Abstract:
The invention relates to a valve ( 32 ) for a fluid, in particular for a liquid, with a housing ( 3, 4 ), which has a flexible valve membrane ( 33 ) mounted in the housing and a valve body ( 34 ) held therein, and with an access point ( 26, 37, 38, 39 ) for the fluid, which opens into a chamber ( 42, 43, 44 ), and an outlet ( 45 ) leading out of the chamber, it being possible to bring the valve body into contact with a flexible element ( 33 ) in order to close the fluid passage of the valve. According to the invention, in a valve of that kind the flexible element is the flexible valve membrane ( 33 ) and a stop ( 36, 55 ) is used to limit the extent to which the valve membrane curves outwards during an increase in pressure in the fluid, the stop moving the flexible element ( 33 ) against the valve body ( 34 ) and closing the fluid passage of the valve.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a valve assembly for fluids, in particular for liquids, and includes a housing, which has an elastic valve membrane mounted in the housing and a valve body held in the elastic valve membrane. The valve assembly includes an inlet for the fluid, opening into a chamber, and an outlet leading out from the chamber, it being possible to bring the valve body into contact with the elastic valve membrane to close the fluid passage portion of the valve. 
         [0002]    The valve is preferably used in a mechanically operated liquid pump, particularly in a liquid pump provided for medical and nutrient liquids, and for liquids in the biological and laboratory sector. It is also conceivable to use the valve for gases, particularly those that have to be delivered in the context of laboratory tests. The main field of application of the valve is in the delivery of a liquid. 
       BACKGROUND OF THE INVENTION 
       [0003]    Many different types of liquid pumps are used to deliver liquids. Pumps that are not operated electrically, such as mechanical infusion pumps, have the disadvantage that they generate different pressures during the period of use. This means that the initial pressure is generally higher than the end pressure. The flow rate is controlled using capillary hoses or glass capillary tubes. These solutions with capillaries give rise to flow rate fluctuations of up to 70% within the period of use. This is a major problem for patients with tolerance difficulties, e.g. allergy sufferers, since excessively high dosing rates may lead to adverse side effects and intolerance phenomena. 
         [0004]    A valve of the type mentioned at the outset, and used for liquids, is known from EP 1 321 156 A1. There, the housing has a chamber, an inlet channel in flow communication with the chamber, and an outlet channel in flow communication with the chamber. A stiff valve body for regulating the flow of the liquid through the chamber is arranged within the chamber. The valve body is connected to a valve membrane clamped in the housing in the area of the circumferential edge, with the valve body being moved according to the movement of the valve membrane. The housing accommodates an annular elastic element concentric to the inlet channel. To close the inlet channel, the valve body can be moved against the elastic element. Because of the dimensions of this valve, and of the flow restrictor assigned to the outlet channel, the resistance against the liquid flowing out of the housing is greater than the resistance made to the liquid flowing into the valve. As the liquid flows into the housing, a hydrostatic pressure arises in the liquid-filled chamber and acts on the valve body and the valve membrane. When spacer parts of the valve body bear without pressure on the elastic element, the liquid channel extending through the latter is not closed, and liquid can flow from the inlet channel into the chamber and from there into the outlet channel. The elasticity of the elastic element has the result that, when a force acts in its direction, and the pressure of the liquid present in the chamber changes, the valve membrane is curved slightly away from the chamber interior, and the valve body is moved in this direction, with the spacer parts of the valve body being pressed into the elastic element. This reduces the gap between the sealing surfaces. The volumetric flow passing through the valve thus decreases. If the force is sufficiently great, the valve body closes the gap, such that liquid present in the inlet channel can no longer penetrate into the chamber. Consequently, the pressure in the chamber decreases. As the pressure decreases, the restoring force of the deflected valve membrane causes the valve body to be lifted from the elastic element, such that the gap forms again between the sealing surfaces. This valve therefore operates in the manner of a pressure reducer, specifically as a function of the developing inlet pressure. With this valve, it is not adequately possible to keep the pressure substantially constant. 
