Abstract:
A lid for a food storage container includes a lid defining a vacuum sense opening and a vent opening extending through the lid body. The lid also includes a releasable cover disposed over the vent opening to impede air flow into the container through the vent opening until the cover is released. The lid further includes a pressure indicating dome defining a cavity therein, the dome in hydraulic communication with the container through the vacuum sense opening, the dome having a membrane that collapses toward the vacuum sense opening in response to negative container pressure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of PCT applications PCT/EP01/13148, filed on Nov. 14, 2001, PCT/EP01/13233, filed on Nov. 15, 2001, and PCT/EP02/14693, filed on Dec. 21, 2002, and claims priority under 35 U.S.C. § 119(a) from German patent applications DE 100 60 999.6 and DE 100 60 995.3, both filed on Dec. 8, 2000, and from German patent application DE 102 30 748, filed on Jul. 9, 2002. 
     
    
     
       TECHNICAL FIELD  
         [0002]    This invention relates to sealable food storage containers.  
         BACKGROUND  
         [0003]    Food storage can be improved by keeping food in a container under vacuum. Keeping the food in a container under vacuum helps to protect the food from certain microorganisms and pests, as well as mold and fungus growth. Furthermore, it helps prevent the food from oxidizing, thereby maintaining the moisture level and aroma of the food. However, with systems of this type it is often difficult to open the storage container because the vacuum inside the container draws on the container lid. In addition, it is often not possible for the user to recognize whether the desired vacuum is still present in the storage container. Furthermore, it can be difficult to maintain an adequate vacuum in the storage container, particularly over a prolonged period of time.  
           [0004]    Food storage container lids with venting or aerating valves for pressure equalization during heating in a microwave oven are known. For example, EP 0 633 196 A2 describes a mechanism of this type. The venting or aerating valves can be used to prevent the build-up of overpressure in the interior of a food storage container when it is heated. Such a build-up of overpressure typically occurs when there are aqueous liquids in the interior of the container, and the liquids evaporate during heating, thereby building up an overpressure in the container interior. The result can be that sauces or other food within the container can spurt out suddenly when the container lid is opened. EP 0 633 196 A2 proposes a venting valve in the lid of the food storage container. The venting valve is to be opened before the container is placed in a microwave oven. The water vapor which develops during heating can then escape unhindered through the valve, without a corresponding build-up of vapor pressure in the interior of the sealed container. It is not intended to achieve thereby the improved storage of food under vacuum, or the indication of the pressure level in the food storage container.  
           [0005]    In EP 0 820 939 A1, the object is to provide a food storage container with venting capability, so that food stored inside the container can be safely heated in a microwave oven with the container lid closed. Unlike EP 0 633 196 A2, a valve mechanism is described which can be opened by way of a joint like a rocker. Hence all that is required is to press in the rocker lever for the valve to open with ease. Here, too, there is no intention to use the valve mechanism to improve the storage of food under vacuum or to indicate the pressure level in the food storage container.  
           [0006]    EP 0 644 128 A1 describes a food storage container having a container lid with a recess in which several vent openings are formed. The vent openings are closed by a seal when a vacuum exists in the holding space. The seal has pin-shaped anchor bars which project upwardly a small amount out of the recess and grow thicker at their ends. These anchor bars serve to lift the seal off the vent openings when air is to enter the holding space of the storage container from outside. Relatively high manual forces need to be applied to open this valve.  
           [0007]    WO 88/00560 describes an opening mechanism for a plastic beverage can, and allows for a kind of visual check of pressure level. The beverage can has a plastic lid (the lids involved tend to be plastic, since one object is to avoid using metal lids) which bulges outward when the pressure inside the container is above atmospheric pressure. Such an arrangement does not allow for any quantitative conclusions about the magnitude of the pressure above atmospheric inside the container. Pressure equalization can occur by opening a venting valve, making it easier to subsequently remove the entire lid. The equalization of overpressure in the container interior (as a result of carbonated beverages, for example) plays a role in this case. This opening mechanism does not, however, allow for re-closure and the corresponding build-up of pressure.  
           [0008]    CH 304 374 discloses a closure lid for an aluminum sterilizing container. The lid has an essentially circular-ring-shaped configuration, and is mounted on a cylindrical aluminum container. A rubber seal is placed between the edge of the lid and the upper brim of the container. In the middle of the container lid there is an additional opening which is covered by a rubber cap. The rubber cap provides a visual check, indicating whether there is a vacuum inside the container. As long as the pressure inside the container is adequately below atmospheric pressure, the rubber cap bulges inward a corresponding amount. This bulge diminishes continually as the vacuum decreases. Hence it is difficult for the observer to decide whether the pressure level inside the container is adequate for ensuring the freshness of the food inside the container.  
