Patent Publication Number: US-2005121638-A1

Title: Needleless valve

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention herein relates to valves and connectors, such as those use in medical liquid flow applications such as intravenous (IV) administration of medications. More particularly it relates to needleless valves for such applications.  
      2. Description of the Prior Art 
          There are many instances, particularly in the medical field, where quantities of liquid must be moved from a source of the liquid to a liquid conduit system under restricted and usually sterile conditions. A principal example is the administration of medication or other liquids to a patient intravenously. When the intravenous administration is to be conducted at periodic intervals over a extended period of time, the conventional practice is to insert a catheter into the patient&#39;s vein, usually through the patient&#39;s forearm, and leave the catheter in place with a portion extending out of the patient&#39;s arm and terminating in a valve (receiver) for periodic connection to the liquid source as required. The presence of the valve avoids the necessity of using direct injection of the patient each time the medication is to be administered, which would be both painful to the patient and also increase the risk of infection each time the skin was penetrated.        

      For many years, receivers of valves were constructed with a resealable membrane, such as a rubber or other elastomeric plug, stretched across the inlet end of the device, closing off the IV fluid conduit. When it was time to administer medication or other fluid, the physician or nurse would use a conventional hypodermic syringe with a sterile hypodermic needle which would penetrate the rubber plug and allow sterile injection of the fluid in the syringe directly into the liquid conduit or cannula. Upon withdrawal of the hypodermic needle, the elastic rubber plug would resile and seal itself, maintaining the sterile condition of the interior of the system.  
      Such practice, however, has numerous disadvantages. Repeated piercing of the plug with the hypodermic needles eventually damages the plug sufficiently that it cannot maintain the appropriate sterile seal. Further, since the valve/receiver devices are normally quite small, the plug is even smaller, often less than ½ inch (6 mm) in diameter. Therefore the person administering the medication had to take care in manipulating the syringe so that the hypodermic needle would pierce the rubber plug and not hit the other portions of the receiver, the patient&#39;s arm, or even the hands or arms of the person himself or herself. To take the appropriate amount of care, of course, required some period of time, thus reducing the number of patients a physician or nurse could serve in a given time period. In addition, it was not uncommon for hypodermic needles to break off in the plug during or before administration of the liquid, thus usually becoming lodged in the rubber plug and requiring the administrator to take time to remove the broken needle. Further, such breakage also commonly caused the loss of all or a portion of the medication or other liquid in the syringe and, of course, not properly administered to the patient.  
      Such problems were particularly common in situations where the medical personnel were required to act very rapidly, such as in emergency room and emergency medical administration settings.  
      The accidental piercing of the skin of the doctor or nurse raised critical problems. If such occurred before administration of the medication to the patient, the medication, or at least a portion of it, was injected into the nurse or doctor, which not only deprived the patient of the medication, but in fact might be quite harmful to the physician or nurse. If the accident occurred after administration of the fluid to the patient, the hypodermic needle could easily be contaminated by the patient&#39;s blood or other bodily fluid, thus being capable of transmitting the patient&#39;s disease to the physician or nurse. While this was a severe problem at any time, it became a truly critical problem as various highly infectious or virulent diseases became more prevalent in the population. The added presence of infectious diseases with extremely high rates of mortality among patients, such as AIDS, gave priority to development of devices which would eliminate the need for use of hypodermic needles.  
      In more recent years, “needleless” connectors and receptors have been developed and widely marketed. In systems using this type of device, the fluid dispenser (usually a syringe) is fitted with a blunt nozzle rather than a hypodermic needle. The blunt nozzle is designed to be received into a corresponding receiver attached to the IV line or other fluid conduit. Within the receiver is normally a hollow tubular cannula, which is a fixed member forming the extended end of the fluid conduit extending into the patient&#39;s veins. Sterility of the receivers is important so that transfer of the liquid from the syringe to the cannula and IV fluid conduit can be conducted under sterile conditions.  
