.
Another object of this invention is to provide an improved liquid filter sock which is both inexpensive and yet efficient in operation and readily and easily reusable.
Another object of this invention is to provide an improved liquid filtration apparatus of the filter-sock type in which liquid-tight sealing problems are significantly reduced.
Still another object of this invention is to provide an improved liquid filter sock which, in addition to having excellent durability, filtering properties and flow-through, is very thin and thereby provides manufacturing advantages and economies.
These and other objects of the invention will be apparent from the following descriptions.
SUMMARY OF THE INVENTION
The invention is an improved liquid filter apparatus of the type including a liquid ves
Hughes Steven L.
Rose Stephen W.
Jansson & Shupe & Munger Ltd.
Kim John
Oberlin Filter Company
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