           [0009]    Finally, DE 100 60 999 C1 describes a food storage container including a container lid with an opening mechanism for ventilating the evacuated container before it is opened. According to one embodiment, a sealing tongue is raised up from a vent via a driver. The sealing membrane and a pressure indicator are fastened directly on the container lid. The opening tab is connected non-releasably to the container lid via a film hinge. This mechanism provides an improved possibility for storing food under vacuum. The opening of the lid is facilitated by prior ventilation and the pressure indicator indicates the state of pressure in the container interior. However, disadvantages of this mechanism include the costly installation of the sealing components directly on the container lid, and the complicated driver mechanism of the one-way valve, which is susceptible to defects. Furthermore, the possibility of exchanging the valve mechanism is limited.  
         SUMMARY  
         [0010]    In one aspect, the invention features a lid for a food storage container. The lid includes a lid body defining a vacuum sense opening. A vent opening extends through the lid body. The lid also includes a releasable cover disposed over the vent opening. The cover impedes air flow into the container through the vent opening until the cover is released. The lid further includes a pressure indicating dome. The pressure indicating dome defines a cavity, and is in hydraulic communication with the container through the vacuum sense opening. The pressure indicating dome includes a membrane that collapses toward the vacuum sense opening in response to negative container pressure. One advantage of this lid and of the pressure indicating dome is that they can be easy and economical to manufacture. The pressure indicating dome can permit simplified evacuation of a container by allowing the user to immediately see when a sufficient vacuum has been attained inside the container. The pressure indicating dome can provide a visual and/or tactile signal of the status of the pressure inside the container.  
           [0011]    The visual impact of the membrane of the pressure indicating dome, which can be made of an elastomeric plastic material, can be increased by, e.g., designing the membrane in an easily visible color. Such an embodiment can allow for particularly easy viewing of the pressure indicating dome, as well as a clear indication of the pressure in the food storage container.  
           [0012]    Another advantage of the pressure indicating dome is that it can enable even users with poor vision to determine the condition of pressure inside a storage container through tactile means (e.g., by determining the degree to which the pressure indicating dome projects beyond, or disappears within, the outer contour of the cover).  
           [0013]    In some embodiments, the lid further includes a resilient layer that is in contact with the membrane. The resilient layer can include a spring sheet and/or an elastomeric polymer. The resilient layer can be formed, for example, by selecting a suitable resilient plastic material for the membrane of the pressure indicating dome or by inserting a spring metal in the membrane of the pressure indicating dome. An advantage of this embodiment is that when the interior of the storage container is at ambient pressure, the membrane of the pressure indicating dome can project distinctly outward.  
           [0014]    In some cases, the pressure indicating dome is capable of indicating two discrete states: (1) the interior of the storage container being at a pressure that is sufficiently below atmospheric pressure, and (2) the interior of the storage container being at a pressure that is insufficiently below atmospheric pressure. An advantage of this embodiment is that the pressure indicating dome can adopt an umnistakable signal position. In other words, if a pre-defined pressure below atmospheric pressure is attained inside the container, then the membrane can “snap” inward. In some cases, e.g., when the membrane includes a spring, the membrane can be guaranteed to snap back into its initial position when a minimum pressure below atmospheric is exceeded inside the storage container. In such cases, the pressure indicating dome can have only two unmistakable positions: sufficient pressure below atmospheric inside the storage container (the pressure indicating dome is snapped inward), and insufficient pressure below atmospheric or ambient pressure (the pressure indicating dome is in its initial position).  
           [0015]    In some cases, the pressure indicating dome has an essentially cup-shaped configuration with a planar top adjoined by a conically widening annular wall. Such an embodiment of the pressure indicating dome can allow for a clear indication of good or poor vacuum in the container interior. It can avoid a gradual shifting motion by the pressure indicating dome. The annular wall can be slightly outwardly domed, which can allow the pressure indicating dome to be folded together with particularly little friction. There can be no notable rubbing of the side wall when the pressure indicating dome is rolled together.  
           [0016]    In certain embodiments, the cover also defines an indicator opening. Under certain pressure conditions, the membrane extends through the indicator opening. A benefit to this embodiment is that the pressure indicating dome can penetrate the indicator opening as soon as the vacuum in the container interior is inadequate (without penetrating the indicator opening when there is sufficient vacuum in the container interior).  
           [0017]    In some cases, the membrane is formed of a plastic resin. The plastic resin can be selected to maintain dimensional stability of the membrane over a temperature range between about −40° C. and about 100° C. An advantage to this embodiment is that it can allow the storage container and its contents to be stored in a freezer and later to be defrosted in a microwave oven.  
           [0018]    In some embodiments, the lid includes a one-way valve. The one-way valve can include a movable sealing tab. The pressure indicating dome can be integrally connected with the one-way valve (e.g., the pressure indicating dome can be integrally connected with the movable sealing tab). In such cases, the integral one-piece construction including the pressure indicating dome and the one-way valve can include a relatively stiff material and/or a material possessing sealing properties. An advantage of this embodiment is that it can be economical to manufacture (e.g., as an injection molding). Furthermore, it can be easily mounted on the storage container.  