      While the “needleless” concept has been well known and is quite simple, implementation of the concept in practice has been quite difficult. Needleless connectors have, for the most part, been designed with a hollow flexible plug which fits over the cannula and which has a self-sealing slit or similar closeable opening in its exterior end. The interior end of the plug is anchored adjacent to the downstream end of the cannula (i.e. the end leading into the IV system and the patient&#39;s arm). Since the cannula is made as a rigid elongated tube, as the nozzle of the fluid dispensing device is pushed into the receiver, it contacts that exterior end of the rubber plug and forces that end inwardly against the distal end of the cannula. The distal end of the cannula contacts the slit at the end of the plug and forces the slit open, so that the plug then becomes a sleeve as it is pushed inwardly along the outer surface of the cannula. Eventually, the distal end of the cannula, now being exposed, contacts the interior fluid transfer tube of the dispensing device as the nozzle of the dispensing device moves further into the receiver. When this connection is made, the fluid can be transferred from the syringe directly into the cannula through which it flows onto the IV system in the patient&#39;s body. Such opening of the device is commonly referred to as “activation” of the “valve.” 
      Once the fluid is fully transferred, the nozzle of the dispensing device is withdrawn outwardly through the receiver, causing the flexible plug to resile and extend distally along the cannula until it passes the cannula end and returns to its “deactivated” position enclosing the end of the cannula with the slit again sealed. Examples of devices of this type are shown in U.S. Pat. No. 5,065,783 (Ogle) and U.S. Pat. No. 5,549,577 (Siegel et al.) and in published PCT application no. WO 93/11828 (Lopez).  
      While such devices have worked well for the most part, they have been found to have some serious deficiencies. One of the most important is the fact that upon deactivation and withdrawal of the nozzle of the syringe or other fluid dispensing device, the compressed plug resiles back to its original position, thus increasing its internal volume back to its deactivated volume, thus creating a partial vacuum in the cannula and attached catheter. This produces a suctioning effect which often causes the patient&#39;s venous blood to be drawn into the catheter where it remains and can clot, thus preventing flow through the catheter. When it comes time to administer the next fluid dose, the plugged catheter prevents administration of the fluid. Remedying of the problem requires that the catheter be cleaned or replaced. This, of course, is a major problem in emergency situations, whether in an emergency room or when a patient on IV suffers some sort of relapse or seizure or other critical condition and medication must be administered through the IV without delay. Even in the absence of an emergency, however, withdrawal of the device for cleaning of the catheter requires that the IV subsequently be reinserted into the patient. In ordinary situations this at least requires the time of a nurse and is a discomfort for the patient. In many cases, however, reinsertion is a problem that requires a doctor&#39;s intervention, as for instance where an new acceptable insertion site is difficult to find or the patient does not tolerate needle insertions well. Thus reinsertion presents a significant cost event for the medical team and subsequently for the patient.  
      Other forms of connectors in needleless couplings have been described. These may have components within the coupling intended to hold the fluid flow conduit open against the tendency of flexible sleeves attached to one or the other end of a coupled tubing to compress and close the fluid flow path. A typical example is shown in U.S. Pat. No. 4,457,749 (Bellotti et al.) in which a “spike” having a cruciform cross section is used to hold open a fluid path within the coupling as the two portions of the tubing are joined together.  
     SUMMARY OF THE INVENTION  
      I have now invented a needless valve which avoids the suctioning problems of the prior needleless devices and which, in fact, can be structured to provide a positive self-purging effect upon deactivation. This device retains all of the favorable aspects of the needleless valve system for activation and administering the medication to the patient, but avoids all of the detrimental effects of the prior art devices that occur during deactivation. The present device is virtually impossible to clog, is self-purging at the end of an administration cycle, and helps ensure that substantially all of the medication dispensed from the syringe is administered into the patient. The device is also extremely simple in design and easy to construct and assemble, since it consists of only three pieces. The device may be made in a variety of different configurations, all of which provide the same self-purging action and clear flow path for the administered liquid.  
      The device of this invention is configured so that a core rod forces the plug to expand during activation in a manner not possible with the prior art devices, which causes the interior volume of the plug to increase substantially from its rest (deactivated) volume and opens a flow path through the valve for the administered fluid. Upon deactivation, the plug resiles and its interior volume returns to rest volume, closing the fluid flow path and displacing residual fluid within the valve, so that the residual fluid is expelled from the valve through its outlet into the downstream conduit or unit, purging the valve and promoting use of all of the administered fluid. In addition, such volume decrease prevents occurrence of any partial vacuum in the valve, and in fact usually creates a transient overpressure, which also assists in purging the valve of residual fluid. The structure thus maintains either a positive or neutral (i.e., non-negative) pressure at all times, preventing any suctioning of blood from a patient into an attached catheter, thus avoiding clogging of the catheter by formation of clots in blood drawn into it.  
