Abstract:
A medical sterilization container has a removable container cover, which is provided in a wall area ( 4 ) with gas-exchange openings ( 5 ), with a filter unit ( 55 ) for gas exchange has an interchangeable filter sheet covering the gas-exchange openings ( 5 ) on the inside, which is arranged within a ring-shaped circumferential frame element ( 15 ) and is held pressably against an inside of the wall area ( 4 ) by a pressure washer ( 36 ) provided with openings ( 45 ). The pressure washer ( 36 ) is detachably connected to frame element ( 15 ) or the wall area ( 4 ) and has a ring groove ( 48 ) with a preferably elastic sealing ring ( 49 ), which seals the wall area ( 4 ) provided with the gas-exchange openings ( 5 ) against the frame element ( 15 ). To prevent a shifting of and/or damage to the filter sheet during a clamping process, the pressure washer ( 36 ) can be pressed against the wall area ( 4 ) by a spring washer ( 35 ). The spring washer ( 35 ) is provided with bayonet connection elements ( 38 ) which can be meshed and unmeshed with bayonet catch elements ( 20 ) of the frame element ( 15 ). The spring washer ( 35 ) is rotatable opposite the pressure washer ( 36 ) about a common central axis of rotation of the pressure washer ( 36 ) and of the spring washer ( 35 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119 of German Utility Model Application DE 20 2010 009 925.0 filed Jul. 6, 2010, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention pertains to a medical sterilization container provided with a removable cover, which is provided in a wall area provided with gas-exchange openings with a filter unit for the gas exchange, which unit has an interchangeable filter sheet covering the gas-exchange openings on the inside, which sheet is arranged within a ring-shaped circumferential frame element and is held pressably against the inside of the wall area by a pressure washer provided with openings, whereby the pressure washer is detachably connected to the frame element or the wall area and has a ring groove with a preferably elastic sealing ring that seals the wall area provided with the gas-exchange openings against the frame element. 
       BACKGROUND OF THE INVENTION 
       [0003]    Sterilization containers of this type are usually used for sterilizing medical instruments. For this, such sterilization containers have a container cover, which is detachably tightly connected to a corresponding lower housing of the sterilization container. In order to guarantee “aeration and ventilation” in closed sterilization containers, such a sterilization container has in one of its wall areas gas-exchange openings, which are covered during operation on the inside by means of a filter sheet. Such a filter sheet usually consists of paper, a nonwoven fabric or textile material. This filter sheet is replaced on a regular basis with increasing duration of operation and/or in case of a change in the instruments to be sterilized. 
         [0004]    For this, the filter sheet is held by a pressure washer which meshes detachably with a frame element arranged on the inside at the wall area, surrounding the gas-exchange openings in a ring-shaped manner. The detachable connection between the pressure washer and frame element is established by a bayonet connection, which is formed from bayonet catch elements or from bayonet connection elements, which can be mutually meshed with one another, at the pressure washer, on the one hand, and, at the frame element, on the other hand. To seal the pressure washer against the wall area of the sterilization container or against the frame element, a preferably elastic sealing ring is provided that is mounted on the wall side in a circumferential ring groove of the pressure washer. In the mounted state, the sealing ring presses against the filter sheet, which is preferably inserted—with a relative accuracy of fit—into the ring-shaped frame element. The pressure washer, filter sheet and frame element thus form a type of filter unit. 
         [0005]    By means of the bayonet connection formed between the frame element and the pressure washer, the pressure washer may only be released from the frame element by means of a rotating relative motion and can again be meshed with same in a positive-locking manner rotating in the opposite direction. Since the sealing ring of the pressure washer presses tightly against the filter sheet and the pressure washer is accordingly to be braced under axial prestress against the filter sheet especially during insertion, this routinely leads to a shifting of filter sheet and/or to its damage. 
       SUMMARY OF THE INVENTION 
       [0006]    Consequently, a basic object of the present invention is to improve the filter unit of a sterilization container of the type mentioned in the introduction in such a way that the filter sheet is not shifted and/or damage during insertion. 
         [0007]    This object is accomplished according to the present invention in that the pressure washer can be pressed by a spring washer against the wall area, and that the spring washer is provided with bayonet connection elements, which can be meshed and unmeshed with bayonet catch elements of the frame element, and that the spring washer can be rotated opposite the pressure washer about a common central axis of rotation of the pressure washer and of the spring washer. 
