Patent Publication Number: US-8534506-B2

Title: Dispensing pack

Description:
This application is an application filed under 35 U.S.C. Sec. 371 as a national stage of international application PCT/EP2004/008524, which was filed Jul. 29, 2004. 
     TECHNICAL FIELD 
     This invention relates to a dispenser pack or dispensing pack. 
     BACKGROUND OF THE INVENTION 
     DE-A-0 342 651 B1 describes a manually operable metering pump with the characteristics contained in the precharacterising part of claim  1 . The ability, provided by standard pumps of this known type, to ventilate a container equipped with such a pump encounters difficulties in those cases where the medium that is contained in the container and that is to be dispensed is highly viscous, such as e.g. creams, and is to be prevented from contacting environmental air so as to prevent loss of function of the pump and contamination of the medium by harmful germs or dirt particles contained in the air. 
     BRIEF SUMMARY OF THE INVENTION 
     It is the object of the invention to improve a dispenser pack of the type mentioned above such that, with the use of standard pumps that normally make possible ventilation of a container equipped with such a pump, the free-flowing medium contained in the container cannot come into contact with air and cannot be contaminated, so that possibly also the quantity of preservatives used in the free-flowing medium can be reduced. In particular, the dispensing of highly-viscous media such as e.g. the dispensing of commonly used cosmetics or medicated creams is possible not only with the exclusion of air but also when the dispenser pack is upside down. This object is to be able to be implemented by a relatively quick and simple retrofit of already existing automatic installation equipment. 
     The invention meets this object by the characteristics contained in claim  1 . Accordingly, the invention starts with a dispenser pack that comprises a metering pump and a container that is tightly connected to said metering pump and that can be ventilated by the pump. The dispenser pack comprises a sealing or closing cap that can be attached to the neck of the container, as well as a cylindrical wall that encloses an axial aperture that is arranged above an internal flange. Furthermore, a retainer for attaching the pump within an aperture of the closing cap is provided, wherein an exterior flange of the retainer can be pressed against an annular seal on an outer face of the container neck so as to be sealed by the closing cap. A pump housing comprises a pump cylinder that surrounds a pump chamber whose upper end comprises an aperture and whose lower end comprises a suction pipe nipple. A pump piston is arranged in the pump chamber so as to be slidable in a sealed manner and comprises a piston shaft which protrudes outward from the pump chamber and at its outer end comprises an activation- and dispensing head. An axial outlet channel extends through the piston shaft and the pump piston and connects the pump chamber with a dispensing aperture of the activation head. Furthermore, an inlet valve and an outlet valve for the free-flowing medium are associated with the pump. A helical compression spring impinges on the pump piston in the direction of its home position. 
     The invention is characterised in that a volume of the container that contains a free-flowing medium can be adjusted to the decrease of the volume of the free-flowing medium dispensed from the container, and the inner hole rim of the seal between the container neck and the sealing cap rests against the outside of the pump housing so as to be airtight. 
     In this way a situation can be achieved in which the free-flowing medium does not establish contact with, and cannot be contaminated by, the air and with bacteria contained in the air and/or with other components contained therein that may be harmful to the medium to be dispensed, for example components such as oxygen or dirt particles. 
     A further improvement of the seal can be achieved in that the inner hole rim forms part of an annular lip. Preferably the thickness of the annular washer tapers off towards the outer end of the annular lip. Furthermore, it is recommended that the annular lip of the washer be formed such that it rests radially inward in the manner of a truncated cone transversely in an annular space against the cylindrical outside of the pump housing so as to provide a seal. In this way the seal can be pressed with increased pressure against the wall of the pump housing during a suction stroke of the pump piston so as to provide a seal. 
     According to one embodiment of the invention, inside the container the medium can be enclosed by a bag made of a flexible material, with the upper aperture rim of said bag being tightly connected to the wall of the container, while in a space between the inside of the container wall and the outside of the bag air at atmospheric pressure is contained. It is particularly preferred if the bag and the container are formed in one part. This is very advantageously carried out in that the aperture rim of the bag is injection-formed to the bottom end of the container neck. Due to the flexibility of the bag it collapses or shrinks to the extent to which the free-flowing medium is dispensed from the bag by means of the pump. 