           [0019]    In some cases, the components of the valve device are provided separately from the food storage container, and are removably fastened to the food storage container. Advantages of such an embodiment can include simple installation during production and/or the repair or exchange of defective components. Furthermore, the components do not need to be assembled at their site of manufacture.  
           [0020]    In some embodiments, the cover is pivotably connected to the lid body by a hinge. The hinge can be formed integrally on, e.g., the lid body. The hinge can be of a material with inherent spring characteristics, which can enable the hinge simply to be snapped into a hinge holder fitted, for example, to the lid body.  
           [0021]    The pressure indicating dome can include a spring. The stiffness of the spring can be set or selected retrospectively to the desired response pressure (i.e. to the value of the container pressure at which the pressure indicating dome is triggered). The pressure indicating dome can include a resilient material. An advantage to such a pressure indicating dome is that it can have a low number of required components and it can be simply installed.  
           [0022]    In some cases, the cover is produced by an injection molding process.  
           [0023]    In another aspect, the invention features a lid for a food storage container. The lid has a lid body with a vent opening in it, and a releasable cover disposed over the vent opening. The releasable cover impedes air flow into the container through the vent opening until the cover is released. The releasable cover has an evacuation opening. The lid also includes a membrane that covers the vent hole until the cover is released. The lid further has a driving element that is connected to the membrane at one end and disposed within the evacuation opening at another end.  
           [0024]    The lid can have the advantage of being easy and economical to manufacture. Further, the lid can be opened easily because the membrane, which simply rests on the vent hole, can be lifted off the vent hole by pulling open the cover by way of the driving element. This operation can be comfortably performed without any particular effort because of the leverage between the cover, the driving element and the sealing tab. This can result in pressure equalization between the interior of the container and the surroundings. The container lid is no longer drawn by the vacuum in the interior of the storage container and can be lifted off it with ease. It is also possible for the opening assembly to be positioned in the upper area of the outer wall of the container, above its maximum filling level, such that no food is sucked into the vacuum pump when air is evacuated from the storage container.  
           [0025]    In some embodiments, the membrane is of an elastomeric plastic and/or acts as a one-way valve. The membrane can be constructed as a rectangular plastic strip, for example, with one narrow side connected to the container lid body or an elastomeric plastic layer attached thereto. This fastening edge can act as an elastic joint. During the evacuation operation the membrane can be swiveled upward from the vent opening by the suction effect of the suction device, i.e., the membrane can be lifted clear of the vent opening, enabling air present in the storage container to be drawn off by the suction device. Once the storage container is evacuated, sealing can take place automatically by the membrane being drawn against the vent opening in the lid body.  
           [0026]    The membrane can be a sealing tab.  
           [0027]    In some cases, the driving element has a rim. This can allow for a simple connection of the driving element to the cover without the parts being joined together by way of threaded connections or any other special connecting elements. If the driving element is elastically made of plastic, the rim can be elastically squeezed together and pushed through the evacuation opening in the cover so that subsequently the rim covers the evacuation opening and can no longer slip through the evacuation opening.  
           [0028]    In some embodiments, the cover can be pressed into a recess of the lid body and locked in the recess for the storage state of the storage container. It can thus be easily possible for several storage containers with their storage lids to be stacked on top of each other without the cover projecting in obstructing manner from the upper side of the container lid body. The lid can include a recessed grip such that it can be possible, even if the cover is clipped in place within a recess of the container lid body, for a user to grip in the gap with one finger in order to lift the cover. The grip surface can be oriented at an upward angle, away from the container lid body.  
           [0029]    The driving element can be integrally connected to the membrane. The driving element can be constructed, for example, as a spigot standing essentially perpendicular on the membrane, with a circumferential edge positioned in its upper area. In this arrangement the driving element can be made of an elastic material.  
           [0030]    In certain embodiments, the cover has a surface that extends about the evacuation opening and that is adapted to receive a sealing lip of a vacuum pump.  
           [0031]    In some cases, the lid body is of a plastic resin (e.g., polypropylene, polyamide, and/or other temperature- and aging-resistant plastic materials) that is selected to maintain dimensional stability of the membrane over a temperature range of between −40° C. and 100° C. In such cases, it can be possible for the storage container and its contents to be stored in a deep-freezer and then to be defrosted in a microwave oven. The vent opening can be opened by way of the cover for heating in a microwave oven. Possible materials are polypropylene and polyamide as well as any other temperature- and aging-resistant plastic material.  
           [0032]    The lid body can further include a pressure indicator.  
           [0033]    In some cases, the container lid body and the cover can be manufactured as a joint injection molding. The cover can be integrally connected to the lid body by a hinge. For the membrane and the pressure indicator, it is possible to use an elastomeric plastic or rubber material, which can then be inserted with a sealing effect in the component made up of the container lid body and the cover.  