         [0008]    By means of this embodiment of the filter unit according to the present invention, it is guaranteed with certainty that the filter sheet cannot be shifted or damaged during insertion, since the pressure washer pressing the filter sheet against the wall area does not have to be rotated itself for fixing the pressure washer. Both the spring washer and the pressure washer have at least one smooth surface on their sides facing one another, such that the spring washer can be easily rotated in relation to the pressure washer for establishing the bayonet connection. Thus, the spring washer can, however, be pressed with relatively great prestress against the pressure washer and rotated, without the pressure washer also being moved with it. Thus, the advantage is also further achieved that a higher pressing pressure is exerted onto the pressure washer directly or by means of a sealing ring lying on the filter sheet, as a result of which the sealing action of the sealing ring is improved. Such higher pressing forces are not possible in the previously known filter units, since there the pressure washer has to be rotated to establish the bayonet connection and would lead to destruction of the filter sheet due to the direct frictionally engaged contact of its sealing ring with the filter sheet. 
         [0009]    According to a further aspect of the invention, provisions can be made that the spring washer is to be provided with openings, which are essentially designed and arranged according to the same surface pattern as the openings of the pressure washer. Provisions are made here that the openings of the pressure washer and the spring washer lie congruently one above the other after establishing the bayonet connection between the spring washer and the frame element. Consequently, a gas exchange that is as large as possible in terms of area is achieved. 
         [0010]    According to a further aspect of the invention, provisions can be made that the bayonet connection elements of the spring washer are formed from cam- or tongue-like projections protruding radially outwardly on their circular circumference, which mesh with radial mounting slots or grooves arranged on the inside of the frame element, which are each connected to the insertion expansions of the frame element in a direction of rotation. Due to this arrangement and embodiment of the bayonet connection elements, the spring washer can be simply and securely fastened to the frame element of the wall area and be removed again as well, if necessary. Another advantage is that the bayonet connection elements of the spring washer can be produced in a simple and easy manner. Thus, the entire spring washer can be produced in a uniform punching process, in which both the outer contour and the openings can be produced at the same time. 
         [0011]    Furthermore, provisions can be made that the insertion expansions extend over the entire height or thickness of the frame element, and in that the pressure washer is provided on its circumference with radially outwardly protruding, cam- or tongue-like projections, each of which is mounted in such an insertion expansion and secure the pressure washer against rotation. By means of this embodiment, it is especially achieved that the pressure washer in the frame element cannot rotate during the rotation of the spring washer, such that an impairment of the filter sheet “clamped” by the pressure washer is ruled out with certainty. 
         [0012]    Further, a further aspect of the invention, provisions may be made that the frame element has a circumferential ring land protruding axially towards the wall area, which ring land meshes with a ring groove of the wall area and is detachably connected to the ring groove via a bayonet connection. By means of this embodiment of the present invention, the frame element can be fastened to the wall area easily and with certainty and can also be removed, if necessary, for example, for cleaning purposes. 
         [0013]    According to a further aspect of the invention, provisions may further be made that the pressure washer and spring washer are essentially the same size, consist of metal or plastic and lie on top of one another within the frame element essentially in a congruent position of their openings. By means of this embodiment, it is especially possible to insert the pressure washer and spring washer together into the frame element after inserting the filter sheet. 
         [0014]    According to a further aspect of the invention, provisions may be made that the spring washer lies axially elastically on the pressure washer in the mounted state and is concentrically rotatably centered on the spring washer by means of a central axial connection. Also by means of this embodiment, the spring washer and the pressure washer can be inserted together into the frame element and can be connected to same in line with the function thereof. By means of the central axial connection, a centering between the pressure washer and the spring washer is achieved, such that these cannot be shifted radially against one another during insertion in or removal from the frame element. Due to the axial, elastic “lying” of the spring washer on the pressure washer, a continuously active spring pressure with a reliable seal is guaranteed, on the one hand, a manual pressing pressure that is too strong is prevented, on the other hand. Thus, too high, harmful pressure forces cannot be exerted onto the pressure washer and thus onto the filter sheet during the insertion of the spring washer. 
         [0015]    Furthermore, provisions may be made according to a further aspect of the invention that the spring washer is provided on its top side with at least one fixed gripping part. By means of this embodiment according to the present invention, the spring washer can be handled in an extremely simple manner. The gripping part here can be arranged centrally on the spring washer. If the common axial connection is also provided, then the spring washer and the pressure washer can be handled via this gripping part together for replacing the filter sheet in an extremely simple manner. 
         [0016]    To be able to apply the necessary force or the necessary torque to the frame element when inserting the frame element into the ring groove of the wall area, the ring-shaped frame element is provided on the top side with at least two essentially diametrically opposed positive-locking elements. With these positive-locking elements, a manually actuatable hand lever can be nonrotatably and detachably meshed in a positive-locking manner. The user is thus enabled in a simple manner to produce a fixed, stable bayonet connection between the frame element and the wall area and to cancel this connection again if this should be necessary, for example, for cleaning purposes. 
