Abstract:
A closure for a keg comprises a housing and at least one valve element that is movable with respect to the housing, inwardly into an open state and outwardly into a closed state. The closure also comprises a lock mechanism having a locking element that is movable with respect to the housing and is capable of holding the valve element in the open state. The lock mechanism includes first and second couplings at which the locking element and the valve element are mutually engageable. The lock mechanism is arranged such that when the locking element and the valve element are engaged at the first coupling, the locking element moves with the valve element as the valve element moves from the open state into the closed state. This movement of the locking element enables engagement between the locking element and the valve element at the second coupling, which engagement at the second coupling occurring on subsequent movement of the valve element into the open state to prevent the valve element returning to the closed state.

Description:
STATEMENT OF RELATED CASES 
     This application is a Continuation of U.S. application Ser. No. 13/883,796, filed Jul. 11, 2013 which is a U.S. National Phase Entry based on PCT/EP2011/069778, filed Jul. 11, 2013 which claims priority to GB 1018927.2, filed Nov. 9, 2010. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to pressurized vessels such as kegs for storing, transporting and dispensing beverages. The invention relates particularly to a closure for a keg, the closure having a safety mechanism to prevent the closure being re-closed after use. This ensures that the keg cannot be left pressurized after use and also that it cannot be refilled with the closure being re-closed afterwards. 
     Kegs are widely used for the distribution and service of beverages such as beer. A closure in a neck of the keg typically includes a filling and dispensing valve that defines multiple flow paths through the closure. In this way, during filling when the keg is usually inverted, beverage can be injected into the keg through the closure via a first flow path while displaced gas can exit the keg through the closure via a second flow path. Conversely, during dispensing, a propellant gas (typically nitrogen or carbon dioxide) can be injected into the keg through the closure via the first flow path to force beverage out of the keg through the closure along the second flow path. In the most common ‘well-type’ and ‘flat type’ arrangements, the closure comprises one or more valve elements and concentric flow paths. 
     When filling the keg at a filling station on a production line, the keg is usually inverted for use with beer and carbonated soft drinks although it could be upright for other beverages, especially those without effervescence, and a filling head is coupled to the closure to form a seal with the closure. The filling head has one or more formations that press against one or more spring-loaded valve elements of the closure to open the flow paths through the closure. Air inside the keg is flushed out with a relatively inert gas, for example carbon dioxide, and beverage is then injected into the keg via a liquid line connected to the filling head. Gas displaced from the keg by the incoming beverage is forced out through a vent in the filling head. When the keg is removed from the filling station, the filling head is uncoupled from the closure and the one or more valve elements of the closure therefore snap shut under spring loading, sealing the beverage and any remaining inert gas within the keg. 
     For the purpose of dispensing the beverage, a dispense head is coupled to the closure to form a seal with the closure. The dispense head has a lever that, when depressed, extends one or more plungers corresponding to the formations of the filling head. The plunger(s) therefore press against one or more valve elements of the closure to re-open the flow paths through the closure. Those flow paths communicate with gas and liquid lines connected to the dispense head. A propellant gas is injected into the keg from an external source connected to the gas line. Beverage is then forced out of the keg when a tap in the liquid line is opened to dispense the beverage. 
     When the dispense head is coupled to the closure, the propellant gas is injected into the keg at super-atmospheric pressure. The keg will remain under super-atmospheric pressure unless and until that gas is vented. It is recommended for safety purposes to vent the propellant gas from the keg when the dispense head is uncoupled from the closure, most commonly when the keg has been emptied and is being interchanged with a fresh, full keg. For this purpose, some dispense heads have a purge valve that is operable to vent propellant gas from the keg before the dispense head is uncoupled from the closure. 
