Abstract:
A method for retrieving excess pharmaceutical process fluid from the hold-up volume of a primary fluid filtration device. The hold-up volume is the volume of excess process fluid which accumulates in the bottom of the filter housing below the outlet opening thereof. Because it is considered valuable, the excess pharmaceutical process fluid is retrieved from the lower housing ( 22 ) via a drainage port ( 23 ) formed therein below the level of the outlet. The excess process fluid is then filtered in a supplemental filtration device ( 100 ) that is connected to the drainage port. The supplemental filtration device has a smaller volumetric capacity than the capacity of the primary fluid filtration device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 08/968,515, now U.S. Pat. No. 5,965,019 filed Nov. 11, 1997, which claims priority to provisional application Ser. No. 60/031,827 filed Nov. 26, 1996. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject invention relates to fluid filtration devices, and more particularly, to a lenticular filter cartridge assembly housed within a disposable capsule and intended for use in conjunction with a fluid processing system. 
     2. Background of the Related Art 
     Cell type filter assemblies, often referred to as lenticular filter assemblies, are well known in the art and have been employed in fluid processing systems for many years. An early example is disclosed in U.S. Pat. No. 2,788,901 to Boeddinghaus et al. Lenticular filter assemblies often include a plurality of vertically oriented coaxially arranged filtration cells disposed within a cylindrical housing. Typically, such a filter housing is formed by structural portions which are secured together by conventional clamping devices that allow for access to the interior of the housing to facilitate filter replacement and maintenance. Examples of prior art filtration cells are disclosed in U.S. Pat. No. 4,783,262 to Ostreicher et al. and U.S. Pat. No. 4,347,208 to Southall. 
     In known prior art lenticular filtration assemblies, the uppermost and lowermost filtration cells in a filter housing are oftentimes provided with a compressible gasket or O-ring to effect a seal against the housing. See, for example, commonly assigned U.S. Pat. No. 4,704,207 to Chu. In other devices, these cells may be welded to the top and bottom of the cartridge housing to seal process fluids within the system. Additionally, it is known to provide sealing gaskets intermediate adjacent filtration cell layers to effect a seal therebetween, as disclosed in U.S. Pat. No. 4,704,207 to Chu. 
     During use, process fluid enters the filter housing through an inlet port, passes through the filtration cells, and exits the housing through an outlet port. Over time, the filtration cells will exhibit plugging or the batch will be completed, and the filtration cells are not reused to prevent cross-contamination of process fluids. Thus, to properly maintain the fluid processing system, the structural portions of a conventional filter housing must be separated, the spent filtration cells must be removed, the housing must be thoroughly cleaned to remove contaminants and residues deposited therein, and new filtration cells must be emplaced in the housing, along with any associated sealing gaskets. Such a maintenance procedure can be time consuming and costly since the fluid processing system must be brought off-line for an excessive time period. Thus, it would be extremely desirable to provide an inexpensive fully encapsulated cell type filter assembly that could be readily removed from a fluid processing system, discarded after removal, and replaced with a new filter assembly. 
     Another problem associated with the use of conventional inline filtration systems such as a lenticular filtration systems is that of hold-up volume. This is the volume of excess process fluid which accumulates in the bottom of the filter housing below the outlet opening thereof. During routine maintenance, or when spent filtration cells are replaced, the filter housing must be opened. This can result in contamination of the excess process fluid which must then be discarded. In filtration systems employed in the manufacture of biopharmaceuticals or pharmaceuticals, process fluids can be extremely valuable, and the loss thereof due to contamination can be very costly. A prior art filter assembly which employs a mechanism for reducing or decreasing hold-up volume in a filter housing is disclosed in U.S. Pat. No. 5,462,675 to Hopkins et al. This prior art assembly does not however, provide a mechanism for recovering excess process fluids from a filter housing. Clearly, the provision of such a mechanism would be extremely desirable. 
