Abstract:
A collapsible dispensing system for flowable materials is disclosed. A conical one-way valve assembly of coaxially conforming parts is attached to a collapsible container. An enclosing sleeve seals an elastomeric sheath to a valve body. Flowable materials are dispensed under positive pressure without back flow of external gases and contaminants, even after repeated dispensing of container contents. This enables flowable materials that are susceptible to oxidation and contamination to be reformulated without antioxidants and/or preservatives. The collapsible multiple dose dispensing system maintains the integrity and sterility of flowable materials, thereby prolonging product use life. The system takes advantage of a conical design, allowing for quicker, easier and cheaper manufacturing and assembly.

Description:
CROSS-REFERENCE TO DISCLOSURE DOCUMENTS 
     This application references and claims the benefit of the filing of Disclosure Document No. 489,311, filed on Feb. 24, 2001 and Disclosure Document No. 491,603, filed on Apr. 4, 2001. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention generally relates to a system for dispensing fluids. More specifically, the present invention relates to a one-way valve assembly for dispensing fluid from a collapsible container. The valve assembly of the present invention also prevents backflow into the container prior to, during and following distribution of the fluid, thereby keeping unwanted items such as contaminants out of the container. 
     BACKGROUND OF THE PRESENT INVENTION 
     There is a great need in many industries to dispense fluid products that are susceptible to oxidation and contamination safely. Many products lose their freshness, potency and/or sterility after only a brief period of use. This period or “use life” varies from product to product. Generally, when fluids are dispensed from a valve assembly, the volume of product delivered from the valve assembly is replaced with an equivalent volume of air. Exposure to this ambient air leads to the entry of oxygen into the container and potentially to contaminants in the air such as microorganisms, atmospheric gases, moisture and dust particles. The quality, potency, safety and/or sterility of the remaining product can be compromised by the air and potential contaminants within. 
     The present invention delivers fluid under positive pressure through a one-way valve from a container that collapses in proportion to the amount of product dispensed. Consequently, air does not enter the dispensing system. 
     The concept of a one-way valve assembly is not new. One-way valves are used extensively throughout the medical field in complex medical device machinery to dispense flowable products. One-way valves are also being used in aerosol dispensers to dispense flowable products. However, the need for a contamination-safe, propellant-free one-way valve that can easily be manufactured and assembled has long been apparent. As the medical field continues to grow, the need to dispense multiple doses of sterile fluids during surgery, diagnostic testing, ophthalmology and other areas without fear of contamination continues to grow as well. Thus, there exists a need for creating a collapsible dispensing system that is simple to manufacture and assemble for dispensing multiple doses of sterile fluids. 
     Several one-way valves contain cylindrical cores encompassed by an elastic cylindrical sheath. The core typically has an entrance tube leading to one area of the sheath, and an exit tube leading away from another area of the sheath. The entrance and exit tubes, while enclosed by the sheath, do not interconnect. To dispense liquid, one would apply pressure to expand the sheath, allowing liquid to pass from the entrance tube to the exit tube. Upon release of that pressure, the sheath would contract, thereby sealing the valve and preventing backflow into the container. 
     For example, U.S. Pat. Nos. RE 34,243; 5,836,484; 5,279,330; 5,305,783; 5,305,786; 5,080,138; 5,080,139; and 5,092,855 all disclose cylindrical one way valves for dispensing liquids and eliminating backflow of unwanted materials. Some of these, such as U.S. Pat. No. 5,080,138, have an excessive number of parts. All of these, particularly the disc shaped valves in U.S. Pat. Nos. 5,080,139 and 5,279,330, are unnecessarily difficult to assemble. 
     Referring to FIG. 1, shown is a dispensing valve assembly for dispensing liquids of different consistencies according to U.S. Pat. No. RE 34,243. Shown is valve assembly  11  containing five pieces. Valve assembly  11  is mounted on flexible container  13  such that fluid will be dispensed when container  13  is compressed. Valve assembly  11  is constructed by stretching sheath  15  over the outside of valve body (not pictured). Sheath  15  is sealed on the outside surface of the valve body by O-rings  17 . 
     The five-piece design disclosed in U.S. Pat. No. RE 34,243, and shown in FIG. 1, has several disadvantages. First, the five-piece design makes the unit costly to manufacture, as at least four distinct units must be manufactured, and each unit must be constructed with precision. The existence of such a five-piece apparatus also necessarily indicates a level of complexity when assembling. Sheath  15  must be stretched over valve body (not pictured) and then secured in place over O-rings  17 . This process is difficult to accomplish. 
