Abstract:
A filter element assembly has at least two cylindrically shaped and concentrically arranged filter media sleeves each connected at one end thereof to an inlet plate and each connected at the other end to a closed end terminal plate. Openings are provided in the inlet plate to permit entry of liquid to be filtered into the annular space between the filter sleeves. The closed end terminal plate prevents flow of unfiltered liquid from the annular space between the sleeves so as to force the liquid through the porous media of the sleeves to effect filtration. The inlet plate includes a central area that is recessed in relation to its outer edge to define an inlet chamber capped by a planar housing lid. The inlet chamber communicates with the inlet conduit via an opening in the central area.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a division of application Ser. No. 09/864,717 filed May 23, 2001 (now U.S. Pat. No. 6,511,598) which was a continuation-in-part of application Ser. No. 09/481,604 filed Jan. 12, 2000 (now U.S. Pat. No. 6,238,560) which was a continuation of application Ser. No. 09/115,118 filed Jul. 14, 1998 (now U.S. Pat. No. 6,030,531) which claimed the priority of provisional application Serial No. 60/057,759, field Sep. 2, 1997, the contents of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to the field of liquid filtration devices and more particularly to filter elements and filter element assemblies known as bag filters and cartridge filters. In particular, this invention is directed to a filter element assembly, for use in a bag filter system or in a cartridge filter system, and has at least two concentrically arranged filter media sleeves connected at one end by an inlet end plate and at the other end by a terminal end plate, and which is adapted to be disposed within a generally cylindrical filter housing. 
     BACKGROUND OF THE INVENTION 
     Bag and cartridge filter systems for liquid filtration are well known in the art and generally comprise a cylindrically shaped filter vessel typically closed at one end, with a removable or openable cap at the other end. Inlet and outlet conduits are connected to the vessel for delivering liquid to be filtered thereto and for removing filtered liquid therefrom. Replaceable filter elements are arranged within the cylindrical vessel in order to filter liquids entering the vessel. Typically bag filters consist of filter media having an open upper end and a closed bottom. The filter bag is usually supported within the vessel within an open mesh tubular basket or cage which is typically suspended within the housing. The basket is intended to support the media of the filter bag to prevent it from bursting as the bag fills with liquid. An example of such a well known filter bag arrangement is shown in the U.S. Pat. Nos. 4,285,814 and 4,669,167. Typical cartridge filters consist of a filter medium (such as filter paper) which is frequently pleated and in which the edges of the medium are brought together to form a cylindrical configuration with the pleats extending either axially or longitudinally. The edges are typically joined together with an adhesive, stitching or other means to maintain the cylindrical configuration. It is also common for the pleated media to be supported by a perforated cylindrical outer cage. End caps are typically received on either end of the filter element with appropriate adhesive being applied between the end caps and the media. One of the end caps has a central opening such that fluid passing radially through the filter media is allowed to flow through the opening to an outlet passage in the housing. Fluid to be filtered typically enters the housing so that it is caused to pass from the outside of the cylindrical configuration radially through the filter medium to the interior space in the center of the cylindrical configuration and then out through an opening in an end cap. An example of such a cartridge is shown in U.S. Pat. No. 4,609,465. Filter cartridges of the foregoing type have become quite popular. 