     SUMMARY OF THE INVENTION 
     The filtration system of the subject invention provides a disposable cartridge housing which encapsulates a lenticular cartridge assembly including a plurality of axially spaced apart filtration cells. The filtration system employs several unique structural features which are not found in prior art filtration systems. These features include, among others, the manner by which the cartridge housing provides a positive sealing force between the cell media layers and between the lowest cell media layer and the cartridge housing, free of any gasket, O-ring, weld or bond; the manner by which the two generally hemispherical structural portions of the cartridge housing are connected to one another by vibration welding along a circumferential joint having a flash trap associated therewith to provide an aesthetically pleasing commercial product; the method by which unfiltered hold-up volume is drained from the cartridge housing, through a flexible connector hose and into a smaller exterior filtration unit to yield clean effluent; and the manner in which hold-up volume within the cartridge housing is reduced by placing an annular volume reducer within the cartridge housing below the lowest point on the filter assembly. 
     In brief, the subject invention provides a fluid filtration device which includes a capsule housing including an upper housing portion defining a fluid inlet and a lower housing portion defining a fluid outlet, a filter assembly including an elongated mounting post and a plurality of filtration cells supported on the mounting post in axially spaced apart relationship, and structure operatively associated with the mounting post and the lower housing portion for effectuating axial compression of the filtration cells relative to the mounting post when the mounting post is engaged in the lower housing portion during assembly, whereby a positive sealing force is established between each cell and between the lowermost cell in the filter assembly and the lower housing portion. 
     The structure for effectuating axial cell compression includes a radially extending compression flange formed at an upper end portion of the mounting post and an engagement fitting formed at a lower end portion of the mounting post. The engagement fitting of the mounting post is dimensioned and configured to engage an annular retention rib formed within the lower housing portion, coaxial with an annular support flange also formed in the lower housing portion. At least one annular sealing rib projects downwardly from a lower surface of the compression flange for sealingly engaging an upper layer of an uppermost filtration cell in the filter assembly, and at least one annular sealing rib projects upwardly from an upper surface of the support flange for sealingly engaging a lower layer of a lowermost filtration cell in the filter assembly. Preferably, annular spacer rings are positioned between adjacent filtration cells in the filter assembly and spacer rings include at least one upper sealing rib for engaging a lower layer of an adjacent filtration cell located thereabove and at least one lower annular sealing rib for engaging an upper layer of an adjacent filtration cell located therebelow. 
     As discussed briefly hereinabove, in a preferred embodiment of the subject invention, an annular volume reducer is disposed in the lower housing portion circumjacent the annular support flange for displacing excess process fluid which accumulates in the lower housing portion, and a drainage port is formed in the lower housing portion for facilitating drainage of excess process fluid therefrom. Additionally, a kit is provided for retrieving excess process fluid from the lower housing portion which is includes a conduit and a portable supplemental filtration unit. The conduit has a connector at one end for mating with the drainage port and a connector at the opposed end for mating with the supplemental filtration unit. The supplemental filtration unit has an outlet port for transferring the excess process fluid to a containment device. 
     In accordance with a preferred embodiment of the subject invention, the upper housing portion and the lower housing portion are joined together along an equatorial joint which is defined by a circumferential tongue on a mating surface of the upper housing portion and a circumferential groove in a mating surface of the lower housing portion. Preferably, the groove is dimensioned and configured as a flash pot to accommodate residual flash material produced when the tongue and groove are joined together by vibratory welding. 