     Referring now to FIG. 2, shown is the valve assembly of U.S. Pat. No. 5,305,783. Shown is valve body  21  covered by elastomeric sleeve  23  with O-ring like enlargements  25  at the each end. Elastomeric sleeve  23  is secured to valve body  21  by O-ring like enlargements  25  by forming a seal at reduced diameter ends  27  of valve body  21 . This design renders assembly of such a valve difficult. 
     To illustrate, the steps required to attach elastomeric sleeve  23  onto valve body  21  are shown in FIGS. 3A-3D. Elastomeric sleeve  23  is first formed on molding core pin  29  as shown in FIG.  3 A. Elastomeric sleeve  23  must then be rolled up on itself on molding core pin  29  as depicted in FIG.  3 B. Molding core pin  29  is then removed as depicted in FIG.  3 C. Elastomeric sleeve  23  is then placed on valve body  21  with O-ring like enlargement  25   a  and elastomeric sleeve  23  is secured to reduced diameter end section  27  of valve body  21  as shown in FIG.  3 D. The assembly is completed when elastomeric sleeve  23  is unrolled and O-ring like enlargement  25   b  secures the reduced diameter end section  27  of the valve body  21  as resulting in the configuration shown in FIG.  2 . 
     This process could be done manually but it would be time consuming. Alternatively, the assembly process could be automated but would involve an unacceptable rate of failure resulting in increased expense. 
     Referring now to FIG. 4, shown is a valve assembly according to U.S. Pat. No. 5,092,855. Sheath  31  has O-rings  33  at both ends of valve body  35 . O-rings  33  secure sheath  31  to valve body  35  when O-rings  33  seat into annular grooves formed on the outside of valve body  35 . Sheath  31  is further secured by enclosing sleeve  37  which fits over sheath  31  and valve body  35  and ensures sheath  31  and valve body  35  are sealed. Once again, sheath  31  must be stretched over valve body  35  rendering assembly of such a valve difficult and costly to manufacture on a commercial scale. 
     Referring next to FIG. 5, shown is a valve assembly according to U.S. Pat. No. 5,305,786. As shown, valve body  41 , elastomeric member  43  and cover member  45  are cylindrical. This cylindrical design is a disadvantage during assembly. For the valve assembly to operate as described, the diameter of cylindrical section  47  of valve body  41  must be only slightly smaller than the diameter of cylindrical section  49  of cover member  45 . Therefore, insertion of valve body  41  into elastomeric member  43  and subsequently into cover member  45  can tolerate only slight deviations in any direction perpendicular to the axis of the valve. 
     Referring again to FIG. 1, to assemble a valve assembly such as the one depicted, sheath  15  is typically rolled axially onto a mandrel or support pin and then carefully rolled up from one end toward the other in preparation for placement on valve body (not pictured). Alternatively, sheath  15  can be fitted on arms for lateral expansion with compressed air while the valve body is inserted into sheath  15 . In either case, assembly, whether performed manually or by complex machinery, is slow, cumbersome, and sometimes ineffective. Another disadvantage with the design depicted in FIG. 1 is that sheath valve is cylindrical, thereby requiring the inside diameter of the sheath to be marginally smaller than the outside diameter of the valve body in order to maintain the necessary sealing tension of sheath  15  against the valve body. As stated above, the cylindrical design necessarily makes the valve assembly of FIG. 1 difficult and costly to manufacture and assemble. 
     Referring now to FIG. 6, shown is a multiple dose dispensing system according to U.S. Pat. No. 5,836,484. Shown are dispensing cartridge  51 , container  53 , delivery block  59  and sheath  55  all contained within housing  57 . Delivery block  59  dispenses liquid  61  through sheath  55 , and sheath  55  prevents the backflow of contaminants into delivery block  59 . 
