PATENT DOCUMENT

Abstract:
A high capacity gravity feed filter for filtering blood and blood products or the like includes a body having an inlet port, an outlet port, two filter wells, at least one filter element disposed in each of said filter wells, between the inlet port and outlet port so as to filter liquid which flows into the filtration device via the inlet port. The filter elements divide each of said filter wells into a first chamber and a second chamber. The device allows gases to vent the filtration device through the outlet port. The means may include a vertical channel within each of said second chambers. The filtration device allows air therein to be purged downstream into a receiving blood bag without the manipulation of the height of the filtration device or the receiving blood bag.

Full Description:
This application claims priority of U.S. Provisional Application Serial No. 60/192,733 filed Mar. 27, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to the filtration field, and more particularly, to an improved gravity feed filtration device for filtering blood and blood products. 
     There are commercially available gravity filtration devices for filtering blood and blood products. The currently available gravity feed blood filters are capable of filtering a single unit of blood. Furthermore, certain types of blood or blood products foul the currently available devices before a single unit of blood can be filtered. 
     It is therefore an object of the present invention to provide a gravity feed filtration device capable of filtering any type of blood or blood product, and capable of filtering at least two units of blood. 
     SUMMARY OF THE INVENTION 
     The foregoing problems of the prior art are solved, and the objects of the present invention are achieved, by use of a filtration apparatus constructed in accordance with the principles of the present invention. 
     In accordance with the present invention, the filtration apparatus for the gravity filtration of blood or blood products is divided into two independent filtration chambers. The apparatus contains a common inlet port that is in fluid flow communication with inlet ports of the two independent filtration chambers, and a common outlet port that is in fluid flow communication with outlet ports of the two independent filtration chambers. The apparatus also contains a means to automatically drain the upstream portion of both of the filtration chambers once the filtration process is complete. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects, features and advantages of the invention will be evident from the following detailed description when read in conjunction with the accompanying drawings in which: 
     FIG. 1A is a front isometric view of the body of the filtration apparatus depicted in FIG. 6; 
     FIG. 1B is a back isometric view of the body of the filtration apparatus depicted in FIG. 6; 
     FIG. 2 is an isometric view, having portions thereof removed, of the body of the filtration apparatus depicted in FIG. 6; 
     FIG. 3A is a partial front isometric view of the top portion of the body depicted in FIG. 1 a ; 
     FIG. 3B is a partial back isometric view of the top portion of the body depicted in FIG. 1 b ; 
     FIG. 4A is a front isometric view of the front cover of the filtration apparatus depicted in FIG. 6; 
     FIG. 4B is a back isometric view of the front cover of the filtration apparatus depicted in FIG. 6; 
     FIG. 5A is a front isometric view of the back cover of the filtration apparatus depicted in FIG. 6; 
     FIG. 5B is a back isometric view of the back cover of the filtration apparatus depicted in FIG. 6; 
     FIG. 6 is an exploded isometric view of the components that comprise the first embodiment of the filtration apparatus, constructed in accordance with the principles of the present invention, usable for the gravity filtration of blood and blood products; 
     FIG. 7 is a cross-sectional view of the filtration apparatus depicted in FIG. 6; 
     FIG. 8 is an isometric view of the filtration apparatus depicted in FIG. 6, having portions thereof removed; 
     FIG. 9 is an isometric view of a blood filtration assembly containing the filtration apparatus depicted in FIG. 6; 
     FIG. 10A is a front isometric view of the body of the filtration apparatus depicted in FIG. 17; 
     FIG. 10B is a back isometric view of the body of the filtration apparatus depicted in FIG. 17; 
     FIG. 11 is a front isometric view having portions thereof removed of the body of the filtration apparatus depicted in FIG. 17; 
     FIG. 12A is a partial front isometric view of the top portion of the body depicted in FIG. 10A; 
     FIG. 12B is a partial back isometric view of the top portion of the body depicted in FIG. 10B; 
     FIG. 13A is a front isometric view of the front cover of the filtration apparatus depicted in FIG. 17; 
     FIG. 13B is a back isometric view of the front cover of the filtration apparatus depicted in FIG. 17; 
     FIG. 14 is a front isometric view having portions thereof removed of the front cover of the filtration apparatus depicted in FIG. 17; 
     FIG. 15A is a front isometric view of the back cover of the filtration apparatus depicted in FIG. 17; 
     FIG. 15B is a back isometric view of the back cover of the filtration apparatus depicted in FIG. 17; 
     FIG. 16 is a back view of the back cover of the filtration apparatus depicted in FIG. 17; 
     FIG. 17 is an exploded isometric view of the of the components that comprise the fifth embodiment of the filtration apparatus, constructed in accordance with the principles of the present invention, usable for the gravity filtration of blood and blood products; 
     FIG. 18 is a cross-sectional view of the filtration apparatus depicted in FIG. 17; 
     FIG. 19 is an isometric view of the filtration apparatus depicted in FIG. 17, having portions thereof removed; 
     FIG. 20 is an isometric view of a blood filtration assembly containing the filtration apparatus depicted in FIG. 17; 
     FIG. 21 is a back view of the front cover of the filtration apparatus depicted in FIG. 6; 
     FIG. 22 is an isometric view, having portions thereof removed, of the body of the filtration apparatus depicted in FIG. 25; 
     FIG. 23A is a front isometric view of the front cover of the filtration apparatus depicted in FIG. 25; 
     FIG. 23B is a back isometric view of the front cover of the filtration apparatus depicted in FIG. 25; 
     FIG. 24A is a front isometric view of the back cover of the filtration apparatus depicted in FIG. 25; 
     FIG. 24B is a back isometric view of the back cover of the filtration apparatus depicted in FIG. 25; 
     FIG. 25 is an exploded isometric view of the components that comprise the third embodiment of the filtration apparatus, constructed in accordance with the principles of the present invention, usable for the gravity filtration of blood and blood products; 
     FIG. 26 is a cross-sectional view of the filtration apparatus depicted in FIG. 25; 
     FIG. 27A is an isometric view of a filter compression ring of the filtration apparatus depicted in FIG. 25; 
     FIG. 27B is a partial isometric view of the top portion of the filter compression ring depicted in FIG. 27A; 
     FIG. 28A is a front isometric view of the body of the filtration apparatus depicted in FIG. 30; 
     FIG. 28B is a back isometric view of the body of the filtration apparatus depicted in FIG. 30; 
     FIG. 29 is an isometric view, having portions thereof removed, of the body of the filtration apparatus depicted in FIG. 30; 
     FIG. 30 is an exploded isometric view of the of the components that comprise the seventh embodiment of the filtration apparatus, constructed in accordance with the principles of the present invention, usable for the gravity filtration of blood and blood products; 
     FIG. 31 is a cross-sectional view of the filtration apparatus depicted in FIG. 30; 
     FIG. 32A is a schematic representation of the pressures in the downstream chamber of the filtration device depicted in FIG. 30, after the filtration device has been primed, for static conditions; 
     FIG. 32B is a schematic representation of the pressures in the downstream chamber of the filtration device depicted in FIG. 30, after the filtration device has been primed, for dynamic conditions. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Although various embodiments of the filtration device constructed in accordance with the present invention are disclosed herein, each embodiment enables the filtration device to filter more than one unit of blood. 
     One embodiment of the filtration device constructed in accordance with the principles of the present invention, is shown in FIG.  1 A through FIG.  8 . Referring to FIG. 6 this embodiment includes the following major components: front cover  20 , body  1 , back cover  30 , filter elements  80 ,  81 ,  82 ,  80   a ,  81   a , and  82   a , and hydrophobic vent filter element  41 . 
     FIG. 1A, FIG. 2, and FIG. 3A show the front part of body  1 . The front part of body  1  contains a first filter well  13 , defined by front flat surface  2  of partition wall  300  and cylindrical surface  14 . The front face of partition wall  300  contains side vertical channels  4 , circular channel  3 , and center vertical channel  5 . Preferably circular channel  3  is wider and deeper than side vertical channels  4 , and center vertical channel  5  is wider than circular channel  3 , and the same depth as circular channel  3 . The upper and lower ends of side vertical channels  4  are in fluid flow relation with circular channel  3 , and circular channel  3  is in fluid flow relation with center vertical channel  5 . Center vertical channel  5  is in fluid flow relation with front outlet port  6 . The upper central part of body  1  contains inlet tube socket  17 , and cross protrusion  19 . Inlet tube socket  17  contains inlet port  9 , and cross protrusion  19  contains a cross port, with the front half of the cross port labeled front cross port  7 , and the back half of the cross port labeled back cross port  7   a . The outer end of cross port  7  contains front inlet channel  8 , bounded by side walls  15  and wall  16 . The lower central part of body  1  contains outlet tube socket  18 . Outlet tube socket  18  contains outlet port  10 . Front outlet port  6  is in fluid flow relation with outlet port  10  through link port  11 . 
     FIG. 1B, and FIG. 3B show the back part of body  1 . The back part of body  1  contains a second filter well  13   a , defined by back flat surface  2   a  of partition wall  300  and cylindrical surface  14   a . The back face of partition wall  300  contains side vertical channels  4   a , circular channel  3   a , and center vertical channel  5   a . Preferably circular channel  3   a  is wider and deeper than side vertical channels  4   a , and center vertical channel  5   a  is wider than circular channel  3   a , and the same depth as circular channel  3   a . The upper and lower ends of side vertical channels  4   a  are in fluid flow relation with circular channel  3   a , and circular channel  3   a  is in fluid flow relation with center vertical channel  5   a . Center vertical channel  5   a  is in fluid flow relation with back outlet port  6   a . The upper central part of body  1  contains inlet tube socket  17 , and cross protrusion  19 . Inlet tube socket  17  contains inlet port  9 , and cross protrusion  19  contains a cross port, with the front half of the cross port labeled front cross port  7 , and the back half of the cross port labeled back cross port  7   a . The outer end of cross port  7   a  contains back inlet channel  8   a , bounded by side walls  15   a  and wall  16   a . The lower central part of body  1  contains outlet tube socket  18 . Outlet tube socket  18  contains outlet port  10 . Back outlet port  6   a  is in fluid flow relation with outlet port  10  through link port  11 . Front outlet port  6  may be a through hole as shown with the front half labeled front outlet port  6 , and the back half labeled back outlet port  6   a . As shown in FIGS. 1A through 3B the back part of body  1  is a mirror image of the front part of body  1 . Body  1  is preferably made from an injection moldable medical grade plastic such acrylic, polycarbonate, polysulfone, polypropylene, polyethylene, but is not limited to these materials. 
     FIG. 4A, FIG. 4B, and FIG. 21 show front cover  20 . Front cover  20  is round in shape to match the shape of body  1 , (if body  1  was square, then front cover  20  would also be square) and contains boss  29  at its upper end. The interior of front cover  20  contains flat surface  23 . Vertical filter support ribs  24  protrude from flat surface  23 . The vertical filter support ribs  24  could be replaced with ribs oriented in a direction other than vertical, or with a pattern of round pins, or with a pattern or rectangular pins, or with a pattern of concentric rings with gaps in the rings, or with any other filter support means that does not contain a closed loop. Outer rib  27  also protrudes from flat surface  23  and follows the outer periphery of front cover  20 . Although it is not necessary for front cover  20  to contain outer rib  27 , outer rib  27  acts as an alignment rib during assembly, and as a flash trap to contain flash when front cover  20  is assembled to body  1 . Front cover  20  also contains round filter support rib  25 . Round filter support rib  25  contains gap  26  located at the upper end of front cover  20 , below boss  29 . Front cover  20  also contains through slots  21 , and vent filter bonding area  28 . Although filter bonding area  28  is shown round for bonding a round vent filter, the vent filter could be square or any other shape, and then the filter bonding area  28  would conform to the shape of the vent filter. Through slots  21  are shown as vertical slots, but could be replaced by a pattern of round holes, or a pattern of square holes, or any other pattern of through holes that provide adequate filter support, and also provide air flow communication between the face of the vent filter that is bonded to flat surface  23 , and to the outside atmosphere of front cover  20 . FIG. 7 shows vent filter element  41  bonded to front cover  20 . The outside of front cover  20  contains flat surface  22 . Referring to FIG. 21, centerline  70  shows the center of the seal between front cover  20  and body  1 . The seal could be an ultrasonic weld, a glue bond, a heat bond, a solvent bond, or any other type of leak tight bond. Front cover  20  is preferably made from an injection moldable medical grade plastic such acrylic, polycarbonate, polysulfone, polypropylene, polyethylene, but is not limited to these materials. 
