Title of Invention: Fluid Separation Chambers For Fluid Processing Systems Abstract: Fluid separation chambers are provided for rotation about an axis in a fluid processing system. The fluid separation chamber may be provided with first and second stages, with the first and second stages being positioned at different axial locations. In another embodiment, at least one of the stages may be provided with a non-uniform outer diameter about the rotational axis, which may define a generally spiral-shaped profile or a different profile for fractionating a fluid or fluid component. One or more of the stages may also have a varying outer diameter along the axis. The profile of the chamber may be provided by the chamber itself (in the case of rigid chambers) or by an associated fixture or centrifuge apparatus (in the case of flexible chambers). Detailed Description: CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of and priority of U.S. Provisional Patent Application Ser. No. 61/591,655, filed Jan. 27, 2012, and U.S. Provisional Patent Application Ser. No. 61/720,518, filed Oct. 31, 2012, the contents of which are incorporated by reference herein. FIELD OF THE DISCLOSURE The disclosure relates to fluid processing systems and methods. More particularly, the disclosure relates to systems and methods for centrifugally separating fluids. DESCRIPTION OF RELATED ART A wide variety of fluid processing systems are presently in practice and allow for a fluid to be fractionated or separated into its constituent parts. For example, various blood processing systems make it possible to collect particular blood constituents, rather than whole blood, from a blood source. Typically, in such systems, whole blood is drawn from a blood source, the particular blood component or constituent is separated, removed, and collected, and the remaining blood constituents are returned to the blood source. Removing only particular constituents is advantageous when the blood source is a human donor or patient, because potentially less time is needed for the donor's body to return to pre-donation levels, and donations can be made at more frequent intervals than when whole blood is collected. This increases the overall supply of blood constituents, such as plasma and platelets, made available for transfer and/or therapeutic treatment. Whole blood is typically separated into its constituents through centrifugation. In continuous processes, this requires that the whole blood be passed through a centrifuge after it is withdrawn from, and before it is returned to, the blood source. To avoid contamination and possible infection (if the blood source is a human donor or patient), the blood is preferably contained within a preassembled, sterile fluid flow circuit or system during the entire centrifugation process. Typical blood processing systems thus include a permanent, reusable module or assembly containing the durable hardware (centrifuge, drive system, pumps, valve actuators, programmable controller, and the like) that spins and controls the processing of the blood and blood components through a disposable, sealed, and sterile flow circuit that includes a centrifugation chamber and is mounted in cooperation on the hardware. The hardware engages and spins the disposable centrifugation chamber during a blood separation step. As the flow circuit is spun by the centrifuge, the heavier (greater specific gravity) components of the whole blood in the flow circuit, such as red blood cells, move radially outwardly away from the center of rotation toward the outer or “high-G” wall of the centrifugation chamber. The lighter (lower specific gravity) components, such as plasma, migrate toward the inner or “low-G” wall of the centrifuge. Various ones of these components can be selectively removed from the whole blood by providing appropriately located channeling seals and outlet ports in the flow circuit. It is known to employ centrifugation chambers that have two stages for separating different blood components such as separating or concentrating red blood cells in a first stage and platelets in a second stage. One possible disadvantage of known systems is that the centrifuge can become unbalanced during use if one stage of a multi-stage separation chamber of the flow circuit positioned in the centrifuge is empty. To avoid centrifuge imbalance, the otherwise empty stage may be supplied with a liquid (e.g., saline) prior to centrifugation, which tends to counter-balance the fluid in the other stage. It would be advantageous to provide a flow circuit with a multi-stage separation chamber that avoids centrifuge imbalance without the need for a counter-balancing liquid. Another possible disadvantage of known systems becomes apparent when a two-stage centrifugation chamber is used to separate platelets from whole blood. In such systems, whole blood is introduced into the first chamber and separated into red blood cells and platelet-rich plasma. The platelet-rich plasma is transferred from the first chamber to the second chamber, where it is separated into platelet-poor plasma and platelet concentrate. The platelet-poor plasma is removed from the second chamber, but the platelet concentrate may remain therein and accumulates throughout the separation procedure. At the end of the procedure, the platelets in the second chamber must be resuspended in plasma or another fluid (e.g., PAS). While effective, resuspension is a manual and operator-dependent procedure that must be performed properly. Further, a procedure requiring a final resuspension step may take longer than a procedure in which the platelets are automatically removed from the second chamber either during use or at the end of the procedure. Thus, it may be advantageous to provide a flow circuit with a multi-stage separation chamber that allows for automated removal of platelets and/or other blood component(s) from the