     One disadvantage of the popular cartridge is that the flow of liquid to be filtered is from the outside of the element to its inner core resulting in dirt or contaminants remaining behind in the housing when the cartridge element is removed from its housing for replacement. Filter bag arrangements have numerous advantages over cartridge systems. One such advantage is that the liquid to be filtered enters the filter bag at its open end so that the liquid can pass through the porous side-walls of the bag and filtered liquid can exit the filter vessel from the space between the outer bag surface and the inner wall of the vessel. In this manner dirt or contaminants can be contained within the bag and easily removed upon opening the vessel, allowing replacement with a clean filter bag. However, this typical arrangement presents a number of severe limitations which inhibits the use of bag filters for certain applications. These limitations relate to the fact that bag filter vessels are typically larger than cartridge housings, but the bag filter elements provide only a limited active filtration surface area and limited life. Bag filters also have a large volume of liquid within the enclosed volume of the bag. If the contours and shape of the bottom of the bag filter does not exactly coincide with the contours and shape of the retaining basket, filter bags will have a tendency to burst as a result of the large volume of liquid which it contains. As a result, most bag filter media can not be manufactured from high efficiency filtration media which is usually more delicate than the more coarse filter media typically used in liquid filter bags. The typical filter bag is also difficult to insert and remove from the vessel as it has no rigid structure other than possibly a retaining ring at the open top end. Filter bags rarely provide a reliable bypass seal even when constructed with elastomeric sealing members at the open top end. 
     Because filter bags have a large holding volume for liquid, removal of a used bag is quite difficult since the bag is typically filled with liquid, which makes the bag heavy and may contain hazardous substances. In order to alleviate this situation, evacuation balloons are frequently used inside the bags to reduce the liquid holding capacity. Handling of such balloons, however, is cumbersome and usually does not overcome this problem. A well known conventional filter bag designated as a “#2” has a liquid holding capacity of 4.3 gallons. Depending upon the specific gravity of the liquid within the bag, a full bag could weigh thirty pounds or more. This is difficult to remove from the filter vessel and since the removal of such a bag from the vessel typically involves contact with a side wall of the vessel, breakage of the bag during removal is not uncommon. This invariably results in contamination of the area around the vessel. 
     When the typical bag is inserted into a cylindrical or conical basket, the bottom of the bag is required to conform to the shape of the basket in three dimensions even though the bag may be manufactured from flat media, i.e., two dimensional. As a result, the filter bags rarely, if ever, fit correctly into the bottom of the basket. To overcome this problem, manufacturers have usually produced oversized bags, longer than the basket, in order to permit forcing of the bottom surface of the bag into the entire contour of the basket. As a result, much of the filter media tends to fold over onto itself and render much of the filter surface unusable. If the filter media is not fully seated in the basket it usually results in the bag bursting along the bottom of the bag as a result of the liquid pressure on the bottom surface. 
     There have been numerous attempts to design variations of the bag filter in order to minimize the liquid holding capacity while increasing the filtration surface area. One such design is shown in Smith U.S. Pat. No. 4,081,379. In the Smith patent a filter bag design has two rings of different diameters. The outer ring is affixed to the top of the body of the vessel, while the inner ring is seated within the outer ring and generally located on a plane below the outer ring in order to form an annularly shaped filter bag that is continuous from the outer to the inner ring. The particular shape of the annular filter bag provides more available surface than the conventional filter bag but it is difficult to produce as it requires manufacture of a complex shape and it does not provide for positive support of the filtration media within a basket. The Smith design typically involves a sleeve made from a single piece of material which is turned inward to form the inner filter. This results in relatively sharp corners which are difficult to insert into the basket. The Smith bag is not positively supported in a retaining basket and is thus also prone to bursting. It is not uncommon to require the use of a special tool in order to insert this type of bag into a vessel. 
     Other variations of this design is shown in U.S. Pat. No. 4,749,485 which proposes a triangularly shaped filter; and U.S. Pat. No. 5,484,529 which discloses a cylindrically shaped filter bag which includes a retaining bottom end cap. This is intended to overcome the problem of fitting a filter bag into a basket but does not result in any increased filtration filter area. 
     It is accordingly a general object of the invention to provide a filter bag and filter bag assembly intended to overcome the disadvantages of the prior art. It is another general object of the invention to provide a filter element assembly, using the principals of the invention to overcome many of the disadvantages of the bag systems and other disadvantages of the cartridge system. 