     However, not all dispense heads have a purge valve and even those that do have a purge valve may not be operated correctly. In practice, a user will often be in a hurry to swap empty kegs for full kegs while dispensing beverages in a busy bar and may not therefore take the time necessary to vent the propellant gas from the empty keg. Instead, the user may simply remove the dispense head from the closure, allowing the spring-loaded valve element(s) of the closure to snap shut and hence to close the flow paths through the closure. The result is that the empty keg remains pressurized, which may not be apparent upon viewing the keg. This is a particular problem where a keg is of flexible material such as blow-moulded polyethylene terephthalate (PET), which is intended to allow the keg to be crushed after use for recycling rather than being returned intact for refilling like a rigid metal keg. Clearly a pressurized keg is not easily crushable. Also, in safety terms, it is undesirable for a pressurized keg to be punctured or ruptured, for example if an attempt is made to crush the keg during waste disposal while believing that the keg is not pressurized. 
     Another problem is that if the valve element(s) of the closure can still be opened and closed after the original beverage has been dispensed, the keg could possibly be re-filled in an unauthorised manner. For example, the keg could be re-filled with a beverage that is not of the appropriate quality; certainly, the keg is unlikely to be re-filled under the controlled conditions necessary to deliver a beverage in optimum condition. This is particularly undesirable as the keg may bear the brand of the original beverage supplier, whose reputation may be damaged by apparently supplying an inferior product. The keg could even be re-filled with a liquid that is not intended for human consumption and that could be dangerous to drink. Unauthorised refilling may not be apparent from a cursory inspection of the keg. 
     For these reasons, various keg closures have been proposed in which a valve element can close after filling but cannot close again after dispensing. For example, the proposal disclosed in U.S. Pat. No. 4,909,289 to Hagan et al employs a ratchet arrangement that limits the number of valve openings to allow keg testing and keg filling procedures before the valve element locks open after dispensing. 
     The proposal in U.S. Pat. No. 4,909,289 is impractical for various reasons. For example, the number of parts in its mechanism, and the way in which those parts interact, leads to long tolerance chains. This renders the mechanism vulnerable to failure where the combined tolerance of the parts causes excessive dimensional fluctuations between different assemblies. Also, the mechanism is not capable of handling the wide variety of filling heads and dispense heads that are available on the market. 
     A later proposal disclosed in DE 10 2007 036 469 to Schäfer Werke involves depressing a valve element to a lesser extent upon coupling a filling head to the closure for filling (i.e. the filling stroke) and to a greater extent upon coupling a dispense head to the closure for dispensing (i.e. the dispense stroke). The greater movement of the valve element through the dispense stroke causes the valve element to lock in a depressed position such that when the dispense head is removed after dispensing, the valve element cannot move back to the closed position. 
     The proposal disclosed in DE 10 2007 036 469 requires the filling stroke to be shorter than the dispense stroke. However, the use of a well-type or flat-type fitting involves a filling stroke that is often equal to or sometimes longer than the dispense stroke. The proposal in DE 10 2007 036 469 cannot handle situations where the filling stroke is longer than or equal to the dispense stroke because the valve element will either lock open prematurely during the filling procedure or will fail to lock open after the dispensing procedure. 
     It is against this background that the present invention has been devised. 
     The invention resides in a closure for a pressure vessel such as a keg, the closure comprising: at least one valve element that is movable with respect to the housing, inwardly into an open state and outwardly into a closed state; and a lock mechanism having a locking element that is movable with respect to the housing and is capable of holding the valve element in the open state; wherein the lock mechanism includes first and second couplings at which the locking element and the valve element are mutually engageable, and is arranged such that when the locking element and the valve element are engaged at the first coupling, the locking element moves with the valve element as the valve element moves from the open state into the closed state, said movement of the locking element enabling engagement between the locking element and the valve element at the second coupling, which engagement at the second coupling occurs on subsequent movement of the valve element into the open state to prevent the valve element returning to the closed state. 
     The lock mechanism employed by the invention does not suffer from the long tolerance chains of U.S. Pat. No. 4,909,289 or the inability of U.S. Pat. No. 4,909,289 to handle the variety of filling heads and dispense heads that are on the market. Also, unlike DE 10 2007 036 469, the mechanism of the invention can be used even if the filling stroke is equal to or longer than the dispense stroke. 
     In the preferred embodiment of the invention to be described below, the first coupling is disposed outwardly with respect to the second coupling. 