     FIG. 5A, FIG. 5B, and FIG. 21 show back cover  30 . Back cover  30  is round in shape to match the shape of body  1 , (if body  1  was square, then back cover  30  would also be square) and contains boss  39  at its upper end. The interior of back cover  30  contains flat surface  33 . Vertical filter support ribs  34  protrude from flat surface  33 . The vertical filter support ribs  34  could be replaced with ribs oriented in a direction other than vertical, or with a pattern of round pins, or with a pattern of rectangular pins, or with a pattern of concentric rings with gaps in the rings, or with any other filter support means that does not contain a closed loop. Outer rib  37  also protrudes from flat surface  33  and follows the outer periphery of back cover  30 . Although it is not necessary for back cover  30  to contain outer rib  37 , outer rib  37  acts as an alignment rib during assembly, and as a flash trap to contain flash when back cover  30  is assembled to body  1 . Back cover  30  also contains round filter support rib  35 . Round filter support rib  35  contains gap  36  located at the upper end of back cover  30 , below boss  39 . The outside of back cover  30  contains flat surface  32 . Back cover  30  is identical to front cover  20  with the exception that back cover  30  does not contain a vent filter. Referring to FIG. 21, centerline  70  shows the center of the seal between back cover  30  and body  1 . Back cover  30  is preferably made from an injection moldable medical grade plastic such acrylic, polycarbonate, polysulfone, polypropylene, polyethylene, but is not limited to these materials. 
     FIG. 6 shows an exploded view of the components that comprise filter device  40 . The components are body  1 , front cover  20 , back cover  30 , vent filter element  41 , and filter elements  80 ,  81 , and  82 , and filter elements  80   a ,  81   a , and  82   a . FIG.  7  and FIG. 8 show filter device  40  in the assembled state. Referring to FIG. 1A, FIG. 1B, FIG. 2, FIG. 4B, FIG. 5B, FIG. 6, FIG. 7, FIG. 8, and FIG. 21, the components that comprise filter device  40  are assembled as follows. The outer periphery of vent filter element  41  is sealed to front cover  20  at filter bonding area  28 . The seal is preferably a heat seal but could be an ultrasonic seal, a glue bond, a solvent bond, or any other type of bond that will produce a leak tight seal capable of maintaining sterility. Filter element  41  is a hydrophobic filter with a pore size of 0.2 μ or smaller to maintain sterility. Filter elements  80 ,  81 , and  82  are placed into first filter well  13 . Front cover  20  is then bonded to body  1  so that edge  12  of body  1  is bonded to front cover  20  along centerline  70  shown in FIG.  21 . The seal between front cover  20  and body  1  forms a single closed loop that encloses the outer periphery of first filter well  13  and the outer periphery of front inlet channel  8 , thereby creating a closed first chamber  44  in first filter well  13 , and a closed front inlet channel  8  that extends from front cross port  7  to first chamber  44  of first filter well  13 , thereby creating a flow path from inlet port  9 , through front cross port  7 , through front inlet channel  8 , into first chamber  44  of first filter well  13 . Outer rib  27  of front cover  20  aligns front cover  20  to body  1  during the assembly procedure and also acts as a flash trap. The bond between front cover  20  and body  1  is preferably an ultrasonic seal but could be a glue bond, a heat bond, a solvent bond or any other type of bond that creates a leak tight seal. Filter elements  80 ,  81 , and  82  are sealed to body  1  with a compression seal between the outer edges  84 ,  85 , and  86  of filter elements  80 ,  81 , and  82  respectively, and cylindrical surface  14  of body  1  in the filter device  40  shown. However, filter elements  80 ,  81 , and  82  could be sealed to body  1  with a glue seal, a heat seal, a compression seal, or any other type of seal that eliminates bypass around filter elements  80 ,  81 , and  82 . Filter device  40  is shown with  3  filter elements  80 ,  81 , and  82  in first filter well  13 . However any number of filter elements greater than or equal to one could be used. The number of filter elements used is determined by the filter type and the fluid being filtered. The same number of filter elements that were placed into first filter well  13  of body  1  are now placed into second filter well  13   a  of body  1 , and are designated as filter elements  80   a ,  81   a , and  82   a . These filter elements are sealed to body  1  using the same method that was used to seal filter elements  80 ,  81 , and  82  to first filter well  13 . Back cover  30  is then bonded to body  1  so that edge  12   a  of body  1  is bonded to back cover  30  along the same path as centerline  70  shown in FIG.  21 . The seal between back cover  30  and body  1  forms a single closed loop that encloses the outer periphery of second filter well  13   a  and the outer periphery of back inlet channel  8   a , thereby creating a closed first chamber  45  in second filter well  13   a , and a closed back inlet channel  8   a  that extends from back cross port  7   a  to first chamber  45  of second filter well  13   a , thereby creating a flow path from inlet port  9 , through back cross port  7   a , through back inlet channel  8   a , into first chamber  45  of second filter well  13   a . Outer rib  37  of back cover  30  aligns back cover  30  to body  1  during the assembly procedure and also acts as a flash trap. The bond between back cover  30  and body  1  is preferably an ultrasonic seal but could be a glue bond, a heat bond, a solvent bond or any other type of bond that creates a leak tight seal. 
     Referring to FIG. 4B, FIG. 6, FIG. 7, and FIG. 8, the assembled filter device  40  contains first chamber  44  of first filter well  13  bounded by flat surface  23  of front cover  20 , inner surface  77  of round rib  25  of front cover  20 , and the upstream surface  46  of the first filter element  80  in first filter well  13  of body  1 . Referring to FIG. 5B, FIG. 6, and FIG. 7, the assembled filter device  40  also contains first chamber  45  of second filter well  13   a  bounded by flat surface  33  of back cover  30 , inner surface  71  of round rib  35  of back cover  30 , and the upstream surface  46   a  of the first filter element  80   a  in second filter well  13   a  of body  1 . Referring to FIG.  3 A and FIG. 7, in the assembled filter device  40 , front inlet channel  8  becomes a closed channel bounded by side walls  15  and wall  16  of body  1 , and by flat surface  23  of front cover  20 . Referring to FIG. 7, front inlet channel  8  places first chamber  44  in fluid flow communication, and in air flow communication with front cross port  7 . Referring to FIG.  3 B and FIG. 7, in the assembled filter device  40 , back inlet channel  8   a  becomes a closed channel bounded by side walls  15   a  and wall  16   a  of body  1 , and by flat surface  33  of back cover  30 . Referring to FIG. 7, back inlet channel  8   a  places first chamber  45  in fluid flow communication, and in air flow communication with back cross port  7   a.    
     Referring to FIG. 1 a , FIG. 2, FIG.  6  and FIG. 7, the assembled filter device  40  contains second chamber  47  of first filter well  13  bounded by the downstream surface  48  of the last filter element  82  in first filter well  13  of body  1 , and by center vertical channel  5 , circular channel  3 , and side vertical channels  4 . Second chamber  47  of first filter well  13  contains front outlet port  6 . Referring to FIG. 1 b , FIG.  6  and FIG. 7, the assembled filter device  40  contains second chamber  47   a  of second filter well  13   a  bounded by the downstream surface  48   a  of the last filter element  82   a  in second filter well  13   a  of body  1 , and by center vertical channel  5   a , circular channel  3   a , and side vertical channels  4   a . Second chamber  47   a  of second filter well  13   a  contains back outlet port  6   a.    
     Referring to FIG. 9 one end of a length of outlet tubing  53  is bonded to outlet tube socket  18  of body  1 , with the other end of said outlet tubing bonded to an empty blood bag  55 . Another length of inlet tubing  52  is bonded to inlet tube socket  17  of body  1 . The end user will preferably purchase the assembly of filter device  40 , inlet tubing  52 , outlet tubing  53 , and receiving blood bag  55 , assembled and sterile. The assembly will also contain an inlet tubing clamp  74  on inlet tubing  52 , and an outlet tubing clamp  75  on outlet tubing  53 . 
     In FIG. 9 the filter device  40  is in an operational assembly with inlet tubing  52 , outlet tubing  53 , feed blood bag  54 , receiving blood bag  55 , inlet tube clamp  76 , and outlet tube clamp  75 . Preferably, the user will purchase the assembly of FIG. 9 sterilized without feed blood bag  54  with the inlet end of inlet tubing  52  sealed to maintain system sterility. For performing filtration the user will first close inlet tube clamp  74  close to the inlet end of inlet tubing  52 . Next the user will make sure that outlet tube clamp  75  is open. Inlet tubing  52  is now bonded by the user to a pigtail on feed blood bag  54  using a sterile docking device as is well known in the art. 
     Once the sterile docking connection is made the user will hang feed blood bag  54  from hook  57  on blood bag pole  56 . Receiving blood bag  55  should be placed on a surface such as a table top or the like. The complete assembly  60  ready for filtration is illustrated in FIG.  9 . 
     Referring to FIG. 1A, FIG. 4B, FIG. 5B, FIG. 7, FIG.  8  and FIG. 9 the filtration is performed as follows. The user opens inlet tube clamp  74 . Gravity now forces blood to flow from feed blood bag  54 , through inlet tubing  52 , through inlet port  9  of body  1 . After passing through inlet port  9 , a portion of the blood passes through front cross port  7 , while the remainder of the blood passes through back cross port  7   a . The portion of the blood that passes through front cross port  7 , then passes through front inlet channel  8 , through gap  26  of front cover  20 , into first chamber  44 . The portion of the blood that passes through back cross port  7   a , then passes through back inlet channel  8   a , through gap  36  of back cover  30 , into first chamber  45 . A portion of the air that was in inlet tubing  52  and inlet port  9  before blood flow started will be pushed ahead of the blood, through front cross port  7 , through front inlet channel  8 , through gap  26  of front cover  20 , into first chamber  44 . The remainder of the air that was in inlet tubing  52  and inlet port  9  before blood flow started will be pushed ahead of the blood, through back cross port  7   a , through back inlet channel  8   a , through gap  36  of back cover  30 , into first chamber  45 . Because the usable surface area of hydrophobic filter  41  is much smaller than the usable surface area of filter elements  80 ,  81 , and  82 ; and because the pressure drop across sterilizing grade hydrophobic filter  41  is much greater per unit volume of air flow per unit surface area of filter material than the combined pressure drop across filter elements  80 ,  81 , and  82  per unit volume of air flow per unit surface area of filter material, only a very small portion of the air that was in inlet tubing  52 , inlet port  9 , front cross port  7 , and front inlet channel  8  before blood flow started, will pass through hydrophobic filter  41 , and then through slots  21  of front cover  20  to atmosphere. 