     A more specific object of the present invention is to provide a filter element assembly which has at least two cylindrically shaped and concentrically arranged filter sleeves, each connected at one end thereof to an inlet plate, which inlet plate has means to permit entry of liquid to be filtered into the annular space between the filter sleeves. Each sleeve is connected at its other end to a closed end plate preventing flow of unfiltered liquid from the annular space between the sleeves so as to force the liquid through the porous media of the sleeves to effect filtration. 
     Yet another object of the invention is to provide a filter assembly which achieves increased dirt holding capacity and increased filtration surface area while minimizing liquid capacity. 
     A still further object of this invention is to provide a liquid filtration element usable in bag filter type vessels which will permit the use of a second stage filter element within the same housing. 
     A further object of the invention is to provide a liquid filter assembly for use in bag filter systems permitting inline, inlet and outlet conduits, such as commonly used in cartridge systems. 
     Yet another object of the invention is to provide a liquid filter element assembly for use in cartridge filter systems so that dirt or contaminants are retained in the annular space between the filter sleeves and thus removed from the housing when the filter element is removed. 
     The above objects, features and advantages, along with other objects, features and advantages will become more apparent from the detailed description of the invention in conjunction with the accompanying drawings to be described more fully hereinafter. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved liquid filter element for use in bag type filter systems and for use in cartridge type filter systems. 
     The filter element assembly of the present invention includes at least two concentrically arranged cylindrically shaped filter sleeves made of porous filter media and which are connected at one end thereof to an inlet plate and at the other end thereof to a terminal or end plate. The inlet plate has inlet holes to allow liquid to enter the annular space between the concentrically arranged cylinders so that filtration of contaminants in the liquid can take place as the liquid passes through both the outer cylinder, into the space between the outer sleeve and the inner wall of the vessel, and through the inner cylinder into the interior space in the center of the inner cylinder. The terminal plate has a single central opening which is smaller in diameter than the diameter of the inner cylinder. Contaminated fluid enters the filter element assembly through the holes in the inlet plate. Contaminated material will thus remain within the annular space formed between the concentric cylinders and between the inlet and terminal plates. Liquid to be filtered will pass through the porous cylinder walls. In one embodiment, the foregoing assembly is collapsible and can be supported within a basket having perforated cylindrical walls or wire mesh walls thus preventing the cylindrical filter walls from bursting, while allowing the liquid to pass through the basket. The filter element assembly and the basket can thus be placed within a typical cylindrical filter vessel having inlet and outlet conduits as well as means for sealing the filter element assembly within the vessel to prevent any bypass of unfiltered liquid around the filter assembly. 
     In another embodiment, the filter element assembly is supported by an outer cylindrical perforated cage, which is connected to at least one end cap adapted to be supported in a standard cartridge filter housing. A perforated inner core element may also be used to support the inner sleeve of filter media. 
     The foregoing and other features of the present invention are more fully described with reference to the following drawings annexed hereto. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side and partial cutaway sectional view of a filter bag assembly according to one embodiment of the present invention; 
     FIG. 2 is a perspective view, partially cut away and shown in section, of the inlet plate shown in FIG. 1; 
     FIG. 3 is a perspective view, partially cut away and shown in section, of the terminal plate shown in FIG. 1; 
     FIG. 4 is a sectional view of yet another embodiment of the present invention depicted within a filter vessel; 
     FIG. 5 is a side view, partially cut away and shown in section of yet another embodiment of the present invention; 
     FIG. 6 is a sectional view depicting a sealing mechanism used in the present invention; 
     FIG. 7 is a sectional view of a filter vessel configuration having bottom inline inlet and outlet conduits which is permitted by the present invention; 
     FIGS. 8 a ,  8   b  and  8   c  are side views of bag type filter vessels having different inlet and outlet configurations made possible by the present invention; 
     FIG. 9 is a cross-sectional view taken along lines  9 — 9  of FIG. 1; 
     FIG. 10 is a longitudinal sectional view of a further embodiment of the invention; and 
     FIG. 11 is a sectional view taken along lines X—X of FIG.  10 . 