second chamber. SUMMARY There are several aspects of the present subject matter which may be embodied separately or together in the devices and systems described and claimed below. These aspects may be employed alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to preclude the use of these aspects separately or the claiming of such aspects separately or in different combinations as set forth in the claims appended hereto. In one aspect, a fluid separation chamber is provided for rotation about an axis in a fluid processing system. The fluid separation chamber comprises a first stage and a second stage, with the first and second stages being positioned at different axial locations. In another aspect, a method is provided for separating a fluid. The method includes rotating a centrifuge containing a fluid about an axis and separating the fluid into a first component and a second component at a first location. One of the components is further separated at a second location, with the first and second locations being spaced along the axis. In yet another aspect, a fluid separation chamber is provided for use in a fluid processing system. The fluid separation chamber comprises a body having a top edge, a bottom edge, and at least one side edge. A first interior wall separates the interior of the body into a first stage and a second stage. Second and third interior walls are positioned within the first stage, while a fourth interior wall is positioned within the second stage. A first fluid passage communicates with one of the edges and is defined at least in part by the first and second interior walls. A second fluid passage communicates with the one of the edges and is defined at least in part by the second and third interior walls. A third fluid passage communicates with one of the edges and is defined at least in part by the third interior wall and one of the edges. A fourth fluid passage communicates with one of the edges and is defined at least in part by the first and fourth interior walls. A fifth fluid passage communicates with one of the edges and is defined at least in part by the fourth interior wall and one of the edges. The first stage is spaced from the bottom edge by the second stage. In another aspect, a fluid separation chamber is provided for use in a fluid processing system. The fluid separation chamber comprises a body including a top edge, a bottom edge, and at least one side edge. A first interior wall separates the interior of the body into a first stage and a second stage. Second and third interior walls are positioned within the first stage, while fourth and fifth interior walls are positioned within the second stage. A first fluid passage communicates with one of the edges and is defined at least in part by the first and second interior walls. A second fluid passage communicates with one of the edges and is defined at least in part by the second and third interior walls. A third fluid passage communicates with one of the edges and is defined at least in part by the third interior wall and one of the edges. A fourth fluid passage communicates with one of the edges and is defined at least in part by the first and fourth interior walls. A fifth fluid passage communicates with one of the edges and is defined at least in part by the fourth and fifth interior walls. A sixth fluid passage communicates with one of the edges and is defined at least in part by the fifth interior wall and one of the edges. The first stage is spaced from the bottom edge by the second stage. In yet another aspect, a fluid separation chamber is provided for use in a fluid processing system. The fluid separation chamber comprises a body including a top edge, a bottom edge, and at least one side edge. A first interior wall separates the interior of the body into a first stage and a second stage. A second interior wall is positioned within the first stage. A first fluid passage communicates with one of the edges and is defined at least in part by the first and second interior walls. A second fluid passage communicates with one of the edges and is defined at least in part by the second interior wall and one of the edges. A third fluid passage communicates with one of the edges and is defined at least in part by the first interior wall and one of the edges. A fourth fluid passage communicates with one of the edges and is defined at least in part by the first interior wall and one of the edges. A fifth fluid passage communicates with one of the edges and is defined at least in part by the first interior wall and one of the edges. The first stage is spaced from the bottom edge by the second stage. In another aspect, a fluid separation chamber is provided for use in a fluid processing system. The fluid separation chamber comprises a body including a top edge, a bottom edge, at least one side edge. A first interior wall separates the interior of the body into a first stage and a second stage. A second interior wall is positioned within the first stage, while a third interior wall is positioned within the second stage. A first fluid passage communicates with one of the edges and is defined at least in part by the first and second interior walls. A second fluid passage communicates with one of the edges and is defined at least in part by the second interior wall and one of the edges. A third fluid passage communicates with one of the edges and is defined at least in part by the first interior wall and one of the edges. A fourth fluid passage communicates with one of the edges and is defined at least in part by the first and third interior walls. A fifth fluid passage communicates with one of the edges and is defined at least in part by the third interior wall and one of the edges. A sixth fluid passage communicates with one of the edges and is defined at least in part by the first interior wall and one of the edges. The first stage is spaced from