     According to a second embodiment the container can comprise a cylindrical internal wall and be open at the bottom end into which a drag-flow piston is inserted so that it is axially movable and seals off the internal wall of the container, wherein said drag-flow piston, depending on the quantity of medium dispensed and the suction pressure exerted on the medium, is slidable in the direction of the pump. As the quantity of medium contained in the container is reduced, the drag-flow piston, which forms the bottom of the container, therefore travels, in the container, in the direction of the pump, i.e. in the normal upright position of dispensing it travels upwards. 
     In a particularly preferred embodiment the aperture of the suction pipe nipple is freely exposed. The absence of a suction pipe above all provides advantages in those cases where the free-flowing medium is highly viscous, such as for example in the case of skin creams or sun creams and also in the case of medicated creams. At the same time this provides an advantage in that the dispenser pack can not only be used in the upright position, but also in any other position, e.g. upside down. 
     Below, the invention is described in more detail with reference to diagrammatic drawings of two embodiments. The following are shown: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  a partially broken longitudinal section of a dispenser pack according to the invention, in which a bag that contains the medium to be dispensed as an integral component of the container is surrounded by air at atmospheric pressure; 
         FIG. 2  the dispenser pack according to  FIG. 1 , with the bag being almost empty; 
         FIG. 3  a longitudinal section of a second embodiment of a dispenser pack in which a drag-flow piston that seals off the container has been inserted in the open bottom end of a container; 
         FIG. 4  the dispenser pack according to  FIG. 3 , in an almost empty state; 
         FIG. 5  an enlarged view of detail A shown in  FIGS. 1 to 4 ; and 
         FIGS. 6 and 7  a detail of an inlet valve, shown in  FIGS. 1 to 4 , in its open and closed positions respectively. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 to 4  show a longitudinal section of several components of the dispenser pack, which components are predominantly made from a relatively hard plastic, such as for example polypropylene. These components are arranged so as to be rotationally symmetrical, and constitute the dispenser pack in relation to a central longitudinal axis  0 - 0 . 
     According to  FIGS. 1 and 2  the dispenser pack comprises a metering pump  20  and a container  26 , tightly connected to said metering pump  20 , to which container a bag  28  made of a flexible material is tightly connected, which bag contains a free-flowing medium  29 , preferably a sprayable liquid such as for example normal or medicated skin cream whose quality can be contaminated by exposure to air, e.g. by bacteria contained therein, so that the dispenser pack according to the invention is to prevent such exposure to air by the medium contained in the container and at the same time is to reduce the quantity of preservatives that have to be added to the medium  29 . 
     A sealing or closing cap  22  is attached to the neck  21  of the container  26  by means of a common screw thread  25 . At its upper end the closing cap  22  comprises a wall  31  with an inner cylindrical aperture  32  which is arranged above an internal flange  34 . A retainer  38  is provided for the pump  20 , which retainer  38  comprises a cylindrical external wall  40  and is arranged within the aperture  32  of the closing cap  22  and which retainer  38  at its bottom end comprises an exterior flange  42 . This exterior flange  42  can be pressed against an annular seal  41  on an outer face  27  of the container neck  21  so as to provide a seal with the interior flange  34  of the closing cap  22 . The function of this seal  41  will be explained below. Instead of a screw thread  25  the closing cap  22  can also be connected to the container neck  21  by means of pressing, welding, gluing or the like, in a way that is known per se. 
     A pump housing  48  comprises a pump cylinder  43  which below the annular seal  41  comprises a small ventilation aperture  51  which connects the internal volume of the bag  28  to the pump chamber  80  and is used for ventilating the pump cylinder  43  during initial operation of the metering pump  20 . 