    
    
     DESCRIPTION OF THE INVENTION 
     With reference to FIG. 1, a preferred embodiment of the filter assembly of the present invention is illustrated. Filter  10  of this embodiment includes an annularly shaped support basket  10   a  and insert or element  10   b  arrange to be carried by the support basket. Support basket  10   a  includes a basket flange  65 , which is adapted to be supported on a shoulder within a filter housing or vessel, and cylindrically shaped wire mesh screens  60  and  61  which depend from the basket flange  65 . Insert  10   b  has a cylindrical outer sleeve  11  and a cylindrical inner sleeve  12  disposed concentrically within the outer sleeve  11 . Outer and inner sleeves  11  and  12  can be made of a variety of porous filter media materials through which liquid to be filtered can pass for filtering out contaminants. Such materials include nylon, polypropylene, needle punched felt and other such similar filter media. The sleeves  11  and  12  are connected at one end to an inlet plate  13  and at the other end to a terminal plate  20 . Inlet plate  13  is shown in greater detail in FIG.  2  and includes an annular sealing ring  14  which is integrally formed with a fluid receiving planar surface  15 . Surface  15  has a series of holes or openings  16  which are arranged so that liquid to be filtered will pass through the holes  16  into the annular space between concentrically arranged sleeves  11  and  12 , as indicated by arrows “A”. Surface  15  also has an area  15 ′ which has no holes and is positioned to prevent flow of liquid into the space interiorly of sleeve  12 . Cylindrically shaped flange  18  depends from the surface  15  in order to provide a surface for attachment of inner sleeve  12 . An annularly shaped flange  17  depends from ring  14  to provide a surface for attachment of outer sleeve  11 . Accordingly, outer sleeve  11  and inner sleeve  12  are connected to the inlet plate  13  at depending annular flanges  17  and  18  respectively. Attachment can be accomplished through a variety of means, the most efficient of which will be ultrasonic welding. 
     The inlet plate can be made of a unitary construction such as by injection molding of polymeric material such as polypropylene. Outer and inner sleeves  11  and  12  can similarly be made from polymeric material such as polypropylene thus permitting easy connection at areas  17  and  18  by ultrasonic welding. Other appropriate means of connecting the outer and inner sleeves to the inlet plate, such as through the use of appropriate adhesives can also be used. 
     Terminal plate  20 , shown in greater detail in FIG. 3, is also preferably formed through a process of injection molding from polymeric material such as polypropylene and includes a closed surface  21  to be located at the bottom of the annular space between sleeves  11  and  12 . A depending annular wall or flange  22  is located at the outer peripheral end of surface  21  to provide a surface area for connecting the bottom of sleeve  11  to the terminal plate. An upwardly extending cylindrical wall or flange  23  is arranged to provide a surface for connecting the bottom of sleeve  12  to terminal plate  20 . Accordingly, outer and inner sleeves  11  and  12  are connected to the terminal plate  20  at areas  22  and  23  respectively. An opening  24  is located at the center of terminal plate  20 . 
     With the bottom of the annular space between outer and inner sleeves  11  and  12  closed by the surface  21 , liquid to be filtered entering the annular space between sleeves  11  and  12  through openings  16  in the inlet plate  13 , as indicated by arrows marked by reference letter “A”, will be forced to pass through the porous filter media of sleeve  11  (arrows “B”) or through the inner sleeve  12  (arrows “C”), thus passing to the area outside of the assembly  10  or through the opening  24  in terminal plate  20  at the bottom of the interior of cylindrical sleeve  12 . 