     Preferably, the couplings are defined by ratchet formations acting between the locking element and the valve element for substantially unidirectional outward movement of the locking element with respect to the housing. Advantageously, the ratchet formations provide reliable movement between the locking element and the valve element. 
     Preferably, the valve element is movable with respect to the housing along an axis, the locking element is movable axially with respect to the housing in response to said axial movement of the valve element, and the couplings comprise axially-spaced engaging formations acting between the locking element and the valve element. Advantageously, axial movement simplifies and so improves the reliability of the closure. 
     Preferably, following engagement between the locking element and the valve element at the first coupling, outward movement of the valve element moves the locking element to a position within the housing in which further outward movement of the locking element with respect to the housing is limited in extent. 
     Preferably, following engagement between the locking element and the valve element at the second coupling, further outward movement of the locking element is limited by encountering a stop formation fixed relative to the housing. 
     Preferably, following engagement between the locking element and the valve element at the first coupling, outward movement of the valve element moves the locking element to a position within the housing in which inward movement of the locking element with respect to the housing is limited in extent. 
     Preferably, upon moving outwardly with the valve element, the locking element passes a ratchet formation that restrains inward movement of the locking element. The ratchet formation may be a shoulder fixed relative to the housing. 
     Preferably, the locking element comprises an opposed formation arranged to engage with the ratchet formation. 
     Preferably, following movement of the valve element from the open state into the closed state, the locking element lies between opposed limit formations disposed respectively outward of an outer end and inward of an inner end of the locking element. 
     Preferably, the limit formations comprise the stop formation and the ratchet formation. 
     Preferably, the couplings comprise resilient snap-fit formations engageable by relative sliding movement of the valve element with respect to the locking element. 
     Preferably, the couplings comprise first and second coupling components on the locking element that are engageable successively by a coupling component on the valve element upon successive opening strokes of the valve element. 
     Of course, the inventive concept extends to a pressure vessel such as a keg, supplied with or fitted with the closure of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings in which: 
         FIG. 1  is a sectional side view through a closure according to a first embodiment of the present invention, fitted in the neck of a plastics keg, showing the closure before filling with the valve element closed; 
         FIG. 2  corresponds to  FIG. 1  but shows the closure during filling when a filling head has been coupled to the closure, with the valve element open; 
         FIG. 3  corresponds to  FIGS. 1 and 2  but shows the closure after filling when the filling head has been uncoupled from the closure, with the valve element again closed; 
         FIG. 4  corresponds to  FIGS. 1 to 3  but shows the closure during dispensing when a dispense head has been coupled to the closure, with the valve element again open; 
         FIG. 5  corresponds to  FIGS. 1 to 4  but shows the closure after dispensing when the dispense head has been uncoupled from the closure, with the valve element now permanently open; 
         FIG. 6  is a sectional side view through a closure according to a second embodiment of the present invention, fitted in the neck of a plastics keg, showing the closure before filling with the valve element closed; 
         FIG. 7  corresponds to  FIG. 6  but shows the closure during filling when a filling head has been coupled to the closure, with the valve element open; 
         FIG. 8  corresponds to  FIGS. 6 and 7  but shows the closure after filling when the filling head has been uncoupled from the closure, with the valve element again closed; 
         FIG. 9  corresponds to  FIGS. 6 to 8  but shows the closure during dispensing when a dispense head has been coupled to the closure, with the valve element again open; 
         FIG. 10  corresponds to  FIGS. 6 to 9  but shows the closure after dispensing when the dispense head has been uncoupled from the closure, with the valve element now permanently open; and 
         FIG. 11  is a schematic sectional view of a latch element of the closure of  FIGS. 6 to 10 . 
     
    
    
     The first and second embodiments of the present invention relate to a keg closure functionally and in key dimensions with existing keg closures known in the art as ‘Flat Type’, ‘Type A’ or ‘Flat Type A’ keg closures. As such, dispensing or filling heads suitable for use with such ‘Flat Type A’ keg closures can also be used in conjunction with the closure of the first and second embodiments of the present invention. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 to 5  relate to the first embodiment of the present invention and  FIGS. 6 to 11  of the drawings relate to the second embodiment of the present invention. The same reference numerals are used to refer to similar features in the first and second embodiments. 