      In a broad embodiment, the invention involves a needleless valve comprising a tubular housing having a fluid inlet end and a fluid outlet end, a solid rod within the housing, and a hollow flexible plug within the housing and moveable along the rod, the hollow plug in response to insertion of a fluid supply nozzle into the inlet end moving in one direction along and cooperating with the rod to increase the volume of the interior of the plug and open a fluid flow path between the inlet and outlet ends, and in response to withdrawal of the fluid supply nozzle from the inlet end moving in an opposite direction along and cooperating with the rod to decrease the volume of the plug interior, close the fluid flow path between the inlet and outlet ends and cause residual fluid in the flow path to be expelled from the valve through the outlet end.  
      In another broad embodiments, the invention involves a needleless valve having a distal end and a proximal end, and comprising a base disposed at the proximal end and comprising a connector for fluid communication attachment to a fluid flow tube, a solid elongated fluid channeling rod extending from a proximal end joined to the base to a distal end, and a fluid flow conduit formed in the base and extending through the connector into the proximal end the rod and disposed for the fluid communication with the tube; a flexible plug having a wall forming a hollow interior bounded by an inward facing surface; the plug fitting over the rod, being sealingly attached to the base and being moveable along the rod between a first activated position and a second deactivated position; in the first activated position the rod maintaining the plug in a form with the interior having a first larger volume, with the plug withdrawn from the distal end of the rod, and creating a fluid flow path through the interior and along the rod; and in the second deactivated position the plug being in a form with the interior having a second smaller volume with the distal end of the rod covered by the plug and the fluid flow path being blocked by the wall of the plug; and a tubular housing fitting over the plug and extending from the distal end of the device to the base, at the distal end the housing having an elongated receiver for releasable fluid communication reception of a nozzle of a fluid source, the receiver configured to guide movement of the nozzle along the receiver into contact with the plug, the plug moving between the first and the second positions in response to movement of and contact from the nozzle; such that movement of the plug from the first position to the second position in response to insertion of the nozzle into the receiver causing the rod and the plug to cooperate to expand the plug and increase the interior volume and open the valve to fluid flow between the source and the tube, and subsequent movement of the plug from the second position to the first position in response to withdrawal of the nozzle from the receiver causing the plug to resile and the interior volume to decrease, closing the valve to the fluid flow, displacing residual fluid within the valve and causing the residual fluid to flow from the proximal end of the valve into the tube.  
      In another embodiment the invention also comprises a rod for a needleless valve comprising a solid elongated core having a plurality of coaxial ribs extending outwardly therefrom.  
      Ribs made be made with a uniform width so that their extended edges are straight, with continuously varying widths so that their edged form straight or curved smooth tapers, or have discontinuously varying widths, so that their edges form one or more steps over the length of each rib. In one embodiment, the ribs terminate at the distal end of the rod in a hollow annular member encircling the rod.  
      Additional features of the invention as well as descriptions of the various forms of the components will be set forth below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of the device of this invention, with the individual components thereof shown in separated relationship;  
       FIG. 2  is an enlarged sectional view taken on Line  2 - 2  of  FIG. 1 ;  
       FIG. 3  is an enlarged sectional view taken on Line  3 - 3  of  FIG. 1 ;  
       FIG. 4  is an enlarged sectional view taken on Line  4 - 4  of  FIG. 1 ;  
       FIG. 5  is a sectional view taken on Line  5 - 5  of  FIG. 4 ;  
       FIG. 6  is a sectional view taken on Line  6 - 6  of  FIG. 3 ;  
       FIG. 7  is a sectional view with the components of  FIGS. 2, 3  and  4  shown in assembled relationship;  
       FIG. 8  is a view similar to  FIG. 7 , with the valve opened by attachment of a typical Luer-Lok connector;  
       FIG. 9  is a sectional view taken on Line  9 - 9  of  FIG. 7 ;  
       FIG. 10  is a sectional view taken on Line  10 - 10  of  FIG. 8 ;  
       FIG. 11  is a sectional view taken on Line  11 - 11  of  FIG. 8 ;  
       FIG. 12  is a perspective view of an alternative embodiment of flexible valve component;  
       FIG. 13  is a sectional view similar to  FIG. 7  showing the alternative valve component in closed position;  
       FIG. 14  is a sectional view taken on Line  14 - 14  of  FIG. 13 ;  
       FIG. 15  is a view similar to  FIG. 13  showing the valve component opened by insertion of a Luer connector; and  
       FIG. 16  is a sectional view taken on Line  16 - 16  of  FIG. 15 .  