     In order to support the sleeves against the pressure of the fluid flow, the element  10   b  is supported by basket  10   a  which includes basket flange  65 , outer rigid mesh cylindrical screen  60 , inner rigid mesh cylindrical screen  61  and a circular rigid mesh bottom screen  62 . Outer screen  60  and inner screen  61  are each connected to and carried by basket flange  65 , which is adapted to be supported within a filter vessel, at one longitudinal end thereof. The bottom screen  62  is connected, such as by welding, to each of cylindrical screens  60  and  61  at their longitudinal end opposite to the longitudinal end of basket flange  65 . Outer cylindrical screen  60  is positioned downstream and concentrically exteriorly of and adjacent to sleeve  11 , while inner cylindrical screen  61  is positioned downstream and concentrically interiorly of and adjacent to sleeve  12 . 
     When the assembly  10  is placed within a filter vessel  30 , such as illustrated in FIG. 4, liquid to be filtered will enter the vessel through the inlet  31 , passing via inlet conduit  32  through an openable top cover  33  of the vessel and onto the plate  15  of the filter element  10   b . The liquid then passes through openings  16  into the annular space between sleeves  11  and  12 . The liquid will then pass through the media of the sleeve  11  and through the mesh of screen  60  into the peripheral space  34  between the inner wall  51  of the vessel  30  and sleeve  11 , surrounding the filter assembly  10 , or through the sleeve  12  and mesh of screen  61  and into the interior cylindrical space  35  formed by sleeve  12 . In the embodiment shown in FIG. 1, the filtered liquid will then pass through the bottom screen  62  to the bottom of the vessel through outlet  36  shown in FIG.  4 . In the embodiment shown in FIG. 4 outlet  36  is only accessible through a second stage cartridge filter  37  which may be positioned interiorly of the cylindrical space formed by sleeve  12  so that filtered liquid entering the peripheral space  34  or interior cylindrical space  35  will thence be forced to pass through cartridge filter  37  before being permitted to exit the outlet  36 . 
     The mesh or perforated basket  10   a  shown schematically in FIG. 4, is positioned within the vessel in order to support the filter media of sleeve  11 . The bottom of the basket can be made of similarly perforated material. The filter assembly  10  can be supported within the vessel  30  by allowing the annular ring  14  of the inlet plate to rest on a support shoulder  39  of the basket flange  65  of basket  10   a , which in turn is supported in the vessel  30  on a support shoulder  41  Sealing O-rings  40  can be positioned to provide an appropriate seal between the cover  33  and the support  41  of the vessel  30 . 
     Annular ring  14  of the inlet plate  13  supports a circumferential groove  14 ′. Groove  14 ′ is shown in greater detail in FIG.  6 . Groove  14 ′ is generally V-shaped and arranged to accommodate a sealing O-ring  42 . Ring  14  is thus bifurcated into an upper fork  44  and a lower fork  45 . Upper fork  44  is engaged by the closure lid  33  of the vessel  30  when the filter assembly  10  is housed in place in the vessel. Thus the pressure caused by lid  33  (schematically indicated by arrows “D”) causes ring  42  to exert outward pressure against inner wall  47  of the basket support  39  (indicated by arrow “E”) thus causing a more positive seal with the inner wall  47  of the basket support  39 . 
     FIG. 5 illustrates yet another embodiment of the present invention consisting of a filter assembly  100  which includes filter insert  10   b  supported by basket  100   a.  Basket  100   a  includes a basket flange  165  having a shoulder  139  and depending mesh screens  160 ,  161  and  163 . Filter insert  100   b  has three concentrically arranged flexible filter media sleeves  111 ,  112  and  113 . In this arrangement, filter insert  100   b  also has an inlet plate  114 , a first terminal plate  120  and a second terminal plate  121 . Inlet plate  114  has a plurality of openings or holes  116  to allow incoming fluid (represented by arrows “AA”) to enter the annular space between filter media sleeves  112  and  113 . Inlet plate  114  also has a central opening  117  which allows incoming liquid (represented by arrows “AAA”) to enter the cylindrical space interiorly of sleeve  111 . Hence, liquid which enters the annular space between sleeves  112  and  113  will be filtered by passing through the media of sleeves  112  and  113  and the screens  160  and  161  respectively of basket  100   a . The liquid being filtered by passing through sleeve  112  (represented by arrows “BB”) will, after being filtered and passing through mesh screen  161 , pass into the annular space formed between sleeves  111  and  112 . Liquid which passes through filter sleeve  113  will pass through screen  160  and enter the annular space formed between screen  160  of basket  100   a  and the inner wall of the vessel (schematically shown and indicated as reference numeral  129  in FIG.  5 ). Liquid “AAA” which enters the cylindrical space within sleeve  111  will be filtered by passing through the filter media of sleeve  111  and screen  163  of basket  100   a  (represented by arrows “BBB”), thus entering the annular space formed between sleeves  111  and  112 . 