     The pump cylinder  43  surrounds a pump chamber  80  that is open towards the top or the outside. A cylindrical internal wall  72  of the retainer  38  coaxially engages the top aperture of the pump chamber  80  and is connected to said pump chamber  80  at the top end by an annular end wall  64 . At the top end the pump housing  48  comprises an outward-projecting annular flange  50 , which is inserted so as to clip into an annular groove  62  at the inner upper end of the retainer  38 . At the bottom end of the pump housing  48  a suction pipe nipple  30  is formed, through which the free-flowing medium  29  within the bag  28  made of a flexible material is sucked in. The aperture of the suction pipe nipple  30  has been left free intentionally in order to also make it possible to suck highly viscous media, such as e.g. creams, and to maintain the dispensing function of the pump even if the dispensing pack is upside down. 
     The bag  28  tightly encloses the medium  29  in that the top aperture rim  33  is tightly connected to the wall of the container  26 , in the present case with the bottom end of the container neck  21 . For this purpose, during manufacture of the container  26  the top end of the bag  28  has been injection-formed, in one piece, in the plastic injection moulding process, to the bottom end of the container neck  21 . If need be it is of course also possible to tightly clamp the aperture rim of a bag for the liquid medium  29 , which bag has been produced separately from the container  26 , between the retainer  38  and the upper end of the container neck  21  or to glue it together or weld it together in a gas-proof manner with the container neck  21 . Between the outside of the bag  28  and the inside of the container  26  an annular space  35  is provided which contains ambient air at atmospheric pressure. 
     A pump piston  45  is slidable in a sealed manner in the pump cylinder  43  and comprises a hollow-cylindrical piston shaft  47  that protrudes from the pump chamber  80  through a cylindrical aperture  23  in the end wall  64  of the retainer  38 , and at its outer end comprises an activation- and dispensing head  90 . An axial outlet channel  98  extends through the piston shaft  47  and the pump piston  45 , and connects the pump chamber  80  with a dispensing aperture  92  of the activation head  90 . A sealing lip  102 ,  103  each, of annular shape, is formed to the top and bottom end of the pump piston  45 , which sealing lips rest tightly with elastic pre-tension against the internal wall of the pump cylinder  43 . In the home position of the pump piston  45  its top end rests against the bottom end  73  of the cylindrical internal wall  72  of the retainer  38  so as to provide a seal. 
     The pump housing  48  comprises a bottom  49  from which a cylindrical tubular feed piece  120  protrudes coaxially to the suction pipe nipple  30  into the pump chamber  80 . 
     An inlet valve  66  is designed as a two-part differential piston and comprises a valve body  150  underneath the pump piston  45 , and a seal sleeve  190 , arranged underneath the valve body  150 , which seal sleeve  190  comprises guide ribs  250  arranged at identical circumferential angle spacing ( FIGS. 2 ,  6  and  7 ). The valve body  150  and the seal sleeve  190  are guided between the pump piston  45  and the feed piece  120  in the pump chamber  80  so as to be axially slidable. 
     The seal sleeve  190  is axially slidable to a limited extent in relation to the valve body  150 , and forms a connecting channel  54  between the pump chamber  80  and the outlet channel  98  with a valve head  170  of the valve body  150  ( FIGS. 2 and 6 ), which valve body  150  is closed during the pumping stroke of the pump piston  45 , and is open during the suction stroke of said pump piston  45  ( FIGS. 6 and 7 ). In  FIG. 2  a cylindrical aperture  226  in the top end of the seal sleeve  190  is provided, which cylindrical aperture  226  is enclosed by an internal flange  210  of the seal sleeve  190 . A guide pin  230  of the valve body  150  extends coaxially through this aperture  226  and comprises longitudinal ribs  234 . A helical compression spring  240 , whose bottom end is supported by the housing bottom  49  and whose top end is supported by bottom faces  235  of the longitudinal ribs  234  of the guide pin  230  is used as a bearing for the internal flange  210  of the seal sleeve  190  in the home position of the pump piston  45  as well as during its suction stroke ( FIGS. 2 ,  6  and  7 ). 
