Abstract:
A metering valve includes a valve stem co-axially slidable within a chamber body. The chamber body and the valve stem define a metering chamber. An outer and an inner annular seal is provided operative between a respective outer end and an inner end of the chamber body and the valve stem to seal the annular metering chamber there between. The inner seal comprises a wiper element.

Description:
BACKGROUND OF INVENTION  
         [0001]    The present application claims priority under 35 USC 119(a)-(d) to UK Patent Application No. 0203657.2 filed in Great Britain on Feb. 15, 2002, which application is hereby incorporated herein by reference.  
           [0002]    Metering valves typically comprise a valve stem co-axially slidable within a chamber body. The chamber body and the valve stem define a metering chamber for metering, in use, the product to be dispensed on each actuation of the apparatus. Outer and an inner annular seals are provided operative between a respective outer end and an inner end of the chamber body and the valve stem to seal the annular metering chamber there between. One problem with such metering valves is that in order for a good seal to be obtained between the seals and the valve stem it is necessary for the seals to tightly engage the valve stem. This can lead to a problem known as “seat drag” wherein on operation of the valve stem the seals are displaced axially due to the resulting friction. Over time seat drag can distort the shape of the seals leading to a reduction in integrity of the seal with the valve stem and also to potential changes in the volume of the metering chamber. A further problem is that the valve stem can be prone to sticking to the seals requiring a high actuation force to start the valve stem moving. The “unstick” force required to move the valve stem can be variable between actuations. This can lead to inconsistency in operation of the apparatus, especially where the actuation is designed to be automatic or semi-automatic such as in a breath actuated device.  
         SUMMARY OF INVENTION  
         [0003]    The invention relates to improvements in valves for dispensers for dispensing an accurately metered dose of a product.  
           [0004]    According to the invention there is provided a metering valve comprising a valve stem co-axially slidable within a chamber body, said chamber body and said valve stem defining a metering chamber, an outer and an inner annular seal being provided operative between a respective outer end and an inner end of the chamber body and the valve stem to seal the annular metering chamber there between, wherein the inner seal comprises a wiper element.  
           [0005]    Preferably, the wiper element is directed away from the outer seal.  
           [0006]    Preferably, the inner seal is formed from a thermoplastic elastomer.  
           [0007]    The metering valve may further comprises a valve body, wherein the inner seal is located between the valve body and the chamber body. Preferably, the inner seal is formed as a co-moulding with the valve body.  
           [0008]    Preferably, the wiper element comprises a wiper portion and a body portion, wherein an undersurface of the body portion is fully supported by the valve body.  
           [0009]    The present invention also provides a dispensing apparatus comprising a metering valve as described above.  
           [0010]    The present invention also provides a metering valve comprising a valve stem having at one end a piston extending within and slidable relative to a cup shaped chamber body, a clearance being provided between an outer surface of the piston and an inner surface of the chamber body to provide a path for product, a spring urging the piston against a base of the chamber body, movement of the valve stem against the spring bias causing the piston to move away from the base of the chamber body to define a temporary metering chamber between the valve stem and chamber body, the metering valve further comprising a sealing member provided such that as an end of the piston moves into contact with the sealing member the flow of product along the path is prevented and the product is dispensed through an outlet in the valve stem, wherein the sealing member comprises a wiper element.  
           [0011]    Preferably, the wiper element is directed away from the base of the chamber body. Preferably, the sealing member is formed from a thermoplastic elastomer.  
           [0012]    The metering valve may further comprises a valve body, wherein the sealing member is located between the valve body and the chamber body.  
           [0013]    Preferably, the sealing member is formed as a co-moulding with the valve body.  
           [0014]    Preferably, the wiper element comprises a wiper portion and a body portion, wherein an undersurface of the body portion is fully supported by the valve body.  
           [0015]    The present invention also provides a dispensing apparatus comprising a metering valve as described above.  
           [0016]    The present invention also provides a method of pressure filling a dispensing apparatus of the type comprising a metering valve closing off a dispensing container, the metering valve comprising a valve stem co-axially slidable within a chamber body, said chamber body and said valve stem defining a metering chamber, an outer and an inner annular seal being provided operative between a respective outer end and an inner end of the chamber body and the valve stem to seal the annular metering chamber there between, wherein the inner seal comprises a wiper element, the method comprising, injecting under pressure a product into the valve stem to cause said wiper element to deflect to permit flow of said product from said valve stem, through said metering chamber and into said dispensing container.  
           [0017]    Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0018]    [0018]FIG. 1 shows a cross-sectional view of a first embodiment of dispensing apparatus according to the present invention in an actuated position.  
         [0019]    [0019]FIG. 2 shows a cross-sectional enlarged view of a part of the dispensing apparatus of FIG. 1 in a non-actuated position.  
         [0020]    [0020]FIG. 3 shows a cross-sectional view of a second embodiment of dispensing apparatus according to the present invention in a non-actuated position.  