     First terminal plate  120  has a closed annular portion  124  and a central opening  125  which forms an outlet opening for filtered liquid “BB” and “BBB” from within the annular space between sleeves  111  and  112  through bottom mesh screen  162 . The closed annular portion  124  prevents liquid from exiting the annular space between sleeves  113  and  112 , thus causing the liquid in this space to pass through the filtration media of sleeves  113  and  112 . Second terminal plate  121  similarly prevents liquid from exiting the central interior space within sleeve  111 , thus causing such liquid in this space to pass through the filtration media of sleeve  111 . Filtered liquid “BB” which entered the annular space between annular sleeve  113  and inner wall  129  of the vessel will pass to the area at the bottom of the vessel along with the filtered liquid exiting the open center  125  of first terminal plate  120  in order to exit the vessel through outlet  140 . 
     First terminal plate  120  is formed with flanges  126  and  127  which form surfaces to which sleeves  113  and  112  respectively, can be connected by ultrasonic welding or other attachment means. Second terminal plate  121  has a flange  128  which forms a surface to which sleeve  111  can be connected by similar means. 
     Inlet plate  114  also has depending annular flanges  131 ,  132  and  133  which form surfaces to which the tops of sleeves  113 ,  112  and  111  respectively can be connected, such as by ultrasonic welding or other attachment means. 
     The embodiment of FIG. 5 accordingly provides a filter element having a cumulative surface area formed by the cylindrical surface areas of sleeves  111 ,  112  and  113 . 
     FIG. 7 illustrates a configuration of a generally cylindrical filter vessel which permits the use of inline, inlet and outlet conduits positioned at the bottom of the filter vessel. The vessel has an interior space with a removable lid  220  to provide access to the interior space when the lid is removed or in the open position. In this arrangement inlet conduit  201  enters through the bottom of the vessel and extends upwardly through the center of the vessel. Outlet conduit  202  is connected to an opening  203  offset from the center of the vessel but located at its bottom to provide means for egress of filtered liquid, such as represented by arrows “X”. In this arrangement, concentrically arranged perforated cylinders  210  and  211  form a support basket which surround the inlet conduit  201  to support the filter assembly  10 . The filter assembly  10 , such as described in connection with FIGS. 1,  2  and  3 , is disposed within the vessel so that sleeves  11  and  12  are located within the annular space between basket walls  210  and  211 . In this embodiment inlet plate  212  has a central “L” shaped flange  213  defining a central opening  214  for receiving and communicating with inlet conduit  201 . 
     Other inlet and outlet conduit arrangements, such as shown in FIGS. 8 a ,  8   b  and  8   c  are thereby made possible through the use of the filter assembly of the present invention. 