the bottom edge by the second stage. In yet another aspect, a fluid separation chamber is provided for use in a fluid processing system. The fluid separation chamber comprises a body including a top surface or edge, a bottom surface or edge, and an interior wall separating the interior of the body into a first stage and a second stage. A first barrier is positioned within the first stage and a second barrier is positioned within the second stage. At least one fluid port is associated with the first stage at least one fluid port is associated with the second stage. The first stage is spaced from the bottom edge by the second stage. In another aspect, a centrifuge is provided for rotation about an axis in a fluid processing system to generate a gravitational field. The centrifuge comprises a centrifuge bowl or rotary member with a gap or channel defined therein for receiving a fluid directly or for receiving a fluid separation chamber. The centrifuge may further comprise an inner spool and an outer bowl, with the spool and the bowl defining therebetween a gap or channel configured to receive a fluid separation chamber. The gap or channel has a non-uniform radius about the axis. In another aspect, a centrifuge is provided for rotation about an axis in a fluid processing system to generate a centrifugal field. The centrifuge comprises a centrifuge bowl or rotary member with a gap or channel defined therein for receiving a fluid directly or for receiving a fluid separation chamber. The centrifuge may further comprise an inner spool having an outer wall and an outer bowl having an inner wall. A gap or channel is defined between the outer wall and the inner wall and configured to receive a fluid separation chamber. At least a portion of the inner wall has a varying radius along its axial height. In yet another aspect, a fluid processing system is provided. The system comprises a centrifuge for rotation about an axis. The centrifuge includes a centrifuge bowl or rotary member with a gap or channel defined therein for receiving a fluid directly or for receiving a fluid separation chamber. The centrifuge may further comprise an inner spool and an outer bowl, with the spool and the bowl defining a gap or channel therebetween. The gap or channel comprises an arcuate first section and an arcuate second section, with the second section having a varying radius about the axis. The system further includes a fluid separation chamber comprising a first stage configured to be at least partially received within the first section of the gap or channel and a second stage configured to be at least partially received within the second section of the gap or channel. The second section comprises an outlet port configured to be positioned at the maximum radius of the second section of the gap or channel. In another aspect, a method is provided for separating a fluid. The method includes rotating a fluid separation chamber containing a fluid about an axis and separating the fluid into a first component and a second component in a first stage of the fluid separation chamber. The method further includes separating one of the fluid components in a second stage of the fluid separation chamber, wherein at least a portion of the second stage is positioned closer to the axis than the first stage. In yet another aspect, method is provided for separating a fluid. The method includes rotating a fluid separation chamber containing a fluid about an axis and separating the fluid into a first component and a second component. At least a portion of one of the fluid components is flowed against a surface having a varying radius along its axial height. In another aspect, a fluid separation chamber is provided for rotation about an axis in a fluid processing system to generate a centrifugal field. The fluid separation chamber comprises: a channel defined between a low-G wall and a high-G wall and a plurality of flow paths in fluid communication with the channel. At least a portion of the channel has a non-uniform radius about the axis. Other aspects include, but are not limited to, fluid processing systems incorporating fluid separation chambers described herein, fluid processing methods employing the fluid separation chambers and/or fluid processing systems described herein, and connection members or plates for connecting multiple stages of a fluid separation chamber. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side section view of a centrifuge receiving a fluid separation chamber that incorporates aspects of the present disclosure; FIG. 2 shows the spool of the centrifuge of FIG. 1, with a fluid separation chamber wrapped about it for use; FIG. 3A is a perspective view of the centrifuge shown in FIG. 1, with the bowl and spool thereof pivoted into a loading/unloading position and in a mutually separated condition to allow the fluid separation chamber shown in FIG. 2 to be secured about the spool; FIG. 3B is a perspective view of the bowl and spool in the loading/unloading position of FIG. 3A, with the bowl and spool in a closed condition after receiving the fluid separation chamber of FIG. 2; FIG. 4 is a plan view of the fluid separation chamber shown in FIG. 2; FIG. 5 is a perspective view of a disposable flow circuit (of which the fluid separation chamber comprises a component), which includes cassettes mounted in association with pump stations of a fluid separation device (of which the centrifuge comprises a component); FIG. 6 is a plan view of an alternative fluid separation chamber that incorporates aspects of the present disclosure; FIG. 7 is a plan view of another alternative fluid separation chamber that incorporates aspects of the present disclosure; FIG. 8 is a plan view of yet another alternative fluid separation chamber that incorporates aspects of the present disclosure; FIG. 9 is a side elevational view of an embodiment of a rigid fluid separation