Abstract:
A shear valve assembly comprises a pair of valve pads having opposing planar surfaces supported for relative sliding engagement. Each valve pad defines a plurality of liquid pathways by which a liquid can be passed from one pad to the other. The planar surface of one of the valve pads has an open channel formed therein, such channel having dimensions to accommodate a prescribed volume of liquid. Liquid is introduced into such channel via a first pair of pathways formed in the other valve pad, and liquid is dispensed from the open channel by a second pair of pathways that are brought into alignment with the channel during sliding movement between the valve pads. The valve assembly is particularly useful in blood-analyzing instruments for isolating and dispensing relatively minute volumes (of the order of microliters) of whole blood for analysis.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates in general to improvements in shear valve assemblies for isolating precise volumes of liquid for subsequent delivery to a utilization device or instrument. The apparatus of the invention is particularly useful in blood analyzing instruments, such as hematology instruments and flow cytometers, for isolating relatively minute volumes (of the order of microliters) of blood for analysis.  
         BACKGROUND OF THE INVENTION  
         [0002]    In automated blood-analyzing instruments, such as hematology instruments and fluorescent flow cytometers, it is necessary to mix precisely measured minute volumes, typically of the order of between 5 and 50 microliters, of patient blood with diluents and/or reagents in order to prepare blood samples for analysis. To do this, it is necessary to isolate small volumes of a blood sample aspirated from a vial of blood and to position these isolated volumes so that they may be readily dispensed into different mixing chambers. There are a number of liquid-metering shear valves that are capable of providing these functions; see, e.g., the blood-sampling shear valve assemblies disclosed in the respective disclosures of U.S. Patents to: Coulter et al, U.S. Pat. No. 3,567,389; Cabrera, U.S. Pat. No. 4,445,391 and  4 , 507 , 977 ; Cabrera et al., U.S. Pat. No. 4,896,546 and U.S. Pat. No. 4,702,889; Pellegrino, U.S. Pat. No. 4,822,569; Proni et al., U.S. Pat. No. 4,957,008; Del Valle et al., U.S. Pat. No. 5,158,751 and U.S. Pat. No. 5,255,568; and Hollinger, U.S. Pat. No. 5,542,305.  
           [0003]    All of the shear valve assemblies disclosed in the above patents comprise a stacked set of three disc-shaped pads having confronting planar surfaces. These pads, each being made of ceramic material, are arranged on a common axis about which at least the middle pad of the set is rotatably mounted. The middle pad defines a cylindrically-shaped “segmenting passageway” that extends axially through the entire width of the pad, i.e., between its opposing planar and parallel surfaces. Thus, the volume of this segmenting passageway is determined by the product of its diameter and the thickness of the middle pad. In use, this passageway is used to isolate one of at least two of the required prescribed volumes of blood needed for analysis in a conventional hematology instrument. A second, and somewhat larger, prescribed volume of blood needed for analysis is provided by a hollow external loop that is fluidly connected in series with the segmenting passageway. Thus, a blood sample entering the valve assembly through a port formed in one of the end pads will fill both the segmenting passageway and the hollow external loop, one after the other. As the middle pad is rotated relative to the end pads from a “blood-loading” position, in which blood can enter and fill the two prescribed volumes, and towards a “blood-dispensing” position, in which the two prescribed volumes can be dispensed, the blood flow entering the assembly is sheared off, and the two prescribed blood volumes contained respectively in the segmenting passageway and the external hollow loop are isolated from each other, as well as from the rest of the blood within the valve assembly. Continued rotation of the middle pad towards its blood-dispensing position operates to align the segmenting passageway and the external hollow loop with different ports formed in the respective end pads, thereby enabling the isolated blood volumes to be dispensed to a mixing station or elsewhere. When so aligned, a diluent or reagent that is to be ultimately mixed with the isolated blood sample is used to drive the sample from isolation, such diluent or reagent entering the assembly under pressure through a port in one of the end pads, engaging the isolated sample, and expelling the sample out of the assembly through a port formed in the opposite end pad.  
           [0004]    From the above description, it will be appreciated that the shear valve assemblies of the type disclosed in the above patents require at least three valve pads in order to extract or dispense the blood contained in the segmenting passageway. This requirement, of course, adds significant cost and complexity to the valve assembly and can adversely affect its reliability.  
