Abstract:
A pump has a flexible liner which is expanded and contracted by application of positive and negative fluid pressure for receiving and discharging fluent material. The liner is received in a rigid shell which defines the maximum volume received. In discharging fluent material, a vacuum is applied to one side of the liner, while applying pressure to the other side so the liner is collapsed against the rigid shell. The liner is arranged so as to be the only part of the pump which contacts the fluent material, and is replaceable to effect rapid and easy cleaning of the pump. The liner has multiple pump cells which can expand and contract for moving fluent material through the pump cell. The pump cells can be sized and arranged so that by selection of particular pump cells which receive the fluent material, precise volumes can be metered by the pump.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to pumps which meter predetermined volumes and more particularly to such a pump employing a flexible liner.  
           [0002]    Pumps are often used in applications where it is important to keep the surfaces contacting the fluent material being pumped clean. For instance, where the fluent material is a food additive for a food product, it is imperative that surfaces contacting the material be maintained in an aseptic condition. Accordingly, the parts of the pump which contact the food are made of materials (e.g., stainless steel) which are highly resistant to corrosion and can be cleaned. However, such materials are expensive and significantly increase the cost of the pump. The pump must be periodically shut down to clean surfaces which handle the food product. Cleaning may also involve continuing to operate the pump while flushing with a cleaning liquid. In any event, the pump is not available for production operation while cleaning is taking place. Many fluent food products are prone to leave residue or debris as they are handled, which cause the pump to become unsanitary. Although necessary, it is inefficient to stop the pump frequently for cleaning and this increases the cost of manufacturing the product.  
           [0003]    Even when it is not necessary to maintain aseptic conditions, it frequently is important that a build up of the fluent material be avoided. As another example, a pump may be used in mixing paint. Operation of the pump can be hindered by a build up of paint in the pump. Moreover, color quality can be affected where paints are mixed by a build up of paint. Accordingly, it is necessary to clean the apparatus frequently.  
           [0004]    Pumps used in situations like those described herein often are called upon to meter fluent materials in precise quantities. Such pumps also have application in the medical field for administration of, for instance, medicaments. It is known to use membrane pumps to administer precise quantities, particularly where small amounts of fluent material are metered. Membrane pumps typically have one or more cavities in a rigid base which are covered by a flexible membrane. A force can be applied, such as by fluid pressure, to the membrane to move it into the cavity to pump fluent material from the cavity. The fluent material still must come into contact with the rigid base in operation of the membrane pumps.  
         SUMMARY OF THE INVENTION  
         [0005]    Among the several objects and features of the present invention may be noted the provision of a pump which facilitates maintenance of sanitary conditions; the provision of such a pump requires minimal effort to clean; the provision of such a pump which contacts the fluent material only with a disposable liner; the provision of such a pump which is useful for dispensing food products; the provision of such a pump which can meter fluent material in precise quantities; the provision of such a pump which is capable of mixing component fluent materials; and the provision of a dispensing apparatus including such a pump.  
           [0006]    Further among the several objects and features of the present invention may be noted the provision of a method of operating a pump which achieves a high level of accuracy; the provision of such a method which reduces undesired movement of pump components; and the provision of such a method which can precisely mix various fluent material components.  
           [0007]    In one aspect of the invention, a pump for pumping a fluent material comprises a liner including opposing walls of flexible material defining at least one pump cell, an inlet and an outlet. The pump cell is sized and shaped for receiving a quantity of the fluent material and is expandable for receiving fluent material and contractible for discharging fluent material. A rigid shell adapted to receive and substantially enclose at least the pump cell of the liner is formed with at least one receptacle therein to receive in close fitting relation the pump cell. The one receptacle is adapted for connection to a source of pressurized gas and for connection to a vacuum source for selectively applying a vacuum pressure and a positive pressure to the cell to selectively expand and collapse the cell for drawing fluent material into the pump cell and expelling the fluent material from the pump cell. Valves associated with the rigid shell and disposed for pinching engagement with the liner adjacent to the pump cell are capable of selectively blocking and opening fluid communication of the pump cell thereby to pump the fluent material.  