     These and other unique features of the encapsulated lenticular filter cartridge assembly of the subject invention will become more readily apparent from the following description of the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that those having ordinary skill in the art to which the subject invention appertains will more readily understand how to construct and use the encapsulated lenticular filter cartridge assembly of the subject invention, reference may be had to the drawings wherein: 
     FIG. 1 is an exterior perspective view of an encapsulated lenticular filter cartridge assembly constructed in accordance with a preferred embodiment of the subject invention illustrated in a service position clamped between inlet and outlet conduits of a fluid processing system, such as, for example, a biopharmaceutical fluid processing system; 
     FIG. 2 is an exploded perspective view of the encapsulated lenticular filter cartridge assembly of FIG. 1 with the upper half or the cartridge housing separated from the lower half of the cartridge housing to illustrate the lenticular cartridge assembly which includes a plurality of axially spaced cylindrical filtration cells supported on a central mounting post; 
     FIG. 3 is an exploded perspective view of the lenticular cartridge assembly shown in FIG. 2 with each of the component parts thereof separated for ease of illustration and including the central mounting post, first through fourth axially spaced apart filtration cells, and first through third spacer rings; 
     FIG. 4 is a cross-sectional view taken along line  4 — 4  of FIG. 3 illustrating the annular sealing ribs which depend from the bottom surface of the compression flange of the central mounting post of the lenticular cartridge assembly; 
     FIG. 5 is a cross-sectional view taken along line  5 — 5  of FIG. 3 illustrating the annular sealing ribs which depend from the top and bottom surfaces of the spacer rings that separate each filtration cell in the lenticular cartridge assembly; 
     FIG. 6 is a side-elevational of the lower half of the cartridge housing and the lenticular cartridge assembly with the cartridge housing shown in partial cross-section to illustrate the manner in which the outwardly extending retention flanges which form the engagement fitting on the lower portion of the mounting post are engaged and retained within the axial outlet passage of the cartridge housing; 
     FIG. 7 is a side-elevational of the lower half of the cartridge housing and the lenticular cartridge assembly with the cartridge housing shown in partial cross-section to illustrate the engaged position of lower engagement fitting of the mounting post within the axial outlet passage of the cartridge housing; 
     FIG. 8 is a cross-sectional view taken along line  8 — 8  of FIG. 7 illustrating the manner in which the annular sealing ribs depending from the bottom surface of the compression flange of the mounting post engage the top surface of the uppermost filtration cell, and the manner in which the annular sealing ribs on the upper and lower surfaces of the uppermost spacer ring engage the bottom surface of the uppermost filtration cell and the top surface of the adjacent filtration cell when the engagement portion of the mounting post is engaged in the reception portion of the lower half of the cartridge housing and the component parts of the lenticular cartridge assembly are in compression; 
     FIG. 9 is a cross-sectional view taken along line  9 — 9  of FIG. 7 illustrating the manner in which the annular sealing ribs depending from the bottom surface of the bottom-most spacer ring engage the top surface of lowest filtration cell, and the manner in which the annular sealing ribs formed about the upper surface or rim of the cylindrical cartridge seat in the lower half of the cartridge housing engage the bottom surface of the lowest filtration cell when the engagement portion of the mounting post is engaged in the reception portion of the lower half of the cartridge housing and the component parts of the lenticular cartridge assembly are in compression; 
     FIG. 10 is a perspective view of the encapsulated lenticular filter cartridge assembly of the subject invention with a substantial portion of the cartridge housing shown in cross-section to illustrate, by way of directional indicator arrows, the flow path of process fluid through the cartridge assembly from the inlet port of the cartridge housing to the outlet port of the cartridge housing; 
     FIGS.  10   a - 10   c  illustrate in sequential order the manner by which the upper and lower halves of the cartridge housing are assembled by means of a vibration welding technique, and the utilization of an equatorial flash trap to promote an aesthetically pleasing commercial product; 
     FIG. 11 is a side-elevational view in partial cross-section of the lower half of the cartridge housing illustrating the utilization of a cylindrical hold-up volume reducer disposed below the lowermost filtration cell in the lenticular cartridge assembly, and the manner in which hold-up volume is drained from the cartridge housing into a supplemental exterior filtration unit by way of a flexible conduit connected to a discharge port of the cartridge housing to yield clean effluent; 
     FIG. 12 is an exploded perspective view of the supplemental filtration unit illustrated in FIG. 11 with the sealing cap associated therewith; and 
     FIG. 13 is a perspective view of a kit having an enclosure containing the supplemental filtration unit and the flexible conduit utilized to connect the supplemental filtration unit to the cartridge housing as illustrated in FIG.  12 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now in detail to the drawings wherein like reference numerals identify similar structural elements of the subject invention, there is illustrated in FIG. 1 a disposable lenticular filter cartridge constructed in accordance with a preferred embodiment of the subject invention and designated generally by reference numeral  10 . Filter cartridge  10  is employed in a fluid processing system  12 , such as, for example, in a system for processing pharmaceutical fluids. In such a system, filter cartridge  10  is detachably supported between an inlet conduit  14  and an outlet conduit  15  by conventional sanitary flanges  16   a  and  16   b  which have mechanical characteristics which are particularly effective at the design pressure and temperature for the system. During routine maintenance periods, clamping devices  16   a  and  16   b  may be readily released to facilitate removal of the filter cartridge  10  from processing system  12 . 