       FIG. 17  is a perspective view illustrating another embodiment of a central rod of the present invention. 
    
    
     DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS  
      The device is best understood by reference to the drawings. For the purposes of description herein, the following conventions of direction will be maintained. The terms “upstream” and “downstream” will be with respect to the normal direction of fluid flow during administration of medication or other liquid through the valve of the present invention to a patient or other receiver. This is indicated in  FIG. 8  by the flow arrows  50  (upstream) and  52  (downstream). Similarly, the terms “distal” and “proximal” will be used with respect to the patient or other receiver, such that the upstream end of the device is also sometimes referred to as the distal end, while the downstream end is also sometimes referred to as the proximal end.  
      One embodiment of the overall device  2  is shown in  FIG. 1 , separated into three components: a base  4 , plug  6  and housing  8 . The principal features of each of the parts may also be seen in  FIG. 1 . The base  4  consists of a connector  10  which connects the device with the fluid flow tubing or conduit  48 , usually through a separate connector  94 , as illustrated in  FIG. 8 ; a radial flange  12 , which serves as a seat for attachment of the plug  6 ; and an elongated rod  14  which, as will be described below, cooperates with the plug  6  to provide the unique and desirable operating features of the present invention.  
      The plug  6  has a seating gasket  16 , a compressible mid-section  18  which usually folds into a configuration similar to a bellows, and, at the distal end  20 , has a closeable slit or similar opening  22 . The housing  8  has a wide diameter expansion portion  24 , a coupling ring  26  which, during assembly, is bonded to the flange  12  to retain the device as a single unit and a receiving portion  28 , the distal end  30  of which can be configured as shown with threads  32  to join with corresponding threads of a liquid dispenser to couple the two together.  
       FIGS. 2, 3  and  4  show respectively the housing  8 , plug  6  and base  4  in cross-section to facilitate understanding of their operations and functions. Considering first  FIG. 4 , the base  4  is formed of the aforementioned coupler  10 , flange  12  and rod  14 . As will be seen from  FIG. 4 , the coupler  10  is has an annular form with its inner wall  34  formed into threads or ribs  36  to allow it to be attached to a corresponding threaded end of coupler such as  94  as will be described below. Centrally disposed within the annular shaped coupler  10  is a hollow tapered cylinder  40  which has fluid flow channel  38  extending through it. Cylinder  40  is an extension of the flange  12  and rod  14  so that it will be desirable for the entire base unit to be molded as a single piece of rigid material, commonly plastic but also possibly of metal. The fluid flow conduit  38  continues as conduit  42  through the center of flange  12  and terminates as a conduit  46  within the proximal end  44  of rod  14 . Fluid flowing downstream along rod  14  from the liquid dispenser  116  during activation of the device  2  thus enters the fluid conduit  46  through the openings  146 , flows through aperture conduit  42  through flange  12 , and on through the channel  38  into coupler  94  and eventually into tubing  48  as shown in  FIG. 8 . The extension of cylinder  40  beyond the proximal end of the base  10  facilitates insertion into the coupler  94  or (in the absence of such a coupler) directly into, for example, tubing  48 . Tubing  48  may be substituted for by other devices to which the valve is to be attached, such as direct coupling to a storage, test or reaction vessel or to a measuring instrument.  
      A preferred embodiment of a plug  6  is shown in  FIG. 3 . The plug  6  is made out of a flexible material, usually a rubber or a polymeric elastomer. In the embodiment shown the plug has a flange  16  which has a flat base  54  to allow it to seat against the corresponding flat distal face  56  of the flange  12  on the base  10 , as shown in  FIGS. 7 and 8 . The most proximal section  18  may be scored with groves  58  on the interior and exterior to permit bellowing or other folding of the section as the plug is compressed and moved posteriorly during activation, as best illustrated in  FIG. 8 . (Another embodiment of the plug  6  will be discussed below, which has a different form of section  18 .) In other embodiments the flange  12  may be eliminated and other means, such as a gripping or adhesive-coated surface (not shown) provided to which the proximal end of plug  6  is secured.  