         [0005]    U.S. Pat. No. 5,616,127 describes a device for delivering a medical liquid to a patient. It comprises a valve for regulating the flow of the liquid medicament. The valve has a housing with a conically arranged valve seat, and a valve body which is displaceable relative to the latter and which likewise has a conical valve seat. The valve body is connected to the valve housing via an elastic intermediate member in the shape of a bellows. The space enclosed by the bellows forms a chamber, which is provided with an outlet channel. The inlet channel is routed through the valve housing. When the pressure in the chamber increases, the bellows expands, as a result of which the valve body reduces the cross section of passage of the valve body until, at a maximum pressure, the inlet channel of the valve housing is closed by means of the valve body. If the valve is free of pressure, the bellows ensures, by virtue of its restoring forces, that the valve body is moved against a further valve seat of the housing and, in this state, also blocks the flow through the valve. 
         [0006]    U.S. Pat. No. 4,852,605 discloses a valve in which a valve housing has a valve seat, and a valve body designed as a ball interacts with the valve seat. This ball is held in a bearing, which in turn is mounted in a valve membrane. When an increased pressure is present in an inlet channel of the housing, the ball lifts from the valve seat. Depending on the pressure increase, a greater or lesser cross section of flow for the liquid from the inlet channel is obtained. 
         [0007]    DE 44 36 540 A1 describes an infusion system for continuous dispensing of a liquid medicament under pressure. A piston is provided there in a state of equilibrium. If too high a volumetric flow is applied by a medicament delivery device, this leads to a displacement of the piston and, depending on the displacement travel of the piston, to a greater or lesser reduction of an inlet channel for the medicament. 
         [0008]    U.S. Pat. No. 3,511,472 describes a valve with an elastic valve membrane for closing the seat of a valve housing. The cross section of flow through the valve can be regulated in a stepless manner by an adjustable screw that supports the valve body. 
       SUMMARY OF THE INVENTION 
       [0009]    The object of the present invention is to develop a valve of the type mentioned at the outset, in such a way as to guarantee that the flow of liquid is kept substantially constant, and thus that the flow of liquid is kept constant within a narrow tolerance range. 
         [0010]    The object is achieved by a valve of the type mentioned at the outset, characterized by the following features:
       the elastic element is the elastic valve membrane,   a stop is used to limit the extent to which the valve membrane curves outward during an increase in pressure of the fluid, the stop moving the elastic element against the valve body and closing the fluid passage of the valve.       
 
         [0013]    It is a particular advantage of the valve according to the invention that the flow of liquid can be kept substantially constant, irrespective of how great the inlet pressure is on the valve. This is possible because of the fact that a pressure arising at the outlet causes the valve membrane to curve outward from its starting position, with the result that the valve membrane is moved against the stop and in this way experiences a deformation, which leads to the closure of the valve body. The relatively high pressure in the area of the outlet, which is of course lower than the pressure in the area of the inlet, is ensured by the flow restrictor. 
         [0014]    In a particularly advantageous embodiment of the valve from the point of view of its construction, the inlet is routed through the valve membrane and the valve body to the chamber. This in particular entails interconnected channels. 
         [0015]    The valve membrane and the valve body are in particular separate structural parts. The valve body is designed in particular as a valve core. This expression is intended to signify that this structural part is arranged in a central area of the valve and in particular is held in the described manner in the valve membrane. 
         [0016]    The valve body is preferably a rigid structural part. It is held in the valve membrane in such a way that it cannot be moved relative to the latter in the direction of movement of the valve body, or in its transverse direction, and, in particular, can also not be rotated with respect to the valve membrane. This ensures that the inlet channels of valve membrane and valve body are aligned in each operating state and, in addition, ensures a defined position of the valve body to the valve membrane, particularly in the area in which the valve body is intended to be closed by the valve membrane. The valve membrane is preferably held in the area of a circumferential edge between two parts of the housing, and in particular is held there by clamping. This affords the possibility of the valve membrane, starting from the edge areas, being able to bulge out sufficiently under the effect of the respective fluid pressure. The valve membrane is preferably profiled in cross section, and a central area of the valve membrane serves to receive the valve body. This central area has a pot-shaped configuration in particular. 