     The valve assembly system depicted in FIG. 6 also has several disadvantages. One disadvantage is that for the design to function properly, sheath  55  must stretch over or envelop delivery block  59 . While O-rings are not part of this invention, the stretching of sheath  55  onto delivery block  59  is a complicated process which slows manufacturing. Another disadvantage is the necessity of protrusions  63  to keep sheath  55  from shifting, contracting, or falling off of delivery block  59 . Further, as before, to ensure that sheath  55  fits tightly on delivery block  59 , the diameter of sheath  55  as manufactured must be smaller than the outer diameter of delivery block  59 . While this design necessarily ensures a taut fit, it causes grave problems during assembly, when a flexible material must tightly envelop a block with a smaller diameter. Therefore, the complications and costs associated with manufacturing such a design and assembling such a valve can be overbearing in a mass product market. 
     SUMMARY OF THE INVENTION 
     The present invention discloses a valve assembly for dispensing flowable materials, wherein said valve assembly comprises a valve body having a longitudinal bore therethrough, an elastomeric sheath having a longitudinal bore therethrough and an enclosing sleeve having a longitudinal bore therethrough, wherein all of said valve body, said elastomeric sheath and said enclosing sleeve are conically shaped, and wherein all of said longitudinal bores of said valve body, said elastomeric sheath and said enclosing sleeve are coaxial. 
     An object of the present invention is to provide a one-way valve which is easily manufactured. The present invention provides a three-piece system which can be manufactured at a lower cost. The system eliminates the use of O-rings and other methods of keeping the sheath attached to the valve body, and dispenses with other non-essential parts. 
     Another object of the present invention is to provide a one-way valve which is easily assembled. The present invention has a conical valve body and a conical elastomeric sheath. The conical shape of these two pieces facilitates the lateral enclosure on the outside surface of the valve body, thereby allowing simple assembly of the unit. The present invention also comprises a rigid sleeve laterally enclosing the elastomeric sheath, spaced radially outward from the elastomeric sheath. This design limits the radially outward displacement of the elastomeric sheath thus preventing sheath membrane distortion or ballooning. Therefore the conical valve assembly can be easily manufactured and assembled on a small scale as well as in a mass market. 
     Yet another object of the present invention is to provide a means for venting the space between the sleeve and the sheath in a one-way valve assembly. By venting the space, air pressure will not build up, and the sheath can expand without unnecessary force and rebound easily into sealing contact with the valve body upon release of pressure. 
     Other objects, features, and characteristics of the present invention, as well as the methods of operation and functions of the related elements of the structure, and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following detailed description with reference to the accompanying drawings, all of which form a part of this specification. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A further understanding of the present invention can be obtained by reference to a preferred embodiment set forth in the illustrations of the accompanying drawings. Although the illustrated embodiment is merely exemplary of systems for carrying out the present invention, both the organization and method of operation of the invention, in general, together with further objectives and advantages thereof, may be more easily understood by reference to the drawings and the following description. The drawings are not intended to limit the scope of this invention, which is set forth with particularity in the claims as appended or as subsequently amended, but merely to clarify and exemplify the invention. 
     For a more complete understanding of the present invention, reference is now made to the following drawings in which: 
     FIG. 1 shows a dispensing valve assembly for dispensing liquids of different consistencies according to U.S. Pat. No. RE 34,243. 
     FIG. 2 shows a valve assembly for dispensing liquids according to U.S. Pat. No. 5,305,783. 
     FIGS. 3A-3D show the steps required to assemble a conventional valve assembly according to U.S. Pat. No. 5,305,783. 
     FIG. 4 shows a valve assembly according to U.S. Pat. No. 5,092,855. 
     FIG. 5 shows a valve assembly according to U.S. Pat. No. 5,305,786. 
     FIG. 6 shows a prior art multiple dose dispensing cartridge for flowable materials according to U.S. Pat. No. 5,836,484. 
     FIG. 7 a  shows the preferred embodiment of the conical valve assembly according to the present invention. 
     FIG. 7 b  shows a side cross sectional view of the conical valve assembly according to the preferred embodiment of the present invention. 
     FIG. 8 shows a cross section of the present invention when assembled. 
     FIGS. 9 a - 9   l  depict alternative embodiments of the present invention, including alternative embodiments of the elastomeric sheath according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As required, a detailed illustrative embodiment of the present invention is disclosed herein. However, techniques, systems and operating structures in accordance with the present invention may be embodied in a wide variety of forms and modes, some of which may be quite different from those in the disclosed embodiment. Consequently, the specific structural and functional details described herein are merely representative, yet in that regard, they are deemed to afford the best embodiment for the purposes of disclosure and to provide a basis for the claims herein which define the scope of the present invention. The following presents a detailed description of a preferred embodiment (as well as some alternative embodiments) of the present invention. 