      In the preferred embodiment shown in the drawings, the plug  6  also has an intermediate section  60  which can be expanded, but which does not normally flex, fold or compress as extensively as section  18 . Both the expansion and compression of section  18  and the expansion of section  60  contribute to the self-purging action of the device  2  as will be described below. The distal portion  62  of the plug  6  extends outwardly just past the tip  64  of rod  14  and normally has a somewhat thicker wall than do sections  18  and  60  to accommodate the opening and subsequent closing of slit  22  in the distal end  20  and to resist buckling of the end  20  when the unit is deactivated. Preferably the slit  22  will be terminated on the interior side of the plug  10  by a “duck bill” flange  66  which assists in causing the slit  22  to resist leakage when internal pressure is present during deactivation.  
      The housing  8  is a simple rigid shell of plastic or metal, which is intended to fit over the plug  6  and attach to flange  12 , thus locking gasket  16  in position, as best shown in  FIGS. 7 and 8 . The inner portion of coupling ring  26  of housing  8  is configured with a generally semi-circular channel  70  incorporated within it, both of which are configured to accommodate the corresponding base  72  and lip  74  of gasket  16 . When the connecting ring  26  is seated against the flange  12  of base  4 , preferably aligned by groove  76  into which rib  78  fits, and the two are sealed together as by a conventional adhesive or by heat, ultrasonic or RF welding, the flange  16  of the plug  6  is firmly held against the flange  12  so that the plug cannot be displaced, and also to provide a firm base for subsequent return or resiling of the plug  6  upon deactivation.  
      The interior of section  24  of the housing  8  is configured to have a substantially greater diameter than the deactivated rest diameter of section  18  of the plug  6 , as indicated in  FIG. 7 , creating an annular space  80  into which the portion  18  can expand as it is compressed to form the generally bellowed configuration shown in  FIG. 8 .  
      The rod  14  can have a number of different configurations, all of which are intended to cause the plug  6  to expand outwardly during activation, thus creating the expansion of the elastic plug and increase of its interior volume, so that the plug  6  upon deactivation will return or resile inwardly, decreasing its interior volume and thereby purging fluid from the fluid flow space  82  along the rod  14 . The rod  14  can be generally described as having a solid core  84  which terminates in a blunt or rounded tip  64  and which has extending radially outwardly therefrom a plurality of ribs  86  (and perhaps also  86 ′). The ribs  86  may have various configurations which will cause the plug to expand and which will prevent prolapsing of the plug during activation. For instance, in various embodiments, an elongated rib may be uniform width over most of its length (with preferably a transition curve or slope at its distal end, to facilitate movement of the end  20  of plug  6  along the rod and rib), or it may have a continuously varying width, so that it has a straight or curved tapered profile, or it may have widths that vary discontinuously along its length, so that it has a stepped profile. It is preferred that for ribs in which the widths vary, either continuously or discontinuously, the widths increase from distal to proximal ends, so that no recess or shoulder is formed upon which a portion of the interior of the plug wall could become snagged, preventing or impeding return or resiling of the plug upon deactivation. In yet another alternative, shown in  FIG. 17 , the proximal ends of the ribs  86  may terminate in a hollow annular member  68  which serves to maintain the maximum expansion of the plug  6  during activation. Conveniently this annular member  68  will be circular, but polygonal shapes are also usable, although polygons of less than six, and probably less than eight, sides should probably be avoided, since they may be unduly angular and tend to impede resiling of the plug upon deactivation.  