     As first chamber  44  fills from the bottom up most of the air in first chamber  44  will be forced through filter elements  80 ,  81 , and  82 , for the same reasons described in the previous paragraph. This initial air will flow into vertical channels  4 , circular channel  3 , and center vertical channel  5 , and then flow through front outlet port  6 , through link port  11 , through outlet port  10 , into outlet tubing  53 , into receiving blood bag  55 . Filter elements  80 ,  81 , and  82  will also wet from the bottom up. The air that is initially in filter elements  80 ,  81 , and  82  will be displaced by blood and flow into vertical channels  4 , circular channel  3 , and center vertical channel  5 , and then flow through front outlet port  6 , through link port  11 , through outlet port  10 , into outlet tubing  53 , into receiving blood bag  55 . Because the volume of first chamber  44  is small, and the flow rate of blood entering first chamber  44  is much greater than the initial flow rate of blood through filter elements  80 ,  81 , and  82 , first chamber  44  will fill in a very small fraction of the time that it takes to wet filter elements  80 ,  81 , and  82 . The pressure head at the bottom of first chamber  44  will be larger than the pressure head at the top of first chamber  44 , because of the height difference between the top and bottom of first chamber  44 . Therefore liquid will start to come through filter element  82  from the bottom up. As liquid starts to come through filter element  82  from the bottom up vertical channels  4 , circular channel  3 , and center vertical channel  5 , of body  1  will fill from the bottom up. Because the total volume of these channels in is small (to minimize holdup) the channels may fill with blood (from the bottom up) before the upper part of filter element  82  has wet with blood. Once blood starts to flow from center, vertical channel  5  of body  1 , into front outlet port  6  of body  1 , through link port  11  of body  1 , through outlet port  10  of body  1 , into outlet tubing  53 , and starts to flow down outlet tubing  53  toward receiving blood bag  55 , the pressure in front outlet port  6  will become negative. Because center vertical channel  5  is in fluid flow relationship with front outlet port  6 , the pressure inside the tube created by center vertical channel  5  and downstream surface  48  of filter element  82  will also be negative. Likewise since circular channel  3  is in fluid flow relationship with center vertical channel  5  the pressure inside the tube created by circular channel  3  and downstream surface  48  of filter element  82  will also be negative. Since the tube segments made up of vertical channels  4  and downstream surface  48  of filter element  82  are in fluid flow relationship with the tube created by circular channel  3  and downstream surface  48  of filter element  82 , any air or liquid that flows from filter element  82  into vertical channels  4  will be sucked into circular channel  3 , and then flow from circular channel  3  into center vertical channel  5 , through front outlet port  6 , through link port  11 , through outlet port  10 , into outlet tubing  53 , and into receiving blood bag  55 . This assures that filter elements  80 ,  81 , and  82  will completely wet, and that all of the air that was in first chamber  44 , filter elements  80 ,  81 , and  82 , vertical channels  4 , circular channel  3 , center circular channel  5 , front outlet port  6 , link port  11 , outlet port  10 , and the interior of outlet tubing  53  will be forced into receiving blood bag  55 . Although vertical channels  4  are shown in the vertical orientation, they could be orientated at any angle from zero degrees to ninety degrees from vertical, as long as they are in fluid flow relationship with circular channel  3 . Other channel designs such as the spiral channel filter underdrain disclosed in U.S. Ser No. 08/524,049 U.S. Pat. No. 5,798,041, and entitled “an In-Line Liquid Filtration Device Usable for Blood, Blood Products and the Like”, could also be used in place of the design illustrated in FIG.  1 A. It is however, imperative that all channels be either directly or indirectly in fluid flow relationship with front outlet port  6 . 
     The portion of blood from feed blood bag  54  which flows through back cross port  7   a , through back inlet channel  8   a , through gap  36 , into first chamber  45 , will fill first chamber  45  from the bottom forcing all of the air in first chamber  45  through filter elements  80   a ,  81   a , and  82   a . This initial air will flow into vertical channels  4   a , circular channel  3   a , and center vertical channel  5   a , and then flow through back outlet port  6   a , through link port  11 , through outlet port  10 , into outlet tubing  53 , into receiving blood bag  55 . Filter elements  80   a ,  81   a , and  82   a  will also wet from the bottom up. The air that is initially in filter elements  80   a ,  81   a , and  82   a  will be displaced by blood and flow into vertical channels  4   a , circular channel  3   a , and center vertical channel  5   a , and then flow through outlet port  6   a , through link port  11 , through outlet port  10 , into outlet tubing  53 , into receiving blood bag  55 . Because the volume of first chamber  45  is small, and the flow rate of blood entering first chamber  45  is much greater than the initial flow rate of blood through filter elements  80   a ,  81   a , and  82   a , first chamber  45  will fill in a very small fraction of the time that it takes to wet filter elements  80   a ,  81   a , and  82   a . The pressure head at the bottom of first chamber  45  will be larger than the pressure head at the top of first chamber  45 , because of the height difference between the top and bottom of first chamber  45 . Therefore liquid will start to come through filter element  82   a  from the bottom up. As liquid starts to come through filter element  82   a  from the bottom up vertical channels  4   a , circular channel  3   a , and center vertical channel  5   a , of body  1  will fill from the bottom up. Because the total volume of these channels in is small (to minimize holdup) the channels may fill with blood (from the bottom up) before the upper part of filter element  82   a  has wet with blood. Once blood starts to flow from center vertical channel  5   a  of body  1 , into back outlet port  6   a  of body  1 , through link port  11  of body  1 , through outlet port  10  of body  1 , into outlet tubing  53 , and starts to flow down outlet tubing  53  toward receiving blood bag  55 , the pressure in back outlet port  6   a  will become negative. Because center vertical channel  5   a  is in fluid flow relationship with back outlet port  6   a , the pressure inside the tube created by center vertical channel  5   a  and the downstream surface  48   a  of filter element  82   a  will also be negative. Likewise since circular channel  3   a  is in fluid flow relationship with center vertical channel  5   a  the pressure inside the tube created by circular channel  3   a  and the downstream surface  48   a  of filter element  82   a  will also be negative. Since the tube segments made up of vertical channels  4   a  and the downstream surface  48   a  of filter element  82   a  are in fluid flow relationship with the tube created by circular channel  3   a  and the downstream surface  48   a  of filter element  82   a , any air or liquid that flows from filter element  82   a  into vertical channels  4   a  will be sucked into circular channel  3   a , and then flow from circular channel  3   a  into center vertical channel  5   a , through back outlet port  6   a , through link port  11 , through outlet port  10 , into outlet tubing  53 , and into receiving blood bag  55 . This assures that filter elements  80   a ,  81   a , and  82   a  will completely wet, and that all of the air that was in first chamber  45 , filter elements  80   a ,  81   a , and  82   a , vertical channels  4   a , circular channel  3   a , center circular channel  5   a , back outlet port  6   a , link port  11 , outlet port  10 , and the interior of outlet tubing  53  will be forced into receiving blood bag  55 . Although vertical channels  4   a  are shown in the vertical orientation, they could be orientated at any angle from zero degrees to ninety degrees from vertical, as long as they are in fluid flow relationship with circular channel  3   a . Other channel designs such as the spiral channel filter underdrain disclosed in U.S. Ser. No. 08/524,049, U.S. Pat. No. 5,798,041, and entitled “an In-Line Liquid Filtration Device Usable for Blood, Blood Products and the Like”, could also be used in place of the design illustrated in FIG.  1 B. It is however, imperative that all channels be either directly or indirectly in fluid flow relationship with back outlet port  6   a.    
     Blood filtration will continue until feed blood bag  54  is empty. When feed blood bag  54  is empty it will be collapsed and therefore close the inlet end of inlet tubing  52 . Because outlet tubing  53  will be full of blood, and because the outside of receiving blood bag  55  is at atmospheric pressure, the pressure head in front outlet port  6 , and the pressure head in back outlet port  6   a  will be negative, as will be the pressure head in vertical channels  4 , circular channel  3 , center vertical channel  5 , vertical channels  4   a , circular channel  3   a , and center vertical channel  5   a , all of body  1 . Once blood flow has stopped the pressure drop across filter elements  80 ,  81 , and  82 , will fall to zero. The pressure drop across filter elements  80   a ,  81   a , and  82   a , will also fall to zero. Hence the pressure in first chamber  44  and first chamber  45  will become negative. Once the pressure in first chamber  44  falls below atmospheric pressure air will begin to flow from atmosphere through slots  21 , through sterilizing grade hydrophobic filter  41 , into first chamber  44 . The sterile air that enters first chamber  44  will bubble up to the top of first chamber  44 , thus causing first chamber  44  to drain from the top down. Because of the negative pressure in first chamber  45 , some of the air that bubbles to the top of first chamber  44  will pass through gap  26 , through front inlet channel  8 , through front cross port  7 , through back cross port  7   a , through gap  36 , through back inlet channel  8   a , into first chamber  45 , causing first chamber  45  to drain from the top down, and causing the blood in front inlet channel  8  to drain into first chamber  44 , and causing the blood in back inlet channel  8   a  to drain into first chamber  45 , and causing the blood in front cross port  7  and back cross port  7   a  to drain into both first chamber  44  and first chamber  45 . Because the air entering first chamber  44  bubbles to the top of first chamber  44 , thus draining first chamber  44  from the top down, vent filter element  41  can be located anywhere on flat surface  23  of front cover  20 . Filter elements  80 ,  81 ,  82 ,  80   a ,  81   a , and  82   a  will be plugged sufficiently at this point, therefore very little if any blood will be sucked from these filter elements by the negative pressure in front outlet port  6 , and by the negative pressure in back outlet port  6   a . Hence blood flow will stop after first chamber  44  and first chamber  45  have drained and blood will remain in filter elements  80 ,  81 ,  82 ,  80   a ,  81   a , and  82   a , and in vertical channels  4 , circular channel  3 , center vertical channel  5 , vertical channels  4   a , circular channel  3   a , and center vertical channel  5   a , and in front outlet port  6 , back outlet port  6   a , link port  11 , outlet port  10  all of body  1 , and in outlet tubing  53 . 
     The user can now close tube clamp  75  on outlet tubing  53  and then seal outlet tubing  53  above tube clamp  75 , and then cut outlet tubing  53  above the seal just made. Feed blood bag  54 , inlet tubing  52 , and filter device  40  can now be discarded in a safe manner. Outlet tubing  53  will have segments marked on them. The user can now seal the tubing at the segment marks. The blood that is left in outlet tubing  53  will be used for cross matching and for quality control purposes. 
     Referring to FIG. 2, with front outlet port  6  and back outlet port  6   a  at the very bottom of center vertical channels  5  and  5   a  respectively, the length of link port  11  is minimized, thereby minimizing the diameter of the pin (a minimum diameter is needed to prevent breakage of the pin) in the injection mold, thereby minimizing the wall thickness of partition wall  300  of body  1 , thereby reducing the cost of body  1 . 
     A second embodiment of the filtration device constructed in accordance with the principles of the present invention, could be constructed by replacing the back cover  30  of the first embodiment with a second front cover  20 . The second embodiment would work the same as the first embodiment, with the exception that after the feed blood bag is empty, air would enter first chamber  45  from the vent filter on the front cover  20  that replaces the back cover  30 . 
     The first and second embodiments of the present invention contain the following shortcoming if it is desired to seal filter elements  80 ,  81 , and  82  into first filter well  13  of body  1  by compressing the outer periphery of said filter elements between round filter support rib  25  of front cover  20  and front flat surface  2  of body  1 . Referring to FIG. 2, FIG.  4 B and FIG. 7, the peripheral compression seal contains a break at gap  26  of round filter support rib  25  of front cover  20 . Therefore a small portion of unfiltered blood will flow into the gap between outer wall  72  of round filter support rib  25  of front cover  20  and cylindrical surface  14  of body  1 . Likewise, referring to FIG. 1B, FIG. 5B, and FIG. 7, if it is desired to seal filter elements  80   a ,  81   a , and  82   a  into second filter well  13   a  of body  1  by compressing the outer periphery of said filter elements between round filter support rib  35  and back flat surface  2   a  of body  1 , said compression seal contains a break at gap  36  of round filter support rib  35  of back cover  30 . Therefore a small portion of unfiltered blood will flow into the gap between outer wall  73  of round filter support rib  35  of back cover  30  and cylindrical surface  14   a  of body  1 . The third embodiment constructed in accordance with the principles of the present invention overcomes these shortcomings. 
     FIG. 25 shows an exploded view of the components that comprise the third embodiment of the present invention. Referring to FIG. 25, body  101  replaces body  1  of the first and second embodiments of the present invention. Likewise, front cover  120  replaces front cover  20 , and back cover  130  replaces back cover  30  of the first and second embodiments of the present invention. The third embodiment also contains two filter compression rings  195 . 