         [0017]    A special configuration of the valve membrane is preferably provided. Accordingly, a closure element is a component part of the valve membrane. The stop moves the closure element against the valve body and in doing so closes the fluid outlet of the valve. 
         [0018]    The outlet of the valve can be designed in different ways. It is conceivable to route the outlet directly from the chamber to the housing and from there via a channel to an outlet conduit connected to the housing. In a modified configuration, it is possible, corresponding to the routing of the inlet channel through the valve membrane, to also provide an outlet channel that is routed through the valve membrane. 
         [0019]    The valve can be simply constructed, particularly in the area of the valve membrane and of the valve body, wherein the valve membrane has a radial inlet channel and the valve body has a radial inlet channel adjoining the latter inlet channel. The inlet channel of the valve body empties into an axial inlet channel of the valve body that can be closed by means of the valve membrane. An outlet channel, starting from the chamber, is preferably formed between the valve body and the valve membrane. 
         [0020]    According to a particular embodiment of the invention, the stop is designed as an adjustable stop. It is designed in particular as an adjusting screw that is screwed into the housing. The further the screw frees the adjustment path of the valve membrane, the greater is the secondary pressure in the valve. 
         [0021]    With the valve according to the invention, the flow of the fluid is regulated in relation to the maximum pressure. The valve membrane is preferably configured with respect to the pressure level to be regulated. This means that the regulation can be effected entirely by means of the elastic valve membrane. According to a development of the invention, however, a spring is provided for resetting the valve membrane to the open position of the valve. This spring assists the resetting movement of the valve membrane. 
         [0022]    The spring is preferably designed as a compression spring supported on the housing and on the valve membrane, and, in particular, the valve membrane can be reset against a stop on the housing side. This stop limits the resetting movement of the valve membrane. 
         [0023]    The outlet of the valve preferably includes a flow restrictor. The latter thus forms a component part of the valve. 
         [0024]    Further features of the invention are set forth in the dependent claims, in the description of the figures, and in the figures themselves. It will be noted that all the individual features and all combinations of the individual features are part of the invention. 
         [0025]    The invention is depicted in the figures on the basis of a mechanically operated liquid pump that is provided with the valve, without being limited to this illustrative embodiment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  shows an exploded view of a mechanically operated liquid pump using the valve according to the invention, 
           [0027]      FIG. 2  shows a vertical longitudinal midsection through the pump shown in  FIG. 1 , in particular to illustrate the drive mechanism of the pump, with a balloon bearing on a core, 
           [0028]      FIG. 3  shows a section according to  FIG. 2 , with the balloon filled with liquid, 
           [0029]      FIG. 4  shows a vertical longitudinal section through the pump shown in  FIG. 1 , at a distance from the longitudinal center axis of the pump, in the area of a valve of the pump, 
           [0030]      FIG. 5  shows a section, cut transversely through the pump illustrated in  FIG. 1 , in the area of the valve, 
           [0031]      FIG. 6  shows a horizontal longitudinal midsection through the pump shown in  FIG. 1 , with the balloon bearing on the core, 
           [0032]      FIG. 7  shows a section according to  FIG. 6 , with the balloon filled with liquid, 
           [0033]      FIG. 8  shows a section through the pump, cut transversely in the area where the core is supported, 
           [0034]      FIG. 9  shows a section through the pump, cut transversely in the area of the unsupported portion of the core and of the liquid-filled balloon, 
           [0035]      FIG. 10  shows an enlarged sectional view of core, balloon and clamping ring for connection of balloon and core, with the balloon bearing on the core, 
           [0036]      FIG. 11  shows a section, cut transversely to the longitudinal extent of the core, through the core and the balloon, with the balloon bearing on the core, 
           [0037]      FIG. 12  shows a sectional view according to  FIG. 11  for a modified cross-sectional configuration of the balloon, 
           [0038]      FIG. 13  shows an enlarged sectional view of the valve shown in  FIG. 4 , and 
           [0039]      FIG. 14  shows a diagram illustrating the operating principle of the mechanically operated liquid pump, and indicating physical parameters. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    For purposes of description herein, the terms “upper”, “lower”, “right”, “left”, “rear”, “front”, “vertical”, “horizontal” and derivatives thereof shall relate to the invention as oriented in  FIG. 1 . However, it is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise. 