     In  FIGS. 1 to 10 , sectional views are shown of the closures  100 . The sections of the closures  100  are taken in an axial direction, with the section plane containing a central longitudinal axis of the neck  12  of a plastics keg  14  onto which each closure  100  is fitted. It will be understood that each closure  100  is substantially symmetrical about the section plane and so features on one side of the section plane are present on the other side of the section plane. 
     The components of each closure  100  are made predominantly of injection-moulded plastics materials such as polyester, polyolefin, polyamide or the like, except where stated otherwise below. It is emphasised that the materials used for the keg  14  and the closure  100  and their methods of manufacture are merely preferred and are not essential to the broad inventive concept. 
     A closure  100  according to the first embodiment of the present invention will now be described in more detail with reference to  FIGS. 1 to 5 . 
     The closure  100  has a generally annular housing  160 , an inner tail portion  161  of which is shaped to fit closely within the tubular neck  12  of a plastics keg  14 . 
     An outer head portion  162  of the closure  100  retains the housing  160  on the keg  14  by resiliently engaging circumferential ridges  20  projecting laterally from the exterior of the neck  12 . An annular groove on the housing  160  defined between the inner tail portion  161  and the outer head portion  162  receives an annular seal  150  that is compressed against the upper end of the neck  12  to seal the housing  160  to the keg  14  when the housing  160  is snap-fitted onto the neck  12 . 
     The housing  160  surrounds a valve element  210  that is displaceable against spring bias axially inwardly toward the interior of the keg  14  to open concentric flow paths extending through the closure  100  and into the keg  14 . 
     Hereinafter, where contextually appropriate, the terms ‘upper’, ‘upward’ or the like should be understood to mean relating to a position or direction that is axially outward, away from the interior of the keg  14  to which the closure  100  is fitted. Similarly, the terms ‘lower’, ‘downward’ or the like relate to positions or directions that are axially inward, towards the interior of the keg  14 . The reader will appreciate that references to ‘upper’ and ‘lower’ relate to the general orientation of the closures shown in the drawings, although that orientation may not necessarily be maintained in use. Furthermore, references pertaining to an axis should be understood to be in respect of the central longitudinal axis of the neck  12  of the keg  14  to which the closure  100  is fitted. 
     The valve element  210  surrounds, can move axially along, and is supported for sliding movement by a tubular spear connector  260 . The spear connector  260  is fixed relative to the housing  160  via a lock ring  320 . A lower portion of the lock ring  320  engages with complementary engagement formations  268  on the exterior of the spear connector  260 . An upper portion of the lock ring  320  is received within the lower section of the tail portion  161 , engaging with openings  164  in the tail portion  161  to enable the lock ring  320  to be snap-fitted to the housing  160 . The upper portion of the lock ring  320  is generally annular in shape, and so defines a cylindrical space within it. The upper end of the lock ring  320  forms an upwardly facing annular ledge  322  extending radially inwardly from the inner wall of the tail portion  161 . 
     The housing  160  comprises an annular shoulder  163  formed at the upper end of the tail portion  161  that faces downward towards the annular ledge  322 . The annular shoulder  163  is defined by the inner facing surface of the tail portion  161  curving radially inward towards the central longitudinal axis of the keg neck  12 . 
     A tube (not shown) communicates with the hollow interior of the spear connector  260  and extends into the base of the keg  14  from the inner end of the spear connector  260 . The tube is typically of extruded plastics material such as polyethylene. 
     The valve element  210  comprises a generally annular head  212  at its upper end. The valve element  210  also comprises a skirt  214  depending downwardly from the radially-outer edge of the annular head  212  and a tubular stem  218  depending downwardly from the radially-inner edge of the annular head  212 . Elongate channels are cut into the skirt  214  to define a plurality of downwardly depending flaps  214 . 
     The valve element  210  comprises webs  219  bridging the region between the annular head  212 , stem  218  and flaps  214 . 