     Referring to FIG. 22, body  101  is the same as body  1  shown in FIG. 1 a , FIG. 1B, and FIG. 2, with the exception that the front part of body  101  contains a counterbore in cylindrical surface  14 , bounded by surface  90  and surface  91 . The back part of body  101  shown in FIG. 25 also contains a corresponding counterbore. Referring to FIG.  23 A and FIG. 23B, front cover  120  is identical to front cover  20  shown in FIG.  4 A and FIG. 4B, with the exception that front cover  120  does not contain round filter support rib  25 . Referring to FIG.  24 A and FIG. 24B, back cover  130  is identical to back cover  30  shown in FIG.  5 A and FIG. 5B, with the exception that back cover  130  does not contain round filter support rib  35 . FIGS. 27A and 27B show filter compression ring  195 . Filter compression ring  195  is a hollow cylinder, and contains one or more notches  196  in face  197 . Each notch  196  is formed by two side walls  194  and an end wall  193 . FIG.  25  and FIG. 26 show filter compression rings  195  properly oriented. When properly oriented notches  196  provide a liquid and gas flow path between front inlet channel  8  and first chamber  44 , and provide a liquid and gas flow path between back inlet channel  8   a  and first chamber  45 , as shown in FIG.  26 . Only one notch  196  is necessary in compression ring  195  if compression ring  195  is properly aligned to front inlet channel  8 , and back inlet channel  8   a . Providing more than one notch  196  in filter compression ring  195  as shown in FIG. 27A, allows for some misalignment of filter compression ring  195  with respect to front inlet channel  8 , and back inlet channel  8   a , provided that the space between notches  196  is less than the width of front inlet channel  8  and back inlet channel  8   a . If filter compression ring  195  contains more than one notch  196 , said notches should be restricted to the top portion of filter compression ring  195  as shown in FIG.  25  and FIG. 27A, so that any blood that enters the notches during the filtration process can drain once filtration has stopped. 
     Referring to FIG. 22, FIG. 25, and FIG. 27 a  filter compression ring  195  should be sized so that outer wall  192  of filter compression ring  195  press fits into surface  90  of body  101 , and so that outer wall  192  of filter compression ring  195  press fits into surface  90   a  of body  101 , so that no gap will exist between outer wall  192  of filter compression ring  195  and surface  90  or surface  90   a  of body  101 . Filter compression ring  195  is preferably made from an injection moldable plastic, and is preferably made of a softer plastic than body  101  to facilitate pressing filter compression ring  195  into body  101 . Alternately filter compression ring  195  can be made of the same material as body  101 , and sealed to body  101  with a sonic weld, a glue bond, a solvent bond or a heat bond, or any other type of suitable bond. 
     Filter device  140  shown in FIG. 26 functions the same as filter device  40  shown in FIG.  7 . However the shortcomings of the first and second embodiments of the present invention as described above are overcome by the filter device shown in FIG. 26, because the filter compression rings provide a 360° compression seal for filter elements  80 ,  81 , and  82 , and for filter elements  80   a ,  81   a , and  82   a , and because the filter compression rings are press fitted into body  101 , unfiltered blood can not flow between the outer wall  192  of the filter compression rings and body  101 . 
     Referring to FIG. 22, with front outlet port  6  and back outlet port  6   a  at the very bottom of center vertical channels  5  and  5   a  respectively, the length of link port  11  is minimized, thereby minimizing the diameter of the pin (a minimum diameter is needed to prevent breakage of the pin) in the injection mold, thereby minimizing the wall thickness of the center section of body  101 , thereby reducing the cost of body  101 . 
     A fourth embodiment of the filtration device constructed in accordance with the principles of the present invention, could be constructed by replacing the back cover  130  of the third embodiment with a second front cover  120 . The fourth embodiment would work the same as the third embodiment, with the exception that after the feed blood bag is empty, air would enter first chamber  45  from the vent filter on the front cover  120  that replaces the back cover  130 . 
     A fifth embodiment of the filtration device constructed in accordance with the principles of the present invention, is shown in FIG.  10 A through FIG.  20 . Referring to FIG. 17 this embodiment includes the following major components: front cover  220 , body  201 , back cover  230 , filter elements  80 ,  81 ,  82 ,  80   a ,  81   a , and  82   a , and hydrophobic vent filter element  41 . 
     FIG. 10A, FIG. 11, and FIG. 12A show the front part of body  201 . The front part of body  201  contains a first filter well  213 , defined by flat surface  202  of partition wall  301  and cylindrical surface  214 . The front part of body  201  also contains side vertical channels  204 , circular channel  203 , and center vertical channel  205 . Preferably circular channel  203  is wider and deeper than side vertical channels  204 , and center vertical channel  205  is wider than circular channel  203 , and the same depth as circular channel  203 . The upper and lower ends of side vertical channels  204  are in fluid flow relation with circular channel  203 , and circular channel  203  is in fluid flow relation with center vertical channel  205 . Center vertical channel  205  is in fluid flow relation with front outlet port  206 . The upper central part of body  201  contains inlet tube socket  217 , and cross protrusion  219 . Inlet tube socket  217  contains inlet port  209 , and cross protrusion  219  contains a cross port, with the front half of the cross port labeled front cross port  207 , and the back half of the cross port labeled back cross port  207   a . The lower central part of body  201  contains outlet tube socket  218 . Outlet tube socket  218  contains outlet port  210 . Front outlet port  206  is in fluid flow relation with outlet port  210  through link port  211 . 
     FIG. 10B, and FIG. 12B show the back part of body  201 . The back part of body  201  contains a second filter well  213   a , defined by flat surface  202   a  of partition wall  301  and cylindrical surface  214   a . The back part of body  201  also contains side vertical channels  204   a , circular channel  203   a , and center vertical channel  205   a . Preferably circular channel  203   a  is wider and deeper than side vertical channels  204   a , and center vertical channel  205   a  is wider than circular channel  203   a , and the same depth as circular channel  203   a . The upper and lower ends of side vertical channels  204   a  are in fluid flow relation with circular channel  203   a , and circular channel  203   a  is in fluid flow relation with center vertical channel  205   a . Center vertical channel  205   a  is in fluid flow relation with back outlet port  206   a . The upper central part of body  201  contains inlet tube socket  217 , and cross protrusion  219 . Inlet tube socket  217  contains inlet port  209 , and cross protrusion  219  contains a cross port, with the front half of the cross port labeled front cross port  207 , and the back half of the cross port labeled back cross port  207   a . The lower central part of body  201  contains outlet tube socket  218 . Outlet tube socket  218  contains outlet port  210 . Back outlet port  206   a  is in fluid flow relation with outlet port  210  through link port  211 . Front outlet port  206  is a through hole with the front half labeled front outlet port  206 , and the back half labeled back outlet port  206   a . As shown in FIG. 10A, FIG. 10B, FIG.  12 A and FIG. 12B the back part of body  201  is a mirror image of the front part of body  201 . Body  201  is preferably made from an injection moldable medical grade plastic such acrylic, polycarbonate, polysulfone, polypropylene, polyethylene, but is not limited to these materials. 
     FIG. 13A, FIG. 13B, and FIG. 14 show front cover  220 . Front cover  220  is round in shape to match the shape of body  201 , (if body  201  was square, then front cover  220  would also be square) and contains boss  229  at its upper end. The interior of front cover  220  contains flat surface  223 . Vertical filter support ribs  224  protrude from flat surface  223 . The vertical filter support ribs  224  could be replaced with ribs oriented in a direction other than vertical, or with a pattern of round pins, or with a pattern or rectangular pins, or with a pattern of concentric rings with gaps in the rings, or with any other filter support means that does not contain a closed loop. Outer rib  227  also protrudes from flat surface  223  and follows the outer periphery of front cover  220 . Although it is not necessary for front cover  220  to contain outer rib  227 , outer rib  227  acts as an alignment rib during assembly, and as a flash trap to contain flash when front cover  220  is assembled to body  201 . Front cover  220  also contains round filter support rib  225 . Round filter support rib  225  does not contain a gap, as round filter support rib  25  of front cover  20  of the first embodiment does. Front cover  220  also contains through slots  221 , and vent filter bonding area  228 . Although filter bonding area  228  is shown round for bonding a round vent filter, the vent filter could be square or any other shape, and then the filter bonding area  228  would conform to the shape of the vent filter. Through slots  221  are shown as vertical slots, they could be replaced by a pattern of round holes, or a pattern of square holes, or any other pattern of through holes that provide adequate filter support, and also provide air flow communication between the face of the vent filter that is bonded to flat surface  223 , and to the outside atmosphere of front cover  220 . Referring to FIG. 13B, FIG. 14, and FIG. 18, front cover  220  contains chamber  262  bounded by side walls  274 , top wall  277 , end wall  278 , and end wall  279 . Front cover  220  also contains port  263  and port  265 . Port  263  is in fluid flow and air flow communication with chamber  262  through port  265 . Referring to FIG. 14, front cover  220  contains energy director  266  if it is desired to bond front cover  220  to body  201  using an energy director ultrasonic weld. FIG. 18 shows vent filter element  41  bonded to front cover  220 . Referring to FIG. 16, centerline  270  shows the center of the seal between front cover  220  and body  201 . The seal could be an ultrasonic weld, a glue bond, a heat bond, a solvent bond, or any other type of leak tight bond. Referring to FIG. 13A, the outside of front cover  220  contains flat surface  222 . Front cover  220  also contains weld rib  260  which protrudes above flat surface  222 . The centerline of weld rib  260  is a mirror image of centerline  270 , the center of the seal between front cover  220  and body  201 . The outside of front cover  220  also contains protrusion  261 , the outer wall of chamber  262  and port  265 . Weld rib  260  is used to transmit sonic energy from a flat ultrasonic horn to energy director  266  (shown in FIG. 14) of front cover  220  during the process of welding front cover  220  to body  201 , when an ultrasonic weld is used. Front cover  220  is preferably made from an injection moldable medical grade plastic such acrylic, polycarbonate, polysulfone, polypropylene, polyethylene, but is not limited to these materials. Front cover  220  is preferably made from the same material that body  201  is made of. 
     FIG. 15A, and FIG. 15B, show back cover  230 . Back cover  230  is round in shape to match the shape of body  201 , (if body  201  was square, then back cover  230  would also be square) and contains boss  239  at its upper end. The interior of back cover  230  contains flat surface  233 . Vertical filter support ribs  234  protrude from flat surface  233 . The vertical filter support ribs  234  could be replaced with ribs oriented in a direction other than vertical, or with a pattern of round pins, or with a pattern or rectangular pins, or with a pattern of concentric rings with gaps in the rings, or with any other filter support means that does not contain a closed loop. Outer rib  237  also protrudes from flat surface  233  and follows the outer periphery of back cover  230 . Although it is not necessary for back cover  230  to contain outer rib  237 , outer rib  237  acts as an alignment rib during assembly, and as a flash trap to contain flash when back cover  230  is assembled to body  201 . Back cover  230  also contains round filter support rib  235 . Round filter support rib  235  does not contains a gap, as round filter support rib of back cover  30  of the first embodiment does. Referring to FIG. 15A, FIG. 15B, and FIG. 18, back cover  230  contains chamber  262   a  bounded by side walls  274   a , top wall  277   a , end wall  278   a , and end wall  279   a . Back cover  230  also contains port  263   a  and port  265   a . Port  263   a  is in fluid flow and air flow communication with chamber  262   a  through port  265   a . Back cover  230  also contains an energy director  266   a  (not shown, like energy director  266  of front cover  220 ) if it is desired to bond back cover  230  to body  201  using an energy director ultrasonic weld. Back cover  230  seals to body  201  along a center line like centerline  270  shown in FIG. 16 for front cover  220 . The seal could be an ultrasonic weld, a glue bond, a heat bond, a solvent bond, or any other type of leak tight bond. Referring to FIG. 15A, the outside of back cover  230  contains flat surface  232 . Back cover  230  also contains weld rib  260   a  which protrudes above flat surface  232 . The centerline of weld rib  260   a  is a mirror image of centerline  270 , the center of the seal between back cover  230  and body  201 . The outside of back cover  230  also contains protrusion  261   a , the outer wall of chamber  262   a  and port  265   a . Weld rib  260   a  is used to transmit sonic energy from a flat ultrasonic horn to energy director  266   a  of back cover  230  during the process of welding back cover  230  to body  201 , when an ultrasonic weld is used. Back cover  230  is preferably made from an injection moldable medical grade plastic such acrylic, polycarbonate, polysulfone, polypropylene, polyethylene, but is not limited to these materials. Back cover  230  is preferably made from the same material that body  201  is made of. Back cover  230  is identical to front cover  220  with the exception that back cover  230  does not contain a vent filter. 