     With continuing reference to FIG. 1, filter cartridge  10  is defined by a capsule housing  18  having a generally hemispherical upper housing portion  20  and a generally hemispherical lower housing portion  22 . The two housing portions are secured to one another about the equatorial centerline of the housing by a vibratory welding method which will be explained in greater detail hereinbelow with respect to FIGS.  10   a  through  10   c.  Housing portions  20  and  22  are preferably constructed from a high strength plastic material, such as, for example, polysulfone, or a similar material. The upper housing portion  20  includes a vent port  21  which allows air to be fully removed from the filter housing during installation to ensure consistent fill volumes. A cap  21 ′ covers vent port  21  during normal system operation. The lower housing portion  22  includes a drainage port  23  which allows for removal and/or recovery of excess process fluid from the housing during routine maintenance of the processing system  12 . Removal of this excess process fluid, commonly referred to as hold-up volume, will be discussed in greater detail hereinbelow with respect to FIG. 11. A cap  23 ′ covers drainage port  23  during normal system operation. 
     Referring now to FIG. 2, the upper housing portion  20  includes an axial inlet portion  24  having a sanitary flange  26  at the upper end thereof which is configured for mated alignment with a complementary flange provided at the end of inlet conduit  14 . The two complementary inlet flanges are detachably secured together by clamping device  16   a,  as shown in FIG.  1 . Similarly, the lower housing portion  22  of filter cartridge  10  includes an axial outlet portion  28  having a sanitary flange  30  at the lower end thereof which is configured for mated alignment with a complementary flange provide at the end of outlet conduit  16 . The two complementary outlet flanges are detachably secured together by clamping device  16   b,  as shown in FIG.  1 . As illustrated in FIG. 10, compressible sanitary gaskets or gaskets  25  are seated between the complementary flanges at the inlet and outlet ends of the cartridge housing. 
     Referring once again to FIG. 2, the filter cartridge  10  of the subject invention further includes a lenticular cartridge assemblage  40  which is seated on an annular support flange  32  that is integrally formed within the interior cavity of lower housing portion  22 , axially aligned with outlet portion  28 . Cartridge assemblage  40  is constructed from a plurality of axially stacked cartridge cells, the construction of which will be described in greater detail hereinbelow, which are supported in axially spaced apart relationship on a uniquely configured mounting post  42 . The number of filtration cells provided in the cartridge assemblage  40  can vary in any number but in practice from two to four, depending upon the filtration requirements of the process and/or system in which filter cartridge  10  is employed. In either instance, the same filter housing is utilized to maintain economics, though it is possible that the size of the housing could vary. However, mounting posts of different length will be employed depending upon the number of filtration cells in the assemblage. 
     Referring to FIG. 3, a preferred embodiment of cartridge assemblage  40  includes first through fourth filtration cells  44 ,  46 ,  48  and  50 , with filtration cell  44  referred to hereinafter as the uppermost cell in the assemblage, cells  46  and  48  referred to hereinafter as the upper and lower intermediate cells, respectively, and filtration cell  50  referred to hereinafter as the lowermost cell in the assemblage. A first annular spacer ring  52  is disposed between the bottom surface of the uppermost cell  44  and the top surface of the upper intermediate cell  46  to maintain the axial spacing therebetween. A second annular spacer ring  54  is disposed between the bottom surface of the upper intermediate cell  46  and the top surface of the lower intermediate cell  48  to maintain the axial spacing therebetween. A third annular spacer ring  56  is disposed between the bottom surface of the lower intermediate cell  48  and the top surface of the lowermost cell  50  to maintain the axial spacing therebetween. 