     Referring first to FIGS. 7 a - 7   b , depicted is the preferred embodiment of the conical valve assembly according to its invention. Such a system as shown in FIG. 7 a , includes a conical valve body  71 , an elastomeric sheath  73  and an enclosing sleeve  75 . Each one of these parts is conically shaped. Valve body  71  has inlet end  77  and outlet end  79 . Elastomeric sheath  73  has inlet end  81  and outlet end  83 . Enclosing sleeve  75  has inlet end  85 , outlet end  87  and venting means  88 . Inlet ends  77 ,  81  and  85  are all preferably wider than the corresponding outlet ends  79 ,  83  and  87  respectively. Valve body  71 , elastomeric sheath  73  and enclosing sleeve  75  have longitudinal bore  89  running along the axis of each part respectively. Inlet ends  77 ,  81  and  85  and corresponding outlet ends  79 ,  83  and  87  respectively are all preferably positioned along axis  89 . 
     Referring now to the side cross sectional view depicted in FIG. 7 b , valve body  71  has an inside conical space that tapers inward along the axis from inlet end  77 . Valve body  71  has inlet port  91  and outlet port  93  on the side for inlet channel  95  and outlet channels  97 . Valve body  71  has inlet channel  95  toward inlet end  77  that passes from the inlet conical space to the outside surface of valve body  71 . Valve body  71  also has outlet channel  97  toward outlet end  87  of the assembled valve pictured in FIG. 7 b . Outlet channel  97  transverses the wall of valve body  71  from the outside surface at an angle to axis  89 . Each of the parts may also have flange  99 ,  101  or  103  on their respective inlet ends. Flange  99 ,  101  or  103  can form a first surface facing in an axial direction facing towards outlet end  87 . The conical shape of these parts leads to reduced manufacturing costs and increased ease of assembly. 
     Previously developed cylindrical valves are extremely sensitive to manufacturing variances in the inside and outside diameters of the component parts. These variances often render assembly impossible. Even when components are optimally manufactured, assembly of cylindrical valve parts is difficult because of the small differences between the diameters of the components. The proposed conical shaped valve eliminates both of these problems. Parts with narrow ends fitting into parts with wide ends obviates the assembly problems discussed above. The conical design is also more forgiving of manufacturing variances in the diameter of component parts. Alternatively, the components may all be wedge shaped with ovular or flat sides. The flat wedge shaped components may be three, four or multi sided. The inwardly tapered nature of the wedge shaped components maintains the above mentioned advantages in manufacturing and assembly albeit to a lesser extent than the conical shape shown in FIGS. 7 a  and  7   b.    
     Referring now to FIG. 8, shown is a cross section of the preferred embodiment of the present invention when assembled. Inlet end  111  is the wider end of valve body  113 . Inlet end  111  leads to the inside conical space of valve body  113 . Valve body  113  has flange  115  on inlet end  111 . Inlet channel  117  passes in a perpendicular direction to axis  89  of the valve from the inside conical space of valve body  113  to the outside of valve body  113 . Outlet end  119  is at the narrower end of the valve body  113 . Outlet channel  121  leads from outlet end  119  for a short distance along the axis of the valve and then turns perpendicular to this axis passing to the outside of the valve body  113 . Inlet channel  117  and outlet channel  121  can be modified in number, size, location and design to facilitate the flow of a wide range of fluid viscosities and flow rates. However, the ports for inlet channel  117  and outlet channel  121  are preferably on opposite sides so that the flowable materials can flow along a path that is greater than the length of valve body  113 . This enables valve body  113  to be smaller, cheaper and easier to assemble without functional sacrifice. Cylindrical valves with opposed ports are more susceptible to sheath membrane distortion or ballooning, and therefore will exhibit a greater inhibition of fluid flow through as compared with the conical embodiment of the present invention. 