         [0041]    The mechanically operated liquid pump  1  illustrated in  FIG. 1  is used in particular for administering medical or nutrient liquids, for example for administering a liquid medicament. 
         [0042]    The pump  1  has a multi-component housing  2  formed by a middle part  3 , by an upper part  4  and a lower part  5  that interact with said middle part  3 , by an upper shell  6  interacting with the upper part, and by a lower shell  7  interacting with the lower part  5 . 
         [0043]    The middle part  3  is provided on its upper face with a recess  8  that is open to the free edge of the middle part  3  and that has a semicircular cross section, and the upper part  4  is provided on its lower face, and in the corresponding edge area, with a corresponding semicircular recess  9 . With the upper part  4  connected to the middle part  3 , the two recesses  8  and  9  form a circular cross section for receiving a conically widened end area  10  of a core  11 . Except at its end area  10 , the core  11  has a constant external diameter. This cylindrical portion of the core  11  is designated by reference number  12 . A channel  13  (see  FIG. 2 ) extends through the core  11  along its longitudinal center axis, and several channels  14  extending radially through the core  11  branch off from the channel  13  in the area of the portion  12  ( FIG. 6 ). In the area of the outer circumference of the core  10 , the radial channels  14  open into circumferential grooves  15  of the core  11 . 
         [0044]    An elastic element interacts with the core  11  and is designed as a silicone balloon  16 . The latter is produced by injection molding. The balloon has a conically widened end area  17  with opening  17   a,  corresponding to the end area  10  of the core  11 , and it has a portion  18  which corresponds to the outer shape of the portion  12  of the core  11  and which merges into the end area  19 , closed on account of the balloon design and remote from the end area  17 . 
         [0045]    The dimensions of core  11  and balloon  16  are such that, as can be seen from  FIG. 2 , the balloon fitted onto the core  11  bears completely on the core  11 , such that the end area  17  of the balloon contacts the end area  10  of the core, and the portion  18  of the balloon  16  contacts the portion  12  of the core  11 , and, finally, the end area  19  of the balloon  16  bears on the free end of the core  11 . The dimensions of the balloon  16  in relation to the core  11  are chosen here such that the balloon  16  bears on the core  11  with relatively little pretensioning, in other words in a relatively unstressed state. 
         [0046]    In order to fasten the end area  17  of the balloon  16  on the core  11 , at the end area  10  of the latter, a clamping ring  20  is provided, which is fitted externally onto the balloon  16  at the end area  17  thereof. The structure thus formed is inserted with the clamping ring  20  into the recess  8  of the middle part  3 , and the upper part  4  is then connected to the middle part  3 , as a result of which the clamping ring  20  and therefore the core  11  and balloon  16  are held secure in the recesses  8  and  9  of middle part  3  and upper part  4 . For the clamping ring  20 , the recesses  8  and  9  have a seat that widens conically in the direction away from the respective free edge of the middle part  3  and upper part  4 , in order to ensure a secure hold of the clamping ring  20 . 
         [0047]    The middle part  3 , the upper part  4  and the lower part  5  serve to receive further operating elements of the pump  1 : 
         [0048]    A Luer check valve or lock valve  21  connected to the upper part  4  passes through an opening  22  in the upper part  4 , and, as is explained in the following description of  FIG. 2 , has a Luer lock valve housing  23  and a Luer lock valve core  24 . By way of a channel  25 , the Luer lock valve  21  is in communication with a channel  26 , which is formed between the upper part  4  and the middle part  3  and which communicates with the channel  13  extending through the core  11 . 