           [0034]    The lid can be universally used with different food storage containers. If the vent assembly is positioned on the container, then the outer surface of the cover adjacent the evacuating opening preferably faces at an angle in an upward direction in order to be better able to mount a vacuum pump on the container wall. This can also facilitate the handling of the vent assembly.  
           [0035]    Implementations of the invention can have one or more of the following advantages. The pressure indicator and/or the opening and closing mechanism of the storage container can be easy and inexpensive to manufacture. The storage container can be opened without any major effort. In some cases, only the smallest possible forces are needed to cause the membrane to lift off of the vent opening and to reduce the vacuum inside the storage container. Uncontrolled spraying of food out of a vent opening due to overpressure can be minimized. As a result, the likelihood of a user being soiled and/or scalded when using the container can be reduced.  
           [0036]    The cover can perform several functions, and thereby save space and cost. In other words, the cover can act as a coupling element for receiving and forming a tight connection with a vacuum pump, as an actuating and opening element for the one-way valve formed together with the membrane and the vent opening, and/or as an impact guard for the container lid.  
           [0037]    The pressure indicating dome can allow a user to immediately see when there is a sufficient vacuum inside a storage container. The pressure indicating dome can provide a visual and/or tactile signal of the pressure condition inside a storage container. The membrane of the pressure indicating dome can include, e.g., an elastomeric plastic material which can be of an easily visible color. The pressure indicating dome can enable a user with poor vision to determine the condition of pressure inside the storage container by means of touch. A lid with a pressure indicating dome can serve as a multi-function component.  
           [0038]    The valve device can have the advantage of being simple to fit and having few components. The valve device can be exchanged or fixed (if, for example, a leakage or the like suddenly occurs). The valve device can be multifunctional, simultaneously providing a connection for a vacuum pump, pressure indication, and ventilation.  
           [0039]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features and advantages of the invention will be apparent from the description and drawings, and from the claims. 
       
    
    
     DESCRIPTION OF DRAWINGS  
       [0040]    [0040]FIG. 1 is a schematic cross-sectional view of a first valve device for a food storage container when there is an insufficient vacuum inside of the container.  
         [0041]    [0041]FIG. 2 is a schematic cross-sectional view of the valve device of FIG. 1, when there is a sufficient vacuum inside of the container.  
         [0042]    [0042]FIG. 3 is a schematic cross-sectional view of the valve device of FIG. 1, when the inside of the storage container is at atmospheric pressure.  
         [0043]    [0043]FIG. 4 is a perspective view, partially in cross-section, of a second valve device for a food storage container, when there is an insufficient vacuum inside of the container.  
         [0044]    [0044]FIG. 5 is a perspective view, partially in cross-section, of the valve device of FIG. 4, when a vent has been opened in the storage container.  
         [0045]    [0045]FIG. 6 is a perspective view of a food storage container including the valve device of FIG. 4.  
         [0046]    [0046]FIG. 7 is a schematic cross-sectional view of a third valve device, in the fitted state.  
         [0047]    [0047]FIG. 8 is a perspective exploded view of the valve device of FIG. 7.  
         [0048]    [0048]FIG. 9 is a perspective view of a fourth valve device, in the fitted state.  
         [0049]    [0049]FIG. 10 is a perspective exploded view of the valve device from FIG. 9. 
     
    
     DETAILED DESCRIPTION  
       [0050]    Referring to FIGS.  1 - 3 , a valve device  1 , which is engageable with a food storage container  15 , includes a pressure indicator  6 .  
         [0051]    Referring now to FIGS.  1 - 6 , valve device  1  is mounted on a container lid  2 . A cover  7  is integrally connected to container lid  2  by means of a film hinge  32 . Cover  7  and container lid  2  are injection moldings made of temperature-resistant thermoplastic material. Cover  7 , which in the plan view can be in the form of an oval plate, includes a connecting device  9 . Connecting device  9  allows container lid  2  to releasably engage a vacuum pump—i.e., connecting device  9  provides a suction port for a vacuum pump. Connecting device  9  is formed by a smooth annular surface  18  on the outer side  210  of cover  7 , and by one or more openings  17  within annular surface  18 . A suitable connecting device is described in a U.S. patent application filed concurrently herewith, entitled “Food Storage Containers” and assigned Ser. No. ______, the entire contents of which are hereby incorporated by reference.  
         [0052]    A sealing tab  3  (of, e.g., elastomeric plastic) is disposed on the lower side of cover  7 , underneath connecting device  9 . In the valve device  1  shown in FIGS.  1 - 3 , sealing tab  3  is fastened to cover  7  by a circular-ring-shaped bar  19 , and is a separate component in the shape of a disk. Bar  19  has an air passage  30 .  