         SUMMARY OF THE INVENTION  
         [0005]    In accordance with the invention, the above-noted shortcomings of the conventional three-pad shear valve architecture described above are effectively obviated by a more compact valve architecture comprising only two valve pads having confronting planar surfaces. According to the invention, a planar surface of one of the valve pads defines an open, liquid-retention channel that is arranged to be brought into and out of alignment with liquid ports formed in the other valve pad as the two valve pads and their respective planar surfaces are slidably moved relative to each other between a liquid-loading position and a liquid-dispensing position. This valve pad configuration enables a prescribed volume of liquid, supplied via liquid ports formed in the other valve pad, to be captured and isolated in the open liquid-retention channel for subsequent delivery to additional liquid-dispense ports of the other pad as a result of said relative movement between the pads. Preferably, the other pad supports an external hollow loop of prescribed volume that is in series communication with the open, liquid-retention channel when the valve pads are in their respective liquid-loading positions. When the valve pads move to their liquid-dispensing positions, the external hollow loop and the open, liquid-retention channel are isolated from each other and the source of liquid, but they are now aligned with liquid-dispensing ports formed in the opposing valve pads. At the same time, the liquid-loading ports formed in each valve pad and through which liquid was previously loaded into the valve assembly are aligned with rinse ports formed in the opposing valve pads, whereby the liquid-load ports may be cleansed during liquid dispensing.  
           [0006]    Pursuant to a non-limiting embodiment of the invention, one of the valve pads is fixed, while the other pad is supported for linear, slidable translation along the one pad within a reduced volume housing. The fixed valve pad contains a plurality of liquid ports, two of which are arranged to become aligned with the above-noted open liquid-retention channel formed in the planar surface of the movable valve pad. Preferably, two of these two liquid ports are ported to the above-noted external hollow loop section. In addition, the fixed valve pad is provided with a cleaning groove ported to a vacuum source.  
           [0007]    According to another aspect of the invention, the valve assembly of the invention is contained in a specialized housing adapted to maintain the necessary relationship between the valve pads during relative movement thereof.  
           [0008]    The invention and its advantages will be better understood from the ensuing detailed description of preferred embodiments, reference being made to the accompanying drawings in which like reference characters denote like parts. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is an exploded perspective illustration of a valve assembly configured in accordance with a preferred embodiment of the invention;  
         [0010]    [0010]FIGS. 2 and 3 illustrate the respective positions of the two valve pads shown in FIG. 1 in liquid-loading and liquid-dispensing positions, respectively;  
         [0011]    [0011]FIGS. 4 and 5 are diagrammatic front and rear perspective views of the dual pad liquid valve device of the invention showing the fixed valve pad installed in a supporting housing.;  
         [0012]    [0012]FIG. 6 is a diagrammatic perspective view of the dual pad liquid valve device of FIG. 5 showing the installation of the movable valve pad;  
         [0013]    [0013]FIG. 7 is a diagrammatic perspective view of the dual pad liquid valve device of FIG. 6 showing the installation of alignment and pressure springs against the movable valve pad;  
         [0014]    [0014]FIG. 8 is a diagrammatic perspective view of the dual pad liquid valve device of FIG. 6 showing the L-shaped cover;  
         [0015]    [0015]FIG. 9 is a diagrammatic perspective view of the dual pad liquid valve device of the invention showing the installation of first and second linear actuators; and  
         [0016]    [0016]FIG. 10 shows an alternative embodiment of the dual pad liquid valve device of the invention having a movable pad return spring in place of a linear actuator. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0017]    Referring now to the drawings, FIGS.  1 - 3  illustrate the basic details of a dual-pad shear valve assembly VA structured in accordance with a preferred embodiment of the invention. The valve assembly includes a first valve body  10 , configured as a ‘tile’ or ‘pad’ of a ceramic material, plastic, stainless steel or like materials used for liquid flow control applications, and having a first, generally planar inner surface  11  (the bottom surface as viewed in FIG. 1) and a second outer surface  12  (the top surface as viewed in FIG. 1) spaced apart therefrom by the thickness of the material of the pad. Although its shape may vary, in accordance with a preferred embodiment, the outer surface  12  of the first valve pad  10  is also preferably generally flat (planar), as shown. Making the outer surface  12  of the valve pad  10  generally flat facilitates installation and retention of the valve pad  10  within the valve housing (as will be described with reference to FIG. 4).  