           [0008]    In another aspect of the present invention, apparatus for dispensing a customized drink mixture comprises a dispensing outlet for dispensing the drink mixture to a container, a first pump for pumping a base liquid of the drink mixture from a source to the dispensing outlet, and a second pump for metering selected quantities of admixtures to the base liquid for forming with the base liquid the drink mixture in the container. The second pump comprises a liner including opposing walls of flexible material selectively joined together to define at least two pump cells sized and shaped for receiving a quantity of one of the admixtures. The liner farther includes inlets and at least one outlet in communication with the pump cell so that admixture passes through the pump contacting only the liner. A rigid shell adapted to receive and substantially enclose at least the pump cell of the liner is formed with receptacles therein to receive in close fitting relation the pump cells. The receptacles are adapted for connection to a source of pressurized gas and for connection to a vacuum source for selectively applying a vacuum pressure and a positive pressure to the cell to selectively expand and collapse the cell for drawing fluent material into the pump cell and expelling the fluent material from the pump cell. Valves associated with the rigid shell and disposed for pinching engagement with the liner adjacent to the pump cells selectively block and open fluid communication of the pump cells with the inlets and the outlet, thereby to pump the admixture.  
           [0009]    In still another aspect of the present invention, a pump for metering a fluent material comprises a pump cell having flexible walls expandable between a fill configuration in which the walls enclose a first volume for receiving fluent material into the pump cell and a discharge configuration in which the walls enclose substantially no volume for discharging fluent material from the pump cell. A shell defining a space therein adapted to receive the pump cell for substantially enclosing the pump shell communicates with a pressure source for applying positive fluid pressure in the space and a vacuum source adapted for fluid communication with the shell space for applying vacuum pressure to the shell space. A control for the pressure source and the vacuum source is operable to first apply a vacuum pressure to the shell space for expanding the pump cell to the fill configuration for receiving fluent material into the pump cell, then to apply both a vacuum pressure and a positive fluid pressure for drawing one of the walls of the pump cell against the shell and pressing another of the walls of the pump cell against said one wall for moving the pump cell to the discharge configuration for discharging the fluent material.  
           [0010]    In a further aspect of the invention, a method of operating a pump including a flexible pump cell expandable to define a volume and contractible to collapse the volume comprises the step of receiving fluent material into the pump cell by creating a vacuum around the pump cell to expand the pump cell. Fluent material is discharged from the pump cell by applying a vacuum pressure generally on one side of the pump cell while applying positive pressure to another side of the pump cell for collapsing said other side of the pump cell against said one side to discharge fluent material from the pump cell.  
           [0011]    In yet a further aspect of the present invention, a pump for metering fluent material having shell adapted to receive a liner including opposed flexible walls. The liner comprises a pump cell defined by said opposed flexible walls and having an inlet opening and an outlet opening. The pump cell is deflectable to a first position defining a first volume corresponding to a volume defined by said shell and to a second position defining a second volume less than said first volume by action of a fluid on said cell outside said opposed flexible walls. A change from said first volume to said second volume pumps said fluent material contained interior to said cell.  
           [0012]    In a still further aspect of the present invention, compounding apparatus for selectively combining components and dispensing admixtures, the compounding apparatus comprises a liner of including opposing walls of flexible material at least partially free of connection to permit motion toward and away from each other. The liner includes an inlet for each component to be compounded and at least one outlet. A shell having multiple receptacles formed therein is adapted to receive the liner with portions of the liner in registration with corresponding receptacles. The wall portions in registration with the receptacles defining pump cells expandable to receive a volume of at least one of the components at a time into the pump cell and collapsible to discharge the component from the pump cell. A pressure control system in fluid communication with the receptacles selectively affects fluid pressure in the receptacle around the pump cells to cause expansion and contraction of the pump cells for receiving and discharging the components to form the admixture.  