     Still referring to FIG. 8, valve body  113  fits inside of elastomeric sheath  123 . Like valve body  113 , elastomeric sheath  123  is conically shaped with flange section  125  at its wider end. Elastomeric sheath  123  also has tapered end section  127  to match with tapered end section  126  of valve body  113 . Elastomeric sheath  123 , prior to placement over the valve body  113 , preferably has an inside diameter smaller than the outside diameter of valve body  113  at inlet end  111 . This allows elastomeric sheath  123  to pass easily over outlet end  119  of valve body  113  and then to stretch in order to fit tightly around inlet end  111  of valve body  113 . Alternatively, elastomeric sheath  123  can have a gum like grabbing texture to further enhance the fit around valve body  113 . In yet another alternative embodiment, the inside surface of elastomeric sheath  123  may be ribbed with slight protrusions which extend in a spiral pattern around the inside surface of elastomeric sheath  123  from the area adjacent to inlet channel  117  to the area adjacent to outlet channel  121 . These ribs facilitate the conduction of the fluid from inlet channel  117  to outlet end  119  channel  121 . Another alternate embodiment has grooves along the outside surface of valve body  113  for directing the fluid flow. The rib and groove alternatives could interfere with the sealing action of elastomeric sheath  123  against valve body  113 , thereby increasing the risk of air and contaminants getting into the system. Therefore, the preferred method of directing fluid flow is through lines of sealing contact with enclosing sleeve  129  along the outside surface of elastomeric sheath  123 . Elastomeric sheath  123  can form a closure axially outward from the valve body to prevent back flow through closure  131 . Closure  131  can be any one of a number of known closures, such as a duckbill closure, a flattened hollow tube of rubber, which when under pressure will expand to permit fluid flow and contract once the pressure is relieved. Alternatively, outlet end  119  may be fitted with a drop meter in place of the duckbill closure, a hypodermic needle or a nozzle for providing the desired form for the fluid being dispensed including a spray or a stream, or any other closure device. Outlet end  119  can also be configured without a discrete outlet channel inside valve body  113  where fluid flows from inlet end  111  along the exterior surface of valve body  113  and the interior surface of elastomeric sheath  123  to outlet end  119 . Enclosing sleeve  129  can be utilized to provide alternative lines of sealing contact to direct the fluid flow through an outlet passageway along the exterior surface of valve body  113  and elastomeric sheath  123  can form closure  131  for such a passageway. This closure can extend axially outward from the outlet end  119 . 
     Both valve body  113  and elastomeric sheath  123  fit inside enclosing sleeve  129 . Enclosing sleeve  123 , like the other two parts is conical in shape. The wide end of enclosing sleeve  129  has increased diameter section  133  to contain flange section  115  of the valve body  113 . On the inside of increased diameter section  133  is a radially inwardly extending shoulder which secures flange section  125  of elastomeric sheath  123 . Enclosing sleeve  129  contains expansion chamber  135  in the inside of conical section  137 . This space allows elastomeric sheath  123  to expand under pressure coming from inlet channel  117 . Enclosing sleeve  129  also features venting means  139  to relieve pressure from the outside of elastomeric sheath  123 . Enclosing sleeve  129  can form a seal with elastomeric sheath  123  and the valve body  113  at inlet end  111  and outlet end  119  allowing elastomeric sheath  123  to remain in tight contact with valve body  113  and therefore provide resistance against forces from outside inlet channel  117  and outlet channel  121  and therefore ensure that the flowable materials pass through and out of the valve without backflow of air and contaminants into the container. Enclosing sleeve  129  can be attached to flange section  115  of valve body  113  via any attaching means, including but not limited to, snap fitting, press fitting, heat sealing or welding. Any other method known for joining parts to obtain a leak free connection may be used. 
     All three components, namely valve body  113 , elastomeric sheath  123  and enclosing sleeve  129  may be coated with an anti-microbial agent to prevent contamination of sterile fluids. An inert, non-elutable anti-microbial agent is preferred. Likewise, all three components may be composed of materials which are stable to solutions under a broad pH range and resistant to degradation under exposure to a wide range of organic and aqueous solvents. Preferable materials for valve body  113  and elastomeric sheath  123  have low absorbance, high adhesive surface characteristics that form bonds that maintain a quick and firm sealing tension. Adhesive bonds between surfaces of elastomeric sheath  123  and valve body  113  can be enhanced by the elastic return forces generated when undersized sheaths are placed on oversized valve bodies. Elastomeric sheaths with a greater wall thickness may be expected to provide more elastic restoring force. Elastomeric sheaths with a smaller wall thickness may be expected to provide greater ejection ease. The wall thickness of the sheath is preferably in the range of 8/1000″ to 35/1000″, and the durometer is preferably in the range of 15-70 (A), although the wall thickness and durometer of the sheath can be adjusted further for optimal sealing and ejection ease. The most preferred materials for elastomeric sheath  123  are silicone, polystyrene butadiene and butyl rubber. The most preferred material for valve body  113  is polysulfone. Other materials, such as polymethacrylate, may be appropriate depending on the nature of the fluid and the application. 