       FIG. 5  shows a mirror image, at an enlarged scale, of the detail designated A in  FIGS. 1 to 4 , which detail relates to the annular seal  41  that is clamped between the container neck  21  and the closing cap  22  and according to the invention rests with its inner hole rim  52  against the outside of the pump housing  48  so as to be gas-proof. In this arrangement the inner hole rim  52  is formed in the manner of an annular lip  53  whose thickness is reduced in the direction of the inner hole rim  52 . The seal  41  extends from the inside of an outer horizontally arranged annular rim  55  radially inward and upward or outward in the form of a truncated cone  58  into an annular space  57  which is enclosed by the cylindrical outside of the pump housing  48  and of the outside wall  40  of the retainer  38  in the sealing cap  22 . The seal  41  preferably comprises silicon or some other rubber-like elastomeric material that is inert in relation to the medium  29  contained in the container  26 . 
     The annular flange  50  at the top end of the pump housing  48  comprises a vertical groove  62 , which in  FIGS. 1 to 4  is shown in the left half of the illustrations. The groove  62  forms an air outlet slot between the pump housing  48  and the external wall  40  of the retainer  38  and interacts with radial air channels  70  in the retainer  38 . The upper end wall  64  of the retainer  38  has a circumferential groove  68  on the underside of the retainer  38 . The groove  68  is connected to the top of the groove  62 . In a position that is offset by 180° in relation to the groove  62 , the groove  68  is connected to the radial air channels  70  that are provided in the underside of the top end wall  64  of the retainer  38 . The air channels  70  extend inward along the wall of the pump housing  48  into the annular space  57  that is sealed off towards the inside or towards the bottom by the seal  41 . 
     The top interior rim of the pump housing  48  is conically enlarged towards the top and forms an annular channel  71  around the retainer  38 . The clearance between the cylindrical internal wall  72 , the piston shaft  47  and the wall of the pump chamber  80  connects an annular space  77  at the bottom end of the cylindrical internal wall  72  of the retainer  38  to the annular channel  71 , which extends around the top end of the pump housing  48 . This results in a ventilation channel which extends from the interior of the pump housing  48  through the radial air channels  70 , around the circumferential groove  68 , through the groove  62  inward or downward between the inside of the cylindrical external wall  40  and the outside of the pump housing  48  right up to the seal  41 . The annular seal  41  prevents air ingress into the bag  28  and thus prevents any contact of the free-flowing medium  29  contained in the bag  28  with outside air, so that the quality of the medium  29  is maintained by excluding the external air. 
     In the case of a partially or fully depressed pump piston  45  the concave sealing lip  102  of the pump piston  45  is separated from the bottom end  73  of the internal wall  72  of the retainer  38 . An annular space  77  thus results between the outside of the upper section, of reduced diameter, of the downward moving piston shaft  47  and the bottom end  73  of the internal wall  72  of the retainer  38 . 
     During movement of the pump piston  45  into the bottom end position of the pump stroke the air flows through the annular gap  23  along the internal wall  72  of the retainer  38  and the pump housing  48  through the radial air channels  70  into the circumferential groove  68 . Here the air is distributed in both directions around the circumference of the retainer  38  across approximately 180° where it then flows through the groove  62  into the annular space  57  of the pump housing  48 . After this, the air is prevented from entering the bag  28  by the annular seal  41  which in the subsequent suction stroke of the pump piston  45 , due to the resulting pressure difference between the interior of the bag  28  and the exterior air, is present in the pump housing  48  at increased pressure. The free-flowing medium  29  is sucked from the bag  28  through the suction pipe nipple  30  into the pump chamber  80 , wherein the bag  28  shrinks as it adapts to the reducing volume of the medium  29 . Furthermore, the pump piston  45  has an enlarged bore  154 , whose top end forms an annular valve seat  158  of an outlet valve in the outlet channel  98 . 