      There may be any convenient number of ribs and they may be disposed at any desired orientation to each other around the circumference of the rod  14 . However, normally there will need to be at least three ribs  86 , preferably equally spaced at 120° from each other, in order to ensure that the elastic plug  6  is stretched to form a space  82  of appropriate volume. Typically there will be four ribs  86  in a cruciform shape as indicated in  FIGS. 9 and 10 ; although a larger number of ribs, such as eight as shown in  FIG. 5 , may also be used. It is also possible, and usually preferred, to have different numbers and lengths of ribs on the same rod  14 , as illustrated in  FIGS. 1 and 5 , where the added ribs  86 ′ are interspersed between the principal cruciform ribs  86  but are foreshortened in axial length and extend distally only as far as the length of the widest section of each rib  86 . The added ribs help support the extended plug wall and prevent prolapse of unsupported portions of the wall and expansion increases and the wall thickness is thinned by stretching. Given the small size of the device and the desire to maximize the flow channels, it is considered that eight to ten ribs are probably the maximum practical number, with four, six or eight ribs being preferred, and other numbers (both between three and ten and greater than ten) being possible. Use of an even number of ribs as shown in the illustrations is preferred since it is easier to mold symmetrical ribs equally spaced than to mold an asymmetric configuration as would be present with and odd number of ribs. Further, the number of width steps may be two or three as shown or may be more, although again the small size of the device acts as a practical limitation on the number of width steps of the ribs  86  which are either feasible or desirable. An alternative embodiment of the plug  6  is shown as  6 ′ in  FIGS. 12-16 . In this embodiment, the plug  6 ′ is configured with an expanded downstream section  18 ′ which substantially replaces sections  18  and  60  in the configuration described above. The section  18 ′ may be somewhat bulbous or it may approximately conform to the shape of the rod  14  (shown in these Figures with an alternative form of the ribs designated as  86 ″), with the plug  6 ′ having conforming hollow ribs  88 . The operation of this alternative plug  6 ′ is illustrated in  FIGS. 13 and 15 . In the deactivated state, shown in  FIG. 13 , the plug is essentially in the shape shown in  FIGS. 12 and 14 . Upon activation by the nozzle  90  of a liquid dispenser, the bulbous section  18 ′ with ribs  88  expands outwardly (as shown in  FIGS. 15 and 16 ) into space  80  and leaves an enlarged open space  92  between the rod  14  and the interior wall surface of the plug  6 ′. Upon deactivation the plug  6 ′ resiles or is caused to return to the configuration shown in  FIG. 13 .  
      It will be evident to those skilled in the art that there are, of course, other configurations of the plug  6  other than that of  6 ′, which will provide equivalent expansion of the plug and increase of its interior volume during activation, and guide the subsequent resiling of the plug and decrease of its interior volume to produce the unique self-purging effect present in the claimed device. It is intended that all such configurations are to be considered within the scope of this invention as defined in the appended claims.  
      The operation of the invention can best be understood by reference to  FIGS. 8, 10  and  11 . In a typical application, device  2  is attached to a Luer-Lok™ coupler  94 . Coupler  94  is formed with a hollow cylindrical connector  96  which extends into the recess  98  inside coupler  10  and which is secured therein by threads  100  cooperating with ribs or threads  36  on the interior of the coupler  10 . In the embodiment shown, cylinder  40  has a tapered outer surface  102  which causes a wedging action with the interior of connector  96  as indicated at  104 , such that as the connector  94  is turned and threaded into the recess  98  the cylinder  40  and connector  96  are tightly wedged together sealing against any loss of fluid. Alternatively both cylinder  40  and connector  96  can be straight with parallel surfaces, and they can be secured together by an adhesive, such as a solvent adhesive, as shown at  97  in  FIG. 15 .  
      Preferably the design of the tapered cylinder  40  and connector  96  are such that the end  106  of cylinder  40  and the opposing surface  108  on the interior of connector  96  are closely adjacent or abutting such that the space  110  between them is minimized.  
      Connection of the device of this invention to tubing  48  or any other device may be configured to be releasable or permanent, as desired. In the embodiment shown, the connector has at its opposite end a nipple  112  to which the conventional tubing  48  is attached. The tubing is normally stretched slightly as indicated at  114  so that the tubing  48  is retained on the nipple  112  by the combination of the elastic resiliency of the tubing and the interference fit between the inner surface of the tubing  48  and the outer surface of the nipple  112 . If there is concern that the tubing  48  may separate from the nipple  112 , a conventional external clamp (not shown) may be placed around the circumference of the tubing  48  where it overlaps the nipple  112  and tightened to ensure good connection between the tubing and the nipple. Alternatively various adhesives or solvents may be used to secure the tubing and nipple together. The solvents or adhesives must be selected such that they do not intrude into the fluid flow path of the device or migrate to cause unwanted adhesion elsewhere in the device.  
      Activation and deactivation of the valve  2  will be best understood by comparison of  FIGS. 7 and 8 . The device in its deactivated configuration is shown in  FIG. 7 , with the plug  6  in its “rest” or fully resiled orientation. (For purposes of comparison, it will be understood that connector  94  and tubing  49  of  FIG. 8  should be imagined also to be present in  FIG. 7 .) Activation comprises joining of the needleless valve  2  to a liquid supply source such as a syringe or other reservoir device, partially shown at  116  in  FIG. 8 . Connection is usually through a coupler  118  which is similar in configuration to the coupler  10  of the valve. Coupler  118  consists of an outer cylindrical wall  120  which has on its inner side ribs or threads  122 . Aligned with the center axis of coupler  118  is nozzle  90  which extends outwardly from the end  124  of coupler  118  and which is tapered to fit into the receiving portion  126  of section  28  of the housing  8 . The interior of nozzle  90  is an open fluid flow channel  128  which is in fluid communication with the interior  130  of liquid reservoir  116 . The reservoir  116  is here illustrated as a conventional syringe device, with a movable piston  132  housed within a cylinder  130 . The piston  132  is manipulated by the physician or nurse as indicated by the arrow  50  to force the liquid forward. Such use and operation of the fluid dispensing device  116  are conventional and need not be described further. Similarly, such devices may take many different forms, all of which are equally applicable to the present invention.  