     A resilient annular seal  220  is defined at the upper end of the annular head  212  of the valve element  210 . The upper radially-outer edge of the annular seal  220  seals against a frusto-conical outer valve seat  240  facing radially inwardly from the housing  160 . An upper, radially-inner edge of the annular seal  220  seals against a frusto-conical inner valve seat  340  defined by a flared upper end of the spear connector  260 . The inner valve seat  340  faces radially outwards. 
     A coil spring (not shown) surrounds the stem  218  of the valve element  210  and biases the valve element  210  upward, urging the annular seal  220  into sealing contact with the inner valve seat  340  and outer valve seat  240 . An upper end of the coil spring bears against the webs  219  of the valve element  210  and a lower end of the coil spring bears against the lock ring  320 . 
     The valve element  210  surrounds the spear connector  260  and can move down along the outer surface of the spear connector  260  against the spring bias. 
     The diameter of the outer surface of the spear connector  260  is reduced adjacent the flared upper end of the spear connector  260  to form a band-shaped indent  262  encircling the spear connector  260 . An opening  261  penetrates the wall of the spear connector  260  communicating with the indent  262 . 
     Referring to  FIGS. 1 and 3 , the indent  262  is completely surrounded by the valve element  210  when the valve element  210  is outwardly biased into sealing contact with the inner and outer valve seats  340 ,  240 . In these configurations of the closure  100 , the flow paths into the keg  14  are closed. 
     A filling head and a dispense head for use with the closure  100  of the present embodiment are conventional and so are omitted from the drawings. However the forces they apply to the valve element  210  of the closure  100 , and their resulting effect on the valve element  210 , is represented by the arrows in  FIGS. 2 and 4  of the drawings.  FIGS. 2 and 4  show the closure  100  with the valve element  210  open. When a filling head is coupled to the closure  100  as represented by the arrows in  FIG. 2 , an annular plunger on the filling head presses down on the annular seal  220  and so depresses the valve element  210 , down towards the interior of the keg  14 . 
     Similarly when a dispense head is coupled to the closure  100  as represented by the arrows in  FIG. 4 , an annular plunger on the dispense head also presses down on the annular seal  220 , depressing the valve element  210 , down toward the interior of the keg  14 . 
     When the valve element  210  is pushed down as shown in  FIGS. 2 and 4 , the valve element  210  moves away from the inner and outer valve seats  340 ,  240  to permit fluid flow along two flow paths around the valve element  210 . 
     An inner flow path runs from the inside of the annular plunger of the filling or dispense head (i.e. between the arrows) around the flared upper end of the spear connector  260 , into the indent  262  and opening  261  and so down into the bottom of the keg  14  via the hollow interior of the spear connector  260  and tube connected to the spear connector  260 . An outer flow path runs from the outside of the annular plunger (i.e. outside of the arrows) between the tail portion  161  of the housing  160  and valve element  210 , via openings in the lock ring  320  and into the neck  12  of the keg  14 . 
     In practice, beverage will flow into the keg  14  along the outer flow path during filling in  FIG. 2  and from the keg  14  along the inner flow path during dispensing in  FIG. 4 . Conversely, gas will flow from the keg  14  along the inner flow path during filling in  FIG. 2  and into the keg  14  along the outer flow path during dispensing in  FIG. 4 . The beverage and gas flows specified during filling assume that the keg  14  is inverted during filling, which is conventional for effervescent drinks such as beer. However it is also possible to fill the keg  14  with suitable beverages when upright, in which case beverage will flow into the keg  14  along the inner flow path and gas will flow from the keg  14  along the outer flow path. 
     In general terms, the above features of the closure  100  are largely conventional. The invention resides in a lock mechanism that includes couplings that act between the valve element  210  and a latch element  500  that is initially disposed axially inwardly of the valve element  210 , toward the interior of the keg  14 . 
     In the present embodiment, the couplings are defined by catch formations  215  on the valve element  210  and latch formations  503 ,  505  on the latch element  500  as will be described in great detail below. 