     Valve body  113 , elastomeric sheath  123  and enclosing sleeve  129  are assembled to make the conical valve. This valve is then attached to a container to form the complete dispensing system. The fluid flows into inlet end  111  and passes into the conical space of valve body  113 . As more fluid enters this space, the pressure increases and fluid is forced through inlet channel  117 . Once the pressure is sufficient, elastomeric sheath  123  deforms and allows fluid in to the expansion chamber  135 . As expansion chamber  135  fills, the fluid preferably flows around valve body  113  in a spiral fashion before it passes back into valve body  113  through outlet channel  121  and finally out of the valve through outlet end  119 . Back flow and therefore contamination is prevented by closure  131  of elastomeric sheath  129 . Further, once the fluid stops flowing through inlet end  111 , the pressure in the conical space of valve body  113  is then reduced. This in turn allows elastomeric sheath  123  to collapse and reseal both the inlet channel  117  and outlet channel  121 , thereby preventing any back flow through the valve. Venting means  139  in enclosing sleeve  129  prevents any vacuum or pressure from forming within expansion chamber  135  between elastomeric sheath  123  and enclosing sleeve  129 . 
     Previous inventions in this area have been used to protect chemicals, medicines, personal hygiene products and other flowable materials susceptible to contaminations by atmospheric gases and microorganisms. This design with its enhanced ease of manufacturing and assembly will decrease the cost of current applications of one-way valves and extend the use of one way valves to previously prohibited applications. The conical shape of this valve allows the fluid to flow through the valve in a spiral fashion. This increases the length of the fluid flow path which in turn reduces the likelihood of back flowing fluid contaminating the fluid in the container. Moreover, the conical shape of the valve creates a vortex like flow of fluid through the valve therefore increased flow rates are possible relative to other non-conical valves of similar shape and design. 
     FIGS. 9 a - 9   l  represent alternative embodiments of a one-way conical valve assembly according to the present invention. Referring to FIGS. 9 a  and  9   b , shown are two components, the rigid valve body  141  and elastomeric valve stem  143 , both having a conical shape. In contrast to the three component embodiment described above, in this alternative embodiment, elastomeric valve stem  143  is contained within rigid valve body  141  which in turn also serves as an enclosing sleeve. In this configuration of the one-way valve, rigid valve body  141  has an inwardly tapered axially extending bore. Elastomeric valve stem  143  is of a corresponding conical shape, and can have a gum-like grabbing texture. Elastomeric valve stem  143  is compressible and deformable. When assembled, elastomeric valve stem  143  is inside the bore of valve body  141  and maintains sealing contact with the inner surface of valve body  141  as depicted in FIG. 9 a . Elastomeric valve stem  143  includes inlet end  149  and outlet end  151  spaced apart in an elongated direction and a conical outside surface extending in an inwardly tapered axial direction between inlet end  145  and outlet end  147  of valve body  141 . Inlet end  149  is preferably wider than outlet end  151 . Inlet channel  153  is located within elastomeric valve stem  143  and has a first end at inlet end  149  of elastomeric valve stem  143  and second end toward but not at outlet end  151  of said elastomeric valve stem  143 . Inlet channel  153  traverses at an angle to the longitudinal axis  159  of the valve. When fluid is to be dispensed from the container, the fluid is pressurized and directed through inlet channel  153  into the space  155  between the inside of valve body  141  and the outside surface of elastomeric valve stem  143 . The fluid then passes along the outside surface of elastomeric valve stem  143  to outlet end  147  of the valve body  141 . The fluid inwardly compresses elastomeric valve stem  143  transversely of the axial direction moving elastomeric valve stem  143  out of sealing contact with the surface of the bore in valve body  141 . When the pressure acting on the fluid is released, elastomeric valve stem  143  rebounds or expands into sealing contact with the inside surface of the bore preventing any back flow into the container. 