         [0053]    In FIGS.  1 - 6 , cover  7  is inserted in a recess  20  in container lid  2 . Recess  20 , which is essentially rectangular, is adapted to conform to cover  7 . Container lid  2  includes a vent hole  4  under connecting device  9  of cover  7 , and under sealing tab  3 . When open, vent hole  4  provides a connection between the atmosphere and the interior  22  of storage container  15 . When closed, vent hole  4  is closed air-tight by sealing tab  3 . Vent hole  4  and sealing tab  3  together form a one-way valve  40 , which closes in the direction of storage container  15 .  
         [0054]    A vacuum sense opening  5  in container lid  2  is arranged adjacent to vent hole  4 . Pressure indicator  6  includes a plastic membrane  220  which provides an air-tight covering for vacuum sense opening  5 . Pressure indicator  6  extends in an upward direction, essentially perpendicular to the plane of container lid  2 . When there is an insufficient vacuum in the container, the entire pressure indicator projects upward relative to the plane of container lid  2 . In other words, pressure indicator  6  displays an essentially cup-shaped and slightly outwardly domed side wall  23 , which tapers in an upward direction and terminates with a horizontally extending circular base  24 , as shown in FIGS. 1 and 3- 5 . Referring specifically to FIGS. 2 and 4, top  24  has a diameter “D” which is smaller than the diameter “d” of the opening on base  25  of pressure indicator  6 . As shown in FIG. 2, side wall  23  of pressure indicator  6  folds into a cavity  26  (FIG. 1) in the pressure indicator when exposed to vacuum.  
         [0055]    Referring to FIGS.  1 - 6 , cover  7  includes an indicator opening  8  at the position of pressure indicator  6 . When the pressure in interior  22  of storage container  15  is not sufficiently below atmospheric pressure, pressure indicator  6  extends vertically out of indicator opening  8 , past the outer surface  33  of cover  7 . Pressure indicator  6  can be made of an elastomeric plastic. Preferably, pressure indicator  6  is of an easily visible color, such as red (to, for example, distinguish it from the surrounding material of the lid). In FIGS.  1 - 3 , pressure indicator  6  is reinforced on its inner side by a layer  12  that preferably includes a resilient material, such as a spring sheet or elastomeric plastic. The surface of layer  12  is engaged with the inner side  34  of the pressure indicator  6 .  
         [0056]    In FIGS.  1 - 6 , the section of cover  7  that is closest to the edge of storage container  15  has a gripping surface  10 . For example, as shown in FIGS.  1 - 6 , an end of cover  7  is beveled slightly upward starting at point  35 , thereby forming gripping surface  10 . Container lid  2  includes a recess  20  with a bottom  37 . Cover  7  is separated from bottom  37  of recess  20  by ribs  29  and  36 . Thus, gripping surface  10  of cover  7  can be comfortably gripped between a user&#39;s finger and thumb (not shown) and pulled open in an upward direction.  
         [0057]    FIGS.  1 - 3  show a retaining clip  11  which presses the elastomeric plastic material of the planar base  25  of pressure indicator  6  against container lid  2 . Retaining clip  11  is supported by walls of container lid  2  (not shown). In FIGS.  1 - 3 , cup-shaped pressure indicator  6  is integrally connected to base  25 . Thus, when pressure indicator  6  is clamped by retaining clip  11 , the pressure indicator effectively is sealed to container lid  2 .  
         [0058]    Referring to FIGS.  4 - 6 , a second example of a valve device  1  also includes a pressure indicator  6  for a food storage container  15 . In the valve device  1  of FIGS.  4 - 6 , cover  7  is again integrally connected to container lid  2  by means of a film hinge  32 . Sealing tab  3  is arranged underneath connecting device  9  of cover  7 . Sealing tab  3  is connected to cover  7  by a driving element  13 . Sealing tab  3 , driving element  13 , base  25 , and pressure indicator  6  all are made of a single elastomeric plastic part which is fastened as an insert to a bead  21  in recess  20  of container lid  2 . The plastic material used for pressure indicator  6  has spring-like properties, such that pressure indicator  6  can snap into a position that indicates whether there is a sufficient vacuum inside the container.  
         [0059]    Thus, there are some differences between the valve device  1  of FIGS.  1 - 3  and the valve device  1  of FIGS.  4 - 6 . In FIGS.  1 - 3 , sealing tab  3  forms a separate sealing part relative to pressure indicator  6 . In the valve device  1  of FIGS.  4 - 6 , on the other hand, these parts are formed by a single elastomeric component—sealing tab  3  is partially cut out of base  25 , thereby forming a gap  28 . Furthermore, in FIGS.  4 - 5 , a circumferential seal  14  is disposed around the edge of container lid  2 . Seal  14  enables lid  2  to be closed air-tight against storage container  15 . In FIGS.  1 - 3 , on the other hand, lid  2  itself forms a tight closure with storage container  15  (i.e., there is no circumferential seal  14 ).  