     FIGS. 10 and 11 illustrate an embodiment of the present invention intended for use in filter housings designed to accommodate standard cartridge type filters rather than the bag filters described hereinabove. Standard cartridge filters typically have an outside diameter of about 2¾ inches and are provided in overall lengths of 10 inches, 20 inches, 30 inches or 40 inches. In this embodiment, filter element  300  is generally cylindrical and can be made to have the same overall dimensions as the standard cartridges. Element  300  has an outer cylindrical sleeve  301  and an inner cylindrical sleeve  302  disposed concentrically interiorly of outer sleeve  301  with an inlet plate  303  and terminal plate  304  located at opposite longitudinal ends of the cylindrical arrangement of sleeves  301  and  302 . For ease of reference, the area of the filter assembly  300  having the inlet plate  303  is hereinafter referred to as the “upper end” of the assembly while the area accommodating the terminal plate  304  is referred to hereinafter as the “lower end”. The inner and outer sleeves  301  and  302  thus form a concentric cylindrical arrangement with the inlet and terminal plates located at opposite longitudinal ends of the cylindrical arrangement. 
     As in the embodiment illustrated in FIG. 1, outer and inner sleeves  301  and  302  can be made of a variety of porous filter media materials through which liquid to be filtered can be passed for filtering out dirt, particles and other contaminants. Such materials include nylon, polypropylene, needle punched felt and other such similar filter media. The sleeves  301  and  302  are connected at their upper end to the inlet plate  303  and at the other or bottom end to terminal plate  304 . Inlet plate  303  is similar to the inlet plate  13  shown in FIG. 2, with some differences. Inlet plate  303  has an annular ring  314  which is integrally formed with a fluid receiving planer surface  315 . Surface  315  has a plurality of holes or openings  316  which communicate with the annular space  305  between the outer and inner sleeves  301  and  302 , respectively. Liquid to be filtered is intended to pass through the openings  316  into the annular space  305 . Planar surface  315  has an area  315 ′, which is positioned centrally of the planar surface, that has no bore holes therethrough. The central area  315 ′ has a diameter approximately the same as the diameter of, and is located directly in alignment with, the interior cylindrical space  306 , which is within the cylindrical space formed by inner sleeve  302 . A cylindrical flange  318  depends from the surface  315  in order to provide a surface for attachment of inner sleeve  302 . Inner sleeve  302  may be attached to flange  318  in a variety of ways, the most efficient of which is ultrasonic welding. Outer sleeve  301  is attached to annular ring  314  also preferably by ultrasonic welding. Many techniques, however, may be employed to attach both outer and inner sleeves  301  and  302  respectively to the inlet plate  303 . Outer and inner sleeves  301  and  302  can be made from a variety of polymeric materials, such as polypropylene. Inlet plate  303  is formed as a unitary construction, such as by injection molding, also of polymeric material such as polypropylene. Thus, attachment of the outer and inner sleeves to the inlet plate  303  is easily accomplished by ultrasonic welding. Other appropriate means for connecting the outer and inner sleeves to the inlet plate  303 , such as through the use of appropriate adhesives, can also be used. 
     Terminal plate  304 , similar to terminal plate  20  illustrated in FIG. 3, is also preferably formed through a process of injection molding from polymeric material, such as polypropylene. Annular closed surface  307  is located at the bottom end of the annular space between sleeves  301  and  302  (i.e., the end opposite inlet plate openings  316 ) to prevent the flow of unfiltered liquid from the annular space  305  so that the liquid to be filtered will be caused to pass through the filter sleeves  301  and  302 . A depending annular wall or flange  322  is located at the outer peripheral surface of closed annular surface  307  to provide an area for connecting end  301  a to the terminal plate  304 . Upstanding cylindrical wall or flange  323  is arranged to provide a surface for connecting the end  302   a  of sleeve  302  to terminal plate  304 . Accordingly, outer and inner sleeves  301  and  302  respectively are connected to the terminal plate  304  at areas  322  and  323  respectively. Opening  324  is located at the central area of terminal plate  304  to provide an exit for liquid that has been filtered through sleeve  302 . 