         [0021]    [0021]FIG. 4 shows a cross-sectional enlarged view of a part of the dispensing apparatus of FIG. 2 in a non-actuated position. 
     
    
     DETAILED DESCRIPTION  
       [0022]    A first embodiment of dispensing apparatus  10  according to the present invention is shown in FIGS. 1 and 2. The dispensing apparatus comprises a metering valve  10  which is attached in use to a pressurized dispensing container (not shown) in which a product to be dispensed in metered doses is stored. The product may be a liquid or a medicament normally in suspension or other excipients or a product which is expelled using a liquefied propellant such as a CFC or HFA or blends thereof.  
         [0023]    The metering valve  10  is held in position to seal the dispensing container by a ferrule  13  which is crimped to the open neck of the container. An elastomeric sealing gasket  34  prevents leakage of the product between the ferrule  13  and container. The metering valve comprises a valve stem  15  which extends co-axially within a generally cup-shaped chamber body  16  so as to be externally accessible. The metering valve further comprises a valve body  17  which supports the chamber body  16  within the metering valve  10 .  
         [0024]    The chamber body  16 , which is made preferably of a polymeric material, has a base  20  in which is located an aperture  21  and side walls  22  defining the open end of the chamber body  16 . Sandwiched between the base  20  of the chamber body  16  and the ferrule  13  is an elastomeric sliding seal  23  which also has an aperture therein.  
         [0025]    The valve stem  15 , which is also preferably made of a polymeric or metallic material, has at one end a generally hollow section  25  defining a dispensing channel in which portion  25  is located, a port  26 , and, at its other end, a solid section  27  which extends within and slidably relative thereto the chamber body  16 . A flange  28  is provided on the solid section 2:7 within the confines of the chamber body  16 . The side wails  22  of the chamber body  16  are preferably cylindrical.  
         [0026]    The valve stem  15  comprises a dependent cylindrical portion  61  which is spaced radially from the solid section  27 . The external diameter of the cylindrical portion  61  is selected to be smaller than the internal diameter of the chamber body  16  thus leaving a radial clearance there between of, typically, between 0.3 mm and 0.8 mm. The cylindrical portion  61  is rigid and preferably moulded as part of the valve stem  15 . A distal end  62  of the cylindrical portion  61  is tapered.  
         [0027]    The valve body  17  covers off the open end of the chamber body IS and is secured in position by a flange portion  30  clamped between the ferrule  13  and the sealing gasket  14 . The valve body  17  has entry ports  31  to allow the liquefied product to access the inside of the metering valve  10 .  
         [0028]    A return spring  32 , preferably of stainless steel is located between a base of the valve body  17  and the flange  28  thereby urging the valve stem  15  into contact with the base  20  of the chamber body  16 . As shown in FIG. 1, preferably, the diameter of the return spring  32  is chosen so as to be a close fit over the solid section  27  of the valve stem  15  so as to provide lateral support to the valve stem  15  during movement thereof to prevent undue lateral deflection of the valve stem  15  under side loading.  
         [0029]    An inner seal  29  is clamped between the chamber body  16  and valve body  17  to prevent fluid passage through the interface. According to the present invention, the inner seal  29  extends radially inwardly into the void space within the chamber body  16 -valve body  17  sub-assembly. A wiper element  60  is provided at the inner, distal edge of the inner seal  29 . The wiper element  60  is inwardly directed such that the wiper is directed towards the valve body  17  and away from the chamber body  16 .  
         [0030]    Preferably, the inner seal  29  is formed as a co-moulding with the valve body  17  to ensure that the inner seal  29  is properly aligned with the axial movement of the valve stem  15 .  
         [0031]    In use, the valve stem  15  is displaced axially relative to the remainder of the metering valve against the bias of the return spring  32 . As this occurs, a temporary chamber  35  (shown in FIG. 1 which shows the valve in an actuated position) is created between the valve stem  15  and the chamber body  16 . The product is drawn in through the clearance between the cylindrical portion  61  and the chamber body  16  and flows into the chamber  35 . Movement of the valve stem  15  then brings the tapered end  62  of the cylindrical portion  61  into contact with the inner seal  29 . A liquid-tight seal is therefore created at the circumferential ring of contact between the external surface of the cylindrical portion  61  and the inner seal  29  which prevents passage of product outwards towards the chamber  35 . At this point, the metered doss of the product to be dispensed is defined by the volume of the chamber  35  and the clearance between the cylindrical portion  61  and chamber body  16  on the outlet side of the point of contact between the cylindrical portion  61  and chamber body  16 .  