         [0049]    The pump is filled with liquid by way of the Luer lock valve  21  and the channels  25 ,  26  and  13 . Starting from the unfilled state shown in  FIG. 2 , and with increasing delivery of liquid, the balloon  16  expands in that area not clamped by the clamping ring  20 , and, when completely filled, adopts the final shape illustrated in  FIG. 3 . The space occupied by the liquid is designated there by reference number  27 . It will be seen from  FIGS. 2 ,  3  and  6  to  12  that, as it fills with liquid, starting from its initial state bearing on the core  11 , the balloon  16  changes shape both in the longitudinal direction of the core and also in transverse directions thereof, i.e. in a first transverse direction and in a second transverse direction perpendicular thereto. 
         [0050]    The upper part  4  and the lower part  5  are provided with locking projections  28 , which serve to receive a cap  29  that is approximately kidney-shaped in cross section. As can be seen from  FIG. 9 , this cap has an extension in its direction of width that is substantially greater than that in the direction of its height. The width-to-height ratio is 2:1, for example. As can be seen from  FIG. 2  for example, the length-to-height ratio of the cap  29  is approximately 2.5:1. The cap  29  is preferably clipped non-releasably onto the housing  2 . When the balloon  16  is filled completely with liquid, it takes up as much as possible of the internal space in the cap  29 . 
         [0051]    This is achieved by the fact that, as can be seen from the view in  FIG. 11  showing the balloon  16  bearing on the core  11 , the balloon  16  has relatively thick wall portions  30  in a first direction of extent X perpendicular to the longitudinal axis of the core  11 , and it has relatively thin wall portions  31  in a second direction of extent Y perpendicular to the longitudinal axis of the core  11  and perpendicular to the first direction of extent X. Thus, when liquid is introduced into its space  27 , the balloon  16  seeks to expand preferably in the direction of extent X, thereby resulting in the expanded oval cross-sectional shape illustrated in the view in  FIG. 9 . Overall, the pump  1  is presented as a flat functional component that can be easily worn on the body, and the balloon  16 , in the state when filled with liquid, likewise adopts a flat shape adapted to the outer contour of the pump  1 . 
         [0052]    The channels  26  and  13  serve not only to deliver the liquid from the Luer lock valve  21  into the balloon  16 , but also to dispense the liquid from the interior of the balloon  16  to the patient. Thus, the channel  26  is continued past the inlet point of the channel  25  to a valve  32  that is mounted in the middle part  3  and upper part  4  and that restricts the volumetric flow of liquid discharged from the balloon  16 . This valve  32  is formed by an elastic valve membrane  33  held at the edge between middle part  3  and upper part  4 , by a valve core  34  that interacts with the valve membrane  33 , by a compression spring  35  supported on the valve membrane  33  and the upper part  4 , and by an adjusting screw  36 , which is mounted in a thread of the upper part  4  and can be brought into operative connection with the valve membrane  33 . 
         [0053]    As can be seen from the detailed view in  FIG. 13 , the channel  26  opens into a radially extending channel  37  of the valve membrane  33  and from there into a radial channel  38  of the valve body  34 , which opens into an axial channel  39  of the valve core  34 . This channel  39  is open in the area of its end directed toward a reinforced portion  40  of the valve membrane  33 . A stop designed as an adjusting screw  36  is arranged on that side of the portion  40  directed away from the channel  39 , which portion  40  has the function of a closure element. In principle, this stop could also be stationary. Between the projections  41  of the valve membrane  33 , the valve core  34  is held so as to be axially immovable relative to the valve membrane  33  and also non-rotatable relative to the latter. 
