Abstract:
Foam dispenser systems, pumps and refill units are disclosed herein. A refill unit for refilling a foam dispenser system comprises a container for holding a supply of foamable liquid and a foam pump connected to the container. The pump incorporates a simple and inexpensive valve arrangement to move liquid through the pump and to create the foam. For example, a liquid foam pump may include a housing and a valve stem that moves in two directions. The valve stem has an inlet liquid pathway and an outlet liquid pathway to convey liquid to a mixing. In addition, a moveable valve body is movable by the valve stem in a first direction to move the valve body to the first position to open a liquid inlet pathway, and moveable in a second direction to move the valve body to the second position to open the outlet liquid pathway.

Description:
RELATED APPLICATIONS 
       [0001]    This non-provisional utility patent application claims priority to and the benefits of U.S. Provisional Patent Application Ser. No. 61/644,699 filed on May 9, 2012 and entitled PULL-ACTIVATED FOAM PUMP. This application is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally to foam dispenser systems and more particularly to pull-activated foam pumps, as well as disposable refill/replacement units for use in such foam pumps. 
       BACKGROUND OF THE INVENTION 
       [0003]    Liquid dispenser systems, such as liquid soap and sanitizer dispensers, provide a user with a predetermined amount of liquid upon actuation of the dispenser. In addition, it is sometimes desirable to dispense the liquid in the form of foam by, for example, injecting air into the liquid to create a foamy mixture of liquid and air bubbles. As a general matter, it is usually preferable to reduce the space taken up by the pumping and foaming apparatus within the overall dispenser system. This maximizes the available space for storing the liquid, and has other benefits. 
       SUMMARY 
       [0004]    Foam dispenser systems and pumps for use in foam dispenser systems are disclosed herein. In one embodiment, a refill unit for refilling a foam dispenser system comprises a container for holding a supply of foamable liquid and a foam pump connected to the container. Corresponding methods of manufacture are provided as well. 
         [0005]    A liquid foam pump may include a housing and a valve stem that moves in two directions. The valve stem has an inlet liquid pathway and an outlet liquid pathway to convey liquid to a mixing. In addition, a moveable valve body is movable by the valve stem in a first direction to move the valve body to the first position to open a liquid inlet pathway, and moveable in a second direction to move the valve body to the second position to open the outlet liquid pathway. 
         [0006]    A liquid foam pump including a pump body and a valve stem portion located at least partly within the pump body is provided herein. The valve stem portion moves in opposite first and second directions within the pump body along a longitudinal axis. The valve stem portion has a liquid pathway therein which extends from an inlet at a liquid charge chamber defined at least in part by the pump body to a mixing chamber defined within the valve stem portion. A first disk connected to the valve stem portion and comprising at least one liquid pathway within the pump body through or past the first disk is provided. In addition, the pump includes a flexible member connected to the valve stem portion and located between the first disk and the valve stem liquid pathway inlet. The flexible member flexes between a first position and a second position with respect to the valve stem portion, such that in the first position the flexible member opens the first disk liquid pathway and closes the valve stem liquid pathway, and in the second position the flexible member closes the first disk liquid pathway and opens the valve stem liquid pathway. Movement of the valve stem portion in the first direction moves the flexible member to the first position, and movement of the valve stem in the second direction moves the flexible member to the second position. 
         [0007]    A liquid foam pump including a liquid charge chamber with a liquid inlet and a first valve through which liquid may enter the liquid charge chamber is disclosed herein. The liquid pump includes a liquid outlet and a second valve through which liquid may pass from the liquid charge chamber. A mixing chamber with a liquid inlet to receive liquid from the liquid outlet of the liquid charge chamber, and an air inlet to receive pressurized air from a pressurized air source, such that the liquid and the pressurized air are mixed within the mixing chamber to form a foamable mixture is also provided. The foam pump further includes a foam enhancing media which receives the foamable mixture, wherein a foaminess of the foamable mixture is enhanced as it passes through the foam enhancing media. Also included is an outlet nozzle for dispensing the enhanced foamable mixture and a suck-back mechanism to prevent foam that is not dispensed during a pumping action from dripping out of the outlet nozzle after the pumping action is completed. When the refill unit is installed in a dispenser, a portion of the suck-back mechanism forms a portion of an air pump that is disposed within the foamable liquid dispenser. The refill unit is disposable without disposing of the entire air pump. 
         [0008]    In this way simple and economical foam dispenser systems, as well as refill units for use in such systems, are provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    These and other features and advantages of the present invention will become better understood with regard to the following description and accompanying drawings in which: 
           [0010]      FIG. 1A  is a cross-sectional illustration of a first exemplary embodiment of a foam pump  100 , in a priming or primed state; 
           [0011]      FIG. 1B  is a cross-sectional illustration of the foam pump  100 , oriented perpendicularly to the view of  FIG. 1A ; 
           [0012]      FIG. 2A  is a cross-sectional illustration of the foam pump  100 , in an intermediate pumping state; 
           [0013]      FIG. 2B  is a cross-sectional illustration of the foam pump  100 , oriented perpendicularly to the view of  FIG. 2A ; 
           [0014]      FIG. 3A  is a cross-sectional illustration of the foam pump  100 , in a final pumping state; 
           [0015]      FIG. 3B  is a cross-sectional illustration of the foam pump  100 , oriented perpendicularly to the view of  FIG. 3A ; 
           [0016]      FIG. 4A  is a cross-sectional illustration of the foam pump  100 , in an intermediate pumping state; 
           [0017]      FIG. 4B  is a cross-sectional illustration of the foam pump  100 , oriented perpendicularly to the view of  FIG. 4A ; 
           [0018]      FIG. 5A  is a cross-sectional illustration of a second exemplary embodiment of a foam pump  200 , in a priming or primed state; 
           [0019]      FIG. 5B  is a cross-sectional illustration of the foam pump  200 , oriented perpendicularly to the view of  FIG. 5A ; 
           [0020]      FIG. 6A  is a cross-sectional illustration of the foam pump  200 , in an intermediate pumping state; 
           [0021]      FIG. 6B  is a cross-sectional illustration of the foam pump  200 , oriented perpendicularly to the view of  FIG. 6A ; 
           [0022]      FIG. 7A  is a cross-sectional illustration of the foam pump  200 , in a final pumping state; 
           [0023]      FIG. 7B  is a cross-sectional illustration of the foam pump  200 , oriented perpendicularly to the view of  FIG. 7A ; 
           [0024]      FIG. 8A  is a cross-sectional illustration of the foam pump  200 , in an intermediate pumping state; 
           [0025]      FIG. 8B  is a cross-sectional illustration of the foam pump  200 , oriented perpendicularly to the view of  FIG. 8 ; 
           [0026]      FIG. 9  is a side perspective view of a foam dispenser system  50  with a third exemplary embodiment of a foam pump  300 , in a priming or primed state; 
           [0027]      FIG. 10  is a side perspective view of the foam dispenser system  50  and foam pump  300 , in a final pumping state; 
           [0028]      FIG. 11  is a cross-sectional illustration of the foam pump  300 , in a priming or primed state; 
           [0029]      FIG. 12  is a cross-sectional illustration of the foam pump  300 , in a final pumping state; 
           [0030]      FIG. 13  is a cross-sectional illustration of the foam pump  300 , in an intermediate pumping state; 
           [0031]      FIG. 14  is a cross-sectional illustration of the foam pump  300 , in an intermediate pumping state; 
           [0032]      FIG. 15  is a cross-sectional illustration of a fourth exemplary embodiment of a foam pump  400 , in a priming or primed state; 
           [0033]      FIG. 16  is a cross-sectional illustration of the foam pump  400 , in a final pumping state; 
           [0034]      FIG. 17  is a cross-sectional illustration of the foam pump  400 , in an intermediate pumping state; and 
           [0035]      FIG. 18  is a cross-sectional illustration of the foam pump  400 , in an intermediate pumping state. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]      FIGS. 1A-1B ,  2 A- 2 B,  3 A- 3 B and  4 A- 4 B illustrate a first exemplary embodiment of a disposable refill unit  10  for use in a foam dispensing system (not shown). The disposable refill unit  10  includes a container  12  connected to a foam pump  100 . The disposable refill unit  10  may be placed within a housing of the dispenser system. The foam dispenser system may be a wall-mounted system, a counter-mounted system, an un-mounted portable system movable from place to place, or any other kind of foam dispenser system. 
         [0037]    The container  12  forms a liquid reservoir  14 . The liquid reservoir  14  contains a supply of a foamable liquid within the disposable refill unit  10  and the dispensing system housing which holds the refill unit  10 . In various embodiments, the contained liquid could be for example a soap, a sanitizer, a cleanser, a disinfectant or some other foamable liquid. In the exemplary refill unit  10 , the liquid reservoir  14  is formed by a collapsible container, such as a flexible bag-like container. In other embodiments, the liquid reservoir  14  may be formed by a rigid housing member, or have any other suitable configuration for containing the foamable liquid without leaking. The container  12  may advantageously be refillable, replaceable, or both refillable and replaceable. In other embodiments the container  12  may be neither refillable nor replaceable. 
         [0038]    The foam pump  100  of the disposable refill unit  10  may be releasably connected in a substantially airtight manner to an air pump (not shown) disposed within the dispensing system housing. More specifically, the pump  100  includes an air inlet  102  as shown in  FIG. 1B  which is connected to the air pump. In one embodiment, the air inlet  102  may be connected to the air pump with a press fit connection. In one alternative embodiment, a mechanical mechanism (not shown) may be used to mechanically releasably secure the air pump to the air inlet  102  of the foam pump  100 . The air pump supplies a source of pressurized air to the air inlet  102  of the foam pump  100 . As described further below, the foam pump  100  uses the pressurized air to mix with the liquid stored in the container  12  to create a foam, and then to dispense the foam. The air pump may be any means of supplying pressurized air to the air inlet  102 , such as for example a bellows pump, a piston pump or a dome pump. 
         [0039]    In one embodiment, air pump (not shown) includes an air inlet having a one-way air inlet valve therethrough. One-way air inlet valve allows air to enter air pump to recharge the air pump. In one embodiment, the air inlet is located inside of a foam dispenser housing so that air from inside of the dispenser is used to feed the air pump. Using air from inside the housing may help to prevent moisture from entering air pump through air inlet and air inlet valve. In one embodiment, a vapor barrier is provided. A vapor barrier allows air to pass through and the air inlet and enter the air pump, but prevents moisture from entering the air pump. A suitable vapor barrier is a woven one-way vapor barrier, such as, for example, Gortex®, that is arranged so that vapor does not enter air pump. 
         [0040]    In one embodiment, the air pump includes an anti-microbial substance molded into the air pump housing. One suitable anti-microbial substance contains silver ions and or copper ions. A silver refractory, such as, for example, a glass, oxide, silver phosphate may be used. One suitable commercially available product is Ultra-Fresh, SA-18, available from Thomson Research Associates, Inc. The anti-microbial substance prevents mold or bacteria from growing inside of the air pump. 
         [0041]    In the event the liquid stored in the reservoir  14  of the installed disposable refill unit  10  runs out, or the installed refill unit  10  otherwise has a failure, the installed refill unit  10  may be removed from the foam dispenser system. The empty or failed refill unit  10  may then be replaced with a new refill unit  10  including a liquid-filled reservoir  14 . The air pump remains located within the foam dispenser system while the refill unit  10  is replaced. In one embodiment, the air pump is also removable from the housing of the dispenser system separately from the refill unit  10 , so that the air pump may be replaced without replacing the dispenser, or alternatively to facilitate removal and connection to the refill unit  10 . A sanitary seal  148  isolates the air pump from the portions of the foam pump  100  that contact liquid, so that the air pump mechanism does not contact liquid during operation of the foam pump  100 . In a addition, a sealing member  153  seals against valve stem  110 B to prevent air from leaking out around the valve stem  110 B. 