chamber that incorporates aspects of the present disclosure; FIG. 10 is a bottom plan view of one of the stages of the fluid separation chamber of FIG. 9; FIG. 11 is a top plan view of one of the stages of the fluid separation chamber of FIG. 9; FIG. 12 is a top plan view of an alternative embodiment of a rigid fluid separation chamber according to an aspect of the present disclosure; FIG. 13 is a top plan view of another embodiment of a rigid fluid separation chamber according to the present disclosure; FIG. 14 is a perspective view of the fluid separation chamber of FIG. 13; FIG. 15 is a diagrammatic view of a portion of a spiral which may describe all or a portion of a fluid separation gap or channel according to the present disclosure; FIG. 16 is a top plan view of another embodiment of a rigid fluid separation chamber according to the present disclosure; FIG. 17 is a top plan view of an alternative embodiment of a rigid fluid separation chamber according to the present disclosure; FIG. 18 is a top plan view of a gap configuration embodying aspects of the present disclosure; FIG. 19 is a plan view of a flexible fluid separation chamber which may be used in combination with a gap of the type illustrated in FIG. 18; FIG. 20 shows an alternative spool of the centrifuge of FIG. 1, with a fluid separation chamber wrapped about it for use; FIG. 21 is a plan view of the fluid separation chamber shown in FIG. 20, showing one fluid flow configuration; FIG. 21A is a plan view of the fluid separation chamber shown in FIG. 20, showing an alternative fluid flow configuration; FIG. 22 is a top plan view of the spool, bowl, and fluid separation chamber of FIG. 20; FIG. 23 is a perspective view of an alternative centrifuge bowl suitable for use in combination with the fluid flow configuration of FIG. 21A; FIG. 24 is a cross-sectional side view of a centrifuge spool and bowl suitable for use in combination with the fluid separation chamber of FIG. 21A; and FIG. 25 is a cross-sectional side view of an alternative centrifuge spool and bowl suitable for use in combination with the fluid separation chamber of FIG. 21A. DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS The embodiments disclosed herein are for the purpose of providing a description of the present subject matter, and it is understood that the subject matter may be embodied in various other forms and combinations not shown in detail. Therefore, specific embodiments and features disclosed herein are not to be interpreted as limiting the subject matter as defined in the accompanying claims. FIG. 1 shows a centrifuge 10 of a fluid processing device 12 (FIG. 5) receiving a fluid separation chamber 14 of a disposable flow circuit 16 (FIG. 5), which is suitable for separating a fluid. While the term “fluid” is frequently used herein, it is not to be construed as limiting the applicability of apparatus and methods according to the present disclosure to particular substances (e.g., blood or a suspension containing one or more blood or cell components), but is instead intended to refer to any substance which is suitable for separation or fractionation by centrifugation. In the illustrated embodiment, the fluid separation chamber 14 is carried within a rotating assembly and, specifically within an annular gap 18 between a rotating spool 20 and bowl 22 of the centrifuge 10. The interior bowl wall 24 defines the high-G wall of a centrifugal field during use of the centrifuge 10, while the exterior spool wall 26 defines the low-G wall of the centrifugal field, as will be described in greater detail herein. Further details of an exemplary centrifuge which is suitable for use with fluid separation chambers according to the present disclosure are set forth in U.S. Pat. No. 5,370,802 to Brown, which is hereby incorporated herein by reference. In one embodiment, the centrifuge 10 comprises a component of a blood processing device of the type currently marketed as the AMICUS® separator by Fenwal, Inc. of Lake Zurich, Ill., as described in greater detail in U.S. Pat. No. 5,868,696 to Giesler et al., which is hereby incorporated herein by reference. However, as noted above, apparatus and methods described herein are not limited to separation of a particular substance and the illustrated fluid processing device 12 is merely exemplary. The bowl 22 and spool 20 are pivoted on a yoke 28 between an upright loading/unloading position, as shown in FIGS. 3A and 3B, and an operating position, as FIG. 1 shows. When upright, the bowl 22 and spool 20 are oriented for access by a user or technician. A mechanism permits the spool 20 and bowl 22 to be opened or separated (FIG. 3A) so that the operator can wrap the illustrated flexible fluid separation chamber 14 about the spool 20, as shown in FIG. 2. When the fluid separation chamber 14 has been properly positioned, the spool 20 may be moved back into the bowl 22 (FIG. 3B), and the spool 20 and bowl 22 can be pivoted into the operating position of FIG. 1. As will be described in greater detail herein, the centrifuge 10 rotates the bowl 22 spool 20 about an axis 30, creating a centrifugal field within the fluid separation chamber 14 to separate or fractionate a fluid. According to an aspect of the present disclosure, the fluid separation chamber 14 is provided with a plurality of stages or sub-chambers, such as a first stage or sub-chamber or compartment and a second stage or sub-chamber or compartment. For purposes of this description, the terms “first” and “second” are denominational only for purposes of identification and do not refer to or require a particular sequence of operation or fluid flow. In the illustrated embodiment, the first and second stages are positioned at different axial locations (with respect to the axis 30) when the fluid separation chamber 14 is loaded within the centrifuge 10. FIG. 4 illustrates an exemplary fluid separation