     FIG. 17 shows an exploded view of the components that comprise filter device  240 . The components are body  201 , front cover  220 , back cover  230 , vent filter element  41 , and filter elements  80 ,  81 , and  82 , and filter elements  80   a ,  81   a , and  82   a . FIG.  18  and FIG. 19 show filter device  240  in the assembled state. Referring to FIG. 10A, FIG. 10B, FIG. 11, FIG. 13B, FIG. 14 FIG. 15B, FIG. 16, FIG. 17, FIG. 18, and FIG. 19, the components that comprise filter device  240  are assembled as follows. The outer periphery of vent filter element  41  is sealed to front cover  220  at filter bonding area  228 . The seal is preferably a heat seal but could be an ultrasonic seal, a glue bond, a solvent bond, or any other type of bond that will produce a leak tight seal capable of maintaining sterility. Filter element  41  is a hydrophobic filter with a pore size of 0.2 μ or smaller to maintain sterility. Filter elements  80 ,  81 , and  82  are placed into first filter well  213 . Front cover  220  is then bonded to body  201  so that edge  212  of body  201  is bonded to front cover  220  along centerline  270  shown in FIG.  16 . The seal between front cover  220  and body  201  forms a double closed loop. The first closed loop encloses the outer periphery of first filter well  213  of body  201 , thereby creating a closed first chamber  244  in first filter well  213 . The second closed loop encloses the outer periphery of front cross port  207 , and the outer periphery of port  263 , thereby creating a flow path from inlet port  209 , through front cross port  207 , through port  263 , through port  265 , into chamber  262 , into first chamber  244  of first filter well  213 . If first chamber  244  is made deeper chamber  262  may be eliminated, and the flow path would flow from inlet port  209 , through port  263 , through port  265 , into first chamber  244 . Outer rib  227  of front cover  220  aligns front cover  220  to body  201  during the assembly procedure and also acts as a flash trap. The bond between front cover  220  and body  201  is preferably an ultrasonic seal but could be a glue bond, a heat bond, a solvent bond or any other type of bond that creates a leak tight seal. Filter elements  80 ,  81 , and  82  are sealed to body  201  with a compression seal between the outer edges  84 ,  85 , and  86  of filter elements  80 ,  81 , and  82  respectively, and cylindrical surface  214  of body  201  in the filter device  240  shown. This seal could be augmented or replaced by a compression seal created by compressing the outer periphery of filter elements  80 ,  81 , and  82  between round filter support rib  225  of front cover  220  and flat surface  202  of body  201 . Filter elements  80 ,  81 , and  82  also could be sealed to body  201  with a glue seal, a heat seal, or any other type of seal that eliminates bypass around filter elements  80 ,  81 , and  82 . Filter device  240  is shown with 3 filter elements  80 ,  81 , and  82  in first filter well  213 . However any number of filter elements greater than or equal to one could be used. The number of filter elements used is determined by the filter type and the fluid being filtered. The same number of filter elements that were placed into first filter well  213  of body  201  are now placed into second filter well  213   a  of body  201 , and are designated as filter elements  80   a ,  81   a , and  82   a . These filter elements are sealed to body  201  using the same method that was used to seal filter elements  80 ,  81 , and  82  to first filter well  213 . Back cover  230  is then bonded to body  201  so that edge  212   a  of body  201  is bonded to back cover  230  along the same path as centerline  270  shown in FIG.  16 . The seal between back cover  230  and body  201  forms a double closed loop. The first closed loop encloses the outer periphery of second filter well  213   a  of body  201 , thereby creating a closed first chamber  245  in second filter well  213   a . The second closed loop encloses the outer periphery of back cross port  207   a , and the outer periphery of port  263   a , thereby creating a flow path from inlet port  209 , through back cross port  207   a , through port  263   a , through port  265   a , into chamber  262   a , into first chamber  245  of second filter well  213   a . If first chamber  245  is made deeper chamber  262   a  may be eliminated, and the flow path would flow from inlet port  209 , through back cross port  207   a , through port  263   a , through port  265   a , into first chamber  245 . Outer rib  237  of back cover  230  aligns back cover  230  to body  201  during the assembly procedure and also acts as a flash trap. The bond between back cover  230  and body  201  is preferably an ultrasonic seal but could be a glue bond, a heat bond, a solvent bond or any other type of bond that creates a leak tight seal. 
     Referring to FIG. 13B, FIG. 17, FIG. 18, and FIG. 19, the assembled filter device  240  contains first chamber  244  bounded by flat surface  223  of front cover  220 , inner surface  277  of round filter support rib  225  of front cover  220 , and the upstream surface  46  of the first filter element  80  in first filter well  213  of body  201 . Referring to FIG. 15B, FIG. 17, and FIG. 18, the assembled filter device  240  also contains first chamber  245  bounded by flat surface  233  of back cover  230 , inner surface  271  of round rib  235  of back cover  230 , and the upstream surface  46   a  of the first filter element  80   a  in second filter well  213   a  of body  201 . Referring to FIG. 18, in the assembled filter device  240 , front cross port  207  of body  201  is in fluid flow communication and air flow communication with first chamber  244  through port  263 , port  265 , and chamber  262  of front cover  220 . Referring to FIG. 18, in the assembled filter device  240 , back cross port  207   a  of body  201  is in fluid flow communication and air flow communication with first chamber  245  through port  263   a , port  265   a , and chamber  262   a  of back cover  220 . 
     Referring to FIG. 10 a , FIG. 14, FIG.  17  and FIG. 18, the assembled filter device  240  contains second chamber  247  of first filter well  213  bounded by the downstream surface  48  of the last filter element  82  in first filter well  213  of body  201 , and by center vertical channel  205 , circular channel  203 , and side vertical channels  204 . Second chamber  247  of first filter well  213  contains front outlet port  206 . Referring to FIG. 10 b , FIG.  17  and FIG. 18, the assembled filter device  240  contains second chamber  247   a  of second filter well  213   a  bounded by the downstream surface  48   a  of the last filter element  82   a  in second filter well  213   a  of body  201 , and by center vertical channel  205   a , circular channel  203   a , and side vertical channels  204   a . Second chamber  247   a  of second filter well  213   a  contains back outlet port  206   a.    
     Referring to FIG. 20 one end of a length of outlet tubing  53  is bonded to outlet tube socket  218  of body  201 , with the other end of said outlet tubing bonded to an empty blood bag  55 . Another length of inlet tubing  52  is bonded to inlet tube socket  217  of body  201 . The end user will purchase the assembly of filter device  240 , inlet tubing  52 , outlet tubing  53 , and receiving blood bag  55 , assembled and sterile. The assembly will also contain an inlet tubing clamp  74  on inlet tubing  52 , and an outlet tubing clamp  75  on outlet tubing  53 . 
     In FIG. 20 the filter device  240  is in an operational assembly with inlet tubing  52 , outlet tubing  53 , feed blood bag  54 , receiving blood bag  55 , inlet tube clamp  74 , and outlet tube clamp  75 . Preferably, the user will purchase the assembly of FIG. 20 sterilized without feed blood bag  54  with the inlet end of inlet tubing  52  sealed to maintain system sterility. For performing filtration the user will first close inlet tube clamp  74  close to the inlet end of inlet tubing  52 . Next the user will make sure that outlet tube clamp  75  is open. Inlet tubing  52  is now bonded by the user to a pigtail on feed blood bag  54  using a sterile docking device as is well known in the art. 
     Once the sterile docking connection is made the user will hang feed blood bag  54  from hook  57  on blood bag pole  56 . Receiving blood bag  55  should be placed on a surface such as a table top or the like. The complete assembly  260  ready for filtration is illustrated in FIG.  20 . 
     Referring to FIG. 10A, FIG. 10B, FIG. 18, FIG.  19  and FIG. 20 the filtration is performed as follows. The user opens inlet tube clamp  74 . Gravity now forces blood to flow from feed blood bag  54 , through inlet tubing  52 , through inlet port  209  of body  201 . After passing through inlet port  209 , a portion of the blood passes through front cross port  207 , while the remainder of the blood passes through back cross port  207   a . The portion of the blood that passes through front cross port  207 , then passes through port  263 , through port  265 , into chamber  262 , and then into first chamber  244 . The portion of the blood that passes through back cross port  207   a , then passes through port  263   a , through port  265   a , into chamber  262   a , and then into first chamber  245 . A portion of the air that was in inlet tubing  52  and inlet port  209  before blood flow started will be pushed ahead of the blood, through front cross port  207 , through port  263 , through port  265 , into chamber  262 , and then into first chamber  244 . The remainder of the air that was in inlet tubing  52  and inlet port  9  before blood flow started will be pushed ahead of the blood, through back cross port  207   a , through port  263   a , thorough port  265   a , into chamber  262   a , and then into first chamber  245 . Because the usable surface area of hydrophobic filter  41  is much smaller than the usable surface area of filter elements  80 ,  81 , and  82 ; and because the pressure drop across sterilizing grade hydrophobic filter  41  is much greater per unit volume of air flow per unit surface area of filter material than the combined pressure drop across filter elements  80 ,  81 , and  82  per unit volume of air flow per unit surface area of filter material, only a very small portion of the air that was in inlet tubing  52 , inlet port  9 , front cross port  207 , port  263 , and port  265  before blood flow started, will pass through hydrophobic filter  41 , and then through slots  221  of front cover  220  to atmosphere. 
     As first chamber  244  fills from the bottom up most of the air in first chamber  244  and in chamber  262  will be forced through filter elements  80 ,  81 , and  82 , for the same reasons described in the previous paragraph. This initial air will flow into vertical channels  204 , circular channel  203 , and center vertical channel  205 , and then flow through front outlet port  206 , through link port  211 , through outlet port  210 , into outlet tubing  53 , into receiving blood bag  55 . Filter elements  80 ,  81 , and  82  will also wet from the bottom up. The air that is initially in filter elements  80 ,  81 , and  82  will be displaced by blood and flow into vertical channels  204 , circular channel  203 , and center vertical channel  205 , and then flow through front outlet port  206 , through link port  211 , through outlet port  210 , into outlet tubing  53 , into receiving blood bag  55 . Because the combined volume of first chamber  244  and chamber  262  is small, and the flow rate of blood entering first chamber  244  is much greater than the initial flow rate of blood through filter elements  80 ,  81 , and  82 , first chamber  244  will fill in a small fraction of the time that it takes to wet filter elements  80 ,  81 , and  82 . The pressure head at the bottom of first chamber  244  will be larger than the pressure head at the top of chamber  244 , because of the height difference between the top and bottom of first chamber  244 . Therefore liquid will start to come through filter element  82  from the bottom up. As liquid starts to come through filter element  82  from the bottom up vertical channels  204 , circular channel  203 , and center vertical channel  205 , of body  201  will fill from the bottom up. Because the total volume of these channels in is small (to minimize holdup) the channels may fill with blood (from the bottom up) before the upper part of filter element  82  has wet with blood. Once blood starts to flow from center vertical channel  205  of body  201 , into front outlet port  206  of body  201 , through link port  211  of body  201 , into outlet tubing  53 , and starts to flow down outlet tubing  53  toward receiving blood bag  55 , the pressure in front outlet port  206  will become negative. Because center vertical channel  205  is in fluid flow relationship with front outlet port  206 , the pressure inside the tube created by center vertical channel  205  and downstream surface  48  of filter element  82  will also be negative. Likewise since circular channel  203  is in fluid flow relationship with center vertical channel  205  the pressure inside the tube created by circular channel  203  and downstream surface  48  of filter element  82  will also be negative. Since the tube segments made up of vertical channels  204  and downstream surface  48  of filter element  82  are in fluid flow relationship with the tube created by circular channel  203  and downstream surface  48  of filter element  82 , any air or liquid that flows from filter element  82  into vertical channels  204  will be sucked into circular channel  203 , and then flow from circular channel  203  into center vertical channel  205 , through front outlet port  206 , through link port  211 , through outlet port  210 , into outlet tubing  53 , and into receiving blood bag  55 . This assures that filter elements  80 ,  81 , and  82  will completely wet, and that all of the air that was in first chamber  244  and chamber  262 , filter elements  80 ,  81 , and  82 , vertical channels  204 , circular channel  203 , center circular channel  205 , front outlet port  206 , link port  211 , outlet port  210 , and the interior of outlet tubing  53  will be forced into receiving blood bag  55 . Although vertical channels  204  are shown in the vertical orientation, they could be orientated at any angle from zero degrees to ninety degrees from vertical, as long as they are in fluid flow relationship with circular channel  3 . Other channel designs such as the spiral channel filter underdrain disclosed in U.S. Ser. No. 08/524,049, U.S. Pat. No. 5,798,041, and entitled “an In-Line Liquid Filtration Device Usable for Blood, Blood Products and the Like”, could also be used in place of the design illustrated in FIG.  10 A. It is however, imperative that all channels be either directly or indirectly in fluid flow relationship with front outlet port  206 . 