         [0060]    Referring back to FIGS.  4 - 6 , when valve device  1  is closed, circumferential rib  29  presses base  25  against the bottom  37  of recess  20 , thus effecting a seal. In FIGS.  1 - 3 , base  25  is pressed against container lid  2  by retaining clip  11 , which is fitted to lid  2  by latching. In FIGS. 4 and 5, cover  7  performs the same function as retaining clip  11  does in FIGS.  1 - 3 , so that there is no need for a separate retaining clip.  
         [0061]    Another difference between the valve device  1  of FIGS.  1 - 3  and that of FIGS.  4 - 6  is that the valve device shown in FIGS.  4 - 6  includes driving element  13 , while the valve device shown in FIGS.  1 - 3  does not.  
         [0062]    In FIGS. 1 and 3- 6 , the pressure in the interior  22  of storage container  15  is equal to ambient pressure. Because of its spring bias, pressure indicator  6  thus projects out through indicator opening  8  and beyond cover  7 .  
         [0063]    In FIG. 2, there is sufficient vacuum in the interior  22  of storage container  15 . Pressure indicator  6  is thus drawn into cavity  26 , toward container interior  22 . The pressure indicator is in a folded or snapped-in condition. In this state, pressure indicator  6  either does not project at all beyond the outer contour of cover  7 , or else projects beyond the outer contour by a negligible amount. Pressure indicator  6  folds like a rolling membrane. The ratio of diameter “D” to diameter “d” is selected based on the wall thickness “f” and the elastic material of pressure indicator  6 , so that pressure indicator  6  will abruptly fold together when there is a sufficient vacuum in the interior of the container (as shown in FIG. 2). If the vacuum in container interior  22  decreases, then at the point of insufficient vacuum, pressure indicator  6  will make an abrupt outward movement, snapping back into the position shown in FIGS. 1 and 3- 6 . Thus, gradual shifting of pressure indicator  6  is avoided, and the user has a clear indication of whether there is a sufficient vacuum in the container.  
         [0064]    A user can first inform himself about the pressure status in container interior  22  by checking the position of pressure indicator  6  when container lid  2  is closed. If the bottom of pressure indicator  6  projects out through indicator opening  8 , then the pressure in container interior  22  is insufficient for guaranteeing the storage of food under vacuum conditions (as is the case in FIGS. 1, 4, and  6 ).  
         [0065]    In FIGS. 1, 3, and  6 , storage container  15  is evacuated. To evacuate the container, a suction port with a circumferential sealing lip of a vacuum pump (not shown) is placed on connecting device  9  of valve device  1 . Then, the vacuum pump is put into operation, causing vent hole  4  of valve device  1  to automatically open. Vent hole  4  opens because the suction effect of the vacuum pump causes sealing tab  3  to lift off from vent hole  4 , and the air contained in storage container  15  is drawn off by the vacuum pump. In FIG. 1, the air is drawn through vent hole  4 , past the side of sealing seat  38  of sealing tab  3 , around the outside of sealing tab  3 , through air passage  30 , and through connecting device  9  to the vacuum pump. As shown in FIG. 2, when a sufficient vacuum is attained in the interior  22  of storage container  15 , pressure indicator  6  suddenly snaps inward, thereby informing the user that he can end the evacuation operation. After the vacuum pump is disengaged from connecting device  9 , sealing tab  3  is pressed against the edge of vent hole  4 , automatically closing it air-tight. This operation also occurs with each return stroke of the vacuum pump, in order to enable a vacuum to be built up in interior  22 . The vacuum in interior  22  keeps enclosed food fresh for a long time because lack of oxygen prevents the food from being oxidized.  
         [0066]    To remove food from storage container  15 , the user grips cover  7  with two fingers under gripping surface  10  and, with little force, swivels cover  7  in a counterclockwise direction (as shown in FIG. 5). Referring to FIG. 3, sealing tab  3  is thus lifted by cover  7  in an upward direction, off sealing seat  38 , and vent hole  4  is cleared. In the valve device  1  shown in FIG. 5, the upper side of cover  7  first comes up against the lower side of a rim  230  formed on driving element  13 . The upper side of cover  7  then pulls driving element  13  and sealing tab  3  upward, until sealing tab  3  lifts off from sealing seat  38  and swivels upward in a counterclockwise direction. Referring to FIGS. 3 and 5, air can now flow into container  2  via vent hole  4 . The distance  5  between rim  230  and the upper side of cover  7  is sufficiently large to prevent the upper side of cover  7  from striking rim  230  until after cover  7  has been released from the latching arrangement (not shown) in recess  20 . Such a structure helps to keep the actuating forces low.  