chamber 14 having such first and second stages 32 and 34. By employing stages which are spaced along the axis 30, the centrifuge 10 does not tend to become imbalanced during use if one of the stages contains a fluid while the other is empty. For example, absent the use of a counter-balancing fluid, the downstream stage of a two-stage separation chamber would typically be empty during priming of the flow circuit, which may take place while the centrifuge is spinning. If the stages are positioned at different angular locations with respect to the rotational axis, the presence of fluid in only one of the stages may lead to centrifugal imbalance, which can cause wear or damage to the centrifuge. As noted above, a counter-balancing fluid is commonly provided in the downstream stage to prevent this imbalance. On the other hand, in fluid separation chambers according to this aspect of the present disclosure, fluid may be present in only one of the stages (e.g., during priming) without causing a centrifugal imbalance. Thus, fluid separation chambers according to the present disclosure eliminate the need for a counter-balancing fluid in the downstream chamber, thereby making it easier for the associated flow circuit to be primed by the fluid to be separated or fractionated. This may also decrease the time required to prime the flow circuit. As illustrated, the stages 32 and 34 are located at substantially the same radial distance from the axis of rotation 30. In other embodiments, as will be described in greater detail herein, the stages 32 and 34 may be located at different radial distances from the axis of rotation 30. In the embodiment illustrated in FIG. 4, the fluid separation chamber 14 is provided as a flexible body with a seal extending around its perimeter to define a top edge 36, a bottom edge 38, and a pair of side edges 40 and 42. A first interior seal or wall 44 divides the interior of the fluid separation chamber 14 into first and second stages 32 and 34. The first interior wall 44 may be variously configured without departing from the scope of this aspect of the present disclosure, provided that it is configured to place the first and second stages 32 and 34 at different axial locations during use of the centrifuge 10 to separate a fluid therein. FIG. 4 shows the first stage 32 positioned above the second stage 34, but the orientation of the stages 32 and 34 is reversed when the fluid separation chamber 14 has been mounted within the centrifuge 10 (FIG. 1). Hence, the first stage 32 may be considered the “lower stage,” while the second stage 34 may be considered the “upper stage” when the centrifuge 10 is in an operating position. However, it is within the scope of the present disclosure to provide a first stage which is positioned above the second stage (i.e., at a higher elevation along the rotational axis) during use. In the illustrated embodiment, the first interior wall 44 extends in a dogleg or L-shaped manner from the top edge 36 toward the bottom edge 38, but extends to terminate at one of the side edges 42 without contacting the bottom edge 38. Thus, the region of the interior of the fluid separation chamber 14 defined by the top edge 36, the first interior wall 44, and the right side edge 42 comprises the first stage 32, while the region defined by the top edge 36, the bottom edge 38, the first interior wall 44, and the two side edges 40 and 42 comprises the second stage 34. It will be seen that, in the embodiment of FIG. 4, the first stage 32 is, in substantial part, spaced from the bottom edge 38 of the fluid separation chamber 14 by the second stage 34. In addition to the first interior wall 44, the illustrated fluid separation chamber 14 includes additional interior walls or seals. The first stage 32 includes two interior seals or walls 46 and 48, which are referred to herein as second and third interior walls, respectively. The second stage 34 includes one interior seal or wall 50, which is referred to herein as the fourth interior wall. In the embodiment of FIG. 4, each interior wall extends in a dogleg or L-shaped manner from the top edge 36 toward the bottom edge 38 and then (in varying degrees) toward the right side edge 42, without contacting either the bottom edge 38 or the right side edge 42. It is within the scope of the present disclosure for these interior walls to be otherwise configured without departing from the scope of the present disclosure. Further, it is within the scope of the present disclosure for the fluid separation chamber to include more (FIG. 6) or fewer than four interior walls or seals. The interior walls of the fluid separation chamber 14 help to define fluid passages which allow for fluid communication between the flow circuit 16 and the first and second stages 32 and 34. In the embodiment of FIG. 4, a first fluid passage 52 is defined at least in part by the first and second interior walls 44 and 46 to allow fluid communication between the first stage 32 and the flow circuit 16 via a port 54 extending through the top edge 36. A second fluid passage 56 is defined at least in part by the second and third interior walls 46 and 48 to allow fluid communication between the first stage 32 and the flow circuit 16 via a port 58 extending through the top edge 36. A third fluid passage 60 is defined at least in part by the third interior wall 48 and the top edge 36 to allow fluid communication between the first stage 32 and the flow circuit 16 via a port 62 extending through the top edge 36. A fourth fluid passage 64 is defined at least in part by the first and fourth interior walls 44 and 50 to allow fluid communication between the second stage 34 and the flow circuit 16 via a port 66 extending through the top edge 36. A fifth fluid passage 68 is defined at least in part by the fourth interior wall 50, the left side edge 40, and the bottom edge 38 to allow fluid communication between