     As illustrated in FIG. 8, and by way of example with reference to the uppermost lenticular filtration cell  44 , each of the lenticular filtration cells which form the assemblage  40  includes an upper cell layer  44 ′ and a lower cell layer  44 ″. The upper and lower cell layers  44 ′ and  44 ″ of filtration cell  44  include complementary radially outer portions  41   a  and  41   b  which are disposed in face-to-face abutting relationship and are secured together by a circumferential edge retention flange  45 . The cell layers further include relatively thicker radially inner portions  43   a  and  43   b  which define an interior cavity  47  therebetween for accommodating the radially inward flow of process fluid through the filtration cell. Interior cavity  47  opens into the center of the filtration cell. The structural integrity of interior cavity  47  is maintained by an interior support structure  49  having a series of concentrically spaced apart support ribs  49   a  and a radially inner annular support collar  49   b.  For a more detailed description of the construction and operation of a similar prior art lenticular filtration cell, reference may be had to commonly assigned U.S. Pat. No. 4,783,262, the disclosure of which is incorporated herein by reference in its entirety. 
     The cell layers of each filtration cell are preferably formed from a filtration media which is constructed into sheets from a slurry of primarily cellulousic fibers. The sheets are cut into discs by stamping or punching, a process which also simultaneously provides an axial aperture in each of the discs. The filtration media is generally rigid in nature. However, it is compressible when acted upon by an applied force. By way of example, if each filtration cell is formed from two of such discs, and each cell has an outer diameter of approximately 7.0 in., the assemblage  40 , which can employ 2-4 filtration cells, will have a total filtration area ranging from 1 to 2 sq. ft. 
     Referring once again to FIG. 3, mounting post  42  extends through the central aperture formed in each filtration cell to maintain the cells, as well as the plural spacer rings, in an axially stacked relationship. Mounting post  42  includes a radial compression flange portion  58  and an elongated descending shaft portion  60 , the length of which can vary depending upon the number of filtration cells in the assemblage. Shaft portion  60  is defined by four radially spaced apart elongate support struts each designated by reference numeral  62 . The lower end portion of each support strut is formed with an inwardly tapered notch portion  63  and a radially outwardly extending terminal portion  64  having an inwardly tapered leading edge  65 . This lower end portion of shaft portion  60  forms an engagement fitting which is configured to engage an annular retention ring  67  projecting radially inwardly from the interior wall of the outlet portion  28  of housing portion  22  when cartridge assemblage  40  is seated on support flange  32 . (See, FIG.  7 ). 
     As best seen in FIG. 6, the terminal end portion  64  of each support strut  62  has an outer diameter that is greater than the inner diameter of the annular retention ring  67  formed within outlet portion  28 , while the tapered leading edge  65  of each terminal end portion  64  dimensionally conforms to the inner diameter of retention ring  67  to ease the passage of the terminal end portions  64  passed retention ring  67  during assembly of filter cartridge  10 . Although not illustrated in the figures, it is envisioned that retention ring  67  could be replaced by four radially spaced apart retention segments which would permit the terminal end portions  64  of each support strut  62  to extend passed the retention structures without interference, whereupon the mounting post  42  would be subsequently rotated 45° into a locked position in which the terminal end portions of the support struts would engage corresponding recesses formed below the four retention segments. With continuing reference to FIG. 6, four radially spaced apart projections  66  extend from the top surface  58   a  of radial flange portion  58  of mounting post  42  to form a handling structure which facilitates ready manipulation of mounting post  42  during assembly of filter cartridge  10 . 