      As the coupler  118  is moved forward (as indicated by the arrow  134 ) by interaction of the threads  32  and  112 , the tapered nozzle  90  interacts with the inner surface  136  of the receiver section  126  of the housing to create a wedging action similar to that described above between the connectors  94  and  10 , thus forming a mechanically tight connection. Simultaneously the front end  138  of coupler  118  comes into contact with distal end surface  20  of plug  6  and forces the plug  6  to compress in the downstream or proximal direction, thus causing the slit  22  to contact the tip  64  of rod  14  and be forced open as it passes over and around the tip  64 , as best illustrated in  FIG. 11 . The compressive movement of the rest of the plug  6  caused by the forward motion of the nozzle  90  causes the other portions of the plug  6  to move along corresponding sections of the rod  14  and ribs  86  (and  86 ′, if present), thus forcing the wall of the plug  6  to be stretched and expanded outwardly, substantially increasing the interior volume of the plug  6  and creating the space  82  through which the fluid can flow along the surfaces of rod  14  and ribs  86 . With the plug  6  thus retracted, the liquid can flow freely from the liquid reservoir or supply device  116  through the nozzle  90  and the now-opened slit  22 , along and adjacent to the outer surfaces of the rod  14  and ribs  86  (through the elongated V-shaped spaces  82  formed by adjacent ribs  86 , the rod  14 , and the inner surface of the plug  6 , and on through the openings  146  and into the conduits  46 ,  42  and  38 , on through the channel  140  in the nipple  112  and into the interior  142  of tubing  48 , and subsequently to the patient or other receiver.  
      Because the liquid source  116  and the valve  2  are securely locked together by the interaction of threads  32  and  112  and the wedging action of the receiver  126  and nozzle  90 , this activated configuration is stable and can be maintained for as long as the physician, nurse or other user wishes to continue dispensing the liquid. It can also, of course, be maintained for an extended period of time without human supervision or control, where the reservoir or liquid supply device  116  is mechanically or electrically operated and provides a continuous or intermittent flow of fluid through the valve  2  to the patient or receiver.  
      In prior art devices, the flexible plug merely slid along the outside of the tubular cannula. Since the cannula had a uniform diameter, the plug remained strongly compressed over substantially all of its length, being stretched or expanded only at the distal tip, and then only by the minimal amount necessary to open the end slit and allow the end of the hollow cannula to protrude into the nozzle of the fluid dispensing device. As the nozzle of the dispensing device was subsequently withdrawn and the plug allowed to resile back in the distal direction along the outer surface of the cannula and closed over the open end of the cannula, a partial vacuum was created in the cannula. This in turn commonly resulted in liquid being withdrawn from the patient or receiver and pulled by suction back into the catheter to which the cannula of the prior art device was connected. Where the receiver was a human patient, the fluid drawn back into the cannula would usually consist in whole or in part of venous blood. The blood thus retained in the cannula would thereafter often congeal and coagulate, causing blockage of the hollow interior cannula and making subsequent administration of fluid difficult or impossible until the valve and cannula were either replaced or cleaned.  
       FIG. 8  illustrates the improvement of the present invention in which such creation of partial vacuum is entirely avoided and the self-purging property of the device is illustrated. The plug, by being stretched to increase the interior volume during activation, resiles and decreases that volume during deactivation, so that the contraction of the plug wall into the space  82  (essentially eliminating space  82 ) displaces substantially all residual fluid remaining within the valve upon deactivation, and forces it to be expelled through the exit conduits. In addition, the resiling of the plug wall often creates a transient overpressure which also assists in expulsion of the residual fluid. Since the plug ultimately resiles back to its rest configuration the overpressure decreases to neutral pressure. Because the center member of this device is solid rod  14  rather than an open cannula, the end  20  of resiling plug  6  passes over distal end  64  of rod  14  and slit  22  closes before the decrease in interior volume, and therefore purging action of the resiling plug, is completed. Consequently, unlike in the prior art valves, no negative pressure is formed by the movement of end  20  and the closing of slit  22 .  