         [0042]    The housing of the dispensing system further contains one or more actuating members (not shown) to activate the foam pump  100 . As will be appreciated by one of ordinary skill in the art, there are many different kinds of pump actuators which may be employed in the foam dispenser system. The pump actuator of the foam dispenser system may be any type of actuator, such as, for example, a manual lever, a manual pull bar, a manual push bar, a manual rotatable crank, an electrically activated actuator or other means for actuating the foam pump  100  within the foam dispenser system. Electronic pump actuators may additionally include a motion detector to provide for a hands-free dispenser system with touchless operation. Various intermediate linkages connect an external actuator member to the foam pump  100  within the system housing. The exemplary foam pump  100  is a “pull-activated” pump. That is, the pump  100  is actuated by pulling a valve stem  110  downwardly. The external actuator may be operated in any manner, so long as the intermediate linkages transform that motion to a downward pulling force on the valve stem  110 . In one embodiment, the downward pulling force is applied to an annular member  112  of the valve stem  110 . 
         [0043]    The container  12  is connected to a pump housing  104  of the foam pump  100 . The container  12  has a threaded insert neck portion  16  which is received within a mating threaded receiving portion  106  of the pump housing  104 . For example, a “quarter turn” rotation may complete the connection between the threaded portions  16  and  106 . An o-ring  107  or other sealing member may be included to help provide a liquid-tight sealed connection. Additional o-rings or sealing members (not shown) may be used, such as for example, between pump housing  104  and container  12 . The air inlet  102  of the pump  100  is formed within the pump housing  104 , to supply pressurized air from the air pump to an interior chamber  108  of the pump housing  104 . In one embodiment, one or more sealing members  149 , such as for example, one or more o-rings, may be used to form a seal with the air pump, or air supply line when the refill unit is placed in a dispenser. 
         [0044]    The foam pump  100  includes several components, such as an air gasket  114 , a pump body  116 , the valve stem  110  and a shuttle valve  118 . These pump components are at least partially held within the interior chamber  108  of the pump housing  104 . When the pump housing  104  is connected to the container  12 , many of the pump components also extend up into the neck portion  16  of the container  12 . The valve stem  110  and the shuttle valve  118  are independently movable up and down longitudinally within the pump body  116  to move liquid through the foam pump  100 , as described further below. In one embodiment, the pump housing  104  may be disposed within the neck  16  of the container  12  with external threads to secure the pump  100  to internal threads in the neck  16 , and the housing  104  also may form the pump body  116 . 
         [0045]    In the particular foam pump  100  embodiment illustrated in the Figures, the valve stem  110  is composed of two separate parts  110 A and  110 B which snap or otherwise connect together to form the valve stem  110 . This design aids the assembly process for making the pump  100 . In use, the two parts  110 A and  110 B function as one integral part. In other embodiments, the valve stem  110  may be composed of one integral part, or three or more connected parts. 
         [0046]      FIGS. 1A and 1B  illustrate the foam pump  100  in a priming or a primed state, that is, before actuation. In that state, both the moveable valve stem  110  and the shuttle valve  118  are in their upper-most positions within the pump body  116 . A liquid inlet gate valve  120  is disposed between the liquid reservoir  14  and a liquid charge chamber  122  within the pump body  116 , as is best shown in  FIG. 1A . The liquid inlet gate valve  120  is comprised of a first valve surface  124  formed on a top portion  126  of the movable valve stem  110 , and a second valve surface  128  formed on the movable shuttle valve  118 . The liquid inlet gate valve  120  opens and closes as the valve stem  110  and the shuttle valve  118  move up and down. In the priming or primed state of  FIGS. 1A and 1B , the valve  120  is in an open position. In that open position, the first valve surface  124  is separated from the second valve surface  128 . That separation permits liquid to be fed under the force of gravity down from the liquid container  12 , through the liquid inlet gate valve  120 . The valve  120  leads to one or more vertical channels  130  in the movable valve stem  110 , with two such vertical channels being illustrated in the embodiment of  FIG. 1A . 
         [0047]    The liquid continues to travel under the force of gravity through the one or more vertical channels  130  down into the liquid charge chamber  122 . The liquid charge chamber  122  is defined between the movable valve stem  110  on the inside and on the top, the pump body  116  on the outside, and the air gasket  114  on the bottom. The air gasket  114  has an upper wiper seal  132  which rests against the movable valve stem  110 , and an annular portion  134  which fits within the pump body  116 , such that a liquid-tight seal is formed at the bottom of the chamber  122 . As the valve stem  110  moves up and down, the distal end portion of the upper wiper seal  132  slides up and down the exterior surface of the valve stem  110  in a liquid-tight manner. In that way, liquid stored in the liquid charge chamber  122  is prevented from escaping downwardly past the seal  132  and the annular portion  134  of the air gasket  114 . Thus, when the valve stem  110  and the shuttle valve  118  are in their upper-most position as shown in  FIGS. 1A and 1B , the pump  100  primes itself as liquid begins to enter the liquid charge chamber  122 , and becomes fully primed when the chamber  122  is full of liquid. 
         [0048]    The pump  100  is actuated by the actuator (not shown) in the foam dispensing system exerting a downward pulling force on the valve stem  110 , such as via the annular member  112 . Initially, the frictional force between the shuttle valve  118  and an interior wall  135  of the pump body  116  prevents the shuttle valve  118  from moving downwardly with the valve stem  110 . In this way, the valve stem  110  moves to the intermediate pumping state of  FIGS. 2A and 2B . In that state, the underside lip of the top portion  126  has moved downwardly far enough that the first valve surface  124  contacts the second valve surface  128 , as best shown in  FIG. 2A . At that point, the liquid inlet gate valve  120  is closed. The contact between the top portion  126  underside lip and the shuttle valve  118  prevents liquid from flowing down out of the liquid container  12  into the vertical channels  130  and the liquid charge chamber  122 . In some embodiments, the first valve surface  124  may be provided with an elastomeric member such as an o-ring in order to enhance the seal when the valve  120  is closed. 
         [0049]    At the same time, however, a liquid outlet gate valve  136  has been opened. The liquid outlet gate valve  136  is comprised of a first valve surface  138  formed on a bottom lip annular extension  140  of the valve stem  110 , and a second valve surface  142  formed on the movable shuttle valve  118 . The liquid outlet gate valve  136  opens and closes as the valve stem  110  and the shuttle valve  118  move up and down. In the priming or primed state of  FIG. 1B , the outlet valve  136  is in a closed position. In that closed position, the first valve surface  138  contacts the second valve surface  142 . That contact prevents liquid from passing out of the liquid charge chamber  122  through the liquid outlet gate valve  136 . In the intermediate pumping state of  FIG. 2B , the first valve surface  138  has been separated from the second valve surface  142 . That separation permits liquid to pass out of the liquid charge chamber  122  through the liquid outlet gate valve  136  and into one or more horizontal channels  143  in the valve stem  110 . Two such horizontal channels  143  are illustrated in the embodiment of  FIG. 2B . 
         [0050]    The actuator (not shown) continues to exert a downward pulling force on the valve stem  110 . The interference between the top portion  126  lip of the valve stem  110  and the shuttle valve  118  overcomes the frictional force between the shuttle valve  118  and the interior wall  135  of the pump body  116 . In this way, the valve stem  110  and the shuttle valve  118  move downwardly together to reach the lower-most final pumping state of  FIGS. 3A and 3B . As they do so, the volume of the liquid charge chamber  122  decreases, creating a positive pressure on the liquid stored in the chamber  122 . The liquid in the chamber  122  is prevented from exiting the top of the chamber  122  via the closed inlet gate valve  120 , and from the bottom of the chamber  122  by the air gasket  114 . Thus, the only exit path available to the liquid is the now open liquid outlet gate valve  136 . As a result, during the downward stroke of the pump  100  from the intermediate state of  FIGS. 2A and 2B  to the final pumping state of  FIGS. 3A and 3B , liquid is forced out of the liquid charge chamber  122  through the liquid outlet gate valve  136 . The liquid then travels through the horizontal channels  143  which lead to a central liquid delivery conduit  144  within the valve stem  110 . The foam output of the pump  100  is adjustable because the valve stem  110  can be moved to any fraction of its full stroke length which is sufficient to open the outlet gate valve  136 . Moving the valve stem  110  less than a full stroke length reduces the volume of liquid pumped from the chamber  122 . Accordingly, the same pump  100  may be used in different applications requiring different foam doses. 
         [0051]    At the same time the valve stem  110  and the shuttle valve  118  are traveling downwardly, the air pump is placed in its “blow” state to deliver pressurized air to the liquid pump air inlet  102 . That pressurized air enters an intermediate air chamber  146  disposed within the pump housing  104 . The air gasket  114  has a lower sanitary wiper seal  148  which rests against the interior wall of the pump housing  104 . The pressurized air delivered by the air pump is sufficient to overcome the lower wiper seal  148 , but not the threading between the neck portion  16  and the receiving portion  106 . That is, the air pressure is high enough to overcome the resiliency of the lower wiper seal  148  pressing against the interior wall of the pump housing  104 , thereby separating the seal  148  from the pump housing  104 . The pressurized air thus escapes from the intermediate air chamber  146  past the seal  148  and into an interior chamber  150  of the air gasket  114 . Apertures  152  may be formed within an interior wall  154  of the air gasket  114  to facilitate air flow. 
         [0052]    The pressurized air has at least one escape path from the interior chamber  150  of the air gasket  114 . In one embodiment, the escape path is provided through one or more air ports  156  in the valve stem  110 , leading to the liquid delivery conduit  144 . Liquid flowing down the liquid delivery conduit  144  from the horizontal channels  143  mixes with the incoming air within a mixing chamber  158 . In one embodiment, the chamber  158  is formed within the conduit  144 . 
         [0053]    In some embodiments, air ports  156  in the valve stem  110  may provide the sole escape path for pressurized air from the interior chamber  150  of the air gasket  114 . In other embodiments, one or more additional escape paths for pressurized air may be provided. In one such embodiment, a second escape path is provided upwardly, past the upper wiper seal  132  of the air gasket  114  and into the liquid charge chamber  122 . That same upward air pressure helps to prevent liquid in the liquid charge chamber  122  from escaping down into the interior chamber  150  past the seal  132 , as the air travels upwardly around the seal  132 . When the pressurized air enters the liquid charge chamber  122 , it helps to force the liquid stored therein out of the chamber  122  through the liquid outlet gate valve  136  and down the delivery conduit  144  to the mixing chamber  158 . 
         [0054]    The incoming air pressure though the air ports  156  in the valve stem  110  helps to prevent liquid and foam in the mixing chamber  158  from escaping through the air ports  156  into the interior chamber  150 . In the mixing chamber  158 , the foamable liquid moving down the liquid delivery conduit  144  and the pressurized air arriving from the air ports  156  mix together in a swirling motion to form a mixture. Thus, the liquid-air mixture within the mixing chamber  158  is forced by gravity and the incoming air pressure within the liquid delivery conduit  144  into an inlet  160  of a foaming chamber  162 . 
         [0055]    In some embodiments, a drip catch  164  may be formed within the conduit  144  between the mixing chamber  158  and the foaming chamber  162 . Such a drip catch  164  operates to prevent leakage between pumping actuations by catching fluid and/or foam which remains within the mixing chamber  158  after the pump  100  actuation is complete. 