     Referring now to FIG. 4, at the time of assembly, mounting post  42  is designed to axially compress each of the axially arranged elements of assemblage  40  into a tightly stacked unit, free of any intermediate sealing or gasketing components between the filtration cells of the assemblage  40  and other structures of the filter cartridge  10  to effect a positive seal therebetween. This is achieved by providing integrally formed sealing structures on several of the component parts of the assemblage  40 , as well as on the lower housing portion  22  of filter cartridge  10 . In particular, the bottom surface  58   b  of circular flange portion  58  includes two concentric sealing ribs  68   a  and  68   b  which are configured as saw-teeth to intimately engage, and more particularly, to penetrate into the compliant top surface  44   a  of the upper cell layer  44 ′ of the uppermost filtration cell  44 , as illustrated in FIG.  8 . 
     Each of the annular spacer rings  52 ,  54 , and  56  of assemblage  40  includes similar cell layer penetrating sealing structures. For example, as illustrated in FIG. 5, annular spacer ring  52  includes upper concentric sealing ribs  70   a  and  70   b  for penetrating the compliant bottom surface  44   b  of the lower cell layer  44 ″ of filtration cell  44  and lower concentric sealing ribs  72   a  and  72   b  for penetrating into the compliant top surface  46   a  of the upper cell layer  46 ′ of upper intermediate filtration cell  46 , as best seen in FIG.  8 . 
     As discussed briefly hereinabove, cartridge assemblage  40  is seated on the annular support flange  32  which projects upwardly from the bottom of lower housing portion  22  in axial alignment with the outlet portion  28 . As best seen in FIG. 9, the top surface of support flange  32  is formed with two closely spaced sealing ribs  74   a  and  74   b  configured to penetrate the compliant bottom surface  48   b  of the lower cell layer  48 ″ of the lowermost filtration cell  48  when the assemblage is seated on support flange  32  to effect a positive seal therebetween. Dual sealing ribs  74   a  and  74   b  are medially aligned between the concentric sealing ribs of the axial spacer rings to evenly support compressive forces established during assembly. 
     As best seen in FIG. 6, prior to assembly, the plural filtration cells of assemblage  40  are disposed in an uncompressed, spaced apart, axial stacked arrangement. At such a time, the axial height of the uncompressed filter stack may be expressed by a dimension H i . To mount the uncompressed assemblage  40  in the lower housing portion  22 , the engagement fitting formed at the bottom end of the descending shaft portion  60  of mounting post  42  is extended into axial support flange  32 . Thereupon, an axially directed downward force is exerted upon mounting post  42  to urge the terminal end portions  64  passed retention ring  67 . Once the terminal end portions  64  of mounting post  42  have moved passed retention ring  67 , the retention ring assumes an engaged position located within the notched region  63  of each support strut  62 . Continued exertion of a downward force on compression flange during assembly, causes the axially spaced apart plural filtration cells of assemblage  40  into a compressed condition which is best seen in FIG.  7 . In this compressed state, such that the filter stack has an axial height H f  which is less than the initial height H i  of the uncompressed filter stack illustrated in FIG.  6 . 
     In the compressed state illustrated in FIG. 6, the cell layer sealing structures on the bottom surface  58   a  of compression flange  58 , on each of the annular spacer rings  52 ,  54 , and  56 , and on the top surface  32   a  of mounting flange  32  penetrate an adjacent compliant filtration cell layer to effect a positive sealing force. The positive sealing force effected by the compressive action of mounting shaft  42  in conjunction with the lower housing portion  22  during assembly obviates the need for supplemental sealing structure such as gaskets or O-rings, particularly between the bottom surface  48   b  of the lower-most filtration cell  48  and the top surface of support flange  32 . 