     An outer cylindrical perforated cage  330 , also preferably made of polymeric materials such as polypropylene, cylindrically encloses the assembly of inner and outer sleeves connected to the inlet plate  303  and outlet plate  304  and is positioned adjacent the exterior of sleeve  301  to support it against the radial outward pressure of liquid. Cage  330  is connected to the outer sleeve  301  at its upper and lower ends  330   a  and  330   b , respectively, similarly, preferably by ultrasonic welding, although other means may be used. The perforations  331  of outer cage  330  may be in the form of holes or may be formed in another configuration, such as a lattice structure that is common in cartridge construction. U.S. Pat. No. 4,956,089 illustrates a typical form of cage. A cylindrical perforated inner core  325  is positioned radially inward of and adjacent inner sleeve  302 . Core  325 , also preferably of polymeric material such as polypropylene, is connected to the inlet plate  303  at annular flange  318  and is connected to the terminal plate  304  at annular flange  323 . Thus, outer sleeve  301  is supported against radially outward pressure by outer cage  330  and inner sleeve  302  is supported against radial inward pressure by core  325 . 
     An end cap  340 , also typically made of polymeric materials such as polypropylene, is used to cap the upper end of the filter assembly  300  to form an assembly end and is connected to the outer cage  330 , the outer sleeve  301 , and the inlet plate  303 , also by ultrasonic welding. End cap  340  is of a design and configuration which is common in cartridge designs so that it can be supported and accommodated within typical cartridge housings. End cap  340  has an inlet opening  341  through which liquid to be filtered can enter the filter assembly. In the typical manner, end cap  340  is provided with O-rings  342  for proper sealing engagement with the housing inlet structure. 
     Thus, in a manner similar to that described in connection with the embodiment shown in FIG. 1, liquid to be filtered will enter the filter assembly  300  through end cap inlet opening  341 , as indicated by arrows marked by reference letter “A” and will pass over the planar surface  315  of inlet plate  303 , passing through openings  316  into the annular space  305  between the outer and inner sleeves  301  and  302 , respectively. With the bottom of the annular space  305  closed by surface  307  of terminal plate  304 , liquid to be filtered that is entering the annular space between the outer and inner sleeves  301  and  302  will thus be forced to pass through the porous filter media of outer sleeve  301  (arrows “B”) and through the porous filter media of inner sleeve  302  (arrows “C”), thus passing to the area outside of the filter assembly  300  or through the opening  324  in the terminal plate  304  at the bottom of the interior of cylindrical space  306 . 
     As noted above, outer cage  330  and inner core  325  support the outer sleeve  301  and inner sleeve  302  respectively against the pressure of the fluid flow. When the filter assembly  300  is placed within a tradition cartridge filter vessel, liquid to be filtered will enter the vessel and be led to the inlet opening  341  of the filter assembly. The liquid will then pass through the openings  316  into the annular space  305  and through the media of outer sleeve  301  as well as through the perforations of outer cage  330  into the peripheral space between the outer surface of cage  330  and the inner wall of the vessel, or through the inner sleeve  302  and the perforations of inner core  325  into the interior cylindrical space  306  formed by core  325 . The filtered liquid will then pass through the bottom opening  324  of the terminal plate  304 . Thus, any dirt or contaminants that were in the liquid stream “A” will be trapped in the annular space  305  between outer and inner sleeves  301  and  302  and can thus be removed from the cartridge vessel or housing with the removal of the filter element  300 , rather than such dirt or contaminants being left behind in the vessel or housing, as is currently typical with cartridge filters in which the liquid flow is from the outside to the inside. 
     This invention has been described and illustrated in connection with certain preferred embodiments which are illustrative of the principals of the invention. However, it should be understood that various modifications and changes may readily occur to those skilled in the art, and it is not intended to limit the invention to the construction and operation of the embodiment shown and described herein. Accordingly, additional modifications and equivalents may be considered as falling within the scope of the invention as defined by the claims hereinbelow. 
     The embodiments of the invention in which an exclusive property or privilege is claimed are defined in the following claims.