         [0018]    The first valve pad  10  is also shown as containing a plurality of liquid pathways  13 A,  14 A,  15 A,  16 A,  17 A, and  18 A that pass perpendicularly through the pad. Preferably, each of such pathways has a circular transverse cross-section so as to define a cylindrical bore that intersects the first and second surfaces of the pad orthogonally. Four of these liquid pathways,  13 A- 16 A, are fluidly connected to four ports,  13 B- 16 B, respectively, such ports preferably extending normal to the second surface  12 . The other two liquid pathways  17 A and  18 A are fluidly connected to an external hollow loop  19  that interconnects these two pathways. Preferably, loop  19  has a circular cross section and a length that, together with the volumes defined by pathways  17 A and  18 A, define one of two prescribed volumes of liquid to be isolated and dispensed by the valve assembly. Also, the surface  11  of valve pad  10  is preferably provided with a cleaning groove  54  (shown in FIG. 4), that is adapted to be ported, via liquid paths  55  and  56 , to a vacuum source (not shown), so as to scavenge any debris that may accumulate on either of the engaging surfaces of the valve pads.  
         [0019]    Confronting the first valve body  10  is a second valve body (tile/pad)  20  having a first generally planar inner surface  21  (its top surface as viewed in FIG. 1) and a second outer surface  22  (the bottom surface as viewed in FIG. 1) spaced apart therefrom by the thickness of the material of the valve pad  20 . It is this planar inner surface  21  that engages the planar inner surface  11  of pad  10  to produce the “shearing” effect by which the different liquid pathways in the valve assembly are opened and closed to liquid flow as the pads are slid relative to each other. As in the case of  10 , it is also preferred that the outer surface  22  of valve pad  20  is generally flat or planar, as shown. Configuring the outer surface  22  of the valve pad to be generally flat facilitates spring-biased retention of the pad  10  within a valve housing, shown in FIGS.  7 - 10 , to be described.  
         [0020]    As shown in FIGS.  1 - 3 , the second valve pad  20  defines a plurality of liquid pathways  22 A,  23 A,  24 A and  25 A. As in the case of pad  10 , each of these liquid pathways are preferably in the form of a cylindrical bore that passes completely through the pad, intersecting the opposing planar surfaces substantially orthogonally. Pathways  22 A - 25 A are fluidly connected to ports  22 B- 25 B, respectively, such ports preferably extending orthogonally outward from outer surface  22 . A key element of valve pad  20  is the presence of an open, liquid-retaining channel  26  that is cut or otherwise formed in the planar surface  21 . The dimensions of this channel are such as to define a second prescribed volume of liquid that is to be isolated and dispensed by the valve assembly of the invention.  
         [0021]    [0021]FIGS. 2 and 3 illustrate, respectively, the relative positions of valve pads  10  and  20  when the valve assembly is operating in its liquid-loading and liquid-dispensing states. While either or both of the pads may be selectively slid in a linear direction parallel to the planar surfaces  11  and  21  for the purpose of opening and closing the aforementioned pathways and ports, in the embodiment shown, only pad  20  slides while pad  10  remains stationary. Further, it will be appreciated that, while a linearly operated shear valve is preferred, the invention has equal utility in shear valves of the rotating variety, as discussed above with reference to the prior art.  
         [0022]    When the valve is operating in its liquid-loading state, pad  10  is in a position in which its pathways  13 A and  18 A are aligned with the open, liquid-retention channel  26  formed in the planar surface  21  of pad  20 . In this position, pathway  17 A in pad  10  is also aligned with pathway  25 A of pad  20 , and its associated port  25 B. Thus, to load liquid into the valve assembly, liquid is pumped into either port  13 B of valve pad  10 , or into port  25 B of valve pad  20 . In the former case, the entering blood will then fill, in order, the volumes defined by pathway  13 A in pad  10 , the open channel  26  in pad  20 , pathway  18 A in pad  10 , external loop  19 , pathway  17 A in pad  10 , pathway  25 A in pad  20 , and port  25 B of pad  20 . Obviously, the filling order is reversed in the case where the liquid enters the valve assembly through port  25 B. To isolate liquid in channel  26  and loop  19 , pad  20  is slid linearly to the liquid-dispense position shown in FIG. 3. In doing so, it will be appreciated that the source of the liquid entering through port  13 B and pathway  13 A (or through port  25 B and pathway  25 A) will be sheared off by the opposing planar surface  11  (or  21 ), and the liquid-retention channel  26  of pad  20  will become aligned with pathways  14 A and  15 A of pad  10 , and their respective ports  14 B and  15 B. At the same time, the external loop  19  will, via the pathways  17 A and  18 A with which it is fluidly connected, become aligned with pathways  24 A and  23 A of pad  20  and their associated ports  24 B and  23 B. Thus, to dispense the isolated volumes trapped in channel  26 , an expelling fluid, e.g., a diluent or non-reactive fluid, is pumped into either port  14 B or  15 B, and the isolated liquid will be expelled from the other port. Similarly, to dispense the liquid trapped in loop  19  and it associated pathways  17 A and  18 A, an expelling liquid (e.g., a diluent) is pumped into either of the ports  24 B or  23 B, and the trapped liquid will be expelled from the other of the two ports. As noted above, it will be appreciated that, while the shear valve assembly described above operates by producing linear motion between the valve pads, the invention is not to be construed as being limited to such movement. Clearly, any relative movement of the pads will produce the same effect, assuming the liquid pathways are appropriately positioned in the pads. In the illustrated example, liquid pathways  16 A and  17 A of pad  10  are arranged in a linear path that is parallel to the direction of linear movement of pad  10 ; the same is true of pathways pairs  15 A and  18 A, and  14 A and  13 A. The spacing between such pairs of pathway is the same for all pairs. Similarly, pathways  25 A and  25 B are aligned with the direction of linear movement of pad  10 .  