         [0017]    The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    In the drawings: 
           [0019]      FIG. 1  is a bottom perspective of a container cover according to the invention; 
           [0020]      FIG. 2  is an enlarged detail II of the ring groove of the container cover from  FIG. 1 ; 
           [0021]      FIG. 3  is a perspective view of a frame element that can be meshed with the ring groove of the container cover from  FIG. 1 ; 
           [0022]      FIG. 4  is a second perspective view showing the frame element from  FIG. 3 , in which the ring land that can be meshed with the ring groove of the container cover can be seen; 
           [0023]      FIG. 5  is an enlarged detail V of the frame element from  FIG. 4 ; 
           [0024]      FIG. 6  is a perspective view of a spring washer; 
           [0025]      FIG. 7  is a perspective view of a pressure washer; 
           [0026]      FIG. 8  is an enlarged, perspective detail of the pressure washer from  FIG. 7 ; 
           [0027]      FIG. 9  is a perspective view of a fixed gripping part that can be connected to the spring washer; 
           [0028]      FIG. 10  is a partial view of the container cover with fully mounted filter unit; 
           [0029]      FIG. 11  is a partial section XI-XI of the container cover from  FIG. 10  with fully mounted filter unit; 
           [0030]      FIG. 12  is an enlarged detail XII of the container cover from  FIG. 11  in the area of the connection of the frame element to the container cover; 
           [0031]      FIG. 13  is an enlarged detail XIII of the container cover from  FIG. 11  in the area of the connection of the gripping part to the spring washer; and 
           [0032]      FIG. 14  is a perspective view of a hand lever that can be coupled with the frame element in a nonrotatable manner. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    Referring to the drawings in particular,  FIG. 1  shows, in an exemplary manner, an embodiment variant of a container cover  1 , which has a rectangular, rounded basic shape. Such a container cover  1  can be placed during operation tightly onto a corresponding container bottom part, which, however, is not shown in the drawing. This container cover  1  forms, with this container bottom part, a medical sterilization container, which is used, for example, to sterilize medical instruments. 
         [0034]    As is evident from  FIG. 1 , the container cover  1  has a circumferential edge flange  2  that encloses a preferably flat wall element  3  of the container cover  1 . Furthermore, a seal is usually provided in the mounted state of the container cover  1  on a container bottom part, such that the container cover  1  can be mounted tightly on the bottom part. Furthermore, it is evident from  FIG. 1  that the wall element  3  has a central wall area  4 , which in the present exemplary embodiment is provided with a plurality of gas-exchange openings  5 . During operation, a gas exchange with the environment takes place through these gas-exchange openings, for example, during the heating or cooling of the entire sterilization container. In this wall area  4 , a ring groove  6  with a ring-shaped design is provided on the inside. This ring groove  6  is provided with recesses  8  directed radially inwards in the area of its circumferential inner edge  7 . As is especially evident from  FIG. 2 , a locking slot  10 , which is covered accordingly by a fixing flange  11 , opens into each of these recesses  8 .  FIG. 2  shows an enlarged view of the area II from  FIG. 1  in this regard. 
         [0035]    A frame element  15  which is shown in an exemplary manner in  FIGS. 3 through 5  can be inserted into the ring groove  6  of the wall element  3  or of the wall area  4 . For this,  FIG. 3  shows a type of top view, while  FIG. 4  shows a bottom view of this frame element  15 . 
         [0036]    It can be seen from  FIG. 3  that the frame element  15  has a ring-shaped design and on the top side has positive locking elements  16  and  17  arranged next to each other in pairs. These positive-locking elements  16  and  17  lie essentially diametrically opposed and are each designed like an elongated hole in the present exemplary embodiment. These positive-locking elements  16  and  17  can be meshed with a hand lever in a positive-locking and detachable manner in order to be able to adjust the frame element by rotating in a simple manner. 
         [0037]    Furthermore, the frame element  15  forms a radially inwards protruding, completely circumferential holding flange  18 , which is provided on the inside with insertion expansions  19  arranged distributed uniformly on the circumference. In the circumferential holding flange  18 , each of these insertion expansions  19  thus forms a radial expansion running in an arc-shaped manner, whose function will be explained in detail later. 
         [0038]    A mounting groove extending over a partial circumference of the frame element  15  that is defined, on the one hand, on the bottom side by a flange element  21  and, on the other hand, on the top side by another flange element  22 , opens into each of these insertion expansions  19 . These insertion expansions  19 , together with the mounting grooves  20  extending in the circumferential direction, form a part of a bayonet connection for detachably holding a spring washer, as will be explained later. 
         [0039]      FIG. 5  shows especially for this an enlarged detail V from  FIG. 4 , in which one of the insertion expansions  19  together with the associated mounting groove  20  as well as the two flange elements  21  and  22  can be seen in detail. 