         [0056]    Within the foaming chamber  162 , the liquid-air mixture is enhanced into a rich foam. For example, the foaming chamber  162  may house one or more foaming elements therein. Suitable foaming elements include, for example, one or more screens, meshes, porous membranes or sponges. In addition, one or more of such foaming element(s) may be disposed in a foaming cartridge within the foaming chamber  162 . The foam pump  100 , for example, has a foaming cartridge  166  with two screen foaming elements  168 . As the liquid/air mixture passes through the foaming element(s), the mixture is turned into an enhanced foam. In some embodiments, the mixing and foaming action may both occur in one single chamber, which is then both a mixing chamber and a foaming chamber. The foam is dispensed from the foaming chamber  162  through a foam outlet  170 . 
         [0057]    In some embodiments, the foam outlet  170  is simply an aperture leading from the foaming chamber  162  directly to the outside atmosphere surrounding the foam dispenser system. In other embodiments, the foam outlet  170  may optionally include tubing or other delivery conduits (not shown) to carry the foam from the foaming chamber  162  to such an aperture. In additional embodiments, the foam outlet  170  may optionally include one or more one-way check valves (not shown) to prevent back flow of foam from the foam outlet  170  into the foaming chamber  162  or to prevent unwanted liquid or foam discharge while the dispenser is not being used. Suitable one-way check valves may include a flapper valve, a conical valve, a plug valve, an umbrella valve, a duck-bill valve, a ball valve, a slit valve, a mushroom valve, a spring and ball valve, or any other one-way check valve. Similar one-way check valves may optionally be placed in other portions of the liquid delivery path from the liquid reservoir  14  to the mixing chamber  158  and then to the foam outlet  170 , as desirable or necessary. They may, for example, be placed in the air ports  156  to help prevent liquid from escaping the liquid delivery conduit  144 . 
         [0058]    In a preferred embodiment, the air to liquid ratio in the mixture formed in the mixing chamber  158  is approximately 10:1, but any ratio may be provided. The air to liquid ratio is determined by the volume and pressure of the air being delivered by the air pump, and the amount of liquid entering the mixing chamber  158  from the liquid delivery conduit  144 . Once these and other applicable design variables are chosen to provide the desired air to liquid ratio, a consistently accurate dosing is thereafter provided. For example, a pressurized air escape path through the liquid charge chamber  122  as described above may be an additional means of controlling the air to liquid ratio by controlling the quantity of pressurized air that is delivered to the liquid charge chamber  122 . The volume of liquid may also be varied by adjusting the stroke of the valve stem  110 . 
         [0059]    The valve stem  110  and the shuttle valve  118  move downward until they stop.  FIGS. 3A and 3B  illustrate a lower-most position, wherein further downward movement is prevented by interference between the annular extension  140  of the valve stem  110  and the annular portion  134  of the air gasket  114 . That position represents the maximum pumping stroke of the valve stem  110 , producing the maximum amount of foam. The pumping actuator of the system may, however, stop the downward movement before that maximum displacement is reached, to reduce the amount of foam dispensed as desired by the user. 
         [0060]    Regardless of the length of the pumping stroke, when downward movement of the valve stem  110  and the shuttle valve  118  stops, the foaming and pumping actions also stop. The relative positions of the valve stem  110  and the shuttle valve  118  will then be as shown in  FIGS. 3A and 3B . In that configuration, the liquid inlet gate valve  120  is closed and the liquid outlet gate valve  136  is open. 
         [0061]    At that time, a restoring force pushes the valve stem  110  to move upwardly within the pump body  116 . The restoring force may be provided, for example, by a compressed coil spring (not shown) pushing up on the annular member  112 . Such a coil spring may alternatively or additionally be provided within the liquid charge chamber  122 , for example. In such embodiments, the downward force provided by the pump actuator overcomes the upward bias of the coil spring(s) in order to perform the pumping action illustrated by  FIGS. 1A-1B ,  2 A- 2 B and  3 A- 3 C. Then the downward actuating force is removed, permitting the coil spring(s) to push the valve stem  110  upwardly. The restoring force may alternatively or additionally be provided by the actuator itself exerting an upward force on the valve stem  110 , such as via the annular member  112 . 
         [0062]    As the valve stem  110  initially begins its upward travel, the frictional force between the shuttle valve  118  and the interior wall  135  of the pump body  116  prevents the shuttle valve  118  from moving upwardly with the valve stem  110 . In this way, the pump  100  moves to the intermediate pumping state of  FIGS. 4A and 4B . In that state, the top portion  126  of the valve stem  110  has moved upwardly far enough that the first valve surface  124  is separated from the second valve surface  128 , as best shown in  FIG. 4A . Therefore, at that point, the liquid inlet gate valve  120  is open and the liquid outlet gate valve  136  is closed. The liquid outlet gate valve  136  becomes closed when the first valve surface  138  contacts the second valve surface  142 , preventing liquid from passing out of the liquid charge chamber  122  into the horizontal channels  143 , as best shown in  FIG. 4B . 
         [0063]    The restoring force continues to exert an upward pushing force on the valve stem  110 . The interference between the bottom lip annular extension  140  of the valve stem  110  and the shuttle valve  118  overcomes the frictional force between the shuttle valve  118  and the interior wall  135  of the pump body  116 . In this way, the valve stem  110  and the shuttle valve  118  move upwardly together to reach the upper-most priming or primed state of  FIGS. 1A and 1B . At that point further upward movement is prevented by interference between the shuttle valve  118  and an inset portion  172  of the pump housing  104 . 
         [0064]    As the valve stem  110  and the shuttle valve  118  move upwardly, the volume of the liquid charge chamber  122  increases. Liquid stored in the liquid reservoir  14  is free to move down into the liquid charge chamber  122  through the open liquid inlet gate valve  120 . It does so not only under the force of gravity, but also by the negative hydraulic pressure generated by the sealed (other than the open valve  120 ) chamber  122 . The closed liquid outlet gate valve  136  prevents the liquid from exiting the chamber  122 . During the upward stroke of the valve stem  110  and the shuttle valve  118 , the air pump may be turned “off” to stop its delivery of pressurized air. Thus, liquid will continue to fill the chamber  122  until it is full, readying the pump  100  for another actuation. 
         [0065]    During operation of the foam pump  100 , the air pump (not shown) preferably remains dry or free from liquids and foamy mixtures, to prevent bacteria from growing in the air pump. This is accomplished by the seal  148  which is a sanitary seal in that it prevents liquid and foam from contaminating the air pump or coming into contact with elements of the foam dispenser system that are located outside of the intended liquid and foam delivery path. Optionally, one-way valves as discussed above may be added to the air ports  156  to further ensure that liquid does not contaminate the air pump. 
         [0066]    The disposable refill unit including the wet portions of the foam pump  100  has many advantages. Among them is the ease by which the unit may be prepared for shipping and delivery to an end user location, without leakage. If the unit  10  is packed with the valve stem  110  held in the uppermost position of  FIGS. 1A and 1B , the liquid inlet gate valve  120  will correspondingly be held closed to prevent liquid from escaping the reservoir  14 . This can easily be accomplished with appropriate packaging materials. It has the added benefit of keeping the unit  10  in its smallest size configuration during shipping. 
         [0067]    Indeed, another potential benefit provided by the foam pump  100  is that it may be used to provide a small pump mechanism. This size advantage arises, in part, because many of the foam pump  100  components extend up into the neck  16  of the container  12 . And, in some cases the diameter of the foam screens  168  may be no more than about 0.6″ in diameter. Further, in one embodiment, substantially all of the working components of the pump  100  are located within the neck  16  of the container  12 . For example, at least fifty percent (50%) of the pump components may fit wholly or partly within the neck portion  16 . 
         [0068]      FIGS. 5A-5B ,  6 A- 6 B,  7 A- 7 B and  8 A- 8 B illustrate a second exemplary embodiment of a foam pump  200 . The foam pump  200  may be used with the same container  12  as the first exemplary foam pump  100  to form a disposable refill unit  20  for use in a foam dispensing system (not shown). The foam pump  200  connects to and operates with the container  12  in the same way as the foam pump  100 . Therefore, a detailed discussion of the container  12  and the overall foam dispensing system is omitted here, having already been described above. 
         [0069]    The foam pump  200  includes many components which are identical to, or at least perform similar functions as, corresponding components within the foam pump  100 . Such components are identified by reference numerals having a different leading digit but the same final two digits. Thus, for example, the foam pump  200  has an air inlet  202  and a pump housing  204  which are substantially identical to the air inlet  102  and the pump housing  104  of the foam pump  100 . The foam pump  200  also has a moveable valve stem  210  which performs a similar function to the valve stem  110  of the foam pump  100 , but in some respects the two valve stems  110 ,  210  are structurally different. 
         [0070]    The components of the foam pump  200  include an air gasket  214 , a pump body  216 , the valve stem  210 , a flexible disk valve  218  and a guide disk  219 . The guide disk  219  may be rigid. Many of these pump components are at least partially held within the interior chamber  208  of the pump housing  204 . When the pump housing  204  is connected to the container  12 , many of the pump components also extend up into the neck  16  of the container  12 . In one embodiment, the pump housing  204  may be disposed within the neck  16  of the container  12  with external threads to secure the pump  200  to internal threads in the neck  16 . 
         [0071]    The valve stem  210  moves up and down longitudinally within the pump body  216  to move liquid through the foam pump  200 , as described further below. In the particular foam pump  200  embodiment illustrated in the Figures, the valve stem  210  is composed of a central stem part  210 A and the guide disk  219 , which snap or otherwise connect together to form the valve stem  210 . This design aids the assembly process for making the pump  200 . In use, the two parts  210 A and  219  function as one integral part. In other embodiments, the valve stem  210  may be composed of one integral part, or three or more connected parts. 
         [0072]    The flexible disk valve  218  and the guide disk  219  are attached to the central stem part  210 A. More specifically, the central stem part  210 A has a top portion  226  with a reduced diameter section receiving the disk valve  218  and the guide disk  219  via central apertures in those disks. The top portion  226  has an enlarged diameter section above its reduced diameter section to hold the disk valve  218  and the guide disk  219  in place. In that way, the disk valve  218  and the guide disk  219  move up and down with the central stem part  210 A longitudinally within the pump body  216 . The disk valve  218  and the guide disk  219  may be made from materials which are flexible enough to receive the enlarged diameter section of the top portion  226  during the assembly process. Alternatively, the central stem part  210 A may be composed of two parts which connect together around the disk valve  218  and the guide disk  219  during the assembly process. In yet another potential embodiment, the disk valve  218  and the guide disk  219  may be formed integrally with the central stem part  210 A, but having relative widths or other characteristics so that they perform as described below. 
         [0073]    The disk valve  218  is made from a flexible and resilient material, such as a thermoplastic rubber, a chemical resistant elastomeric polymer, such as, for example, thermoplastic rubber, TPV, silicone, trade name ENGAGE, urethane, a BoPet film, such as Mylar of less than 0.30″ thick. It flexes up and down, as described further below, as the valve stem  210  moves up and down in order to operate the foam pump  200 . The outer edge of the disk valve  218  comprises a wiper seal which rests against the interior wall  235  of the pump body  216 . As the valve stem  210  moves up and down, the outer wiper seal moves up and down the interior wall  235  of the pump body  216 . 