         [0023]    Referring to FIG. 3, it will be appreciated that, as the isolated prescribed volumes of liquid are being dispensed, pathways  25 A and port  25 B which, during the liquid-loading operation contained the liquid being loaded, can be rinsed with a diluent or other cleansing liquid by pumping such liquid through port  16 B and pathway  16 A. Similarly, port  13 B and pathway  13 A can be rinsed by pumping a suitable rinsing liquid through port  22 B and pathway  22 A.  
         [0024]    In should be noted that the present invention is not limited to using a particular number, size or configuration of the liquid-retention channel(s). One or a plurality of such channels may be provided in either or both of the valve pads and arranged to be ported to associated loading and dispensing ports in the opposite valve pad depending upon an intended application. Only a single liquid channel has been illustrated as being provided in the valve body  20  in order to reduce the complexity of the drawings and attendant description.  
         [0025]    Attention is now directed to FIGS.  4 - 10  which show the manner in which the components of the linearly sliding, dual valve pad mechanism of FIGS. 3 and 4, described above, may be compactly supported within a common housing for relative translational movement therebetween by respective linear actuator mechanisms coupled to opposite ends of the movable valve pad  20 . As shown in the perspective view of FIG. 4 and its associated obverse perspective view of FIG. 5, the valve housing comprises a generally hollow, solid rectangular block  60  having a set of mutually intersecting opposite end walls  61 ,  62 , respective front and rear walls  63 ,  64 , and a bottom wall or floor  65  portion that define an interior valve cavity  66 .  
         [0026]    The body&#39;s rear wall  64  has an interior edge surface  67  that is adapted to engage a first side  71  of the first (fixed) valve pad  10 , when the valve pad  10  is placed against the interior surface of the floor portion  65  of the body. As shown in FIG. 6, to avoid crimping or damage to the loop of conduit  42  which extends from the surface  12  of the valve pad  10 , the conduit may be bent generally parallel with the surface  12  of the valve pad  10 . Also, to enhance the fitting strength between the liquid conduits and the liquid paths of the valve pads, relatively shallow depressions may be formed in the surfaces  12  and  22  of the valve pads  10  and  20 , to which the liquid conduits are ported, to allow for the addition of a strengthening adhesive, such as epoxy, and the like, at the liquid conduit to valve pad attachment locations.  
         [0027]    A second, opposite side edge  72  of the fixed valve pad  10  is engageable by an interiorly projecting lip portion  82  of a generally L-shaped cover  80  that is attachable to the top and rear walls  64  and  69 , respectively, of the housing block  60 . When so attached, the interiorly projecting lip portion  82  of the L cover  80  holds the valve pad  10  against the interior edge surface  67  of the rear wall  64  of the housing block  60 .  
         [0028]    Protruding from the outer surface of the block&#39;s end wall  61  is a (generally cylindrical) mesa  90  having a bore  91  therethrough that opens into the housing&#39;s interior valve cavity  66 . The bore  91  is sized to receive the drive rod  92  of a first linear actuator, shown at  93  in FIG. 9. As a non-limiting example, this and a second linear actuator shown at  96  in FIG. 9 may comprise readily commercially available components, such as pneumatic actuators, solenoid actuators, and the like. As shown in the perspective view of FIG. 6, the actuator drive rod  92  is adapted to engage an end surface  97  of the second, translatable valve pad  20 .  