           [0013]    Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a schematic of a drink dispensing apparatus of the present invention;  
         [0015]    [0015]FIG. 2 is a schematic of a pump of the present invention;  
         [0016]    [0016]FIG. 3 is a perspective of a shell of a pump of the present invention in the form of a compounding apparatus;  
         [0017]    [0017]FIG. 4 is a plan of a liner of flexible material of the pump of FIG. 3;  
         [0018]    [0018]FIG. 5 is a plan of a lower half of the pump shell with the liner received therein and schematically illustrating valves;  
         [0019]    [0019]FIG. 6 is a cross section of the pump with halves of the pump shell and the pump liner exploded;  
         [0020]    [0020]FIG. 7 is a schematic of a pinch valve of the pump;  
         [0021]    FIGS.  8 A- 8 D are fragmentary cross sections of the pump showing a single pump cell and illustrating the operation of the pump; and  
         [0022]    FIGS.  9 A- 9 D are fragmentary cross sections of a pump of a second embodiment illustrating its operation. 
     
    
       [0023]    Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    Referring now to the drawings and in particular to FIG. 2, a pump  11  constructed according to the principles of the present invention is shown to comprise a liner  13  made of a limp, flexible material, such as an appropriate polymer, including without limitation polyvinyl chloride, polyolefin, polymer laminates and polymer alloys. In a preferred embodiment, the liner  13  comprises two sheets of the material (designated  13 A and  13 B, respectively) in face-to-face relation which are joined together at their peripheral edge margins as by welding, leaving a weld seam around the peripheral edge (see FIGS. 4 and 6). The sheets  13 A,  13 B may be secured together in any other suitable manner, such as by adhesive or mechanical fasteners. The liner may be formed with a single sheet folded over and joined to itself, or otherwise so as to form a thin enclosure of flexible material capable of receiving and discharging fluent material. The sheets  13 A,  13 B are also welded together to define multiple pump cells  17 , manifold pump cells  19  and a header pump cell  21  in the interior of the liner  13 . All of these may be generally considered to be “pump cells” in that they are expandable for receiving fluent material and contractible for discharging the fluent material in operation of the pump  11 . “Fluent material” is used to convey that a pump of the present invention can be used for gases and liquids, but it is also envisioned that the pump could be used with very finely divided solids. However in the preferred embodiments described herein, the fluent material is a liquid and so the term “liquid” will be used herein without limitation as to the type of material which can be acted upon by a pump of the present invention As will be described more fully hereinafter, the pump  11  has application for use in a drink dispenser, generally indicated at  23 , capable of making a drink with different selected mixes of flavorings, as schematically illustrated in FIG. 1.  
         [0025]    The sheets  13 A,  13 B of the liner  13  are also welded together so as to form inlets  25  and passages  27  for receiving liquid into the liner. The liner  13  illustrated in FIG. 4 is particularly configured for delivering variable and precise volumes to form a mixture. The pump cells  17  and manifold pump cells  19  are arranged in five groups (designated generally at  29 ) each including three pump cells of differing size and volume and a manifold pump cell. The pump cells  17  and manifold pump cell  19  of each group  29  communicate with the header pump cell  21  extending laterally of the liner  13  and having an outlet, constituting in this embodiment the outlet of the pump  11 . The manifold pump cell  19  of each group  29  communicates with the passages  27  from the inlets, with each pump cell  17  in the group and also with the manifold pump cells  19 . Liquid from the manifold pump cell  19  can enter either one of the pump cells  17  or the manifold pump cells  19 , as will be described hereinafter. Although the pump of the preferred embodiment is illustrated as having multiple cells ( 17 ,  19 ,  21 ) and passages  27 , it is to be understood that a pump (not shown) could have any number of cells, including only a single cell, without departing from the scope of the present invention. Moreover, the passages do not have to be expandible and collapsible for pumping fluid like passages  27 , but may be of a fixed volume, in the manner of the inlets  25 . The number and configuration of the cells and passages will be dictated by the particular application of the pump.  