the second stage 34 and the flow circuit 16 via a port 70 extending through the top edge 36. While FIG. 4 shows all of the ports and fluid passages associated with the top edge, it is within the scope of the present disclosure for one or more of the ports and fluid passages to be instead associated with a side edge or bottom edge of the fluid separation chamber. An exemplary use for each of the fluid passages during a fluid separation procedure will be described in greater detail below. The ports may be made of a generally more rigid material and configured to accommodate flexible tubing 72 which connects the fluid separation chamber 14 to the remainder of the flow circuit 16. In the illustrated embodiment, portions of the tubing 72 are joined to define an umbilicus 74 (FIG. 1). A non-rotating (zero omega) holder 76 holds an upper portion of the umbilicus 74 in a non-rotating position above the spool 20 and bowl 22. A holder 78 on the yoke 28 rotates an intermediate portion of the umbilicus 74 at a first (one omega) speed about the spool 20 and bowl 22. Another holder 80 rotates a lower end of the umbilicus 74 at a second speed twice the one omega speed (referred to herein as the two omega speed), at which the spool 20 and bowl 22 also rotate to create a centrifugal field within the fluid separation chamber 14. This known relative rotation of the umbilicus 74 keeps it untwisted, in this way avoiding the need for rotating seals. FIG. 5 shows the general layout of an exemplary flow circuit 16, in terms of an array of flexible tubing 82, fluid source and collection containers 84, and fluid-directing cassettes. In the illustrated embodiment, left, middle, and right cassettes 86L, 86M, and 86R (respectively), centralize many of the valving and pumping functions of the flow circuit 16. The left, middle, and right cassettes 86L, 86M, and 86R mate with left, middle, and right pump stations 88L, 88M, and 88R (respectively) of the fluid processing device 12. The tubing 82 couples the various elements of the flow circuit 16 to each other and to a fluid source, which may be a human body, but may also be one of the containers 84 or some other non-human source. Additional details of an exemplary flow circuit and fluid processing device suitable for use with fluid separation chambers according to the present disclosure are set forth in U.S. Pat. No. 6,582,349 to Cantu et al., which is hereby incorporated herein by reference. The fluid separation chamber 14 may be used for either single- or multi-stage processing. When used for single-stage processing, a fluid is flowed into one of the stages (typically the first stage 32), where it is separated into at least two components. All or a portion of one or both of the components may then be flowed out of the first stage 32 and harvested or returned to the fluid source. When used for multi-stage processing, a fluid is flowed into the first stage 32 and separated into at least a first component and a second component. At least a portion of one of the components is then flowed into the second stage 34, where it is further separated into at least two sub-components. The component not flowed into the second stage 34 may be flowed out of the first stage 32 and harvested or returned to the fluid source. As for the sub-components, at least a portion of one may be flowed out of the second stage 34 for harvesting or return to the fluid source, while the other remains in the second stage 34. In an exemplary multi-stage fluid processing application, the fluid separation chamber 14 is used to separate whole blood into platelet-rich plasma and red blood cells in the first stage 32. The platelet-rich plasma is then flowed into the second stage 34, where it is separated into platelet concentrate and platelet-poor plasma. In the exemplary procedure, whole blood is flowed into the first stage 32 of a fluid separation chamber 14 received in a spinning centrifuge 10 (as in FIG. 1). The whole blood enters the first stage 32 via port 58 and the second fluid passage 56 (FIG. 4). The centrifugal field present in the fluid separation chamber 14 acts upon the blood to separate it into a layer substantially comprised of platelet-rich plasma and a layer substantially comprised of red blood cells. The higher density component (e.g., red blood cells) gravitates toward the high-G wall 24, while the lower density component (e.g., platelet-rich plasma) remains closer to the low-G wall 26 (FIG. 1). The red blood cells are flowed out of the first stage 32 via port 54 and the first fluid passage 52 (FIG. 4), where they are either harvested or returned to the blood source. The platelet-rich plasma is flowed out of the first stage 32 via port 62 and the third fluid passage 60. The high-G wall 24 may include a projection or dam 90 (FIG. 4) which extends toward the low-G wall 26, across the third fluid passage 60. The dam 90 is configured to intercept red blood cells adjacent thereto and prevent them from entering the third fluid passage 60 and thereby contaminating the platelet-rich plasma. The term “contaminating” as used here means having more of a component (here, more red blood cells) in the fluid flowing to the second stage (here, plasma) than is desired and does not refer to or imply a biological hazard. The platelet-rich plasma flowed out of the first stage 32 is directed into second stage 34, such as by operation of one or more of the flow control cassettes of the flow circuit 16. The platelet-rich plasma enters the second stage 34 via port 66 and the fourth fluid passage 64. The centrifugal field acts upon the platelet-rich plasma to separate it into a layer substantially comprised of platelet concentrate and a layer substantially comprised of platelet-poor plasma. The higher density component (e.g., platelet concentrate) gravitates toward the high-G wall 24, while the lower density component (e.g., platelet-poor plasma) remains