     Valve body  141  and the elastomeric valve stem  143  each have a flange section  109  adjacent to inlet channel  153 . Flange sections  157  form a surface facing in the axial direction toward outlet  151  with a radially outer diameter that includes an axially extending conical section extending from flange section  157  toward outlet  151  and tapering inwardly toward axis  159 . The conical shape of elastomeric valve stem  143  and valve body  141  facilitates an easy fit of elastomeric valve stem  143  into inlet end  145  of valve body  141 . As mentioned above, the seal between elastomeric valve stem  143  and valve body  141  is improved by compressing elastomeric valve stem  143  against outlet end  147  of valve body  141 . Conical valves of this type can be assembled by inserting elastomeric valve stem  143  into valve body  141  through inlet end  145 . Outlet end  151  of elastomeric valve stem  143  can be positioned below outlet end  147  of valve body  141 , up to outlet end  147  of valve body  141  or through outlet end  147 , projecting slightly outwardly from valve body  141 . A nozzle located at the outlet end of the valve body can provide the desired form for the fluid being dispensed including a drop, a spray or a stream. Flange section  157  of elastomeric valve stem  143  can be attached to flange section  157  of valve body  141  by any attachment means, including but not limited to press fitting, heat sealing or welding. Any other method known for joining parts to obtain a leak free connection may be used. Valve body  141  is sealed to the neck portion of a container so that the fluid cannot leak out around valve body  141 . 
     Both components, namely valve body  141  and elastomeric valve stem  143  may be coated with an anti-microbial agent to prevent contamination of sterile fluids. Any inert, non-elutable anti-microbial agent is preferred. Likewise, both components may be composed of materials which are stable to solutions under a broad pH range and resistant to degradation under exposure to wide range of organic and aqueous solvents. Preferable materials for valve body  141  and elastomeric valve stem  143  have low absorbance, high adhesive surface characteristics that form bonds that maintain a quick and firm sealing tension combined with ejection ease. Preferable materials for elastomeric valve stem  143  include silicone, polystyrene butadiene and butyl rubber. A preferable material for valve body  141  is polysulfone. Other materials, such as polymethacrylate, may be appropriate depending on the nature of the fluid and the application. 
     In another alternative embodiment of the present invention, elastomeric valve stem  143  is formed from compressible solid material and is secured in the bore of valve body  141  so that it is not displaced during the dispensing operation. 
     Other alternative embodiments of elastomeric stem  143  are depicted in FIGS. 9 c  and  9   d . In yet another alternative embodiment, elastomeric valve stem  143  can be formed with a hollow cavity to make it less rigid and increase compressibility. This feature allows the valve to be activated under lower pressure as depicted in FIGS. 9 e ,  9   f ,  9   g  and  9   h.    
     In yet another alternative embodiment, elastomeric valve stem  143  can be formed so that as it is compressed and deforms radially inwardly, an annular flow path is provided between elastomeric valve stem  143  and the surface of the bore in valve body  141 . To maintain the sealing tension between elastomeric valve stem  143  and the surface of the bore, axially extending supports can be incorporated into elastomeric valve stem  143  with the supports extending to the surface of the bore. Elastomeric valve stem  143  then deforms radially inwardly only between the supports so that, in place of an annular passageway, individual passageways will be provided between the supports. The supports extend in the manner of spokes. To increase the length of the flow passages through the valve, the supports can be arranged helically whereby the flow passages have a length greater than the axial length of elastomeric valve stem  143  due to the helical arrangement as depicted in FIGS. 9 i ,  9   j ,  9   k  and  9   l.    
     The above described alternative embodiments offer advantages in manufacturing. In addition to the ease of manufacturing and assembly characteristic of the conical shape discussed above, the elastomeric valve stem design offers flexibility in manufacturing. Performance criteria such as flow rate, prevention of back flow, resistance to solvent degradation and pH stability can all be changed by modifying only the elastomeric valve stem. This flexibility can even be extended to the user who can substitute elastomeric valve stems appropriate for each application. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention and its operating advantages, reference should be made to the drawing and descriptive matter which illustrates and describes preferred embodiments of the invention. 
     While the present invention has been described with reference to one or more preferred embodiments, such embodiments are merely exemplary and are not intended to be limiting or represent an exhaustive enumeration of all aspects of the invention. The scope of the invention, therefore, shall be defined solely by the following claims. Further, it will be apparent to those skilled in the art that numerous changes may be made in such details without departing from the spirit and the principles of the invention. It should be appreciated that the present invention is capable of being embodied in other forms without departing from its essential characteristics.