         [0026]    Referring now to FIG. 3, the liner  13  is received between an upper half  33 A and lower half  33 B of a rigid shell (generally indicated at  33 ). In the preferred embodiment, the material is a metal, but could be another rigid material such as a polymeric material. The shell  33  may have fewer or greater number of component parts. Moreover, the terms “upper” and “lower” have been chosen for convenience, as the component parts of the shell  33  may assume other relative positions. As shown, the upper and lower halves  33 A,  33 B are connected together by a hinge  35  for ease of opening and closing the shell  33  to remove, adjust or replace the liner  13  between the shell halves. The halves  33 A,  33 B need not be permanently connected. It will be readily appreciated that each shell half ( 33 A,  33 B) is formed with cooperating receptacle members arranged identically to the arrangement of pump cells  17 , the manifold pump cells  19 , the header pump cell  21 , the inlets  25  and the passages  27  of the liner  13 . The receptacle members are designated by the same reference number as the part of the liner  13  which they receive, but with the prefix “1” and the suffix “A” or “B” indicating their association with the upper shell half  33 A or lower shell half  33 B (e.g.,  117 A for the receptacle member receiving the pump cell  17  in the upper shell half  33 A).  
         [0027]    The receptacle members ( 117 A,  117 B,  119 A,  119 B,  121 A,  121 B,  125 A,  125 B,  127 A,  127 B) of the upper and lower halves  33 A,  33 B are aligned when the shell  33  is closed to define receptacles having a shape closely corresponding to the shape of one of the pump cells  17 , manifold pump cells  19  or of the header pump cell  21  for receiving the one pump cell, manifold pump cell or the header pump cell. Engagement of the shell halves  33 A,  33 B with the liner  13  should be sufficiently firm to produce a fluid tight seal of each receptacle formed for the mating receptacle members ( 117 A et seq.), for reasons which will become apparent. It is envisioned that the seal could be sufficiently tight as to omit the necessity of preforming the welded seal around the peripheral edge, the pump cells  17 , manifold pump cells  19 , header pump cell  21 , the inlets  25  and the passages  27 . The liner  13  has a hole  39  at each of its four comers which is received on a respective stud  41  on the lower half  33 B of the shell  33  to register the liner with the lower shell half  33 B so that the pump cells  17 , manifold pump cells  19  and header pump cell  21  are received in their corresponding receptacle members. Apertures  43  in the upper shell half  33 A receive the studs  41  so that flat faces of the upper and lower halves  33 A,  33 B surrounding the receptacle members ( 117 A et seq.) are parallel when closed. The apertures  43  are elongated so that they may receive the studs  41  as the upper shell half  33 A pivots down to the closed position of the shell  33 . The liner  13  on the lower shell half  33 B is illustrated in FIG. 5.  
         [0028]    The upper shell half  33 A mounts a plurality of pinch valves  47  operable to open and close communication of the pump cells  17 , manifold pump cells  19 , header pump cell  21  and passages  27  as needed for operation. One of the pinch valves  47  is shown in FIG. 7 to comprise a cylinder  49  and a piston  51  having a head  51 A slidingly received in the cylinder. The free end of the piston  51  outside the cylinder mounts a wedge  53  arranged to bear down against the liner  13  to bring the opposing walls (i.e., the interior surfaces of the liner sheets  13 A,  13 B) of the liner into sealing engagement for pinching off the liner to prevent fluid flow past the valve  47 . The lower shell half  33 B and the wedge  53  are shaped in a complementary manner so as to have a close fitting relationship when the pinch valve  47  is actuated to facilitate a tight closure. As illustrated, a spring  55  in the cylinder  49  engages one side of the piston head  51 A and biases the piston  51  to a retracted position into the cylinder such that the wedge  53  does not pinch off the liner  13  and fluid may flow through the liner past the valve. Air under pressure may be received through an inlet  57  in the cylinder  49  on the opposite side of the piston head  51 A from the spring  55  to force the head down against the bias of the spring to extend the piston for pinching off the liner  13 . However, the pinch valve  47  may be actuated other than pneumatically (e.g., electrically) without departing from the scope of the present invention. Moreover, the sheets  13 A,  13 B could be forced together such as by application of air pressure directly to the sheets or by magnet attraction, without the use of a separate mechanical valve. It is to be understood that the term “valve” as used herein is intended to encompass arrangements which use air pressure or magnetic force to close the liner. The valves  47  may be actuated independently, in sets or simultaneously as needed for operation of the pump  11  in a particular application.  