         [0067]    Container lid  2  can now be removed from storage container  15  without any notable effort. In FIGS.  4 - 5 , sealing tab  3 , which is partially separated from the rest of planar base  25  by gap  28 , and which is connected to base  25  only in area  39 , repeatedly falls back onto vent hole  4  as a one-way valve acting under the force of gravity. Thus, it is relatively easy to produce a vacuum in the container. It also is conceivable, however, for cover  7  to be designed to snap into place by means of clip connectors on container lid  2 , thereby enabling sealing tab  3  to close vent hole  4 . The material of sealing tab  4  and base  25  can be elastic enough as to cause vent hole  4  to be closed a result of the closing moment acting on it when there is no difference in pressure. Sealing tab  3  does not lift off vent hole  4  until there is a difference in pressure (i.e., sealing tab  3  works like a one-way valve). Referring to FIG. 3, sealing tab  3  is lifted when cover  7  is swiveled around film hinge  32  because sealing tab  3  is fastened with clearance to cover  7 , in order to perform the function of a one-way valve.  
         [0068]    Referring to FIG. 6, a thermoplastic food storage container  15  includes valve device  1  from FIG. 4. Storage container  15  has a container body  16  in the shape of a right-parallelepiped and, when viewed from the top, has an essentially rectangular container lid  2  with a circumferential rim  27 . Valve device  1  is arranged in a recess  20  on one of the narrow sides of container lid  2 . Gripping surface  10  of cover  7  terminates approximately with outer surface  33  of container lid  2 . When there is insufficient vacuum inside of the container, only pressure indicator  6  projects vertically out of indicator opening  8  of cover  7 .  
         [0069]    Adjacent to pressure indicator  6  are connecting device  9  (e.g., a circular connecting device), with smooth annular surface  18 , and evacuation hole  17 , from which driving element  13  projects with its rim  230 . Rim  230  improves the driving effect of driving element  13  when cover  7  is swiveled upward. Through the leverage produced by distances “R” and “r” (shown in FIG. 5), relatively little manual force “F” (shown in FIG. 4) needs to be applied to grip surface  10  and lift sealing tab  3  from sealing seat  38 , even when there is still a vacuum in interior  22  of the container. As distance “r” becomes smaller and distance “R” becomes larger, it becomes easier to open valve device  1 .  
         [0070]    When the valve device is assembled, the upper area of the driving element can be pushed with the rim through evacuation hole  17 , with the rim being elastically squeezed together until it has penetrated the evacuation hole from the bottom up. Thereafter, the rim can widen and act as a sort of barb. When cover  7  is swiveled open, driving element  13  is moved upward over the rim in a curved path. The loose end of the sealing tab which is connected to the driving element is thus moved likewise in an upward direction, and lifted clear of the vent hole.  
         [0071]    Because of the distance between the lower side of the driving element rim and the upper side of the evacuation hole, the driving element initially slides through the evacuation hole when the cover is swiveled. The rim does not abut and take support upon the upper side of the cover until after the cover has executed a certain swiveling motion about the bearing point, preferably in a counterclockwise direction. From this moment on, the distance between the lower side of the cover and the upper side of the container lid is large enough for several fingers to grip underneath the cover. Thus it is possible, with greater force if at all necessary, to lift the sealing tab off the vent hole by the cover, moving the driving element (and hence the sealing tab) in an upward direction.  
         [0072]    The fact that the driving element extends with a clearance in evacuation hole  17  and is also elastically deformable within certain limits means that the swivel movement of the cover on the driving element is deflected in a direction of force extending essentially perpendicular to the sealing surface of the valve opening, with the result that only a small valve opening force is needed to cause the sealing tab to lift off the valve seat of the vent hole and to relieve the vacuum inside the storage container.  
         [0073]    The cross-section of the rim of the driving element preferably is dimensioned sufficiently large for the rim to display adequate rigidity, and not to slip through the evacuation hole when the cover is pulled open. It is preferable instead for the rim to rest on the upper side of the cover, and for the sealing tab to reliably lift clear of the vent hole even in the presence of vacuum in the container interior.  
         [0074]    In FIGS. 7 and 8, a first example of a valve device  101  is in the fitted, opened state. Valve device  101  is fitted to a container lid  109  of a storage container  121  for food. Valve device  101  can be used to evacuate air from closed container  121 , by means of a connection surface  115  and an extraction opening  117 . Valve device  101  can also be used to ventilate evacuated container  121  for easy opening of container lid  109 . In addition, the negative pressure in the container is indicated by a pressure indicator  113  integrated in valve device  101 .  
         [0075]    Container lid  109  sits in the closed state on a container wall  108  of storage container  121  and seals the latter in a gas-tight manner together with a container seal  107 , which is designed as an encircling flat seal made from elastomeric plastic. Container lid  109  (which can be produced from thermoplastic) has an elongate depression  126  for holding valve device  101 . A measuring opening  112  with a circular cross section and a vent  111  having a likewise circular cross section are provided in depression  126 . Vent  111  is fitted to a frustoconical projection.  
         [0076]    Valve device  101  has a valve housing  104  that can be produced from thermoplastic. Valve housing  104  has an elongate shape which tapers in one direction and has rounded ends and an encircling edge  123 . In this case, a hinge  118  is integrally formed on valve housing  104  at the wider end.  