     At the top end the valve body  150  is shaped so as to form a valve cone  182  of the outlet valve, which valve cone rests tightly against the annular valve seat  158  in the pump piston  45  so as to prevent the medium  29  from flowing from the pump chamber  80  through the outlet channel  98 . The valve body  150  has a valve head  170  with a top head surface  172  that comprises radial ribs  174  ( FIG. 3 ) which, arranged at even circumferential angle spacing, extend radially outward and protrude from the top head surface  172 . 
     The underside of the valve head  170  comprises an annular groove  179  ( FIG. 6 ) which is trapezoidal in cross section and forms an integral part of the inlet valve  66 . To this purpose the outer side wall of the annular groove  179  forms a valve surface  180  that expands conically downward and outward in order to provide a seal with the top conical contact surface  218  of the seal sleeve  190 . The contact surface  218  is connected to the valve body  150  such that it is axially adjustable to a limited extent. The valve surface  180  and the conical contact surface  218  essentially form the connecting channel  54  in the shape of a truncated cone, wherein the internal side wall of the annular groove  179  is formed by the cylindrical guide pin  230 . 
       FIGS. 6 and 7  clearly show that the seal sleeve  190  at its face facing the container comprises an essentially cylindrical piston mantle  202 . The top end of the seal sleeve  190  comprises an annular internal flange  210  whose underside forms an annular support  211  that rests on the top end  241  of the helical compression spring  240  when the pump piston  45  is in its top home position. In this home position the inlet valve  66  with its connecting channel  54  is open ( FIG. 6 ). The internal flange  210  can be axially moved from its home position to an operating position in which the connecting channel  54  of the inlet valve  66  is closed. The support surface  211  and the top  212  of the internal flange  210  extend at a right angle to the pump axis  0 - 0  as well as extending axially into the annular groove  179  of the valve head  170 . 
     The helical compression spring  240  comprises a spring wire of round cross section. The diagram shows that the top end  241  of the spring  240  with the inner half of the wire cross section rests against the face  235  of the longitudinal ribs  234 , i.e. across a tangential angle of approximately 80°. Lower longitudinal sections  236  of the longitudinal ribs  234  radially protrude only by about a third of the width of the longitudinal ribs  234 . Optionally, instead of a spring wire of circular cross section a spring wire of some other cross section, e.g. of rectangular cross section can be used, provided the diameter of the spring wire exceeds the radial width of the longitudinal ribs  234  so that part of the wire cross section forms the support for the annular support surface  211  of the seal sleeve  190 . If necessary a washer can be arranged between the upper end  241  of the compression spring  240  and the face  235  of the longitudinal ribs  234 , which washer extends parallel to the support surface  211  and the faces of the longitudinal ribs  234 . Due to this bottom end stop, which is created by the top end  241  of the compression spring  240  for the seal sleeve  190 , a clearance  220  ( FIG. 7 ) is created which allows limited axial movement between the valve body  150  and the seal sleeve  190 . This relative mobility of the seal sleeve  190  has been selected such that the contact face  218  of the seal sleeve  190  rests against the inner valve surface  180  of the exterior rim  171  of the valve head  170  in one end position of the relative movement region of the seal sleeve  190  so that the inlet valve  66  formed by the aforementioned parts is enclosed. The bottom end of the seal sleeve  190  has been dimensioned such that it can be slid telescopically and so that it provides a seal in close contact with the outside of the fixed tubular feed piece  120 . 
     The components of the pump  20  can be produced from thermoplastic materials. The spring  240  preferably comprises stainless steel. Expediently, the pump housing  48  with the tubular feed piece  120  is made from polypropylene. Other internal components such as for example the pump piston  45 , the valve body  150  and the seal sleeve  190  or parts of these other components can be made from polyethylene so as to provide better sealing performance. Due to the axially limited mobility in relation to the valve body  150 , the movable seal sleeve  190  can be pressed directly onto the guide pin  230  of the valve body  150  without contacting other components, after which the top end of the compression spring  240  is pressed onto the guide pin  230  and consequently the seal sleeve  190  is to a limited extent kept axially mobile on the valve body  150 . 