     The portion of blood from feed blood bag  54  which flows through back cross port  7   a , through port  263   a , through port  265   a , into chamber  262   a , into first chamber  245 , will fill first chamber  245  from the bottom up forcing all of the air in first chamber  45  and chamber  262   a  through filter elements  80   a ,  81   a , and  82   a . This initial air will flow into vertical channels  204   a , circular channel  203   a , and center vertical channel  205   a , and then flow through back outlet port  206   a , through link port  211 , through outlet port  210 , into outlet tubing  53 , into receiving blood bag  55 . Filter elements  80   a ,  81   a , and  82   a  will also wet from the bottom up. The air that is initially in filter elements  80   a ,  81   a , and  82   a  will be displaced by blood and flow into vertical channels  204   a , circular channel  203   a , and center vertical channel  205   a , and then flow through outlet port  206   a , through link port  211 , through outlet port  210 , into outlet tubing  53 , into receiving blood bag  55 . Because the combined volume of first chamber  245  and chamber  262   a  is small, and the flow rate of blood entering chamber  262   a  and first chamber  245  is much greater than the initial flow rate of blood through filter elements  80   a ,  81   a , and  82   a , first chamber  245  and chamber  262   a  will fill in a small fraction of the time that it takes to wet filter elements  80   a ,  81   a , and  82   a . The pressure head at the bottom of first chamber  245  will be larger than the pressure head at the top of first chamber  245 , because of the height difference between the top and bottom of first chamber  245 . Therefore liquid will start to come through filter element  82   a  from the bottom up. As liquid starts to come through filter element  82   a  from the bottom up vertical channels  204   a , circular channel  203   a , and center vertical channel  205   a , of body  201  will fill from the bottom up. Because the total volume of these channels in is small (to minimize holdup) the channels may fill with blood (from the bottom up) before the upper part of filter element  82   a  has wet with blood. Once blood starts to flow from center vertical channel  205   a  of body  201 , into back outlet port  206   a  of body  201 , through link port  211  of body  201 , into outlet tubing  53 , and starts to flow down outlet tubing  53  toward receiving blood bag  55 , the pressure in back outlet port  206   a  will become negative. Because center vertical channel  205   a  is in fluid flow relationship with back outlet port  206   a , the pressure inside the tube created by center vertical channel  205   a  and the downstream surface  48   a  of filter element  82   a  will also be negative. Likewise since circular channel  203   a  is in fluid flow relationship with center vertical channel  205   a  the pressure inside the tube created by circular channel  203   a  and the downstream surface  48   a  of filter element  82   a  will also be negative. Since the tube segments made up of vertical channels  204   a  and the downstream surface  48   a  of filter element  82   a  are in fluid flow relationship with the tube created by circular channel  203   a  and the downstream surface  48   a  of filter element  82   a , any air or liquid that flows from filter element  82   a  into vertical channels  204   a  will be sucked into circular channel  203   a , and then flow from circular channel  203   a  into center vertical channel  205   a , through back outlet port  206   a , through link port  211 , through outlet port  210 , into outlet tubing  53 , and into receiving blood bag  55 . This assures that filter elements  80   a ,  81   a , and  82   a  will completely wet, and that all of the air that was in chamber  245 , chamber  262   a , filter elements  80   a ,  81   a , and  82   a , vertical channels  204   a , circular channel  203   a , center vertical channel  205   a , back outlet port  206   a , link port  211 , outlet port  210 , and the interior of outlet tubing  53  will be forced into receiving blood bag  55 . Although vertical channels  204   a  are shown in the vertical orientation, they could be orientated at any angle from zero degrees to ninety degrees from vertical, as long as they are in fluid flow relationship with circular channel  203   a . Other channel designs such as the spiral channel filter underdrain disclosed in U.S. Ser. No. 08/524,049, U.S. Pat. No. 5,798,041, and entitled “an In-Line Liquid Filtration Device Usable for Blood, Blood Products and the Like”, could also be used in place of the design illustrated in FIG.  10 B. It is however, imperative that all channels be either directly or indirectly in fluid flow relationship with back outlet port  206   a.    
     Blood filtration will continue until feed blood bag  54  is empty. When feed blood bag  54  is empty it will be collapsed and therefore close the inlet end of inlet tubing  52 . Because outlet tubing  53  will be full of blood, and because the outside of receiving blood bag  55  is at atmospheric pressure, the pressure head in front outlet port  206 , and the pressure head in back outlet port  206   a  will be negative, as will be the pressure head in vertical channels  204 , circular channel  203 , center vertical channel  205 , vertical channels  204   a , circular channel  203   a , and center vertical channel  205   a , all of body  201 . Once blood flow has stopped the pressure drop across filter elements  80 ,  81 , and  82 , will fall to zero. The pressure drop across filter elements  80   a ,  81   a , and  82   a , will also fall to zero. Hence the pressure in first chamber  244  and chamber  262 , and the pressure in first chamber  245  and chamber  262   a  will become negative. Once the pressure in chamber  244  and chamber  262  falls below atmospheric pressure air will begin to flow from atmosphere through slots  221 , through sterilizing grade hydrophobic filter  41 , into first chamber  244 . The sterile air that enters first chamber  244  will bubble up to the top of first chamber  244  and chamber  262 , thus causing first chamber  244  and chamber  262  to drain from the top down. Because of the negative pressure in first chamber  245 , some of the air that bubbles to the top of first chamber  244  will pass through port  265 , through port  263 , through front cross port  207 , through back cross port  207   a , through port  263   a , through port  265   a , into chamber  262   a  and first chamber  245 , causing chamber  262   a  and first chamber  245  to drain from the top down, and causing the blood in port  263  and port  265  to drain into chamber  262 , and causing the blood in port  263   a  and port  265   a  to drain into chamber  262   a , and causing the blood in front cross port  207  and back cross port  207   a  to drain into both chamber  262  and chamber  262   a . Because the air entering first chamber  244  bubbles to the top of first chamber  244  and to the top of chamber  262 , thus draining first chamber  244  and chamber  262  from the top down, vent filter element  41  can be located anywhere on flat surface  223  of front cover  220 . Filter elements  80 ,  81 ,  82 ,  80   a ,  81   a , and  82   a  will be plugged sufficiently at this point, therefore very little if any blood will be sucked from these filter elements by the negative pressure in front outlet port  206 , and by the negative pressure in back outlet port  206   a . Hence blood flow will stop after first chamber  244  and chamber  262 , and after first chamber  245  and chamber  262   a  have drained and blood will remain in filter elements  80 ,  81 ,  82 ,  80   a ,  81   a , and  82   a , and in vertical channels  204 , circular channel  203 , center vertical channel  205 , vertical channels  204   a , circular channel  203   a , and center vertical channel  205   a , and in front outlet port  206 , back outlet port  206   a , link port  211 , outlet port  210 , all of body  201 , and in outlet tubing  53 . 
     The user can now close tube clamp  75  on outlet tubing  53  and then seal outlet tubing  53  above tube clamp  75 , and then cut outlet tubing  53  above the seal just made. Feed blood bag  54 , inlet tubing  52 , and filter device  240  can now be discarded in a safe manner. Outlet tubing  53  will have segments marked on it. The user can now seal the tubing at the segment marks. The blood that is left in outlet tubing  53  will be used for cross matching and for quality control purposes. 
     Referring to FIG. 10A, FIG. 10B, FIG. 13B, FIG. 15B, and FIG. 18, front cover  220  and back cover  230  of filter device  240  provide a 360° continuous filter compression seal via round filter support rib  225  and round filter support rib  235  respectively. Because unfiltered blood enters chamber  262  and first chamber  244  on the inside of round filter support rib  225 , unfiltered blood is prevented from entering the gap between the outside of round filter support rib  225  of front cover  220  and cylindrical surface  214  of body  201 . Likewise, unfiltered blood enters chamber  262   a  and first chamber  245  on the inside of round filter support rib  235 , thus unfiltered blood is prevented from entering the gap between the outside of round filter support rib  235  of back cover  230  and cylindrical surface  214   a  of body  201 . Hence the fifth embodiment of the present invention overcomes the shortcomings of the first two embodiments of the present invention, with the added benefit that the two filter compression rings of the third embodiment are not required in the fifth embodiment. 
     Referring to FIG. 11, with front outlet port  206  and back outlet port  206   a  at the very bottom of center vertical channels  205  and  205   a  respectively, the length of link port  211  is minimized, thereby minimizing the diameter of the pin (a minimum diameter is needed to prevent breakage of the pin) in the injection mold, thereby minimizing the wall thickness of partition wall  301  of body  201 , thereby reducing the cost of body  201 . 
     A sixth embodiment of the filtration device constructed in accordance with the principles of the present invention, could be constructed by replacing the back cover  230  of the fifth embodiment with a second front cover  220 . The sixth embodiment would work the same as the fifth embodiment, with the exception that after the feed blood bag is empty, air would enter first chamber  245  and chamber  262   a  from the vent filter on the front cover  220  that replaces the back cover  230 . 
     A seventh embodiment of the filtration device constructed in accordance with the principles of the present invention, is shown in FIG. 28 a , FIG. 28 b , FIG. 29, FIG. 30, and FIG.  31 . FIG. 30 shows an exploded view of the components that comprise filter device  440 . Filter device  440  includes the following major components: front cover  20 , body  401 , back cover  30 , filter elements  80 ,  81 ,  82 ,  80   a ,  81   a , and  82   a , and hydrophobic vent filter element  41 . The only difference between filter device  40  of the first embodiment, shown in FIG. 6, and filter device  440  of the seventh embodiment, shown in FIG. 30, is that body  1  of the first embodiment is replaced with body  401  in the seventh embodiment. 