         [0029]    Referring again to FIG. 2, the upper shell half  33 A further includes a first port  61  connected by a valve  63  to a source of pressurized air (or other gas) indicated generally at  65 . The lower shell half  33 B includes a second port  67  connected by a valve  69  to a vacuum source indicated generally at  71 . Valve  63  is also capable of connecting the first port  61  to the vacuum source  71 . The locations of the first port  61  and second port  67  could be reversed. The pressure source  65  includes a first compressor  73 , a higher pressure reservoir  75  and a lower pressure reservoir  77 . The first compressor  73  is operated by a first compressor control  79  which receives a signal from a first pressure transducer  81  indicating the pressure of the air in the higher pressure reservoir  75  for operating to keep the air pressure in the higher at a selected value. The higher pressure reservoir  75  is connected via a pressure regulator  83  and a valve  85  to the lower pressure reservoir  77  containing air at an elevated pressure, but lower than that of the higher pressure reservoir. The valve  85  is operated by a control  87  according to the air pressure in the lower pressure reservoir  77  detected by a second pressure transducer  89  to open to allow air to enter the lower pressure reservoir for maintaining a predetermined air pressure in the reservoir. The pressure regulator  83  controls the pressure of the air entering the lower pressure reservoir  77  from the higher pressure reservoir  75  to stabilize the pressure in the lower pressure reservoir. The vacuum source  71  includes a second compressor  91  and a vacuum reservoir  93 . The second compressor  91  is operated by a second compressor control  95  which receives a signal from a third pressure transducer  97  to maintain a substantially constant vacuum pressure in the lower pressure reservoir  93 .  
         [0030]    The base operation of the pump  11  for a single pump cell  17  (as illustrated in FIG. 2 and FIGS.  8 A- 8 D) relies on the liner  13  extending between the receptacle members  117 A,  117 B so that although the receptacle members are closely adjacent to define the pump receptacles, they are fluidically separated from each other. In other words, the liner  13  and each receptacle member  117 A,  117 B define an independently sealed chamber. First, the valves  63  and  69  are actuated so that the receptacle member  117 A of the upper shell half  33 A and the receptacle member  117 B of the lower shell half  33 B are both exposed to vacuum pressure from the vacuum reservoir  93 . For purposes the of this description the specific pinch valves will be designated as  47 ′ and  47 ″ to distinguish the upstream and downstream pinch valves. The pinch valves  47 ′,  47 ″ are operated by valves, designated  99 A and  99 B, respectively, which connect the cylinders  49  of the valves to the lower pressure reservoir  77  of the pressure source  65 . At the same time the pinch valve  47 ′ on the inlet side of the pump cell  17  is opened and the pinch valve  47 ″ on the outlet side of the pump cell is closed. The valves  63  and  69  are operated to connect the upper and lower receptacle members  117 A,  117 B to the vacuum reservoir  93  of the vacuum source  71 . The pump cell  17  expands by separation of the walls (i.e., the sheets  13 A,  13 B) of the liner  13  at the pump cell to create a volume and draw liquid into the pump cell (FIG. 8A). The walls  13 A,  13 B of the liner  13  are expanded substantially against the shell  33  in the receptacle members  117 A,  117 B so that the receptacle members define the maximum volume of the pump cell  17 . The vacuum drawn has the effect of pulling the upper and lower shell halves  33 A,  33 B together as the pump cell  17  is filled. This increases the accuracy of the pump  11  because the volume defined by the receptacle members  117 A,  117 B formed within the rigid shell  33  is highly accurate and repeatable. When the shell halves  33 A,  33 B are drawn together so that spacing and hence the volume defined by the receptacle members  117 A,  117 B is always precisely the same.  