         [0074]    In one embodiment, the guide disk  219  is more rigid than the flexible disk valve  218 , due to its material characteristics or relative thickness. Chemical resistant low friction rigid plastics, such as, for example Polypro, HDPE, LDPE, Acetal and Nylon may be useful materials for making the flexible disk. The guide disk  219  forms one or more liquid pathways through or past the guide disk. For example, the guide disk  219  may have apertures and/or castellated indentations  274  around its periphery, to help promote the flow of liquid from the container  12  through or around the guide disk  219  and down into a liquid charge chamber  222 . The guide disk  219  may alternatively or additionally have an outer diameter which is small enough to permit liquid to flow around the disk  219  within the cavity of the pump body  216  as another type of liquid pathway past the guide disk  219 . Some embodiments may forego a guide disk  219 , instead having only a disk valve  218  mounted on the valve stem  210 . In such a case the disk valve  218  could have a thick base so that the valve  218  would not invert during a pumping action. 
         [0075]      FIGS. 5A and 5B  illustrate the foam pump  200  in a priming or a primed state, that is, before actuation. In that state, the moveable valve stem  210  and the flexible disk valve  218  are in their upper-most positions within the pump body  216 . A liquid inlet gate valve  220  is disposed between the liquid reservoir  14  and the liquid charge chamber  222  within the pump body  216 . In one embodiment, the liquid inlet gate valve  220  is a wiper seal. The liquid inlet gate valve  220  is comprised of a first valve surface  224  formed on the interior wall  235  of the pump body  216 , and a second valve surface  228  formed on the outer wiper seal of the flexible disk valve  218 . The liquid inlet gate valve  220  opens and closes as the valve stem  210  and the flexible disk valve  218  move up and down within the pump body  216 . In the priming or primed state of  FIGS. 5A and 5B , the valve  220  is in a closed position. In that closed position, the first valve surface  224  contacts the second valve surface  228 . The contact between the two valve surfaces  224  and  228  prevents liquid from passing through the inlet gate valve  220 . 
         [0076]    The liquid inlet gate valve  220  may be opened in any one of a number of fashions. In one embodiment, the force of gravity of the liquid stored in the container  12  by itself is sufficient to separate the two valve surfaces  224  and  228  to open the valve  220 . Such separation permits liquid to be fed under the force of gravity down from the liquid container  12  through the liquid inlet gate valve  220 . The valve  220  then closes when the liquid charge chamber  222  is full of liquid. In another embodiment, the resiliency of the flexible disk valve  218  is such that the force of gravity of the liquid in the container  12  by itself is not sufficient to open the valve  220 . In such an embodiment, the negative hydraulic pressure formed within the chamber  222  during an upward stroke of the valve stem  210  and the flexible disk valve  218  (as discussed below) separates or aids in the separation of the two valve surfaces  224  and  228  to open the valve  220 . 
         [0077]    The liquid charge chamber  222  is defined between the movable valve stem  210  on the inside, the flexible disk valve  218  on the top, the pump body  216  on the outside, and the air gasket  214  on the bottom. The air gasket  214  has an upper wiper seal  232  which rests against the movable valve stem  210 , and an annular portion  234  which fits within the pump body  216 , such that a liquid-tight seal is formed at the bottom of the chamber  222 . As the valve stem  210  moves up and down, the distal end portion of the upper wiper seal  232  slides up and down the exterior surface of the valve stem  210  in a liquid-tight manner. In that way, liquid stored in the liquid charge chamber  222  is prevented from escaping downwardly past the seal  232  and the annular portion  234  of the air gasket  214 . Thus, when the valve stem  210  and the flexible disk valve  218  are moving to or in their upper-most position as shown in  FIGS. 5A and 5B , the pump  200  primes itself as liquid begins to enter the liquid charge chamber  222  and becomes fully primed when the chamber  222  is full of liquid. 
         [0078]    The pump  200  is actuated by the actuator (not shown) in the foam dispensing system exerting a downward pulling force on the valve stem  210 . In one embodiment, the downward pulling force is applied to an annular member  212 . Initially, the frictional force between the flexible disk valve  218  and the interior wall  235  of the pump body  216  causes the flexible disk valve  218  to flex upwardly. In this way, the pump  200  moves to the intermediate pumping state of  FIGS. 6A and 6B . As the valve stem  210  and the flexible disk valve  218  continue to move downwardly together within the pump body  216 , the flexible disk valve  218  will continue to hold its upwardly flexed position relative to the valve stem  210  as shown in those Figures. At the same time, the volume of the liquid charge chamber  222  decreases, creating a positive pressure on the liquid stored in the chamber  222 . These effects combine to produce at least two results during a downward stroke of the valve stem  210  and flexible disk valve  218 . 
         [0079]    First, the liquid inlet gate valve  220  is held closed by hydraulic pressure, despite the force of gravity from the liquid in the container  12  urging the valve  220  to open. At the top of the liquid charge chamber  222 , the hydraulic pressure within the chamber  222  increases the force acting to press the outer wiper seal of the flexible disk valve  218  against the interior wall  235  of the pump body  216 . The contact between the two valve surfaces  224  and  228  prevents liquid from being fed under the force of gravity down from the liquid container  12  into the liquid charge chamber  222 . In embodiments having a guide disk  219  above the flexible disk valve  218 , the guide disk  219  may provide a firm support for shaping the flexible disk valve  218  in a closed position. Thus, during a downward stroke of the valve stem  210  and the flexible disk  218 , the liquid inlet gate valve  220  is closed. 
         [0080]    Second, the downward movement of the valve stem  210  and the flexible disk  218  opens a liquid outlet gate valve  236 . The liquid outlet gate valve  236  is comprised of a first valve surface  238  formed on the valve stem  210 , and a second valve surface  242  formed on the flexible disk valve  218 . In the priming or primed state of  FIG. 5B , the outlet valve  236  is in a closed position. In that closed position, the first valve surface  238  contacts the second valve surface  242 . That contact prevents liquid from passing out of the liquid charge chamber  222  through the liquid outlet gate valve  236 . In the intermediate pumping state of  FIGS. 6A and 6B , the upward flexing of the flexible disk valve  218  has separated the first valve surface  238  from the second valve surface  242 . That separation permits liquid to pass out of the liquid charge chamber  222  through the liquid outlet gate valve  236  and into one or more channels  243  in the valve stem  210 . Two such channels  243  are illustrated in the embodiment of  FIG. 6A . 
         [0081]    The liquid in the chamber  222  is prevented from exiting the top of the chamber  222  via the closed inlet gate valve  220 , and from exiting the bottom of the chamber  222  by the air gasket  214 . Thus, the only exit path available to the liquid is the now open liquid outlet gate valve  236 . As a result, during the downward stroke of the pump  200  moving it from the intermediate state of  FIGS. 6A and 6B  to the final pumping state of  FIGS. 7A and 7B , liquid is forced out of the liquid charge chamber  222  through the liquid outlet gate valve  236  by a positive hydraulic pressure. The liquid then travels through the channels  243  which lead to a central liquid delivery conduit  244  within the valve stem  210 . The foam output of the pump  200  is adjustable because the valve stem  210  can be moved to any fraction of its full stroke length which is sufficient to open the outlet gate valve  236 . Moving the valve stem  210  less than a full stroke length reduces the volume of liquid pumped from the chamber  222 . Accordingly, the same pump  200  may be used in different applications requiring different foam doses. 
         [0082]    At the same time the valve stem  210  and the flexible disk valve  218  are traveling downwardly, the air pump is placed in its “blow” state to deliver pressurized air to the liquid pump air inlet  202 . That pressurized air enters an intermediate air chamber  246  disposed within the pump housing  204 . The air gasket  214  has a lower sanitary wiper seal  248  which rests against the interior wall of the pump housing  204 . The pressurized air delivered by the air pump is sufficient to overcome the lower wiper seal  248 , but not the threading between the neck portion  16  and the receiving portion  206 . That is, the air pressure is high enough to overcome the resiliency of the lower wiper seal  248  pressing against the interior wall of the pump housing  204 , thereby separating the seal  248  from the pump housing  204 . The pressurized air thus escapes from the intermediate air chamber  246  past the seal  248  and into an interior chamber  250  of the air gasket  214 . Apertures  252  may be formed within an interior wall  254  of the air gasket  214  to facilitate air flow. In a addition, a sealing member  253  seals against valve stem  210  to prevent air from leaking out around the valve stem  210 . 
         [0083]    The pressurized air has at least one escape path from the interior chamber  250  of the air gasket  214 . In one embodiment, the escape path is provided through one or more air ports  256  in the valve stem  210 , leading to the liquid delivery conduit  244 . Liquid flowing down the liquid delivery conduit  244  from the channels  243  mixes with the incoming air within a mixing chamber  258 . In one embodiment, the chamber  258  is formed within the conduit  244 . 
         [0084]    In some embodiments, air ports  256  in the valve stem  210  may provide the sole escape path for pressurized air from the interior chamber  250  of the air gasket  214 . In other embodiments, one or more additional escape paths for pressurized air may be provided. In one such embodiment, a second escape path is provided upwardly, past the upper wiper seal  232  of the air gasket  214  and into the liquid charge chamber  222 . That same upward air pressure helps to prevent liquid in the liquid charge chamber  222  from escaping down into the interior chamber  250  past the seal  232 , as the air travels upwardly around the seal  232 . When the pressurized air enters the liquid charge chamber  222 , it helps to force the liquid stored therein out of the chamber  222  through the liquid outlet gate valve  236  and down the delivery conduit  244  to the mixing chamber  258 . 
         [0085]    The incoming air pressure though the air ports  256  in the valve stem  210  helps to prevent liquid and foam in the mixing chamber  258  from escaping through the air ports  256  into the interior chamber  250 . In the mixing chamber  258 , the foamable liquid moving down the liquid delivery conduit  244  and the pressurized air arriving from the air ports  256  mix together in a swirling motion to form a mixture. Thus, the liquid-air mixture within the mixing chamber  258  is forced by gravity and the incoming air pressure within the liquid delivery conduit  244  into an inlet  260  of a foaming chamber  262 . 
         [0086]    In some embodiments, a drip catch  264  may be formed within the conduit  244  between the mixing chamber  258  and the foaming chamber  262 . Such a drip catch  264  operates to prevent leakage between pumping actuations by catching fluid and/or foam which remains within the mixing chamber  258  after the pump  200  actuation is complete. 
         [0087]    Within the foaming chamber  262 , the liquid-air mixture is enhanced into a rich foam. For example, the foaming chamber  262  may house one or more foaming elements therein. Suitable foaming elements include, for example, one or more screens, meshes, porous membranes or sponges. In addition, one or more of such foaming element(s) may be disposed in a foaming cartridge within the foaming chamber  262 . The foam pump  200 , for example, has a foaming cartridge  266  with two screen foaming elements  268 . As the liquid/air mixture passes through the foaming element(s), the mixture is turned into an enhanced foam. In some embodiments, the mixing and foaming action may both occur in one single chamber, which is then both a mixing chamber and a foaming chamber. The foam is dispensed from the foaming chamber  262  through a foam outlet  270 . 
         [0088]    In some embodiments, the foam outlet  270  is simply an aperture leading from the foaming chamber  262  directly to the outside atmosphere surrounding the foam dispenser system. In other embodiments, the foam outlet  270  may optionally include tubing or other delivery conduits (not shown) to carry the foam from the foaming chamber  262  to such an aperture. In additional embodiments, the foam outlet  270  may optionally include one or more one-way check valves (not shown) to prevent back flow of foam from the foam outlet  270  into the foaming chamber  262  or to prevent unwanted liquid or foam discharge while the dispenser is not being used. Suitable one-way check valves may include a flapper valve, a conical valve, a plug valve, an umbrella valve, a duck-bill valve, a ball valve, a slit valve, a mushroom valve, a spring and ball valve, or any other one-way check valve. Similar one-way check valves may optionally be placed in other portions of the liquid delivery path from the liquid reservoir  14  to the mixing chamber  258  and then to the foam outlet  270 , as desirable or necessary. They may, for example, be placed in the air ports  256  help prevent liquid from escaping the liquid delivery conduit  244 . 