         [0077]    Encircling edge  123  surrounds a planar plastic surface  127  which, in its wider section arranged level with the vent  111 , has a first circular cutout  124  concentrically with vent  111 . Edge  123 , which virtually forms an encircling wall, protrudes vertically above and below plastic surface  127 . Furthermore, a second circular cutout  125  is provided in the narrow section of surface  127 , i.e. in the region of pressure indicator  113 .  
         [0078]    Encircling edge  123  provides a boundary and holder for a membrane  102 . Encircling edge  123  also serves as a clamping connection for a valve housing cover  105 . Valve housing cover  105  is likewise produced from thermoplastic. The valve housing and the valve housing cover can be connected to each other by, e.g., a film hinge. Valve housing cover  105  has essentially the same outer contour as valve housing  104 . A connection surface  115  having a lenticular curvature and a central evacuation hole  117  is provided in the region of first cutout  124 . A circular indicator opening  114  is fitted in valve housing cover  105 , in the region of second cutout  125 . Webs which are arranged on the inside of the valve housing cover  105  cause membrane  102  to be pressed against plastic surface  127  of valve housing  104 .  
         [0079]    Membrane  102  is an essentially sheet-like sealing insert which can be produced from elastomeric plastic (e.g., polybutadiene, butadiene-styrene polymer, acrylonitrile copolymer, polychlorobutadiene, isoprene rubber, aftertreated polyolefins, polyurethane, or silicone rubber). In some cases, membrane  102  can be produced from natural rubber or cork. Membrane  102  carries out a plurality of functions simultaneously. First, membrane  102  has, level with vent  111  and evacuation hole  117 , a U-shaped incision, what is referred to as sealing tongue  110 . Sealing tongue  110  acts as a one-way valve, i.e. sealing tongue  110  raises off from vent  111  during the extraction process undertaken by a vacuum pump (not illustrated) which is fitted to connection surface  115 . As soon as the vacuum pump is removed, sealing tongue  110  closes vent  111  because of the negative pressure produced in container  121 .  
         [0080]    Second, one region of membrane  102  is designed as a pressure indicator  113  which indicates the vacuum state in the container interior. If a sufficient vacuum prevails in storage container  121 , the approximately semispherical pressure indicator  113  is pushed in counter to the pressure of a spring  103  in the direction of container  121 , virtually in the manner of a concertina. If a limit value is exceeded or if the pressure between the container interior and surroundings is equalized, pressure indicator  113  is pushed out through indicator opening  114  by compression spring  103 , which is designed as a helical spring.  
         [0081]    Compression spring  103  is held in a spring holder  119  on valve housing  104 .  
         [0082]    Finally, in the case of the valve device  101  of FIGS. 7 and 8, a sealing ring  106  is provided in the region of second cutout  125 , said sealing ring sealing the connection of valve housing  104  to measuring opening  112  in container lid  109 .  
         [0083]    After storage container  121  has been filled with food, container lid  109  is placed onto container wall  108 , which is provided with a container seal  107 . Valve device  101  here is closed, i.e. the food is packed in a gas-tight manner. A vacuum pump (not illustrated) is now used to extract the air enclosed in container  121  via evacuation hole  117 , sealing tongue  110 , and vent  111 . So that air is exclusively extracted from container  121 , and not from the surroundings, a sealing edge  122  is formed on membrane  102  and seals the frustoconical elevation around vent  111 . The reaching of the required minimum negative pressure can be read off using pressure indicator  113 . Pressure indicator  113  disappears in indicator opening  114  as soon as the required negative pressure is reached.  
         [0084]    When the equalization of pressure occurs over time, the time at which a critical point is reached is indicated by pressure indicator  113 . Pressure indicator  113  is designed, if appropriate, to be colored, and protrudes through indicator opening  114 . In other words, pressure indicator  113  is pressed beyond indicator opening  114  by the spring force of spring  103 . A spring with an appropriate spring stiffness can be installed in pressure indicator  113  to help indicate pressure equalization.  
         [0085]    In order to open container lid  109 , which is sucked on firmly by the negative pressure of the container, valve device  101  is grasped at handle  116  and pivoted about hinge  118 . This causes sealing tongue  110  to be lifted off from vent  111 , and sealing ring  106  to be lifted off from sealing seat  128 . Thus, storage container  121  is ventilated. After ventilation, container lid  109  can easily be lifted off from container  121 .  
         [0086]    Referring now to FIGS. 9 and 10, a second example of a valve device  101  in the fitted state has essentially three components: valve housing  104 , valve housing cover  105 , and membrane  102 . Such a structure is possible in particular by the changed design of pressure indicator  113 , which is produced from a material having inherent spring stiffness. This renders superfluous the compression spring provided in the first example of the valve device. In addition, the integration of a sealing lip  121  on the lower edge of pressure indicator  113  saves an additional sealing ring for sealing the measuring opening  112 . Otherwise, the construction and the function of the second valve device  101  correspond to that described with reference to FIGS. 7 and 8.  
         [0087]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.