     Referring now to FIG. 10, as discussed briefly hereinabove, the generally hemispherical upper and lower housing portions  20  and  22  of capsule housing  18  are secured to one another about the equatorial centerline of the housing. To effectuate this securement, the two housing portions form an equatorial joint defined by an upper circumferential flange  80  on the upper housing portion  20  and a lower circumferential flange  82  of the lower housing portion  22 . As best seen in FIG.  10   a,  the upper circumferential flange  80  has an axially projecting circumferential tongue  84  which interacts with an axially extending circumferential groove  86  formed in the lower circumferential flange  82 . Groove  86  has a radial profile which is wider than that of tongue  84  and thus is it serves to facilitate relative movement of the tongue, and in addition it serves as a containment area or trap for flash material  88  which is produced by the vibratory welding process employed to join the two housing portion together during assembly of filter cartridge  10 . 
     As shown in FIG.  10   b,  during the vibratory welding process, with the tongue  84  and groove  86  engaged, the lower housing portion  22  is maintained in a stationary position, and the upper housing portion  20  is oscillated relative thereto at an extremely low frequency, in the range of 50-100 Hz, along the equatorial plane of the capsule housing  18 . At the same time, a downward force is exerted on the upper housing portion  20  to further effectuate the welding process. As illustrated in FIG.  10   c,  the flash material which results from the vibratory welding process remains entirely within groove  86 , which, as stated above acts as a flash trap. Consequently, a clean circumferential seamline  88  is created between the upper and lower housing portions  20  and  22 , thereby producing an aesthetically pleasing commercial product. 
     Referring once again to FIG. 10, when fluid processing system  12  is operating, unfiltered process fluids, indicated by directional flow lines, ingress into axial inlet portion  24  from inlet conduit  14  and flow into capsule housing  18 . System pressure draws the unfiltered process fluid into the filtration cells of assemblage  40  in a radially inward direction, through the filter media, into the radial flow passages defined therein, and out to the central bore of the assemblage. The filtered process fluids are then drawn down through the center of filter assemblage  40 , into the outlet portion  28  whereupon the filtered process fluid egresses from the capsule housing  18  through outlet conduit  15 . 
     Referring now to FIG. 11, in a preferred embodiment of the encapsulated filter cartridge  10  of the subject invention, a cylindrical ring  90  is disposed in the bottom of lower housing portion  22 , below the lowermost filtration cell  50 , circumjacent support flange  32  for reducing the hold-up volume or excess unfiltered process fluid which accumulates below the level of the outlet port defined by support flange  32 . In essence, ring  90  displaces a certain volume of fluid in the lower housing portion. The ring is preferably formed form a material which is compatible with the filtrate used in the subject filtration apparatus. 
     Because the filter device  10  of the subject invention is particularly adapted for use in conjunction with a system for processing relatively expensive pharmaceutical fluids, it is extremely desirable to reclaim or recover excess process fluid which may accumulate in lower housing portion  22  below the level of the outlet port thereof. Accordingly, as illustrated in FIG. 11, a supplemental filtration device  100  may be connected to the drainage port  23  by way of a flexible conduit  102  to reclaim the unfiltered or excess process fluid. A connective fitting  104  is provided at one end of conduit  102  to mate with the drainage port  23  of housing portion  22 , and a connective fitting  106  is provided at the other end of conduit  102  to mate with an inlet port  108  of supplemental filtration device  100 . The connective fittings are preferably luer lock connections, although alternative mechanical connections may be employed. A second conduit  110  is connected to the outlet port  112  of supplemental filtration device  100  to transfer the supplementally filtered excess process fluid to a containment vessel. 
     As best seen in FIG. 12, the secondary filtration device  100  includes an upper filter body  120  defining inlet port  108  and a vent port  109 , a lower filter body  122  defining outlet port  110 , and a filter member  124  constructed from a filtrate or media that is substantially similar to that from which the filtration cells of assemblage  40  are constructed. Referring to FIG. 13, the secondary filtration device  100 , fluid conduit  102 , and associated connective fittings  104  and  106  are preferably marketed and sold by the manufacturer of filtration device  10  as a kit, and therefore have an associated packaging enclosure  126  furnished therewith. 
     Although the fluid filtration apparatus of the subject invention has been described with respect to a preferred embodiment, it is apparent that modifications and changes can be made thereto without departing from the spirit and scope of the invention as defined by the appended claims.