     Catch formations  215  are integrally-moulded at the lower end of each flap  214  of the valve element  210 . The catch formations  215  face radially outward and on their lower end define a downwardly and radially-outwardly facing ramp. On their upper side, the catch formations  215  define a hook. These catch formations  215  are arranged to interact with complementary latch formations  503 ,  505  on the latch element  500  as will be described. 
     The latch element  500  is substantially tubular and comprises an annular body  502 , a set of fingers  504  and a plurality of legs  506 . The fingers  504  and legs  506  extend respectively upwards and downwards at the upper and lower ends of the annular body  502  and are circumferentially curved to match the curvature of the annular body  502 . Latch formations  503 ,  505  are integrally-moulded with the latch element  500  and are complementary in shape and function to the catch formations  215  of the valve element  210 . 
     A first set of latch formations  505  are disposed circumferentially about the upper tips of the fingers  504 . A second set of latch formations  503  are disposed below the first set, circumferentially about the interior of the annular body  502 , in the region where the legs  506  extend from the annular body  502 . Each of the first and second set of latch formations  505 ,  503  face radially inward. On their upper sides each of the first and second set of latch formations  505 ,  503  define an upwardly and radially-inwardly facing ramp. On their lower end they each define a hook. 
     Feet  507  are disposed about the lower end of the legs  506 . The feet  506  face radially outward and stand proud of the general outer diameter of the latch element  500 . 
     The interaction between the valve element  210 , the latch element  500  and other components of the closure  100  will now be described. 
       FIG. 1  shows the closure  100  before filling, where the valve element  210  is closed, biased upward by the aforementioned coil spring. The latch element  500  is at its lowermost position within the tail portion  161  of the housing  160 . The lower part of the latch element  500  is received within the cylindrical space defined by the upper portion of the lock ring  320 . The feet  507  bear against the inside surface of the upper portion of the lock ring  320  causing the legs  506  to deflect radially-inwardly. 
     At the upper part of the latch element  500 , the fingers  504  extend upwards toward the flaps  214  in mutual angular alignment. The fingers  504  and flaps  214  are axially spaced from one another and so do not yet make contact with one another. 
       FIG. 2  shows the closure during filling when a filling head has been coupled to the closure with the valve element open. 
     Comparing  FIG. 1  with  FIG. 2 , as the valve element  210  is driven downward into the keg  14  for the first time the complementarily-ramped surfaces on the catch formations  215  and first set of latch formations  505  allow them to slide over one another until they snap over one another. 
     After the first downward movement of the valve element  210  to the position shown in  FIG. 2 , the valve element  210  can then be allowed to rise again under the biasing action of the coil spring to the position shown in  FIG. 3 . Thus, after the first stroke that opens the flow paths for filling the keg  14  with beverage, the flow paths can be re-closed again for the storage and/or transportation of the keg  14 . In particular, the valve element  210  is able to rise again under the biasing action of the coil spring to re-close the flow paths into the keg  14 . In doing so, the hook parts of the catch formations  215  engage with the hook parts of the first set of latch formations  505  thereby carrying the latch element  500  upwardly with the valve element  210 . 
     During movement from the configuration shown in  FIG. 2  to that of  FIG. 3 , the latch element  500  moves upwardly and slides clear of the lock ring  320 . In the process of doing so, the feet  507  snap over the annular ledge  322  formed by the upper end of the lock ring  320 . As will be described below, the feet  507  and the ledge  322  together now prevent downward movement of the latch element  500  into its original position. 
       FIG. 3  shows the latch element  500  and the valve element  210  hooked together having come to the end of their upward movement after the valve elements  210  first downward and upward stroke of the valve element  210 . As mentioned, the flow paths have re-closed, and the keg closure  100  can be stored and transported without spillage or spoiling of a beverage within the keg  14 . 
     Once the keg  14  is filled, the closure  10  is preferably covered with means for dust protection and tamper evidence, such as a foil cap (not shown). The filled keg  14  may then be stored and delivered to customers for dispensing as required. To facilitate transportation, a handle (not shown) may be attached to the neck  12  of the keg  14 . 
       FIG. 4  shows the configuration of the closure  100  during dispensing, when a dispense head has been coupled to the closure  100 . In this configuration, the valve element  210  is moved down to re-open the flow paths into the keg  14 . 