         [0089]    In a preferred embodiment, the air to liquid ratio in the mixture formed in the mixing chamber  258  is approximately 10:1, but any ratio may be provided. The air to liquid ratio is determined by the volume and pressure of the air being delivered by the air pump, and the amount of liquid entering the mixing chamber  258  from the liquid delivery conduit  244 . Once these and other applicable design variables are chosen to provide the desired air to liquid ratio, a consistently accurate dosing is thereafter provided. For example, a pressurized air escape path through the liquid charge chamber  222  as described above may be an additional means of controlling the air to liquid ratio by controlling the quantity of pressurized air that is delivered to the liquid charge chamber  222 . The volume of liquid may be varied by adjusting the stroke of the valve stem  210 . 
         [0090]    The valve stem  210  and the flexible disk valve  218  move downward until they stop.  FIGS. 7A and 7B  illustrate the lower-most position, wherein further downward movement is prevented by interference between an annular extension  240  of the valve stem  210  and the annular portion  234  of the air gasket  214 . That position represents the maximum pumping stroke of the valve stem  210 , producing the maximum amount of foam. The pumping actuator of the system may, however, stop the downward movement before that maximum displacement is reached, to reduce the amount of foam dispensed as desired by the user. 
         [0091]    Regardless of the length of the pumping stroke, when downward movement of the valve stem  210  and the flexible disk valve  218  stops, the foaming and pumping actions also stop. The relative positions of the valve stem  210  and the flexible disk valve  218  will then be as shown in  FIGS. 7A and 7B . In that configuration, the liquid inlet gate valve  220  is closed and the liquid outlet gate valve  236  is open. 
         [0092]    At that time, a restoring force pushes the valve stem  210  to move upwardly within the pump body  216 . The restoring force may be provided, for example, by a compressed coil spring (not shown) pushing up on the annular member  212 . Such a coil spring may alternatively or additionally be provided within the liquid charge chamber  222 , for example. In such embodiments, the downward force provided by the pump actuator overcomes the upward bias of the coil spring(s) in order to perform the pumping action illustrated by  FIGS. 5A-5B ,  6 A- 6 B and  7 A- 7 B. Then the downward actuating force is removed, permitting the coil spring(s) to push the valve stem  210  upwardly. The restoring force may alternatively or additionally be provided by the actuator itself exerting an upward force on the valve stem  210 , such as via the annular member  212 . 
         [0093]    As the valve stem  210  and the flexible valve disk  218  initially begin their upward travel, the forces previously acting to hold the flexible valve disk  218  in the upwardly flexed position of  FIGS. 7A and 7B  are removed. In this way, the pump  200  moves to the intermediate pumping state of  FIGS. 8A and 8B . In that state, the valve stem  210  has moved upwardly far enough that the flexible disk valve  218  has moved back to its rest position. As will be appreciated, in that position, the liquid outlet gate valve  236  is closed by the first valve surface  238  contacting the second valve surface  242 , preventing liquid from passing out of the liquid charge chamber  222  into the channels  243 . 
         [0094]    The restoring force continues to exert an upward pushing force on the valve stem  210  and the flexible disk valve  218 . At this point the liquid inlet gate valve  220  may be opened by separation of the first valve surface  224  from the second valve surface  228 . Such separation may be caused solely by the force of gravity from the liquid in the container  12  acting on the flexible disk valve  218 . It may also be aided by a hydraulic force acting within the liquid charge chamber  222 . That is, as the valve stem  210  and the flexible disk valve  218  move upwardly, the volume of the liquid charge chamber  222  increases. The chamber  222  is sealed closed at the outlet gate valve  236  and at the air gasket  214 . Thus, the increasing volume of the chamber  222  creates a negative hydraulic force acting to open the inlet gate valve  220  and pull liquid into the chamber  222 . During the upward stroke of the valve stem  210  and the flexible disk valve  218 , the air pump may be turned “off” to stop its delivery of pressurized air. Thus, liquid will continue to fill the chamber  222  until it is full, readying the pump  200  for another actuation. 
         [0095]    In this way, the valve stem  210  and the flexible disk valve  218  move upwardly together to reach the upper-most priming or primed state of  FIGS. 5A and 5B . At that point further upward movement is prevented by interference between the flexible disk valve  218 , or the guide disk  219  if present, and an inset portion  272  of the pump housing  204 . 
         [0096]    During operation of the foam pump  200 , the air pump (not shown) preferably remains dry or free from liquids and foamy mixtures, to prevent bacteria from growing in the air pump. This is accomplished by the seal  248  which is a sanitary seal in that it prevents liquid and foam from contaminating the air pump or coming into contact with elements of the foam dispenser system that are located outside of the intended liquid and foam delivery path. Optionally, one-way valves as discussed above may be added to the air ports  256  to further ensure that liquid does not contaminate the air pump. 
         [0097]    The disposable refill unit including the wet portions of the foam pump  200  has many advantages. Among them is the ease by which the unit may be prepared for shipping and delivery to an end user location, without leakage. If the unit  20  is packed with the valve stem  210  held in the uppermost position of  FIGS. 5A and 5B , the liquid inlet gate valve  220  will correspondingly be held closed to prevent liquid from escaping the reservoir  14 . This can easily be accomplished with appropriate packaging materials. It has the added benefit of keeping the unit  20  in its smallest size configuration during shipping. 
         [0098]    Indeed, another potential benefit provided by the foam pump  200  is that it may be used to provide a small pump mechanism. This size advantage arises, in part, because many of the foam pump  200  components extend up into the neck  16  of the container  12 . And, in some cases the diameter of the foam screens  268  may be no more than about 0.06″ in diameter. Further, in one embodiment, substantially all of the working components of the pump  200  are located within the neck  16  of the container  12 . For example, at least fifty percent (50%) of the pump components may fit wholly or partly within the neck portion  16 . 
         [0099]    Yet an additional benefit which may be provided by the foam pump  200  is that it has very few working parts, relative to many past pump designs. Thus the pump  200  provides very little resistance to the flow of liquid through it, and may be relatively less expensive to manufacture. 
         [0100]      FIGS. 9-14  illustrate a third exemplary embodiment of a disposable refill unit  30 , for use for example in a foam dispenser system  50 . Referring initially to  FIGS. 9 and 10 , the disposable refill unit  30  includes a container  12  connected to a foam pump  300 . The disposable refill unit  30  may be placed within a housing  52  of the dispenser system  50 . The foam dispenser system  50  is a wall-mounted system. The foam pump  300  may alternatively be used in a counter-mounted system, an un-mounted portable system movable from place to place, or any other kind of foam dispenser system. 
         [0101]    The container  12  forms a liquid reservoir  14 . The liquid reservoir  14  contains a supply of a foamable liquid within the disposable refill unit  30  and the dispensing system housing  52  which holds the refill unit  30 . In various embodiments, the contained liquid could be for example a soap, a sanitizer, a cleanser, a disinfectant or some other foamable liquid. In the exemplary refill unit  30 , the liquid reservoir  14  is formed by a rigid housing member. In other embodiments, the liquid reservoir  14  may be formed by a collapsible container such as a flexible bag-like container, or have any other suitable configuration for containing the foamable liquid without leaking. The container  12  may advantageously be refillable, replaceable, or both refillable and replaceable. In other embodiments the container  12  may be neither refillable nor replaceable. 
         [0102]    In the event the liquid stored in the reservoir  14  of the installed disposable refill unit  30  runs out, or the installed refill unit  30  otherwise has a failure, the installed refill unit  30  may be removed from the foam dispenser system  50 . The empty or failed refill unit  30  may then be replaced with a new refill unit  30  including a liquid-filled reservoir  14 . 
         [0103]    The housing  52  of the dispenser system  50  further contains one or more actuating members to activate the foam pump  300 , such as a manual lever  54 . As will be appreciated by one of ordinary skill in the art, there are many different kinds of pump actuators which may be employed in the foam dispenser system. The pump actuator of the foam dispenser system may be any type of actuator, such as, for example, a manual lever, a manual pull bar, a manual push bar, a manual rotatable crank, an electrically activated actuator or other means for actuating the foam pump  300  within the foam dispenser system. Electronic pump actuators may additionally include a motion detector to provide for a hands-free dispenser system with touchless operation. Various intermediate linkages connect an external actuator member to the foam pump  300  within the system housing. Thus, in the embodiment of  FIGS. 9 and 10 , the actuating member  54  is a U-shaped manual lever. The lever  54  has two legs  56 , only one of which is shown in the Figures, which extend into the housing  52 . Each leg  56  has a slot  58  formed therein, and is mounted within the housing  52  at a pivot joint  60 . The slots  58  respectively receive bosses  62  formed on opposite sides of the foam pump  300  within the dispenser system housing  52 . 
         [0104]    The exemplary foam pump  300  is a “pull-activated” pump. That is, the pump  300  is actuated by pulling a lower pump body  302  downwardly with respect to an upper pump body  304 . The external actuator may be operated in any manner, so long as the intermediate linkages transform that motion to a downward pulling force on the lower pump body  302 . Thus, the foam pump  300  is moved from its rest position in  FIG. 9  to its activated position in  FIG. 10  by a user pulling down on the actuating member  54 . The member  54  therefore pivots downwardly around the axis defined by the pivot joints  60 . That causes the bosses  62  to move downwardly within the slots  58 , thereby translating the downward pivoting movement into a downward vertical movement of the lower pump body  302 . 
         [0105]    Now referring additionally to  FIG. 11 , the container  12  is connected to the upper pump body  304  of the foam pump  300 . The container  12  has a threaded neck portion  16  which is received within a mating threaded receiving portion  306  of the upper pump body  304 . For example, a “quarter turn” rotation may complete the connection between the container  12  and the upper pump body  304 . An o-ring or other sealing member  307  may be included to help provide a liquid-tight sealed connection between the two parts of the unit  30 . 
         [0106]    The foam pump  300  includes several components, including the lower pump body  302 , the upper pump body  304 , a bottom plate  314 , a shuttle valve  318 , an external bellows  376  and an internal bellows  378 . When the upper pump body  304  is connected to the neck  16  of the container  12 , a valve stem portion  310  of the lower pump body  302  extends up into the neck  16  of the container  12 . More specifically, the valve stem portion  310  extends up through the sealing member  307  into the neck  16 . The neck portion  16 , in turn, is held within the upper pump body  304  of the foam pump  300 . In one embodiment, the upper pump body  304  may be disposed within the neck  16  of the container  12  with external threads to secure the pump  300  to internal threads in the neck  16 . 
         [0107]    The lower pump body  302  moves up and down longitudinally within the container  12  and the upper pump body  304 . The shuttle valve  318  also moves up and down around the valve stem portion  310  of the lower pump body  302 , between a top lip portion  380  and a bottom lip portion  382 . These combined movements of the lower pump body  302  and the shuttle valve  318  operate to move liquid through the foam pump  300 , as described further below. 
         [0108]      FIGS. 9 and 11  illustrate the foam pump  300  in a priming or a primed state, that is, in a rest state before actuation. In that state, the lower pump body  302  is in its upper-most position, and the shuttle valve  318  is in its lower-most position adjacent the bottom lip portion  382 . A liquid inlet gate valve  320  is disposed between the liquid reservoir  14  and a liquid charge chamber  322 . The liquid charge chamber  322  is defined by the valve stem portion  310 , an interior wall  335  of the neck  16 , and a sealing member  307 . The liquid inlet gate valve  320  is comprised of one or more inlet openings  324  in the valve stem portion  310 , and the movable shuttle valve  318 . The liquid inlet gate valve  320  opens and closes as the valve stem portion  310  and the shuttle valve  318  move up and down. In the priming or primed state of  FIGS. 9 and 11 , the valve  320  is in an open position. In that open position, the shuttle valve  318  is in its downward position, exposing the inlet openings  324  to the liquid in the reservoir  14 . That exposure permits liquid to be fed under the force of gravity, or by a vacuum created by expansion of liquid charge chamber  322 , down from the liquid container  12 , through the inlet openings  324  and into the liquid charge chamber  322 . 