         [0032]    Advantageously, the cylindrical portion  61  contacts the wiper element  60  of the inner seal  29 . Movement of the valve stem  15  and cylindrical portion  61  deflects rather than distorts the wiper element  60  during operation. In this way an effective seal is produced without damaging the inner seal  29 . The geometry of the inner seal  29  does not require as much axial deflection when compared to traditional gliding seals since the majority of the movement is accommodated by deflection of the wiper element  60 . Therefore the structure of the valve body  17  immediately underneath the inner seal  29  may be enlarged to provide a greater degree of support thereby reducing excessive axial deflection of the seal  29  during operation. This effect is known as “seat drag” and, where it occurs, can lead to inconsistency in the shot weight delivered by the valve during its working life. In addition, the force required to actuate the valve is less since the magnitude of the friction between the wiper  60  and the valve stem  15  is less than with a traditional seal. In the sealed position, the pressure of the contents of the dispensing container acts on the back of the wiper element  60  tending to increase the sealing efficiency of the wiper element  60  against the cylindrical portion  61 . Further depression of the valve stem  15  causes the port  26  in the hollow section  25  of the valve stem  15  to pass through the sliding seal  23  and into the chamber  35  as shown in FIG. 1. The propellant systems used in the dispensing apparatus are liquefied gases or combinations thereof having boiling temperatures significantly below room temperature. As a result, the product boils off evacuating the contents of the chamber  35  through the port  26  into the dispensing channel in the hollow section  25  of the valve stem  15  thus providing an exit path for the product.  
         [0033]    At its maximum point of travel, the distal end of the solid section  27  of the valve stem  15  comes into contact with an abutment surface of the valve body  17  limiting the axial movement of the valve stem  15 .  
         [0034]    Release of the valve stem  15  allows the spring  32  to recover thereby forcing the valve stem  15  to return to its rest position and chamber  35  to be removed as the solid section  27  and cylindrical portion  61  approach the base  20 . Any product left in the chamber  35  is forced to return to the dispensing container via the clearance thereby preventing sedimentation.  
         [0035]    Advantageously, the metering valve of the present invention may be easily and rapidly filled by a pressure-filling technique. A further advantage of the inward pointing geometry of the wiper element  60   15  that pressure filling through the metering valve is made easier since the wiper element  60  is more readily deflected away, and out of contact, from the cylindrical portion  61  during the pressure filling procedure. During pressure filling, product is forced, under pressure, through the valve stem  15  from the hollow end  25  with the valve stem in the depressed, “firing” position. The product passes through the valve stem, chamber  35  and inlets of the valve body  17  into the dispensing container. Normally the pressure used must be great enough to overcome the internal seal between the valve stem and the chamber body or valve body. However, in the present invention the pressure may easily “blow past” the inner seal  29  by distorting the wiper  60  downwardly. Consequently, pressure filling is quicker and more consistent since the flow resistance is less. Conversely, in normal operation of the metering valve, the positioning of the chamber body inlets means that the internal pressure of the dispensing container is acting on the inside of the wiper  60  in the “firing” position forcing the wiper  60  against the cylindrical portion  61 , thus improving the integrity of the seal.  
         [0036]    In the first embodiment the invention has been described incorporated into a valve having a temporary metering chamber  35  that is created and filled during actuation.  
         [0037]    However, the invention also finds application in other types of valves where a permanent metering chamber is present as shown, for example, in the second embodiment illustrated in FIGS. 3 and 4. Like components to those described above with reference to the first embodiment have been referenced with like numerals.  
         [0038]    The metering valve  10  of the second embodiment comprises a permanent metering chamber  71  defined by a chamber body  70  held securely in place between the valve body  17  and the ferrule  13 . The valve stem  15  is slidably movable within the chamber body  70  between a non-actuated position (shown in FIG. 3) and an actuated position. The valve stem  15  comprises, as above, an outlet port  26  through which product is dispensed from the metering chamber  71  in the actuated position. The valve stem  15  also comprises a transfer channel  74  communicating with the metering chamber  71  by means of a transfer port  73  and with the bulk product in the dispensing container  76  by means of an inlet port  72 . The valve stem  15  is biased into the non-actuated position by means of a spring  32  spanning between the valve body  17  and a flange  75  on the valve stem  15 . In the non-actuated position the metering chamber  71  is in communication with the dispensing container  76  via the transfer port  73 , transfer channel  74  and inlet port  72 . In the actuated position the metering chamber  71  is in communication with the hollow part  25  of the valve stem  15  via the outlet port  26 . According to the present invention the inner seal  29  again comprises a wiper element  60  although in the second embodiment the wiper element  50  extends inwardly into contact with the valve stem  15 . As shown most clearly in FIG. 4 the valve body  17  in the region  77  immediately underneath the inner seal  29  is extended inwardly to provide axial support to the body portion  79  of the inner seal  29 . Preferably, the portion  77  beneath the inner seal is extended or otherwise shaped such that only the wiper element  60  of the inner seal  29  protrudes inwardly and is unsupported. This is advantageous as discussed above in relation to the first embodiment in reducing “seat drag.” Preferably, the seal  29  and portion  7  are keyed into one another by means of a ridge  78 , rib or similar feature. Optionally, the seal  29  and valve body  17  may be formed as a co-moulding.