closer to the low-G wall 26 (FIG. 1). The platelet-poor plasma is flowed out of the second stage 34 via port 70 and the fifth fluid passage 68 (FIG. 4), where it is either harvested or returned to the blood source. The platelet concentrate remains in the second stage 34, where it may be stored for later use. When used for processing blood, a blood component, or any other body fluid, devices and methods according to the present disclosure may be used with any suitable fluid source. For example, the fluid source may be a living human or non-human animal whose bodily fluid is directly drawn into the device for processing. In other embodiments, the fluid to be processed does not come directly from a living human or non-human animal, but is instead provided directly from a non-living source, such as a container holding an amount of fresh or stored fluid (e.g., blood or a blood component that has been previously drawn from a living source and stored). In additional embodiments, there may be a plurality of fluid sources, which may all be living sources or non-living sources or a combination of living and non-living sources. An alternative embodiment of a fluid processing chamber is illustrated in FIG. 6. The fluid processing chamber 92 of FIG. 6 is structurally comparable to the fluid processing chamber 14 of FIG. 4. The fluid separation chamber 92 is provided as a flexible body with a seal extending around its perimeter to define a top edge 94, a bottom edge 96, and a pair of side edges 98 and 100. A first interior seal or wall 102 divides the interior of the fluid separation chamber 92 into first and second stages 104 and 106. As in the embodiment of FIG. 4, the illustrated first interior wall 102 extends from the top edge 94 toward the bottom edge 96, but extends to terminate at one of the side edges 100 without contacting the bottom edge 96. Thus, the region of the interior of the fluid separation chamber 92 defined by the top edge 94, the first interior wall 102, and the right side edge 100 comprises the first stage 104, while the region defined by the top edge 94, the bottom edge 96, the first interior wall 102, and the two side edges 98 and 100 comprises the second stage 106. As in the embodiment of FIG. 4, the first stage 104 is spaced from the bottom edge 96 of the fluid separation chamber 92 by the second stage 106. In addition to the first interior wall 102, the illustrated fluid separation chamber 92 includes additional interior walls or seals. The first stage 104 includes two interior seals or walls 108 and 110, which are referred to herein as second and third interior walls, respectively. The second stage 106 includes two more interior seals or walls 112 and 114, which are referred to herein as the fourth and fifth interior walls, respectively. As in the embodiment of FIG. 4, each interior wall extends from the top edge 94 toward the bottom edge 96 and then (in varying degrees) toward the right side edge 100, without contacting either the bottom edge 96 or the right side edge 100. It is within the scope of the present disclosure for these interior walls to be otherwise configured without departing from the scope of the present disclosure. The interior walls of the fluid separation chamber 92 help to define fluid passages which allow for fluid communication between the flow circuit 16 and the first and second stages 104 and 106. In the embodiment of FIG. 6, a first fluid passage 116 is defined at least in part by the first and second interior walls 102 and 108 to allow fluid communication between the first stage 104 and the flow circuit 16 via a port 118 extending through the top edge 94. A second fluid passage 120 is defined at least in part by the second and third interior walls 108 and 110 to allow fluid communication between the first stage 104 and the flow circuit 16 via a port 122 extending through the top edge 94. A third fluid passage 124 is defined at least in part by the third interior wall 110 and the top edge 94 to allow fluid communication between the first stage 104 and the flow circuit 16 via a port 126 extending through the top edge 94. A fourth fluid passage 128 is defined at least in part by the first and fourth interior walls 102 and 112 to allow fluid communication between the second stage 106 and the flow circuit 16 via a port 130 extending through the top edge 94. A fifth fluid passage 132 is defined at least in part by the fourth and fifth interior walls 112 and 114 to allow fluid communication between the second stage 106 and the flow circuit 16 via a port 134 extending through the top edge 94. A sixth fluid passage 136 is defined at least in part by the fifth interior wall 114, the left side edge 98, and the bottom edge 96 to allow fluid communication between the second stage 106 and the flow circuit 16 via a port 138 extending through the top edge 94. While FIG. 6 shows all of the ports and fluid passages associated with the top edge, it is within the scope of the present disclosure for one or more of the ports and fluid passages to be instead associated with a side edge or bottom edge of the fluid separation chamber. An exemplary use for each of the fluid passages during a fluid separation procedure will be described in greater detail below. As for the ports and the remainder of the flow circuit 16 of which the fluid separation chamber 94 is a component, they may conform to the preceding description of the ports and flow circuit 16 associated with the fluid separation chamber 14 of FIG. 4, with the exception that the flow circuit is configured to accommodate an additional fluid passage and port. Similar to the fluid separation chamber 14 of FIG. 4, the fluid separation chamber 92 of FIG. 6 may be used for either single- or multi-stage processing. When used for single-stage processing, a fluid is flowed into one of the stages (typically the first stage 104), where it is separated into at