     In its home position the seal sleeve  190  assumes the end position, as shown in  FIGS. 1 to 4  and  6 , in relation to the valve head  170 . When the pump  20  is activated the pump piston  45  and the valve body  150  move downward in the pump housing  48 , wherein the compression spring  240  is compressed. The seal sleeve  190  temporarily follows this movement while the internal flange  210  with its annular support surface  211  is supported by the compression spring  240 . When the bottom free end of the seal sleeve  190  contacts the tubular feed piece  120  the movement of the seal sleeve  190  is briefly interrupted. The top end of the seal sleeve  190  is quickly reached by the valve head  170  so that both components take up the closed position shown in  FIG. 7 . From this point onwards the valve head  170  guides the seal sleeve  190  down with it so that the seal sleeve  190  is pushed telescopically, and so as to provide sealing action, onto the tubular feed piece  120 . The friction that occurs in this process contributes to the relative pressure of the internal flange  210  acting on the annular groove  179  so that the connecting channel  54  between the contact surface  218  of the seal sleeve  190  and the valve surface  180  of the valve head  170  is closed or sealed off. From this moment onward, which commences immediately after activation of the pump  20 , the pump chamber  80  is completely closed. By further depressing the pump piston  45  the pressure within the pump chamber  80  is increased. 
     However, this increase depends on the selection of the position at which the internal flange  210  is supported on the valve body  150 . For, as long as the pressure in the pump chamber  80  increases, an axial outward directed force is added to the friction between the seal sleeve  190  and the feed piece  120 . 
     As soon as there is no longer any pressure exerted on the pump piston  45 , the compression spring  240  pushes the valve body  150  back. The valve body  150  thus moves away from the seal sleeve  190 , which due to the friction stays back at the tubular feed piece  120 . The seal sleeve  190  then moves from the closed position to the open position. The connecting channel  54  between the valve head  150  and the internal flange  210  of the seal sleeve  190  is then open and connects the container  26  to the pump chamber  80  by way of the clearances or grooves between the longitudinal ribs  250 . The compression spring  240  on which the inner support surface  211  of the internal flange  210  rests then at the same time takes the seal sleeve  190  and the valve body  150  along towards the top. In this way the volume of the pump chamber  80  increases. Because the connecting channel  54  is open, the medium  29  can flow into the pump chamber  80 . The connecting channel  54  makes it possible to fill the pump chamber  80  to the extent to which the volume of the pump chamber  80  increases. When the pump  20  has reached its top home position, in which the seal sleeve frees itself of the top end  121  of the tubular feed piece  120 , liquid medium  29  can no longer enter the pump chamber  80  by way of said tubular feed piece  120 . 
     When the metering pump  20  is operated the connecting channel  54  thus closes almost at the same point in time at which the seal sleeve  190  is pushed onto the feed piece  120 . However, when the pump piston  45  moves upward the connecting channel  54  opens before the seal sleeve  190  separates from the feed piece  120 . This results in a significantly smaller vacuum in the pump chamber  80 . Consequently, if at all, air can enter only to a lesser extent, even in a case where sealing of the pump piston  45  in relation to the pump cylinder  43  happens not to be fully ensured. For sealing the pump piston  45  there is a lower sealing lip  103  that faces the container  26  so that during dispensing of the free-flowing medium  29  the pressure prevailing in the pump chamber  80  increases the sealing effect. 
     The two interacting parts  150  and  190  of the inlet valve  66  therefore interact by way of the compression spring  240  and make it possible for the liquid medium  29  during operation of the metering pump  20  to be sucked into the pump chamber  80 . When the pump chamber  80  is filled with air during the first pump stroke, the pressure in the pump chamber  80  during downward movement of the movable parts  45 ,  150 ,  190  in the pump housing  48  is not increased to such an extent that the outlet valve  162  could open. The connecting channel  54  between the pump chamber  80  and the container  26  opens immediately at commencement of the upward movement of the pump piston  45  so that the air in the pump chamber  80  can spread out while being prevented by the seal  41  from entering the bag  28 . During further upward movement of the pump piston  45  the volume of the pump chamber  80  increases and therefore creates a vacuum that leads to accelerated filling of the pump chamber  80  with the liquid medium  29 . 