         [0031]    After the pump cell is filled, the pinch valve  47 ′ is closed and the pinch valve  47 ″ is opened. A vacuum is maintained on the pump cell  17  in the receptacle member  117 B in the lower shell half  33 B, while the valve  63  is operated to expose the receptacle member on the upper shell half  33 A to a positive pressure from the pressure source  65 . As a result the bottom wall  13 B of the liner  13  remains substantially conformed against the shell  33  in the lower shell half receptacle member  117 B. The top wall  13 A collapses against the lower wall  13 B to discharge the liquid from the pump cell  17 . This discharge process is illustrated in FIGS.  8 B- 8 D. By maintaining the lower wall  13 B in contact with the shell  33  to discharge, the material of the liner  13  is held without wrinkles, which can affect the actual volume in the pump cell  17  and reduce accuracy. The overall operation of the pump  11  is the same for each pump cell  17  (the manifold pump cells  19 , header pump cell  21  and passages  27  also operate in the same way). However, the sequence of operation of the valves ( 47 ′,  47 ″,  63 ,  67 ) can be selected to achieve the specific function needed for the pump  11 .  
         [0032]    A sequence of operation of the single pump cell  17  is illustrated in FIGS.  8 A- 8 D. These figures show the pump cell  17  as being equipped with capacitance-type liquid level sensors  101 . An example of a suitable sensor would be a QProx capacitive sensor available from Quantum Research Group Ltd. of Southampton, England. Sensors of this type operate by detection of the liquid mass, rather than direct detection of volume. These sensors  101  are mounted in the upper shell half  33 A at the top of the receptacle member  117 A and are connected to a pump master control  103  (FIG. 2). Other types of sensors (not shown), such as optical or ultrasonic sensors, could be mounted on the shell  33  for detecting the fill state of the pump cell  17 . The sensors  101  are capable of detecting the separation of the liquid from the top of the receptacle member  117 A. This permits the control  103  to calculate the precise, instantaneous volume of the pump cell  17 . The sensors  101  may be used to operate the valves  47 ′,  47 ″ by detection of when the pump cell  17  is completely full or completely empty. Moreover, the sensor  101  can detect a blockage in the pump cell  17 . However it is envision that by knowing the instantaneous volume of liquid in the pump cell  17  during discharge, the valves  47 ″ may also be actuated to close off the pump cell  17  for delivery of partial volumes. In other words, the valve  47 ″ could be actuated at a point during the discharge, such as shown in FIGS. 8B or  8 C, to prevent further liquid from leaving the pump cell  17 .  
         [0033]    The operation of a single pump cell of a pump  211  of a second embodiment is shown in FIGS.  9 A- 9 D for use in delivering precise incremental volumes of liquid. Corresponding parts of the pump  211  of the second embodiment will be designated by the same reference numerals as the pump  11  of the first embodiment, with the prefix “2”. A pair of pinch valves ( 247 A,  247 B) on the outlet side of the pump cell  217  are capable of segregating a very small, discrete volume of the pump cell for delivering this small, discrete volume. It will be appreciated that if a pump cell has a very small maximum volume, it will be possible to deliver a very precise volume from the pump cell (even where the pump cell is fully emptied with each cycle of operation of the pump). However, delivery of such small volumes will require many cycles of operation to achieve the total volume of liquid needed. The pump  211  of FIGS.  9 A- 9 D allows a full volume of the pump cell  217  to be discharged until the precise total volume is neared, at which time the valves  247 A,  247 B are operable to permit a partial volume to be discharged until the total volume is reached. The valves  247 A,  247 B include wedges  253 A,  253 B which are in the illustrated embodiment, slidingly connected to each other, such as by a dovetail connection. In full volume discharge operation of the pump cell  217 , the valve  247 A moves up to pinch off the outlet side of the pump cell and down to permit liquid to be discharged from the pump cell. The valve  247 B is not used.  