     Referring to FIG. 1, FIG. 2, FIG. 28 a , FIG. 28 b , and FIG. 29, body  401  is identical to body  1  with the following exceptions. Side vertical channels  4 , circular channel  3 , and center vertical channel  5  of front flat surface  2  of partition wall  300  of body  1  are eliminated from body  401 . Referring to FIG. 28 a  and FIG. 29, the front part of body  401  replaces these components with well  469 , defined by flat surface  489  of partition wall  300 , and side wall  488  of partition wall  300 . Vertical filter support ribs  498  protrude from flat surface  489  of partition wall  300 . A gap must exist between the top of vertical filter support ribs  498  and side wall  488 . The gap should small enough to provide the proper support for filter elements  80 ,  81 , and  82 , but large enough to allow liquid or gas to flow through the gap to the top of vertical channel  487 . The top face of filter support ribs  498  should lie in the same plane as flat surface  2  of partition wall  300 . Vertical filter support ribs  498  could be replaced with a pattern of round pins, or with a pattern or rectangular pins, or with any other filter support means that will allow air to bubble to the top of well  469 . Body  401  contains two vertical filter support ribs  499  that are attached to side wall  488  at the bottom of side wall  488 . A gap must exist between the top of vertical support ribs  499  and side wall  488 . Vertical channel  487  is bounded by the side walls of vertical filter support ribs  499  adjacent to channel  487 , and by flat surface  489 . The bottom of vertical channel  487  is in fluid flow communication with outlet port  10  via link port  11  and front outlet port  6 . The top of vertical channel  487  is open. Referring to FIG. 28 b , the back face of partition wall  300  of body  401  is a mirror image of the front face of partition wall  300  of body  401  just described. 
     The components that comprise filter device  440  are assembled in the same manner as those of filter device  40  as described above for the first embodiment. 
     Referring to FIG. 4B, FIG. 30, and FIG. 31, the assembled filter device  440  contains first chamber  44  of first filter well  13  bounded by flat surface  23  of front cover  20 , inner surface  77  of round rib  25  of front cover  20 , and the upstream surface  46  of the first filter element  80  in first filter well  13  of body  401 . Referring to FIG. 5B, FIG. 30, and FIG. 31, the assembled filter device  440  also contains first chamber  45  of second filter well  13   a  bounded by flat surface  33  of back cover  30 , inner surface  71  of round rib  35  of back cover  30 , and the upstream surface  46   a  of the first filter element  80   a  in second filter well  13   a  of body  401 . Referring to FIG.  3 A and FIG. 31, in the assembled filter device  440 , front inlet channel  8  becomes a closed channel bounded by side walls  15  and wall  16  of body  401 , and by flat surface  23  of front cover  20 . Referring to FIG. 31, front inlet channel  8  places first chamber  44  in fluid flow communication, and in air flow communication with front cross port  7 . Referring to FIG.  3 B and FIG. 31, in the assembled filter device  440 , back inlet channel  8   a  becomes a closed channel bounded by side walls  15   a  and wall  16   a  of body  401 , and by flat surface  33  of back cover  30 . Referring to FIG. 31, back inlet channel  8   a  places first chamber  45  in fluid flow communication, and in air flow communication with back cross port  7   a.    
     Referring to FIG. 28 a , FIG. 29, FIG.  30  and FIG. 31, the assembled filter device  440  contains second chamber  447  of first filter well  13  bounded by the downstream surface  48  of the last filter element  82  in first filter well  13  of body  401 , and by well  469 . Second chamber  447  of first filter well  13  contains vertical channel  487 , vertical filter support ribs  499 , vertical filter support ribs  498 , and front outlet port  6 . As shown in FIG. 28 a  and FIG. 29, the portion of well  469  outside of vertical channel  487  is an open well with a pattern of vertical filter support ribs  498  protruding from flat surface  489 . The space between vertical filter support ribs  498  should be small enough to provide the proper support for filter elements  80 ,  81 , and  82 , but large enough to allow gas, or gas bubbles in liquid to freely flow vertically through second chamber  447 , between vertical filter support ribs  498 . Furthermore, the height of vertical filter support ribs  498  and  499  should be high enough to allow gas, or gas bubbles in liquid to freely flow vertically through second chamber  447 , between vertical filter support ribs  498 . Referring to FIG. 28 b , FIG.  30  and FIG. 31, the assembled filter device  440  contains second chamber  447   a  of second filter well  13   a  bounded by the downstream surface  48   a  of the last filter element  82   a  in second filter well  13   a  of body  401 , and by well  469   a . Second chamber  447   a  of second filter well  13   a  contains vertical channel  487   a , vertical filter support ribs  499   a , vertical filter support ribs  498   a , and back outlet port  6   a . As shown in FIG. 28 b  the portion of well  469   a  outside of vertical channel  487   a  is an open well with a pattern of vertical filter support ribs  498   a  protruding from flat surface  489   a . The space between vertical filter support ribs  498   a  should be small enough to provide the proper support for filter elements  80 ,  81 , and  82 , but large enough to allow gas, or gas bubbles in liquid to freely flow vertically through second chamber  447   a , between vertical filter support ribs  498   a . Furthermore, the height of vertical filter support ribs  498  and  499  should be high enough to allow gas, or gas bubbles in liquid to freely flow vertically through second chamber  447 , between vertical filter support ribs  498 . 
     Filter device  440  could replace filter device  40  of assembly  60  shown in FIG.  9 . Referring to FIG. 28A, FIG. 4B, FIG. 5B, FIG. 9, and FIG. 31 the filtration with filter device  440  replacing filter device  40  in FIG. 9 is performed as follows. The user opens inlet tube clamp  74 . Gravity now forces blood to flow from feed blood bag  54 , through inlet tubing  52 , through inlet port  9  of body  401 . After passing through inlet port  9 , a portion of the blood passes through front cross port  7 , while the remainder of the blood passes through back cross port  7   a . The portion of the blood that passes through front cross port  7 , then passes through front inlet channel  8 , through gap  26  of front cover  20 , into first chamber  44  of filter device  440 . The portion of the blood that passes through back cross port  7   a , then passes through back inlet channel  8   a , through gap  36  of back cover  30 , into first chamber  45  of filter device  440 . A portion of the air that was in inlet tubing  52  and inlet port  9  before blood flow started will be pushed ahead of the blood, through front cross port  7 , through front inlet channel  8 , through gap  26  of front cover  20 , into first chamber  44  of filter device  440 . The remainder of the air that was in inlet tubing  52  and inlet port  9  before blood flow started will be pushed ahead of the blood, through back cross port  7   a , through back inlet channel  8   a , through gap  36  of back cover  30 , into first chamber  45  of filter device  440 . Because the usable surface area of hydrophobic filter  41  is much smaller than the usable surface area of filter elements  80 ,  81 , and  82 ; and because the pressure drop across sterilizing grade hydrophobic filter  41  is much greater per unit volume of air flow per unit surface area of filter material than the combined pressure drop across filter elements  80 ,  81 , and  82  per unit volume of air flow per unit surface area of filter material, only a very small portion of the air that was in inlet tubing  52 , inlet port  9 , front cross port  7 , and front inlet channel  8  before blood flow started, will pass through hydrophobic filter  41 , and then through slots  21  of front cover  20  to atmosphere. Therefore, most of the air that is forced into first chamber  44  by blood flow from the blood bag, and most of the air that was initially in first chamber  44  will be forced by the positive pressure (due to the blood flow) in first chamber  44 , through filter elements  80 ,  81 , and  82 , into second chamber  447 , through vertical channel  487 , through front outlet port  6 , through link port  11 , through outlet port  10 , through outlet tubing  53 , into receiving blood bag  55 ; and all of the air that is forced into first chamber  45  by blood flow from the blood bag, and all of the air that was initially in first chamber  45  will be forced by the positive pressure (due to the blood flow) in first chamber  45 , through filter elements  80   a ,  81   a , and  82   a , into second chamber  447   a , through vertical channel  487   a , through back outlet port  6   a , through link port  11 , through outlet port  10 , through outlet tubing  53 , into receiving blood bag  55 . 
     As first chamber  44  of filter device  440  fills from the bottom up most of the air in first chamber  44  will be forced (by the positive pressure in first chamber  44 ) through filter elements  80 ,  81 , and  82 , for the same reasons described in the previous paragraph. This initial air will flow into second chamber  447  of first filter well  13  of filter device  440 . Second chamber  447  is a closed chamber bounded by flat surface  489  and side wall  488 , both of partition wall  300  of body  401 , and by downstream surface  48  of filter element  82 . Second chamber  447  contains closed vertical channel  487 , bound by flat surface  489  of partition wall  300  of body  401 , the side walls of vertical filter support ribs  499  of body  401  adjacent to vertical channel  487 , and by downstream surface  48  of filter element  82 . The bottom of vertical channel  487  is in fluid flow relation to outlet port  10  via front outlet port  6  and link port  11 . The top end of vertical channel  487  is open to the top portion of second chamber  447 . The initial air that enters second chamber  447  from filter elements  80 ,  81 , and  82  plus all of the initial air that was in second chamber  447  will be forced from second chamber  447 , through vertical channel  487 , through front outlet port  6 , through link port  11  through outlet port  10 , through outlet tubing  53 , into receiving blood bag  55 . Because the volume of first chamber  44  is small, and the flow rate of blood entering first chamber  44  is much greater than the initial flow rate of blood through filter elements  80 ,  81 , and  82 , first chamber  44  will fill in a very small fraction of the time that it takes to wet filter elements  80 ,  81 , and  82 . The pressure head at the bottom of first chamber  44  will be larger than the pressure head at the top of first chamber  44 , because of the height difference between the top and bottom of first chamber  44 . Therefore liquid will start to come through filter element  82  into second chamber  447  from the bottom up. As second chamber  447  fills from the bottom up with blood the remaining air in second chamber  447  will be forced from second chamber  447 , through vertical channel  487 , through front outlet port  6 , through link port  11  through outlet port  10 , through outlet tubing  53 , into receiving blood bag  55 . Because the total volume of second chamber  447  is small (to minimize holdup) second chamber  447  may fill with blood (from the bottom up) before the upper part of filter element  82  has wet with blood. Once second chamber  447  is filled with blood, the blood from the top of second chamber  447  will flow through vertical channel  487 , through front outlet port  6 , through link port  11  through outlet port  10 , through outlet tubing  53 , into receiving blood bag  55 . Once blood starts to flow through outlet tubing  53  the pressure head at the top of vertical channel  487  will become negative. (The negative pressure head at the top of vertical channel  487  will reach its maximum negative value when the blood in outlet tubing reaches receiving blood bag  55 ). Any additional air that is forced through the filter elements into second chamber  447  by blood flowing through and wetting the top portion of the filter elements will bubble to the top of second chamber  447  (because of the buoyancy of air in the blood) and be sucked out of second chamber  447 , through vertical channel  487 , through front outlet port  6 , through link port  11  through outlet port  10 , through outlet tubing  53 , into receiving blood bag  55 , by the negative pressure at the top of vertical channel  487  (as long as blood flow continues). This assures that filter elements  80 ,  81 , and  82  will completely wet, and that all of the air that was in first chamber  44 , filter elements  80 ,  81 , and  82 , second chamber  447 , front outlet port  6 , link port  11 , outlet port  10 , and the interior of outlet tubing  53  will be forced into receiving blood bag  55 . 