     The embodiment of a dispenser pack shown in  FIGS. 3 and 4  contains the same pump  20  as the first embodiment described with reference to  FIGS. 1 ,  2  and  5  to  7 . In this second embodiment merely another way of storing the free-flowing medium  29 , for example in a bottle-shaped container  200  with a rigid wall, is provided, whose bottom is formed by a drag-flow piston  242  that is axially movable on the rigid cylindrical internal wall  244  of the container  200  so as to provide a seal, such that after a certain quantity of the liquid medium  29  has been removed as a result of the suction pressure exerted by the pump  20 , the drag-flow piston  242  is lifted in the container  200  to an extent that approximately corresponds to the volume of the quantity of the liquid medium  29  dispensed by the pump  20 . In this embodiment too the liquid medium  29  is sucked into the pump chamber  80  due to the suction pressure exerted by the pump  20 . Since for the remainder the construction of the pump  20  is identical to the construction described in the context of  FIGS. 1 ,  2  and  5 , to this extent reference is made to the above-mentioned description of the pump  20 . 
     In summary, the function of the dispenser pack according to the invention can be described as follows: during the first pump stroke the air present underneath the pump piston  45  is displaced into the bag  28 /container  200  and after exiting from the suction pipe nipple  30  rises in the free-flowing medium  29  within the bag  28 /container  200  above the level of the medium  29 . At the same time the pump piston  45  sucks air from the free atmosphere through the annular gap  23 . Furthermore, a small vacuum arises in the annular space  57  between the outer circumferential surface of the pump housing  48  and the inside of the cylindrical wall  40  of the retainer  38 , because the annular space  77  is connected by way of the channels  62 ,  68 ,  70  to this annular space  57  above the seal  41 . However, the resulting suction pressure is too small to be able to lift the seal  41  from the outside of the pump cylinder  43 . 
     Because the suction pipe nipple  30  is situated far below the level of the free-flowing medium  29 , during the subsequent suction stroke only the free-flowing medium  29  is sucked into the pump chamber  80 . The air above the pump piston  45  escapes through the annular gap  23  in the end wall  64  of the retainer  38 . In this process a small quantity of air is pressed through the channels  62 ,  68 ,  70  into the annular gap  57  as a result of which the seal pressure of the seal  41  to the outside of the pump cylinder  43  is further increased and in this way the medium  29  in the bag  28 /container  200  is even better protected against the effect of interaction with air. 
     In a following pump stroke, after short stroke travel the through channel between the sealing body  170  and the seal sleeve  190  closes as a result of the pressure increasing in the pump cylinder  43  and as a result of the frictional resistance which the seal sleeve  120  is subjected to when it is slid onto the tubular feed piece  120 . With further increasing pressure in the pump cylinder  43  the seal cone  162  of the valve body  170  with the seal sleeve  120  is raised from its valve seat  158  in the piston shaft  47  against the pressure of the compression spring  240  so that the free-flowing medium  29  is dispensed through the dispensing head  90 . It should thus be noted that due to sealing the pump housing  48  off from the container neck  21  by means of the seal  41  the described dispenser pack according to the invention prevents air ingress and thus deterioration of the quality of a liquid medium  29  contained in the bag  270  of the container  26 , or contained in the container  200  itself, without this requiring any further design change of the pump  20 , which in the case of the pump housing  48  not being sealed off from the container neck  21  and from the sealing cap  22  can be used for free-flowing media that are insensitive to contact with air. Furthermore, it is understood that the invention is not limited to the use of the above-described standard pump but can be applied to any pumps that make possible ventilation of the associated container and its free-flowing content and that can be retrofitted for the purpose according to the invention.