         [0034]    The operation of the pump  211  for the pump cell  217  to deliver a partial volume is shown in FIGS.  9 A- 9 D. In this embodiment, it is not necessary to detect instantaneous volumes or to time the closure of pinch valves to discharge a partial volume. In each cycle, the full volume of the pump cell or segregated portion of the pump cell is discharged. Initially, valve  247 A is actuated to pinch off the outlet of the pump cell  217  and the entire pump cell is filled by application of a vacuum pressure to the pump cell (FIG. 9A). The valve  247 B is actuated to pinch off the pump cell  217  just upstream of the outlet (FIG. 9B). It may be seen that the valve wedges  253 A,  253 B are shaped so as to define a small volume  200  in an outlet end region of the pump cell  217 . The valve  247 A is opened and pressure is applied to the pump cell  217  so that liquid is discharged from the small volume  200  is the only liquid discharged from the cell (FIG. 9C). The valve  2478  holds the liquid in the remainder of the cell  217  from leaving the cell. Eventually, the small volume  200  is emptied (FIG. 9D) and the pump  211  is ready to repeat the operation or to return to discharging the full volume of the pump cell  217 .  
         [0035]    Having described the base operation (and one variant) of the pump  11  ( 211 ) for a single pump cell  17  ( 217 ), we will now discuss the operation of the pump  11  formed for using the specific liner  13  shown in FIGS. 4 and 5, with particular reference being made to FIG. 5. The pinch valves  47  mounted in the upper shell half  33 A are shown in phantom. In a preferred embodiment, the pump  11  applies a vacuum to all of the pump cells  17 , manifold pump cells  19 , header pump cell  21  and passages  27  at the same time. Similarly, any air pressure applied in a discharge operation would be applied to all of the aforementioned components at the same time. While it would be possible to apply a vacuum or positive pressure to the various components individually, the arrangement would be more complex and costly. The pinch valves  47  can be used as needed to isolate or block off one or more of the cells ( 17 ,  19 ,  21 ) or passages ( 27 ) not to be filled with or emptied of liquid.  
         [0036]    Operation will be described with reference to one of the groups  29  of pump cells  17  and manifold pump cells  19 , the operation of the others being substantially the same. The passages  27  are connected to one or more liquid sources (not shown) at the inlets  25  for admitting the liquid into the pump  11 . To draw liquid into the passages  27 , valves  63 ,  69  are opened to apply a vacuum to the entire shell  33  and specifically to the passage receptacles  127 A,  127 B. The pinch valves  47  at the inner ends of the passages  27  are closed so that liquid is drawn into the fingers, but passes no further in this cycle of operation of the pump  11 . Preferably, each of the passages  27  has suitable fill sensors, such as the capacitive liquid level sensors  101  shown in FIGS.  8 A- 8 D. Such sensors would be capable of detecting that a particular one of the passages  27  had not filled in the cycle. In response, an indication may be given that one of the liquid sources is empty or that a blockage is present. Before the liquid source is replaced or immediately after the blockage is removed, the pump  11  is actuated to collapse the one passage  27  so that any liquid and air in the passage is expelled back into the inlet  25  and the liquid source. All of the pinch valves  47  except the one at the inlet  25  of the one passage  27  will have been closed so that the pump  11  does not otherwise operate to pump the liquid even though pressure and vacuum is applied to all of the cells ( 17 ,  19 ,  21 ) and the passages  27 . In this way, the inlet  25 , and any delivery tube (not shown) connecting the inlet to the liquid source, is re-primed so that after replacement of the liquid source (or removal of the blockage) the one passage  27  will not be again partially filled with air. The pump  11  is made to recycle with the pinch valves  47 , save the pinch valve connecting the one passage  27  to the liquid source, in the same manner to fill the one passage. The pump  11  then returns to normal operation. It will be appreciated that closely similar kinds of detection and remedy could be applied for the cells ( 17 ,  19  and  21 ) fitted with liquid level sensors. The need for such detection varies with the particular application of the pump  11 . The passages  27  generally have an elongate, curved shape which facilitates the expulsion or “scavenging” of liquid from the passages, which increases the accuracy of the pump  11 .  