     As first chamber  45  of filter device  440  fills from the bottom up all of the air in first chamber  45  will be forced (by the positive pressure in first chamber  45 ) through filter elements  80   a ,  81   a , and  82   a , for the same reasons described in the previous paragraph. This initial air will flow into second chamber  447   a  of second filter well  13   a  of filter device  440 . Second chamber  447   a  is a closed chamber bounded by flat surface  489   a  and side wall  488   a , both of partition wall  300  of body  401 , and by downstream surface  48   a  of filter element  82   a . Second chamber  447   a  contains closed vertical channel  487   a , bound by flat surface  489   a  of partition wall  300  of body  401 , the side walls of vertical filter support ribs  499   a  of body  401  adjacent to vertical channel  487   a , and by downstream surface  48   a  of filter element  82   a . The bottom of vertical channel  487   a  is in fluid flow relation to outlet port  10  via back outlet port  6   a  and link port  11 . The top end of vertical channel  487   a  is open to the top portion of second chamber  447   a . The initial air that enters second chamber  447   a  from filter elements  80   a ,  81   a , and  82   a  plus all of the initial air that was in second chamber  447   a  will be forced from second chamber  447   a , through vertical channel  487   a , through back outlet port  6   a , through link port  11  through outlet port  10 , through outlet tubing  53 , into receiving blood bag  55 . Because the volume of first chamber  45  is small, and the flow rate of blood entering first chamber  45  is much greater than the initial flow rate of blood through filter elements  80   a ,  81   a , and  82   a , first chamber  45  will fill in a very small fraction of the time that it takes to wet filter elements  80   a ,  81   a , and  82   a . The pressure head at the bottom of first chamber  45  will be larger than the pressure head at the top of first chamber  45 , because of the height difference between the top and bottom of first chamber  45 . Therefore liquid will start to come through filter element  82   a  into second chamber  447   a  from the bottom up. As second chamber  447   a  fills from the bottom up with blood the remaining air in second chamber  447   a  will be forced from second chamber  447   a , through vertical channel  487   a , through back outlet port  6   a , through link port  11  through outlet port  10 , through outlet tubing  53 , into receiving blood bag  55 . Because the total volume of second chamber  447   a  is small (to minimize holdup) second chamber  447   a  may fill with blood (from the bottom up) before the upper part of filter element  82   a  has wet with blood. Once second chamber  447   a  is filled with blood, the blood from the top of second chamber  447   a  will flow through vertical channel  487   a , through back outlet port  6   a , through link port  11  through outlet port  10 , through outlet tubing  53 , into receiving blood bag  55 . Once blood starts to flow through outlet tubing  53  the pressure head at the top of vertical channel  487   a  will become negative. (The negative pressure at the top of vertical channel  487   a  will reach its maximum negative value when the blood in outlet tubing reaches receiving blood bag  55 ). Any additional air that is forced through the filter elements into second chamber  447   a  by blood flowing through and wetting the top portion of the filter elements will bubble to the top of second chamber  447   a  (because of the buoyancy of air in blood) and be sucked out of second chamber  447   a , through vertical channel  487   a , through back outlet port  6   a , through link port  11  through outlet port  10 , through outlet tubing  53 , into receiving blood bag  55 , by the negative pressure at the top of vertical channel  487   a  (as long as blood flow continues). This assures that filter elements  80   a ,  81   a , and  82   a  will completely wet, and that all of the air that was in first chamber  45 , filter elements  80   a ,  81   a , and  82   a , second chamber  447   a , back outlet port  6   a , link port  11 , outlet port  10 , and the interior of outlet tubing  53  will be forced into receiving blood bag  55 . 
     FIG. 32A shows a schematic representation of second chamber  447  after the initial air that was in first chamber  44  and in second chamber  447  has been forced form chamber  447 , through vertical channel  487 , through front outlet port  6 , through link port  11 , through outlet port  10 , through outlet tubing  53 , into receiving blood bag  55 ; and after blood has filled second chamber  447 , and at least a portion of the top of vertical channel  487 , as explained above. FIG. 32A shows that the blood level has reached point  1  in outlet tubing  53 . Because the receiving blood bag is surrounded by atmospheric pressure, point  1  is considered to be at atmospheric pressure. In FIG. 32A it is assumed that blood flow from the feed blood bag has been shut off, so that blood flow through filter elements  80 ,  81 , and  82  has also stopped. Applying Bernoulli&#39;s equation to FIG. 32A, we have: 
     
       
         ( v   1   2 /2 g )+( p   1   /ρg )+( z    1 )=( v   2   2 /2 g )+( p   2   /ρg )+( z   2 )=( v   3   2 /2 g )+( p   3   /ρg )+( z   3 ) 
       
     
     Where: 
     (v 2 /2g) is the velocity head 
     (p/ρg) is the pressure head 
     z is the elevation head 
     Because the blood bag is surrounded by atmospheric pressure: 
     
       
         ( p   1   /ρg )=0 
       
     
     Because it is assumed that flow has stopped: 
       v   1   =v   2   =v   3 =0 
     Therefore: 
     
       
           z   1 =( z   2 +( p   2   /ρg ))=( z   3 +( p   3   /ρg )) 
       
     
     Therefore the pressure at any point on any horizontal line in second chamber  447  is equal to the pressure at any other point on the same horizontal line, as shown by points  2  and  3  in FIG.  32 A. Because there is no pressure differential between point  2  inside of vertical channel  487  and point  3  outside of vertical channel  487 , or between any other two points on any horizontal line in second chamber  447 , any air that bubbles to the top of second chamber  447  because of the buoyancy of the air will not be sucked out of second chamber  447  into vertical channel  487  if there is no blood flow through the filter elements. 
     FIG. 32B shows a schematic representation of second chamber  447  after the initial air that was in first chamber  44  and in second chamber  447  has been forced form chamber  447 , through vertical channel  487 , through front outlet port  6 , through link port  11 , through outlet port  10 , through outlet tubing  53 , into receiving blood bag  55 ; and after blood has filled second chamber  447 , and at least a portion of the top of vertical channel  487 , as explained above. FIG. 32A shows that the blood level has reached point la in outlet tubing  53 . Because the receiving blood bag is surrounded by atmospheric pressure, point la is considered to be at atmospheric pressure. In FIG. 32B it is assumed that blood is flowing from the feed blood bag, hence blood will also be flowing through filter elements  80 ,  81 , and  82 . 
     Applying Bernoulli&#39;s equation to FIG. 32B, we have: 
      ( v   1a   2 /2 g )+( p   1a   /ρg )+( z   1a )=( v   2a   2 /2 g )+( p   2a   /ρg )+( z   2a )=( v   3a   2 /2 g )+( p   3a   /ρg )+( z   3a )=( v   4a   2 /2 g )+( p   4a   /ρg )+( z   4a )=Total Head 
     Because the blood bag is surrounded by atmospheric pressure: 
     
       
         ( p   1a   /ρg )=0 
       
     
     Because all of the blood flow through filter elements  80 ,  81 , and  82 , must flow through vertical channel  487  and outlet tubing  53 , the flow rate through vertical channel  487  and outlet tubing will be at least ten times the flow through any channel between adjacent pairs of vertical filter support ribs outside of vertical channel  487 . Since the velocity head is proportional to the square of velocity it is assumed that the velocity head outside of vertical channel  487  equals zero, hence: 
     
       
         ( v   3a   2 /2 g )=( v   4a   2 /2 g )=0 
       
     
     Therefore applying Bernoulli&#39;s equation to FIG. 32B, it can be seen that when blood flows through the filter elements because of a positive pressure on the upstream side of the filter elements, the head pressure inside of vertical channel  487  will be negative, with the maximum negative value at the top of vertical channel  487 . It can also be seen that in a small region immediately outside of vertical channel  487  the head pressure will be negative, but less negative than the head pressure at the top of vertical channel  487 . For all other points outside of vertical channel  487 , inside of second chamber  447  the head pressure will be positive. Hence any air that is forced from the filter elements into second chamber  447  by blood flow through the filter will bubble to the top of second chamber  447  because of the buoyancy of the air in blood, and will then be sucked into vertical channel  487  because of the negative pressure head inside of vertical channel  487 , and the positive pressure head outside of vertical channel  487 . Both the forcing of air out of the filter elements into second chamber  447 , and the sucking of the air out of the top of second chamber  447  into vertical channel  487 , are dependent on blood flow through the filter elements, which is in turn dependent upon a positive pressure in first chamber  44 . The positive pressure in first chamber  44  can be created by gravity flow from a reservoir positioned above chamber  44 , or by any other source of positive pressure such as a pump. 
     Bernoulli&#39;s equation can be applied in the same way as above, for first chamber  45 , filter elements  80   a ,  81   a ,  82   a , and second chamber  447   a.    
     In FIG. 32B it is assumed that the cross-sectional area of the vertical channel and that of the outlet tubing are equal. Therefore, the velocity head at point  2  equals the velocity head at point  1 . 
     However, in FIG. 2, FIG. 11, and in FIG. 29, the cross-sectional area of the link port is shown smaller than that of the vertical channels of either the first filter well or the second filter well. Therefore, by applying Bernoulli&#39;s equation it can be seen that the maximum negative pressure will occur in the link port, not at the top of the vertical channel, because the velocity head will have its maximum value in the link port, and the total head at all points on the downstream side of the filter elements must be equal as described above. With the cross-sectional area of the link port less than that of the vertical channel, air that bubbles to the top of the second chamber will be sucked into the vertical channel as described above. Hence it can be seen that the link port, or the front outlet port, or the back outlet port, or the outlet port may have a cross-sectional area less than that of the vertical channel. 
     Blood filtration will continue until feed blood bag  54  is empty. When feed blood bag  54  is empty it will be collapsed and therefore close the inlet end of inlet tubing  52 . Because outlet tubing  53  will be full of blood, and because the outside of receiving blood bag  55  is at atmospheric pressure, the pressure head in front outlet port  6 , and the pressure head in back outlet port  6   a  will be negative, as will be the pressure head in second chamber  447 , and second chamber  447   a , all of body  401 . Once blood flow has stopped the pressure drop across filter elements  80 ,  81 , and  82 , will fall to zero. The pressure drop across filter elements  80   a ,  81   a , and  82   a , will also fall to zero. Hence the pressure in first chamber  44  and first chamber  45  will become negative. Once the pressure in first chamber  44  falls below atmospheric pressure air will begin to flow from atmosphere through slots  21 , through sterilizing grade hydrophobic filter  41 , into first chamber  44 . The sterile air that enters first chamber  44  will bubble up to the top of first chamber  44 , thus causing first chamber  44  to drain from the top down. Because of the negative pressure in first chamber  45 , some of the air that bubbles to the top of first chamber  44  will pass through gap  26 , through front inlet channel  8 , through front cross port  7 , through back cross port  7   a , through gap  36 , through back inlet channel  8   a , into first chamber  45 , causing first chamber  45  to drain from the top down, and causing the blood in front inlet channel  8  to drain into first chamber  44 , and causing the blood in back inlet channel  8   a  to drain into first chamber  45 , and causing the blood in front cross port  7  and back cross port  7   a  to drain into both first chamber  44  and first chamber  45 . Because the air entering first chamber  44  bubbles to the top of first chamber  44 , thus draining first chamber  44  from the top down, vent filter element  41  can be located anywhere on flat surface  23  of front cover  20 . Filter elements  80 ,  81 ,  82 ,  80   a ,  81   a , and  82   a  will be plugged sufficiently at this point, therefore very little if any blood will be sucked from these filter elements by the negative pressure in second chamber  447 , and by the negative pressure in second chamber  447   a . Hence blood flow will stop after first chamber  44  and first chamber  45  have drained and blood will remain in filter elements  80 ,  81 ,  82 ,  80   a ,  81   a , and  82   a , in second chamber  447 , in second chamber  447   a , and in front outlet port  6 , back outlet port  6   a , link port  11 , outlet port  10  all of body  401 , and in outlet tubing  53 . 
     The user can now close tube clamp  75  on outlet tubing  53  and then seal outlet tubing  53  above tube clamp  75 , and then cut outlet tubing  53  above the seal just made. Feed blood bag  54 , inlet tubing  52 , and filter device  440  can now be discarded in a safe manner. Outlet tubing  53  will have segments marked on them. The user can now seal the tubing at the segment marks. The blood that is left in outlet tubing  53  will be used for cross matching and for quality control purposes. 
     Although the filter support means (including vertical channel  487 ) of second chamber  447  and the filter support means (including vertical channel  487   a ) of second chamber  447   a  are used in conjunction with the two sided filter device of the seventh embodiment of the present invention it will be appreciated by those skilled in the art that the same filter support means could be used with a single sided filter. 
     Body  101 , and body  201 , could also be modified to incorporate second chamber  447  of body  401 , and second chamber  447   a  of body  401 . Hence any of the embodiments from the first embodiment to the sixth embodiment could function like the seventh embodiment. 
     Although the present invention has been shown and described in terms of specific preferred embodiments, it will be appreciated by those skilled in the art that changes or modifications are possible which do not depart from the inventive concepts described and taught herein. Such changes and modifications are deemed to fall within the purview of these inventive concepts. In addition it is contemplated that the filter assembly may be employed in an environment other than blood filtration. A fluid system in which components of the fluid must be removed can benefit from the use of a filter apparatus embodying the teachings of the present invention.