         [0029]    Referring to FIG. 7, the opposite end wall  62  of the support block  60  has an opening (not shown) that is sized to receive a generally cylindrical leg portion  101  of a generally ‘T’-shaped end fitting  100 . Leg portion  101  of the T fitting  100  includes a semi-cylindrical end portion  102 , that accommodates sliding translation of the second valve pad  20  thereover. The end fitting  100  also includes an end plate portion  103  sized to engage the external surface of the end wall  62 . The generally cylindrical leg portion  101  of the T fitting  100  has an axial bore that sized to receive the drive rod  95  of the second external actuator  96 , shown in FIG. 9, referenced above. The second actuator&#39;s drive rod  95  is adapted to engage a second end surface  98  of the translatable valve pad  20 .  
         [0030]    The length of the leg portion  101  of the T fitting  100  is defined such that, when the end plate portion  103  is placed upon the external surface of the end wall  62 , the semi-cylindrical end portion  102  engages an end wall  73  (shown in FIG. 1) of the fixed valve pad  10  that has been placed against the interior of the first end wall  61 , as described above. In this manner, opposite ends  73  and  74  of the valve pad  10  are captured between the first end wall  61  and the T fitting  100 .  
         [0031]    Also, the first and second sides  71  and  72 , respectively, of the fixed valve pad  10  are captured between the interior edge  67  of the block&#39;s rear wall  63  and the interior lip portion  82  of the L-shaped cover  80 , as described above. The end plate portion  103  of the T fitting  100  is retained against the external surface of the block&#39;s end wall  62  by means of an actuator bracket  110  placed thereon and attached to the end wall  62  by means of suitable fittings (e.g., screws  112 ) that pass through bores in the T-fitting&#39;s end plate  103 .  
         [0032]    As shown in FIGS. 6 and 7, the second (movable) valve pad  20  has a first side  123  urged against an interior side ledge portion  131  of the support block&#39;s rear wall  64  by an alignment biasing spring  140 . The alignment spring  140  is captured between the interior surface of the L-cover  80  and a second side  124  of the moveable valve pad  20 . In a similar manner, as shown in FIG. 8, a valve pad sealing pressure spring  150  is captured between the interior lip regions  84  and  85  of the cover  80  and the surface  22  of the movable valve pad  20 , so that surface  21  of the movable pad  20  is urged with a prescribed sealing pressure against the opposing surface  11  of the fixed valve pad  10 . To reduce wear on the spring, strips of low friction material, such as Teflon or the like, may be provided along the surface  22  of the movable valve pad  20 , so that the spring slides along the low friction strips during linear translation of the movable valve pad.  
         [0033]    Although the foregoing embodiment employs respective linear actuators to engage opposite ends of the movable valve pad  20 , as shown in FIG. 11, one of the linear actuators (e.g., actuator  96 ) may be replaced by a return spring, such as the coil spring  160  in FIG. 10. In this alternative embodiment, the return spring  160  is used to bias the translatable valve pad  20  to a first, preset liquid flow position, against which the linear actuator  93  operates to displace the movable valve pad  20  to a second liquid flow position.  
         [0034]    In operation, in response to control of the actuator(s) to place the movable valve pad in a first translational position (shown in FIG. 2), the liquid-retention channel  26  in the movable valve pad  20  becomes part aligned with liquid flow ports in the fixed pad  10  within a liquid charging path, allowing the channel  26  to be filled with charging liquid, as described above. Thereafter, as the actuator(s) are controlled to cause the movable pad  20  to be linearly displaced to a second translation position (shown in FIG. 3), the engaging surfaces  11  and  21  of the two valve pads provides for retention by the liquid-retention segment  26  of the charged liquid volume.  
         [0035]    At the second translation position, the prescribed volume of liquid that has been captured by and retained in the liquid-retention channel  51  of the movable valve pad  20  may then be removed by porting its pair of liquid paths to a carrier transport path through the fixed valve pad  10 . As pointed out above, since the volume of captured liquid is defined by the geometry of the retention channel  26  and therefore known a priori, the ratio of captured liquid to carrier volume is readily determined.  
         [0036]    As will be appreciated from the foregoing description, the present invention effectively overcomes the noted shortcomings of conventional liquid valve structures including rotational pad configured architectures, by means of a relatively physically compact, dual pad-based valve arrangement, in which at least one of a pair of generally planar surface engaging valve pads contains one or more liquid retention channels adapted to be brought into alignment with liquid ports of the adjacent pad. This open channel architecture obviates the need for three separate pads as has been traditionally used to isolate and dispense a prescribed volume of liquid, the result being a more reliable and lower cost product.  
         [0037]    While the invention has been described with reference to particularly preferred embodiments, it is to be understood numerous changes and modifications can be made without departing from the spirit of the invention, and such changes and modifications are intended to be encompassed by the ensuing claims.