         [0109]    The sealing member  307  at the bottom of the liquid charge chamber  322  prevents liquid from escaping the chamber  322  past the seal  307 . The sealing member  307  has an inner wiper seal  332  which rests against the movable valve stem portion  310 . As the valve stem portion  310  moves up and down within the sealing member  307 , the inner wiper seal  332  slides up and down the exterior surface of the valve stem portion  310  in a liquid-tight manner. In that way, liquid stored in the liquid charge chamber  322  is prevented from escaping downwardly past the seal  307 . In addition, a spring-loaded outlet ball valve  336  is closed in the priming or primed state of the pump  300 . Thus, when the valve stem portion  310  and the shuttle valve  318  are in their respective positions as shown in  FIG. 11 , the pump  300  primes itself as liquid begins to enter the liquid charge chamber  322 , and becomes fully primed when the chamber  322  is full of liquid. 
         [0110]    An air pump  384  disposed underneath the liquid charge chamber  322  is also primed, as shown in  FIGS. 9 and 11 . The air pump  384  comprises an air chamber  386  defined by the lower pump body  302  at the top, the external bellows portion  376 , the bottom plate  314 , and the internal bellows portion  378 . A one-way air inlet valve  303  disposed in the bottom plate  314  permits the air chamber  386  to be recharged with a new supply of air after the pump  300  is actuated, as described further below. Sanitary sealing through the tortuous path  390  isolates the air pump  384  from the other portions of the foam pump  300  that contact liquid, so that the air pump  384  mechanism does not contact liquid during operation of the foam pump  300 . 
         [0111]    The foam pump  300  is actuated by the actuator in the foam dispensing system, such as the manual lever  54  in dispensing system  50  described above, exerting a downward pulling force on the lower pump body  302 . Initially, the frictional force between the shuttle valve  318  and the interior wall  335  of the container  12  prevents the shuttle valve  318  from moving downwardly with the lower pump body  302 . In this way, the valve stem portion  310  moves to the intermediate pumping state of  FIG. 13 . In that state, the top lip portion  380  of the valve stem portion  310  has moved downwardly far enough to contact the shuttle valve  318 . At that point, the liquid inlet gate valve  320  is closed because the shuttle valve  318  is covering the inlet openings  324 , preventing liquid from being fed down from the liquid container  12  into the liquid charge chamber  322 . 
         [0112]    The actuator continues to exert a downward pulling force on the lower body portion  302  of the foam pump  300 . The interference between the top lip portion  380  of the valve stem portion  310  and the shuttle valve  318  overcomes the frictional force between the shuttle valve  318  and the interior wall  335  of the container  12 . In this way, the lower body portion  302  and the shuttle valve  318  move downwardly together to reach the lower-most final pumping state of  FIGS. 10 and 12 . As they do so, the volume of the liquid charge chamber  322  decreases, creating a positive pressure on the liquid stored in the chamber  322 . The liquid in the chamber  322  is prevented from exiting the top of the chamber  322  via the closed inlet gate valve  320 , and from the bottom of the chamber  322  by the sealing member  307 . Thus, the only exit path available to the liquid is the spring-loaded outlet ball valve  336 . 
         [0113]    The closing force exerted by the spring on the ball of the valve  336  is large enough to hold the valve  336  closed when the only opposing opening force is the force of gravity acting on the liquid stored in the liquid charge chamber  322 . It is, however, small enough to be overcome and open the valve  336  by the positive pressure arising in the chamber  322  from the decreasing volume of the chamber  322  during a downward stroke of the foam pump  300 . As a result, during the downward stroke of the pump  300  moving it from the intermediate state of  FIG. 13  to the final pumping state of  FIGS. 10 and 12 , liquid is forced out of the liquid charge chamber  322  through the liquid outlet gate valve  336 . The liquid then travels down through a central liquid delivery conduit  344  within the valve stem portion  310 . 
         [0114]    The downward movement of the lower pump body  302  during actuation of the pump  300  also operates the air pump  384  underneath the liquid charge chamber  322 . As the lower pump body  302  travels downward, the bellows portions  376  and  378  contract, thereby decreasing the volume of the air chamber  386  and creating a positive pressure on the air stored in the chamber  386 . The air in the chamber  386  is prevented from exiting the bottom of the chamber  386  via the one-way inlet air valve  303 , which permits air to travel only into the chamber  386 , not out of the chamber  386 . The air in the chamber  386  is thereby forced into one or more air ports  388  in the valve stem portion  310 . 
         [0115]    The air ports  388  lead to labyrinthine air channels  390  which provide a tortuous path within the valve stem portion  310 . The channels  390  lead from the air ports  388  to inner air ports  356  located next to the liquid delivery conduit  344 . Liquid flowing down the liquid delivery conduit  344  from the outlet ball valve  336  of the liquid charge chamber  322  mixes with the incoming air from the inner air ports  356  within a mixing chamber  358 . The incoming air pressure though the inner air ports  356  helps to prevent liquid and foam in the mixing chamber  358  from entering into the labyrinthine air channels  390 . And, to the extent liquid or foam does enter the channels  390 , the tortuous path formed by the channels  390  prevents the liquid or foam from reaching the air chamber  386 . 
         [0116]    In the mixing chamber  358 , the foamable liquid moving down the liquid delivery conduit  344  and the pressurized air arriving from the air pump  384  mix together in a swirling motion to form a mixture. Thus, the liquid-air mixture within the mixing chamber  358  is forced by gravity and the incoming air pressure within the liquid delivery conduit  344  into an inlet  360  of a foaming chamber  362 . 
         [0117]    Within the foaming chamber  362 , the liquid-air mixture is enhanced into a rich foam. For example, the foaming chamber  362  may house one or more foaming elements therein. Suitable foaming elements include, for example, one or more screens, meshes, porous membranes or sponges. In addition, one or more of such foaming element(s) may be disposed in a foaming cartridge within the foaming chamber  362 . The foam pump  300 , for example, has a foaming cartridge  366  with two screen foaming elements  368 . As the liquid/air mixture passes through the foaming element(s), the mixture is turned into an enhanced foam. In some embodiments, the mixing and foaming action may both occur in one single chamber, which is then both a mixing chamber and a foaming chamber. The foam is dispensed from the foaming chamber  362  through a foam outlet  370 . 
         [0118]    In some embodiments, the foam outlet  370  is simply an aperture leading from the foaming chamber  362  directly to the outside atmosphere surrounding the foam dispenser system. In other embodiments, the foam outlet  370  may optionally include tubing or other delivery conduits to carry the foam from the foaming chamber  362  to such an aperture. For example, in the pump  300 , such a conduit is formed by the internal bellows portion  378 . In additional embodiments, the foam outlet  370  may optionally include one or more one-way check valves (not shown) to prevent back flow of foam from the foam outlet  370  into the foaming chamber  362  or to prevent unwanted liquid or foam discharge while the dispenser is not being used. Suitable one-way check valves may include a flapper valve, a conical valve, a plug valve, an umbrella valve, a duck-bill valve, a ball valve, a slit valve, a mushroom valve, a spring and ball valve, or any other one-way check valve. Similar one-way check valves may optionally be placed in other portions of the liquid delivery path from the liquid reservoir  14  to the mixing chamber  358  and then to the foam outlet  370 , as desirable or necessary. They may, for example, be placed in the inner air ports  356  to ensure liquid cannot escape the liquid delivery conduit  344 . 
         [0119]    In a preferred embodiment, the air to liquid ratio in the mixture formed in the mixing chamber  358  is approximately 10:1, but any ratio may be provided. The air to liquid ratio is determined by the volume and pressure of the air being delivered by the air pump  384 , and the amount of liquid entering the mixing chamber  358  from the liquid delivery conduit  344 . Once these and other applicable design variables are chosen to provide the desired air to liquid ratio, a consistently accurate dosing is thereafter provided. The volume of liquid may also be varied by adjusting the stroke of the valve stem portion  310 . 
         [0120]    The lower pump body  302  and the shuttle valve  318  move downward until they stop.  FIGS. 10 and 12  illustrate a lower-most position, wherein further downward movement is prevented by interference between the lower pump body  302  and the bottom plate  314 . That position represents the maximum pumping stroke of the lower pump body  302 , producing the maximum amount of foam. The pumping actuator of the system may, however, stop the downward movement before that maximum displacement is reached, to reduce the amount of foam dispensed as desired by the user. 
         [0121]    Regardless of the length of the pumping stroke, when downward movement of the lower pump body  302  and the shuttle valve  318  stops, the foaming and pumping actions also stop. The relative positions of the valve stem portion  310  and the shuttle valve  318  will then be as shown in  FIG. 12 . In that configuration, the liquid inlet gate valve  320  is closed. 
         [0122]    At that time, a restoring force pushes the lower pump body  302  to move upwardly with respect to the upper pump body  304  and the bottom plate  314 . The restoring force may be provided, for example, by a resilient nature of the bellows portions  376  and  378 . It may also be provided by a compressed coil spring (not shown) disposed in the air chamber  386  and pushing up on the lower pump body  302 . In such embodiments, the downward actuating force provided by the pump actuator overcomes the upward bias of the bellows and/or coil spring in order to perform the pumping action illustrated by  FIGS. 11 ,  12  and  13 . Then the downward force is removed, permitting the bellows and/or coil spring to push the lower pump portion  302  upwardly. The restoring force may alternatively or additionally be provided by the actuator itself exerting an upward force on the lower pump body  302 . 
         [0123]    As the lower pump body  302  initially begins its upward travel, the frictional force between the shuttle valve  318  and the interior wall  335  of the container  12  prevents the shuttle valve  318  from moving upwardly within the container  12 . In this way, the pump  300  moves to the intermediate pumping state of  FIG. 14 . In that state, the valve stem portion  310  has moved upwardly far enough that the shuttle valve  318  contacts the bottom lip portion  382 . Therefore, at that point, the liquid inlet gate valve  320  is open. 
         [0124]    The restoring force continues to exert an upward pushing force on the lower valve body  302 . The interference between the bottom lip portion  382  of the valve stem portion  310  and the shuttle valve  318  overcomes the frictional force between the shuttle valve  318  and the interior wall  335  of the container  12 . In this way, the valve stem portion  310  and the shuttle valve  318  move upwardly together to reach the upper-most priming or primed state of  FIGS. 9 and 11 . At that point further upward movement is prevented by interference between the lower body portion  302  and the sealing member  307  or the upper body portion  304 . 
         [0125]    As the lower body portion  302  and the shuttle valve  318  move upwardly, the volume of the liquid charge chamber  322  increases. Liquid stored in the liquid reservoir  14  is free to move down into the liquid charge chamber  322  through the open liquid inlet gate valve  320 . It does so by the force of gravity and by the negative hydraulic pressure generated by the sealed (other than the open valve  320 ) chamber  322 . The outlet ball valve  336  prevents the liquid from exiting the chamber  322  into the mixing chamber  358 . Thus, liquid will continue to fill the chamber  322  until it is full, readying the pump  300  for another actuation. 
         [0126]    At the same time, both of the bellows portions  376  and  378  are expanding. This has at least two effects. First, the volume of the air chamber  386  in the air pump  384  increases, creating a negative air pressure within the air chamber  386 . That negative air pressure opens the one-way air inlet valve  303  to let air into the chamber  386 , thus recharging the air pump  384 . 