      The self-purging and pressure-creating operation of the device is evident from  FIG. 8 . As the nozzle  90  is withdrawn from the receiver, section  18  of plug  6  which has been under compression and has been stretched and expanded over the ribs  86  of the rod  14 , begins to resile and return toward the configuration shown in  FIG. 7 . This causes the space  82  to be closed, completely or substantially, and all fluid which has been in that space is thus forced through openings  146  into conduit  46  and on through to conduits  42 ,  38 ,  140  and  142  and into the receiver or patient, leaving no significant amount of fluid remaining in the valve, as will be evident by comparison of  FIGS. 9 and 10 . This is the exact opposite of the operation the prior art devices, where return of the plug to the deactivated position has no effect on the interior volume of the cannula, since the cannula is made of a rigid plastic or similar material and therefore is not deformed by pressure from the plug. Thus the liquid remaining in the interior of the cannula cannot be purged by the return of the plug to its deactivated position. In the present invention, by contrast, the resiling or return of the plug to its deactivated position forces the remaining fluid in the valve downstream to the receiver or patient.  
      In most cases, the return and closing action of the plug  6  (or  6 ′) will be adequately accomplished entirely by the resiliency of the elastic material forming the plug, such that no outside biasing or urging of the plug is necessary. However, if desired, one could supplement the normal resiliency of plug  6  by, during assembly of the device, filling the space  80  with an inert gas  144  such as nitrogen or argon, preferably under pressure. Thus, as the device is activated and the wall of the plug  6  is forced to expand outwardly by the rod  14  and ribs  86 , it encounters the compressed gas within the space  80  and, while reducing the volume of space  80 , compresses (or further compresses) the gas  144 . Consequently, when the device is deactivated, the compressed gas  144  acts on the outside surface of the plug  6  and as the volume of chamber  80  begins to increase (and space  82  decrease), the pressure of the expanding gas supplements the normal resiliency of the plug  6  material, causing the device to purge itself more quickly and completely. The expanding compressed gas  144  forces the plug material to assume the configuration shown in  FIG. 9  more completely, with closer fitting between the interior wall of the plug  6  and the exterior surface of the rod  14  and ribs  86 . The same effect will be seen by comparison of  FIGS. 14 and 16  for the embodiment of the rib  6 ′ shown in  FIG. 12 , involving spaces  80  and  92 . (One could also achieve the same effect by mechanical rather than pneumatic action if one were to emplace small springs (not shown) within space  82  and in contact with the outer surface of the plug wall and the inner surface of the housing wall, and which would be compressed when the plug  6  expanded. Upon deactivation, the compressed would then resile and expand, urging the plug wall inward and assisting in decreasing the interior volume of the plug.  
      It will thus be seen that, unlike prior art devices in which the fluid flow channel through the valve has a fixed volume within a cannula, the device of the present invention with its variable volume flow path formed by the interaction of the center rod and ribs and the expanding and contracting interior dimension of the plug, employs a unique self-purging and pressure-generating action that causes essentially all of the fluid to be forced into the receiver or patient. This not only keeps the valve from being clogged by return flow of blood or other receiver fluid, but also ensures that substantially all of the dosage of the fluid intended for the patient or receiver is, in fact, administered, with no signficant amounts retained or lost within the valve structure itself.  
      For brevity, the device and its operation have been described herein in terms of administration of IV fluid or similar medications to a human patient. However, it will be evident that this valve also has numerous other uses in related medical areas, such as administration of medications or nutrients through the gastrointestinal system of a patient. It also has many uses outside the medical field, such as administration of small quantities of liquid reactants or reagents in chemical or biological or medical testing procedures, or in the precise administration and delivery of chemical reactants in processes to produce small quantities of specialty chemicals. Other uses may include precise delivery of standard fluids for calibration of test instruments or for conducting hydraulic or other fluid flow experiments or small scale production processes.  
      It will be evident to those skilled in the art that there are numerous embodiments of the present invention which, while not expressly described above, are clearly within the scope and spirit of the invention. The above description is therefore intended to be exemplary only and the scope of the invention is to be determined solely from the appended claims.