         [0054]    The valve  32  is used to stop the volumetric flow in the event of too high a pressure. Two separate chambers  42  and  43  are formed in the valve and are connected to each other via a channel  44 , which extends through the valve core  34  and is arranged parallel to the channel  40 . The chamber  42 , which lies in the direction of flow to the inlet, and therefore to the channel  26 , serves as a blocking chamber. The chamber  43  lies in the direction of flow to the outlet  45 . To filter the liquid dispensed through the valve  32 , a filter  46  is provided which is clamped at the edge between the middle part  3  and the lower part  5 . Starting from the chamber  43  and the outlet  45 , the liquid passes to a channel  47  ( FIG. 5 ) in flow communication with the outlet  45 , and from there to a Luer lock attachment  48  held between the middle part  3  and the lower part  5 . A Luer lock connector  49 , provided with a hose  50  leading to the patient, can be connected to the Luer lock attachment  48 . 
         [0055]    As can be seen from the view in  FIG. 5 , a glass capillary  53  is fitted into the channel  47 . This glass capillary constitutes a flow restrictor, which is able to restrict the volumetric flow passing through the channel  47  out of the pump, since the flow restrictor has a smaller cross section than the channel  37  lying in the inlet. By selecting various flow restrictors, it is possible to set various constant flow rates, as long as the pressure at the inlet does not drop below a defined value. In principle, the cross-sectional area of flow of the inlet is greater than the cross-sectional area of flow of the outlet. Of course, the flow restrictor can be designed other than in the form of a glass capillary. For example, it is entirely conceivable to provide downstream of the valve, in the outlet of the pump, a meander chip that restricts the through-flow. 
         [0056]    Because of the stated diameters of the channels that connect the space  27  of the balloon to the valve  32 , and the diameter of the channels arranged behind the valve  32  with the flow restrictor  53 , the resistance that the channel  47  with flow restrictor  53  sets against the outflow of liquid from the housing  2  is greater than the resistance made to the liquid flowing into the valve  32 . 
         [0057]    In an initial state, the valve membrane  33  is located in the position shown in  FIG. 13 , in which the valve membrane  33  bears largely on the middle part  3 , without requiring any action of the compression spring  35 . Because of the positioning of the valve core  34  relative to the portion  40  of the valve membrane  33 , a small gap is provided between the portion  40  and an encircling and therefore annular projection  54  of the valve core  34 . This projection  54  encloses the channel  43 . Accordingly, liquid flows through the channel  13  of the core  11  and through the adjoining housing channel  26  into the channel  37  of the valve membrane  33  and from there into the channels  38  and  39  of the valve core  34 . From the channel  39  of the valve core  34 , the liquid flows through the gap formed between the projection  54  and the portion  40  of the valve membrane  33 , and into the chamber  42  located there, and from the chamber  42  through the channel  44  between valve membrane  33  and valve core  34  to the chamber  43 , passes the filter  46  and travels through the outlet  45  to the channel  47  with the flow restrictor  53 . If a higher liquid pressure is established in the inlet, thus also in the channel  39 , without a greater volumetric flow being able to issue from the pump as a result of the flow restrictor  43 , this has the result that the valve membrane  33 , which is clamped in the edge area between the middle part  3  and the upper part  4 , deforms in the central area in the direction of the adjusting screw  36  with the stop function, specifically counter to the force of the compression spring  35 . When the valve membrane  34  with its portion  40  comes up against the projection  55  of the adjusting screw  36  directed toward the portion  40 , the portion  40  makes contact there with the adjusting screw  36 , such that, since the valve membrane  33  cannot move any farther up in the direction of the upper shell, the portion  40  is pressed against the projection  54  of the valve core  34  and thus closes the flow through the channel  39 . As the liquid flows out through the flow restrictor  53 , the pressure in the chamber  43  decreases, with the result that the membrane, by virtue of its own elasticity, moves back again in the direction of its initial state according to  FIG. 13 , such that the portion  40  disengages from its contact with the adjusting screw  36 , and the flow gap between the projection  54  and the portion  40  is again freed. Depending on the pressure prevailing in the balloon  16 , this state can be obtained only when the initial position of the valve membrane  33  is reached, as shown in  FIG. 13 , or even earlier, in other words with the valve membrane  33  still deflected. The adjusting screw  36  serves to modify the opening and closing behavior of the valve  32 . The further the screw frees the adjustment path of the valve membrane, the greater is the secondary pressure in the valve. In principle, it is not necessary to provide the compression spring  35 . It is of advantage when greater pressures are intended to be dealt with by the pump  1  and, accordingly, the elastic restoring behavior of the valve membrane  33  is not sufficient to move it into the initial position according to  FIG. 13 . 