     During movement from the configurations shown in  FIG. 3  to that of  FIG. 4 , the valve element  210  is depressed against the bias of the coil spring, and slides down into the keg  14 . In doing so, the catch formations  215  unhook themselves from the first set of latch formations  505  of the latch element  500  and slide down towards the second set of latch formations  503 . As mentioned, downward movement due to force transmitted to the latch element  500  from the valve element  210  is restrained by the feet  507  abutting against the annular ledge  322 . 
     As the valve element  210  approaches the end of its downward travel, the catch formations  215  slide over the second set of latch formations  503  of the latch element  500  and snap over them, in the same way as described above in relation to the first set of latch formations  505 . 
     When the valve element  210  is released again after dispensing, as shown in  FIG. 5 , the upward travel of the valve element  210  is limited to an extent that the flow paths can no longer close. This is because the upper edge of the latch element  500 , onto which the valve element  210  is hooked, has engaged with the annular shoulder  163  of the housing  160 . In particular, the engagement of the catch formations  215  with the second set of latch formations  503  draws the latch element  500  up with the valve element  210  to bring the upper edge of the latch element  500  into contact with the annular shoulder  163 . The latch element  500  thus restrains axial movement of the valve element  210  against the annular shoulder  163 . 
     A second embodiment of the present invention will now be described. In the interests of clarity and brevity, mainly the differences between the first and second embodiments will be described. Unless specified to the contrary, features present in the first embodiment should be assumed to be present in the second embodiment where context allows. The same reference numerals will be used for like features. 
     In this second embodiment, catch formations  215  of the valve element  210  are provided on the tubular stem  218 . The catch formations  215  are disposed on the lower end of the tubular stem  218 , on its radially-inward facing surface. The catch formations  215  interact with the latch element  500  to control the position of the valve element  210  as will be described. 
     The latch element  500  surrounds and is supported for sliding movement by the spear connector  260  rather than being supported by the housing  160  as in the first embodiment. 
     The latch element  500  is generally annular in shape, its radially-inward surface sliding along the radially-outward surface of the spear connector  260 . 
     The radially-outward surface of the spear connector  260  is substantially cylindrical and defines a circumferential groove  264  disposed axially below an opening  261  and band-shaped indent  262  towards the upper end of the spear connector  260 . The circumferential groove  264  includes a downward-facing annular shoulder  263  and an upward-facing ring-shaped ledge  265  that face toward one another. 
       FIG. 11  is a schematic sectional view of the latch element  500  of the closure of  FIG. 6 . The latch element  500  is shown in isolation to the other components of the closure  100 . It will be noted that the features of the latch element  500  are exaggerated in  FIG. 11  to aid the understanding of the features of the latch element  500 . 
     The radially-inward surface of the latch element  500  is divided into two sections, an upper inner-facing section  510  and a lower inner-facing section  512 , each being substantially parallel to the central longitudinal axis of the keg neck  12  and one another, the upper inner-facing section  510  having a smaller diameter than the lower inner-facing section  512 . An annular downward-facing lip  507  separates the upper and lower inner-facing sections  510 ,  512 . 
     The radially-outward surface of the latch element  500  is also divided into two sections, an upper outer-facing section  514  and an lower outer-facing section  516 , both sloping relative to the central longitudinal axis of the keg neck  12  to define ramps that face both upward and radially outwards. 
     The upper outer-facing section  514  slopes to meet the upper inner-facing section  510  at the upper end of the latch element  500 . The lower edge of the ramp defined by the upper outer-facing section  514  has a diameter greater than that of the upper edge of the ramp defined by the lower outer facing section  516 . A downward facing overhang  505  is thus defined and separates the upper and lower outer-facing sections  514 ,  516 . 
     An annular downward facing edge  503 , at the lowermost end of the latch element  500 , separates the lower inner-facing section  516  and the lower outer-facing section  512 . 
     Slots  520  are defined at intervals circumferentially about the upper-end of the latch element  500  interrupting its generally annular shape, thereby defining fingers at the upper end of the latch element  500 . 