         [0037]    All of the passages  27  communicate with the manifold pump cell  19  of the group  29 . The other three pump cells  17  are all connected to the manifold pump cell  19  and the manifold pump cell has an outlet opening directly into the header pump cell  21 . Thus, it will be understood that the manifold pump cell  19  can operate just like a standard pump cell  17  described previously, by receiving liquid and discharging the liquid into the header cell  21  without involving any of the other pump cells. If the passages  27  are connected to sources containing a different liquids, the manifold pump cell  19  also becomes a pre-mixing chamber prior to any mixing which may occur in the header pump cell  21 .  
         [0038]    The manifold pump cell  19  and the pump cells  17  in the group  29  have different sizes preferably selected to give flexibility in discharging the precise amounts needed in a particular application. Each of the pump cells  17  can be filled with liquid from the manifold pump cell  19  by opening the pinch valve  47  leading to that particular pump cell, applying a vacuum to both receptacle members  11   7 A,  11   7 B, and to the manifold pump cell via the receptacle members  119 A,  119 B. The manifold pump cell  19  and at least some of the passages  27  remain in fluid communication with the liquid source(s) so that they refill with liquid at the same time the pump cell(s)  17  is filled. The pump  11  can be operated to discharge from the manifold pump cell  19  into any one or any selected set of the pump cells  17  in the group  29 . This is accomplished by closing the pinch valves  47  leading to the pump cells  17  not to be filled. The control  103  is operable to select the pump cells  17  in the group  29  (including the manifold pump cell  19  which also can discharge directly into the header pump cell  21 ) to be used in order to achieve the volume of the particular liquid needed in the fewest number of cycles of operation. Again, this is carried out by opening and closing the particular pinch valves  49 . The pump cells  17  are capable of discharging into the header pump cell  21  by substantially the same operation The flexibility in operation of the individual pinch valves depends upon the precision as well as the variations in liquid volume and composition which is required for a particular application.  
         [0039]    The pump  11  of the present invention has application in various systems, including compounding or mixing systems, such as the drink dispenser  23  shown in FIG. 1. The dispenser has a selected number (three in the illustrated embodiment) of reservoirs  104  of drink flavorings, each of which is connected by a respective line  105  to the pump  11  of the present invention for dispensing to a container C. The internal construction of the pump  11  would be different than shown in FIGS. 4 and 5, requiring fewer pump cells, but having the same general components. The pump  11  is configured so that the flavorings can be intermixed in the pump (such as in a header pump cell) prior to discharge from the pump. The pump  109  shown diagrammatically in FIG. 1 would also have the pressure source and vacuum source, such as is shown at  65  and  71  in FIG. 2, for full operation. A discharge line  106  is connected to the pump outlet and also to a mixing chamber  107  which receives a base liquid (e.g., carbonated water) from a base liquid reservoir  108 . As shown, the base liquid reservoir has its own pump  109  for feeding the base liquid to the mixing chamber  107 . The pump  109  may have a similar or substantially different construction than the pump  11  of the present invention.  
         [0040]    Notably, it is possible to keep the pump  11  clean with a minimum of labor. The line connections from the flavoring reservoirs  104  can be disconnected and the pump shell  33  can be opened to expose the liner  13 . The liner can be simply removed and replaced with a fresh liner. Preferably the discharge line  106  is formed as part of the liner  13  so that it is simultaneously replaced. As can be seen, it is not necessary to use any detergents or other cleaning chemicals or implements. No flushing of the pump  11  is required. It will be understood that the drink dispenser  23  is but one application in which a pump of the present invention is useful. The pump is envisioned as being useful in any application in which it will be necessary to frequently clean the pump, or in which small, relatively precise quantities are to be metered by the pump.  
         [0041]    In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.  
         [0042]    When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.  
         [0043]    As various changes could be made in the above without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.