         [0127]    Second, the volume of an outlet chamber  392 , formed by the internal bellows portion  376  near the foam outlet  370 , also increases. That likewise creates a negative air pressure in the outlet chamber  392 , which will tend to create a suction force to pull back foam from the foam outlet  270  as the pump  300  expands. The foam outlet  370  may optionally include one or more one-way check valves, as discussed above, in order to aid this process. In this way, the foam pump  300  incorporates an “anti-drip” feature. 
         [0128]    During operation of the foam pump  300 , the air pump  384  preferably remains dry or free from liquids and foamy mixtures, to prevent bacteria from growing in that area. This is accomplished by the tortuous path of the labyrinthine channels  390 . For example, the tortuous path may include changes in angular direction that add up to at least 180 degrees, at least 270 degrees, at least 360 degrees, or more. Optionally, one-way valves as discussed above may be added to the air ports  356  to further ensure that liquid does not contaminate the air pump  384 . 
         [0129]    The disposable refill unit including the wet portions of the foam pump  300  has many advantages. Among them is the ease by which the unit may be prepared for shipping and delivery to an end user location, without leakage. If the unit  30  is packed with the lower pump body  302  held in the lowermost position of  FIGS. 10 and 12 , the liquid inlet gate valve  320  will correspondingly be held closed to prevent liquid from escaping the reservoir  14 . This can easily be accomplished with appropriate packaging materials. 
         [0130]    Indeed, another potential benefit provided by the foam pump  300  is that it may be used to provide a small pump mechanism. This size advantage arises, in part, because many of the foam pump  300  components extend up into the neck  16  of the container  12 . And, in some cases the diameter of the foam screens  368  may be no more than about 0.06″ in diameter. Further, in one embodiment, substantially all of the working components of the pump  300  are located within the neck  16  of the container  12 . For example, at least fifty percent (50%) of the pump components may fit wholly or partly within the neck portion  16 . 
         [0131]    At least a portion of the air pump  384  may remain attached to the dispenser  50 , such as the bellows  376  and the bottom plate  314 . Such portions of the air pump  384  are advantageously reusable, so that they do not need to be disposed of and replaced with the refill unit  30 . 
         [0132]      FIGS. 15-18  illustrate a fourth exemplary embodiment of a disposable refill unit  40 , which may be used for example in the foam dispenser system  50 . Referring initially to  FIG. 15 , the disposable refill unit  40  includes a container  12  connected to a foam pump  400 . The disposable refill unit  40  may be placed within the same foam dispenser system  50  which is discussed above in connection with the disposable refill unit  30 . The disposable refill unit  40  fits and operates within the dispenser system  50  in the same way as the disposable refill unit  30 . Therefore, a detailed discussion of the dispenser system  50  and its interaction with the unit  40  is omitted here, having already been described above. The disposable refill unit  40  may alternatively be used in a counter-mounted system, an un-mounted portable system movable from place to place, or any other kind of foam dispenser system. 
         [0133]    The foam pump  400  includes many components which are similar to, or at least perform similar functions as, corresponding components within the foam pump  300 . Such components are identified by reference numerals having a different leading digit but the same final two digits. Thus, for example, the foam pump  400  has an air pump  484  which is similar to the air pump  384  of the foam pump  300 . The foam pump  400  also has a moveable valve stem portion  410  which performs a similar function to the valve stem portion  310  of the foam pump  300 , but in some respects the two valve stem portions  310 ,  410  are structurally different. 
         [0134]    The container  12  forms a liquid reservoir  14 . The liquid reservoir  14  contains a supply of a foamable liquid within the disposable refill unit  40  and the dispensing system housing which holds the unit  40 . In various embodiments, the contained liquid could be for example a soap, a sanitizer, a cleanser, a disinfectant or some other foamable liquid. In the exemplary disposable refill unit  40 , the liquid reservoir  14  is formed by a rigid housing member. In other embodiments, the liquid reservoir  14  may be formed by a collapsible container such as a flexible bag-like container, or have any other suitable configuration for containing the foamable liquid without leaking. The container  12  may advantageously be refillable, replaceable, or both refillable and replaceable. In other embodiments the container  12  may be neither refillable nor replaceable. 
         [0135]    In the event the liquid stored in the reservoir  14  of the installed disposable refill unit  40  runs out, or the installed refill unit  40  otherwise has a failure, the installed refill unit  40  may be removed from the foam dispenser system. The empty or failed refill unit  40  may then be replaced with a new refill unit  40  including a liquid-filled reservoir  14 . 
         [0136]    The foam pump  400  includes several components, including a lower pump body  402 , an upper pump body  404 , a bottom plate  414 , a shuttle valve  418 , an external bellows  476  and an internal bellows  478 . When the upper pump body  404  is connected to the container  12 , a valve stem portion  410  of the lower pump body  402  extends up into the neck  16  of the container  12 . More specifically, the valve stem portion  410  extends up through a sealing member  407  into the neck  16  of the container  12 . The neck portion  16 , in turn, is held within the upper pump body  404  of the foam pump  400 . In one embodiment, the upper pump body  404  may be disposed within the neck  16  of the container  12  with external threads to secure the pump  100  to internal threads in the neck  16 . 
         [0137]    In the particular foam pump  400  embodiment illustrated in the Figures, the valve stem portion  410  is composed of three separate parts  410 A,  410 B and  410 C which snap or otherwise connect together to form the valve stem portion  410 . The valve stem portion  410  in turn is connected to a plate  402 B to form the lower pump body  402 . This design aids the assembly process for making the pump  400 . In use, the four parts  410 A,  410 B,  410 C and  402 B function as one integral lower pump body  402 . In other embodiments, the lower pump body  402  may be composed of one integral piece, or other numbers of connected parts. 
         [0138]    A gasket or seal  499  forms a seal between valve stem  410  and lower pump body  402 . In one embodiment, seal  499  contains a surface having an adhesive covered by a peel away film (not shown). Prior to installing the refill unit  40 , which has a seal  499  attached to valve stem  410 , the peel away film is removed. Thus, when the refill unit  40  is placed in the foam dispenser  50 , seal  499  adhesively bonds with lower pump body  402 . The adhesive bond has enough strength to temporarily bond lower valve body  402  to valve stem  410  during operation of the foam dispenser  50 , but is weak enough so that the bond is easily broken when the refill unit  40  is being replaced. 
         [0139]    The lower pump body  402  moves up and down longitudinally within the container  12  and the upper pump body  404 . The shuttle valve  418  also moves up and down around the valve stem portion  410  of the lower pump body  402 , between a top lip portion  480  and a bottom lip portion  482 . These combined movements of the lower pump body  402  and the shuttle valve  418  operate to move liquid through the foam pump  400 , as described further below. 
         [0140]      FIG. 15  illustrates the foam pump  400  in a priming or a primed state, that is, in a rest state before actuation. In that state, the lower pump body  402  is in its upper-most position, and the shuttle valve  418  is in its lower-most position adjacent the bottom lip portion  482 . A liquid inlet gate valve  420  is disposed between the liquid reservoir  14  and a liquid charge chamber  422 . Apertures  493  provided in the valve stem part  410 A permit fluid communication such that the liquid charge chamber  422  includes an interior cavity of the part  410 A as well as an annular space between the valve stem part  410 C and the interior wall  435  of the container  12  above the sealing member  407 . The liquid inlet gate valve  420  is comprised of one or more inlet openings  424  in the valve stem portion  410 , and the movable shuttle valve  418 . The liquid inlet gate valve  420  opens and closes as the valve stem portion  410  and the shuttle valve  418  move up and down. In the priming or primed state of  FIG. 15 , the valve  420  is in an open position. In that open position, the shuttle valve  418  is in its downward position, exposing the inlet openings  424  to the liquid in the reservoir  14 . That exposure permits liquid to be fed under the force of gravity down from the liquid container  12 , through the inlet openings  424  and into the liquid charge chamber  422 . 
         [0141]    The sealing member  407  at the bottom of the liquid charge chamber  422  prevents liquid from escaping the chamber  422  past the seal  407 . The sealing member  407  has an inner wiper seal  432  which rests against the movable valve stem portion  410 . As the valve stem portion  410  moves up and down within the sealing member  407 , the inner wiper seal  432  slides up and down the exterior surface of the valve stem portion  410  in a liquid-tight manner. In that way, liquid stored in the liquid charge chamber  422  is prevented from escaping downwardly past the seal  407 . In addition, a liquid outlet gate valve  436  is closed in the priming or primed state of the pump  400 . Thus, when the valve stem portion  410  and the shuttle valve  418  are in their respective positions as shown in  FIG. 15 , the pump  400  primes itself as liquid begins to enter the liquid charge chamber  422 , and becomes fully primed when the chamber  422  is full of liquid. 
         [0142]    An air pump  484  disposed underneath the liquid charge chamber  422  is also primed, as shown in  FIG. 15 . The air pump  484  comprises an air chamber  486  defined by the lower pump body plate  402 B at the top, the external bellows portion  476 , the bottom plate  414 , and the internal bellows portion  478 . A one-way air inlet valve  403  disposed in the bottom plate  414  permits the air chamber  486  to be recharged with a new supply of air after the pump  400  is actuated, as described further below. Sanitary sealing  498  isolates the air pump  484  from the other portions of the foam pump  400  that contact liquid, so that the air pump  484  mechanism does not contact liquid during operation of the foam pump  400 . 
         [0143]    The foam pump  400  is actuated by the actuator in the foam dispensing system exerting a downward pulling force on the lower pump body  402 . Initially, the frictional force between the shuttle valve  418  and the interior wall  435  of the container  12  prevents the shuttle valve  418  from moving downwardly with the lower pump body  402 . In this way, the valve stem portion  410  moves to the intermediate pumping state of  FIG. 17 . In that state, the top lip portion  480  of the valve stem portion  410  has moved downwardly far enough to contact the shuttle valve  418 . At that point, the liquid inlet gate valve  420  is closed because the shuttle valve  418  is covering the inlet openings  424 , preventing liquid from being fed under the force of gravity down from the liquid container  12  into the liquid charge chamber  422 . 
         [0144]    The actuator continues to exert a downward pulling force on the lower body portion  402  of the foam pump  400 . The interference between the top lip portion  480  of the valve stem portion  410  and the shuttle valve  418  overcomes the frictional force between the shuttle valve  418  and the interior wall  435  of the container  12 . In this way, the lower body portion  402  and the shuttle valve  418  move downwardly together to reach the lower-most final pumping state of  FIG. 16 . As they do so, the volume of the liquid charge chamber  422  decreases, creating a positive pressure on the liquid stored in the chamber  422 . The liquid in the chamber  422  is prevented from exiting the top of the chamber  422  by the closed inlet gate valve  420 , and from the bottom of the chamber  422  by the sealing member  407 . Thus, the only exit path available to the liquid is the liquid outlet gate valve  436 . 
         [0145]    The liquid outlet gate valve  436  is disposed between the liquid charge chamber  422  and a mixing chamber  458  within the valve stem portion  410 . The valve  436  has a valve member  494  which includes an elastomeric spring portion  495  integrally connected to an upwardly extending valve portion  496 . The liquid outlet gate valve  436  is comprised of a first valve surface  438  formed on the valve portion  496  and a second valve surface  442  formed on the valve stem part  410 C. The liquid outlet gate valve  436  opens and closes as the valve portion  496  moves up and down. In the priming or primed state of  FIG. 15 , the valve  436  is in a closed position. In that closed position, the first valve surface  438  is pressed into contact with the second valve surface  442  by the compressed elastomeric spring portion  495 , which rests on the floor  497  of the mixing chamber  458 . That contact prevents liquid from passing out of the liquid charge chamber  422  through the liquid outlet gate valve  436 . Other types of one-way valves, such as those described throughout the specification may be used a liquid outlet gate valve. 