         [0058]    With the valve  32 , the volumetric flow of liquid is therefore restricted as a function of the pressure prevailing in the balloon  16 , and the volumetric flow of liquid is maintained substantially constant via the flow restrictor  53 . In principle, the liquid pump could be modified by providing only a device for maintaining substantially constant the volumetric flow of liquid dispensed from the elastic element, or only a device for restricting the volumetric flow of liquid dispensed from the elastic element. 
         [0059]    Before using the mechanically operated liquid pump, liquid is delivered through the Luer lock valve  21 , as a result of which the liquid passes into the balloon  16 , and the filling level of the balloon can be read off through the transparent cap  29  on the basis of the markings  51  which are arranged in the transverse direction of the cap and which are a reference for the transverse expansion of the balloon as a function of its state of filling. After the pump  1  has been filled and the pump has been attached to the patient via the hose  50 , liquid is dispensed out of the pump through the valve  32 , with elastic pretensioning of the expanded balloon  16 , and this is done until the balloon has been completely emptied and bears on the core  11 . 
         [0060]    The particularly simple design of the described liquid pump allows it to be used in a variety of different ways. The user is able to operate the pump anywhere, and immediately, without long start-up times. It can be used carried around by the user, or used in one place, specifically in all normal life situations in or outside the field of medicine. The pump can be used in a sterile state and requires minimal operating/handling effort. Because of the simple construction of the small number of component parts, the pump is inexpensive to produce. This is a condition for its being able to be used particularly in outpatient care, and in financially weak markets. The low weight of the pump permits its use in accident and emergency situations, in field hospitals and in disaster areas. Some or all of the functional elements of the pump are exchangeable. The pump is suitable for short or long dispensing times, for example in the case of a balloon with a capacity of 25 ml, for a flow rate of 2.5 ml per hour, that is to say a running time of 10 hours. It is of course possible to use other balloons with other volumes, for example 10 ml, 50 ml, 100 ml or 150 ml. The running time can be much longer, for example up to 24 hours. Although flow rates of &gt;1000 ml per hour are entirely possible, a flow rate of 0.5 to 10 ml per hour is considered the preferred option. 
         [0061]    According to the illustrative embodiment, a balloon is described which is produced by injection molding and serves as a container for the medicament solution and as a pressure reservoir. The balloon has a defined contour in cross section and in expansion, for filling flat housing spaces and for avoiding pressure peaks. It is radially and/or axially pretensioned on a one-part or multi-part core, in order to increase the restoring forces. One end of the balloon is sealed off in an airtight manner over the core and fixed in position by a clamping ring with a form fit. The balloon is freely movable in the axial and radial directions during filling and emptying, being elastically deformable and able to move in a manner free from friction inside the cap. 
         [0062]    The pump  1  can additionally be provided with a bolus reservoir. In  FIG. 1 , the provision of such a bolus is indicated by reference number  52 . The pump can be converted to this extent, as and when required. 
         [0063]      FIG. 14  is a diagram illustrating how the above-described mechanically operated pump works and showing the physical parameters. The contour of the pump is indicated by the dot-and-dash line. 
         [0064]    In the foregoing description, it will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed herein. Such modifications are to be considered as included in the following claims, unless these claims by their language expressly state otherwise.