least two components. All or a portion of one or both of the components may then be flowed out of the first stage 104 and harvested or returned to the fluid source. When used for multi-stage processing, a fluid is flowed into the first stage 104 and separated into at least a first component and a second component. At least a portion of one of the components is then flowed into the second stage 106, where it is further separated into at least two sub-components. The component not flowed into the second stage 106 may be flowed out of the first stage 104 and harvested or returned to the fluid source. As for the sub-components, at least a portion of one or both may be flowed out of the second stage 106 for harvesting or return to the fluid source. In an exemplary multi-stage fluid processing application, the fluid separation chamber 92 is used to separate whole blood into platelet-rich plasma and red blood cells in the first stage 104. The platelet-rich plasma is then flowed into the second stage 106, where it is separated into platelet concentrate and platelet-poor plasma. In the exemplary procedure, whole blood is flowed into the first stage 104 of a fluid separation chamber 92 received in a spinning centrifuge 10 (as in FIG. 1). The whole blood enters the first stage 104 via port 122 and the second fluid passage 120 (FIG. 6). The centrifugal field present in the fluid separation chamber 92 acts upon the blood to separate it into a layer substantially comprised of platelet-rich plasma and a layer substantially comprised of red blood cells. The higher density component (red blood cells) gravitates toward the high-G wall 24, while the lower density component (platelet-rich plasma) remains closer to the low-G wall 26 (FIG. 1). The red blood cells are flowed out of the first stage 104 via port 118 and the first fluid passage 116 (FIG. 6), where they are either harvested or returned to the blood source. The platelet-rich plasma is flowed out of the first stage 104 via port 126 and the third fluid passage 124. The high-G wall 24 may include a first projection or dam 140 (FIG. 6) which extends toward the low-G wall 26, across the third fluid passage 124. The first dam 140 is configured to intercept red blood cells adjacent thereto and prevent them from entering the third fluid passage 124 and thereby contaminating the platelet-rich plasma. The platelet-rich plasma flowed out of the first stage 104 is directed into the second stage 106 by operation of one or more of the cassettes of the flow circuit 16. The platelet-rich plasma enters the second stage 106 via port 134 and the fifth fluid passage 132. The centrifugal field acts upon the platelet-rich plasma to separate it into a layer substantially comprised of platelet concentrate and a layer substantially comprised of platelet-poor plasma. The higher density component (platelet concentrate) gravitates toward the high-G wall 24, while the lower density component (platelet-poor plasma) remains closer to the low-G wall 26 (FIG. 1). The platelet concentrate is flowed out of the second stage 106 via port 130 and the fourth fluid passage 128 (FIG. 6), where it is either harvested or returned to the blood source. The platelet-poor plasma is flowed out of the second stage 106 via port 138 and the sixth fluid passage 136, where it is either harvested or returned to the blood source. The low-G wall 26 may include a second projection or dam 142 (FIG. 6) which extends toward the high-G wall 24, across the fourth fluid passage 128. The second dam 142 is configured to intercept platelet-poor plasma adjacent thereto and prevent it from entering the fourth fluid passage 128 and thereby diluting the platelet concentrate. FIG. 7 shows an alternative embodiment of a fluid separation chamber 144 provided as a body with a top edge 146, a bottom edge 148, and a pair of side edges 150 and 152. A first interior seal or wall 154 divides the interior of the fluid separation chamber 144 into first and second stages 156 and 158. In the illustrated embodiment, the first interior wall 154 extends in a generally U-shaped manner from the top edge 146 toward the bottom edge 148, toward one of the side edges 150, 152, and then back to terminate at the top edge 146. Thus, the region of the interior of the fluid separation chamber 144 defined by the top edge 146 and the first interior wall 154 comprises the first stage 156, while the remainder of the interior of the fluid separation chamber 144 comprises the second stage 158. It will be seen that, in the embodiment of FIG. 7, the first stage 156 is, in substantial part, spaced from the bottom edge 148 of the fluid separation chamber 144 by the second stage 158. In addition to the first interior wall 154, the illustrated fluid separation chamber 144 includes a second interior seal or wall 160 positioned within the first stage 156. In the embodiment of FIG. 7, the second interior wall 160 extends in a dogleg or L-shaped manner from the top edge 146 toward the bottom edge 148 and then toward the right side edge 152, without contacting the first interior wall 154. It is within the scope of the present disclosure for the second interior wall to be otherwise configured without departing from the scope of the present disclosure. Further, it is within the scope of the present disclosure to provide the second chamber with an interior seal or wall positioned therein (as shown in FIG. 8 and described in greater detail below). The interior walls 154 and 160 of the fluid separation chamber 144 help to define fluid passages which allow for fluid communication between the flow circuit and the first and second stages 156 and 158. In the embodiment of FIG. 7, a first fluid passage 162 is defined at least in part by the left side of the first interior wall 154 and the second interior wall 160 to allow fluid communication between the
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