     As will be described in greater detail below, the overhang  505  and the edge  503  of this second embodiment are respectively functionally equivalent to the first and second latch formations  505 ,  503  described in relation to the first embodiment of the present invention. Similarly, the lip  507  serves a similar function to the feet  507  of the first embodiment. 
     Referring back to  FIG. 6 , the closure  100  is shown before filling, where the valve element  210  is closed, biased axially upward. The latch element  500  is at its lowermost position, surrounding and supported by the cylindrical outer surface of the spear connector  260 . The fingers of the latch element  500  flex by virtue of contact between the upper inner-facing section  510  with the spear connector  260 , and so exert a radially inward biasing force against it. 
     Referring to  FIG. 7 , as the valve element  210  is driven downward into the keg  14  for the first time, the catch formations  215  slide over the ramp of the upper outer-facing section  514  until the catch formations  215  snap over the overhang  505 . 
     After this first axially downward movement of the valve element  210  to the position shown in  FIG. 7 , the valve element  210  can then be allowed to rise again under the biasing action of the coil spring to the position shown in  FIG. 8 . Thus, after the first stroke used to open the flow paths for filling the keg  14  with beverage, the flow paths can be re-closed again for the storage and/or transportation of the keg  14 . 
     In particular, the valve element  210  is able to rise again under the biasing action of the coil spring to re-close the flow paths into the keg  14 . In doing so, the catch formations  215  of the valve element  210  and the overhang  505  of the latch element  500  hook into one another thereby carrying the latch element  500  up with the valve element  210 . 
     The latch element  500  slides axially upward outwardly away from the interior of the keg  14 . In the process of doing so, the upper inner-facing section  510  which was previously biased radially-inward against the spear connector  260  is guided up it to snaps into the circumferential groove  264  defined by the spear connector  260 . 
       FIG. 8  shows the latch element  500  and the valve element  210  latched together having come to the end of their upward movement after the first downward stroke of the valve element  210 . As mentioned, the flow paths have re-closed, and the keg closure  100  can be stored and transported without spillage or spoiling of a beverage within the keg  14 . 
       FIG. 9  shows the configuration of the closure  100  during dispensing, when a dispense head has been coupled to the closure  100 . In this configuration, the valve element  210  has once again moved down to re-open the flow paths into the keg  14 . 
     During movement from the configuration shown in  FIG. 8  to that of  FIG. 9 , the valve element  210  is depressed against the bias of the coil spring, and slides down into the keg  14 . In doing so, the catch formations  215  unhook away from the overhang  505  of the latch element  500  and slide down along the ramp of the lower outer-facing section  516  towards the annular edge  503  of the latch element  500 . 
     The latch element  500  is restrained against movement back down in towards the keg  14  by virtue of the lip  507  abutting against the ring-shaped ledge  265  of the circumferential groove  264 . 
     As the valve element  210  approaches the end of its travel downwardly in towards the interior of the keg  14 , the catch formations  215  slide over and beyond the lower end of the latch element  500  snapping over the annular edge  503 . 
     When the valve element  210  is released again after dispensing, as shown in  FIG. 10 , the upward travel of the valve element  210  is restricted to an extent that the flow paths can no longer close. This is because the axially upper edge of the latch element  500 , onto which the valve element  210  is hooked, has engaged with the annular shoulder  263  of the circumferential groove  264  of the spear connector  260 . 
     In particular, the engagement of the catch formations  215  with the annular axially-downward facing edge  503  of the latch element  500  restrains further upward movement of the valve element  210 . 
     In this way, the mechanisms of the first and second embodiments of the present invention ensure that the keg cannot be left pressurized after use and also that it cannot be refilled with the closure being re-closed afterwards. As noted above, these mechanisms do not suffer from the long tolerance chains of U.S. Pat. No. 4,909,289 or the inability of U.S. Pat. No. 4,909,289 to handle the variety of filling heads and dispense heads that are on the market. Also, unlike DE 10 2007 036 469, the mechanisms of the invention can be used even if the filling stroke is equal to or longer than the dispense stroke.