         [0146]    The closing force exerted by the elastomeric spring portion  495  is large enough to hold the valve  436  closed when the only opposing opening force is the force of gravity acting on the liquid stored in the liquid charge chamber  422 . It is, however, small enough to be overcome and open the valve  436  by the positive pressure arising in the chamber  422  from the decreasing volume of the chamber  422  during a downward stroke of the foam pump  400 . As a result, during the downward stroke of the pump  400  moving it from the intermediate state of  FIG. 17  to the final pumping state of  FIG. 16 , the first valve surface  438  is separated from the second valve surface  442 . Liquid is thereby forced out of the liquid charge chamber  422  through the opened liquid outlet gate valve  436 . The liquid then travels down through a central liquid delivery conduit  444  within the valve stem portion  410  which includes the mixing chamber  458 . 
         [0147]    The downward movement of the lower pump body  402  during actuation of the pump  400  also operates the air pump  484  underneath the liquid charge chamber  422 . As the lower pump body  402  travels downward, the bellows portions  476  and  478  contract, thereby decreasing the volume of the air chamber  486  and creating a positive pressure on the air stored in the chamber  486 . The air in the chamber  486  is prevented from exiting the bottom of the chamber  486  via the one-way inlet air valve  403 , which permits air to travel only into the chamber  486 , not out of the chamber  486 . The air in the chamber  486  is thereby forced into one or more air ports  488  in the lower pump body  402 . 
         [0148]    The air ports  488  lead to vertical air channels  443  within the valve stem portion  410 . The vertical air channels  443  lead from the air ports  488  to inner air ports  456  located next to the liquid delivery conduit  444 . A wiper seal  498  is located next to the inner air ports  456 . The pressure of the air arriving from the chamber  486  opens the wiper seal  498  so that the air passes through the ports  456  and into the mixing chamber  458 . Liquid flowing down the liquid delivery conduit  444  from the liquid outlet gate valve  436  mixes with the incoming air from the inner air ports  456  within the mixing chamber  458 . The incoming air pressure though the inner air ports  456  helps to prevent liquid and foam in the mixing chamber  458  from entering into the vertical air channels  443 . Wiper seal  498  closes when the air pressure is removed. 
         [0149]    In the mixing chamber  458 , the foamable liquid moving down the liquid delivery conduit  444  and the pressurized air arriving from the air pump  484  mix together in a swirling motion to form a mixture. Thus, the liquid-air mixture within the mixing chamber  458  is forced by gravity and the incoming air pressure within the liquid delivery conduit  444  into an inlet  460  of a foaming chamber  462 . In the pump  400 , the inlet  460  is formed by one or more apertures (not shown) in the floor  497  of the mixing chamber  458 . 
         [0150]    Within the foaming chamber  462 , the liquid-air mixture is enhanced into a rich foam. For example, the foaming chamber  462  may house one or more foaming elements therein. Suitable foaming elements include, for example, one or more screens, meshes, porous membranes or sponges. In addition, one or more of such foaming element(s) may be disposed in a foaming cartridge within the foaming chamber  462 . The foam pump  400 , for example, has a foaming cartridge  466  with two screen foaming elements  468 . As the liquid/air mixture passes through the foaming element(s), the mixture is turned into an enhanced foam. In some embodiments, the mixing and foaming action may both occur in one single chamber, which is then both a mixing chamber and a foaming chamber. The foam is dispensed from the foaming chamber  462  through a foam outlet  470 . 
         [0151]    In some embodiments, the foam outlet  470  is simply an aperture leading from the foaming chamber  462  directly to the outside atmosphere surrounding the foam dispenser system. In other embodiments, the foam outlet  470  may optionally include tubing or other delivery conduits to carry the foam from the foaming chamber  462  to such an aperture. For example, in the pump  400 , such a conduit is formed by the internal bellows portion  478 . In additional embodiments, the foam outlet  470  may optionally include one or more one-way check valves (not shown) to prevent back flow of foam from the foam outlet  470  into the foaming chamber  462  or to prevent unwanted liquid or foam discharge while the dispenser is not being used. Suitable one-way check valves may include a flapper valve, a conical valve, a plug valve, an umbrella valve, a duck-bill valve, a ball valve, a slit valve, a mushroom valve, a spring and ball valve, or any other one-way check valve. Similar one-way check valves may optionally be placed in other portions of the liquid delivery path from the liquid reservoir  14  to the mixing chamber  458  and then to the foam outlet  470 , as desirable or necessary. For example, the wiper seal valve  498  placed next to the inner air ports  456  ensures liquid cannot escape the liquid delivery conduit  444  and into the vertical air channels  443 . 
         [0152]    In a preferred embodiment, the air to liquid ratio in the mixture formed in the mixing chamber  458  is approximately 10:1, but any ratio may be provided. The air to liquid ratio is determined by the volume and pressure of the air being delivered by the air pump  484 , and the amount of liquid entering the mixing chamber  458 . Once these and other applicable design variables are chosen to provide the desired air to liquid ratio, a consistently accurate dosing is thereafter provided. The volume of liquid may be varied by adjusting the stroke of the valve stem portion  410 . 
         [0153]    The lower pump body  402  and the shuttle valve  418  move downward until they stop.  FIG. 16  illustrates a lower-most position, wherein further downward movement is prevented by interference between the lower pump body plate  402 B and the bottom plate  414 . That position represents the maximum pumping stroke of the lower pump body  402 , producing the maximum amount of foam. The pumping actuator of the system may, however, stop the downward movement before that maximum displacement is reached, to reduce the amount of foam dispensed as desired by the user. 
         [0154]    Regardless of the length of the pumping stroke, when downward movement of the lower pump body  402  and the shuttle valve  418  stops, the foaming and pumping actions also stop. The relative positions of the valve stem portion  410  and the shuttle valve  418  will then be as shown in  FIG. 16 . In that configuration, the liquid inlet gate valve  420  is closed. 
         [0155]    At that time, a restoring force pushes the lower pump body  402  to move upwardly with respect to the upper pump body  404  and the bottom plate  414 . The restoring force may be provided, for example, by a resilient nature of the bellows portions  476  and  478 . It may also be provided by a compressed coil spring (not shown) disposed in the air chamber  486  and pushing up on the lower pump body plate  402 B. In such embodiments, the downward actuating force provided by the pump actuator overcomes the upward bias of the bellows and/or coil spring in order to perform the pumping action illustrated by  FIGS. 15 ,  16  and  17 . Then the downward force is removed, permitting the bellows and/or coil spring to push the lower pump portion  402  upwardly. The restoring force may alternatively or additionally be provided by the actuator itself exerting an upward force on the lower pump body  402 . 
         [0156]    As the lower pump body  402  initially begins its upward travel, the frictional force between the shuttle valve  418  and the interior wall  435  of the container  12  prevents the shuttle valve  418  from moving upwardly within the container  12 . In this way, the pump  400  moves to the intermediate pumping state of  FIG. 18 . In that state, the valve stem portion  410  has moved upwardly far enough that the shuttle valve  418  contacts the bottom lip portion  482 . Therefore, at that point, the liquid inlet gate valve  420  is open. 
         [0157]    The restoring force continues to exert an upward pushing force on the lower valve body  402 . The interference between the bottom lip portion  482  of the valve stem portion  410  and the shuttle valve  418  overcomes the frictional force between the shuttle valve  418  and the interior wall  435  of the container  12 . In this way, the valve stem portion  410  and the shuttle valve  418  move upwardly together to reach the upper-most priming or primed state of  FIG. 15 . At that point further upward movement is prevented by interference between the lower body portion plate  402 B and the sealing member  407  or the upper body portion  404 . 
         [0158]    As the lower body portion  402  and the shuttle valve  418  move upwardly, the volume of the liquid charge chamber  422  increases. Liquid stored in the liquid reservoir  14  is free to move down into the liquid charge chamber  422  through the open liquid inlet gate valve  420 . It does so by the force of gravity and by the negative hydraulic pressure generated by the sealed (other than the open valve  420 ) chamber  422 . The closed liquid outlet gate valve  436  prevents the liquid from exiting the chamber  422  into the mixing chamber  458 . Thus, liquid will continue to fill the chamber  422  until it is full, readying the pump  400  for another actuation. 
         [0159]    At the same time, both of the bellows portions  476  and  478  are expanding. This has at least two effects. First, the volume of the air chamber  486  in the air pump  484  increases, creating a negative air pressure within the air chamber  486 . That negative air pressure opens the one-way air inlet valve  403  to let air into the chamber  486 , thus recharging the air pump  484 . 
         [0160]    Second, the volume of an outlet air chamber  492 , formed by the internal bellows portion  476  near the foam outlet  470 , also increases. That likewise creates a negative air pressure in the outlet air chamber  492 , which will tend to create a suction force to pull back foam from the foam outlet  270  as the pump  400  expands. The foam outlet  470  may optionally include one or more one-way check valves, as discussed above, in order to aid this process. In this way, the foam pump  400  incorporates an “anti-drip” feature. 
         [0161]    During operation of the foam pump  400 , the air pump  484  preferably remains dry or free from liquids and foamy mixtures, to prevent bacteria from growing in that area. This is accomplished by the wiper seal  498 . 
         [0162]    The disposable refill unit  40  including the wet portions of the foam pump  400  has many advantages. Among them is the ease by which the unit may be prepared for shipping and delivery to an end user location, without leakage. If the unit  40  is packed with the lower pump body  402  held in the lowermost position of  FIG. 16 , the liquid inlet gate valve  420  will correspondingly be held closed to prevent liquid from escaping the reservoir  14 . This can easily be accomplished with appropriate packaging materials. 
         [0163]    Indeed, another potential benefit provided by the foam pump  400  is that it may be used to provide a small pump mechanism. This size advantage arises, in part, because many of the foam pump  400  components extend up into the neck  16  of the container  12 . And, in some cases the diameter of the foam screens  468  may be no more than about 0.06″ in diameter. Further, in one embodiment, substantially all of the working components of the pump  400  are located within the neck  16  of the container  12 . For example, at least fifty percent (50%) of the pump components may fit wholly or partly within the neck portion  16 . 
         [0164]    At least a portion of the air pump  484  may remain attached to the dispenser  50 , when the refill unit  40  is removed from the dispenser  50 . These portions may include lower pump body  402 , bellows portion  476  and lower plate  414 . Such portions of the air pump  484  are advantageously reusable because they do not come in contact with liquid during operation of the pump. Thus, they do not need to be disposed of and replaced with the refill unit  40 . The refill unit  40  including valve same  410  and bellows portion  478  are readily removable upward from lower pump body, bellows  476  and bottom plate  470 , which are secured to the foam dispenser  50 . 
         [0165]    The above-described removable and replaceable refill units  10 ,  20 ,  30  and  40  for a foam dispenser system may be manufactured and assembled in any convenient manner. Such methods including providing the various parts for building the foam pump  100 ,  200 ,  300  or  400 , and then assembling the parts into a completed pump. Then a liquid container is filled with a supply of foamable liquid, and connected to the completed pump in order to form a refill unit. No particular order is required to perform these processes, and various combinations or groupings of different steps may be used in accordance with the present invention. 
         [0166]    While the present invention has been illustrated by the description of embodiments thereof and while the embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Moreover, elements described with one embodiment may be readily adapted for use with other embodiments. Therefore, the invention, in its broader aspects, is not limited to the specific details, the representative apparatus and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicants&#39; general inventive concept.