         [0040]    It is easily conceivable that, for example, a washer with radially protruding connection elements can be axially inserted into the insertion expansions  19  and subsequently can be rotated in the direction of arrow  23  and can thus be meshed in a fixed manner with the mounting grooves  20  in the manner of a bayonet connection. 
         [0041]    Further, it is evident from  FIG. 4  that the frame element  15 , on the bottom side, forms an axially protruding ring land  25 , with which the frame element  15  can be inserted into the ring groove  6  of the container cover  1  from  FIG. 1 . In the present exemplary embodiment, this ring land  25  forms a plurality of centering elements distributed uniformly on the circumference and lying on a greater diameter, with which the ring land  25  can be inserted concentrically into the ring groove  6  of the container cover  1  of  FIG. 1 . In a corresponding embodiment of the ring groove  6 , these centering elements  26  with the ring groove also form a type of bayonet connection. 
         [0042]    In the present exemplary embodiment, the ring land  25  of the frame element  15  has in the area of its inner edge  27  a plurality of holding flanges  28  arranged uniformly on the circumference, which are used for the fixed and detachable holding of the frame element  15  in the ring groove of the wall element  3 . Accordingly, these holding flanges  28  can each be meshed in a positive-locking manner with one of the locking slots  10  of the ring groove  6  of the container cover  1 . 
         [0043]    For this, it can be seen, in particular, from the enlarged partial view of  FIG. 5  that these holding flanges  28  have such a distance to the bottom side  29  of the inner circumferential holding flange  18  that a clearance  30  is formed between the respective holding flange  28  and this bottom side  29  for receiving the respectively assigned fixing flange  11  of the ring groove  6 . 
         [0044]    It is now easily conceivable that, in a corresponding angle orientation, the frame element  15  can be axially inserted into the recesses  8  of the ring groove  6  with its radially inwards directed holding flanges  28  of its ring land  25 . Here, the holding flanges  28  reach, in the axial direction, the same plane as the locking slots  10  described with regard to  FIG. 2 . By rotating the entire frame element  15  in the direction of arrow  9 , the holding flanges are inserted into the locking slots  10 , so that a type of bayonet connection is formed between the frame element  15  and the ring groove  6  or the container cover  1 . Thus, in case of a corresponding direction of rotation opposite to arrow  9 , the frame element  15  is again detachable from the locking slots  10  and can be removed from the inside of the container cover  1 , for example, for cleaning purposes. 
         [0045]    In the present exemplary embodiment, this frame element  15  is used to lock or hold a filter sheet in a clamped manner, as is still explained in detail later especially with regard to  FIGS. 12 and 13 . 
         [0046]    In order to fix such a filter sheet that completely covers the entire wall area  4  with its gas-exchange openings  5  of the container cover  1  ( FIG. 1 ) interchangeably in this wall area  4 , a spring washer  35  ( FIG. 6 ) as well as a pressure washer  36  ( FIG. 7 ) are provided according to the present invention. 
         [0047]    As is evident from  FIG. 6 , the spring washer  35  is designed as a circular disk, whereby its outer diameter is adapted to the inner diameter of the holding flange  18  of the frame element  15 , so that the spring washer  35  can be inserted into the holding flange  18  with little play. The spring washer  35  has a plurality of large-area openings  37 , which are arranged uniformly on the circumference and distributed over the radius in the spring washer  35 . 
         [0048]    Furthermore, a plurality of cam- or tongue-like projections  38 , whose number and arrangement on the circumference of the spring washer  35  correspond to the number and arrangement of the insertion expansions  19  of the holding flange  18  of the frame element  15 , are provided on the outer circumference of the spring washer  35 . 
         [0049]    Thus, the spring washer  35  with its projections  38  can be inserted into the holding flange  18  of the frame element  15  in a predetermined angular position. In the present exemplary embodiment, a type of holding plate  39 , which is used for the fixed fastening of a gripping part  40  ( FIG. 9 ), is provided in the center of the spring washer  35 . Accordingly, in the present exemplary embodiment, this holding plate  39  has three through holes  41 ,  42  and  43 , in whose area the gripping part  40  can be placed on the holding plate  39 . 
         [0050]    The pressure washer  36  is designed in a similar construction as the spring washer  35 . The pressure washer  36  also has a plurality of openings  45 , which are arranged distributed uniformly in the pressure washer  36  both in the circumferential direction and in the radial direction. The pressure washer  36  likewise has a circular design in its basic structure and on its outer circumference has a plurality of cam- or tongue-like projections  46 , which are arranged uniformly distributed and are protruding radially outwards. Also, these projections  46  are arranged on the outer circumference of the pressure washer  36  in their number and arrangement likewise corresponding to the arrangement and number of the insertion expansions  19  of the holding flange  18  of the frame element  15 . Thus, the pressure washer  36  can also be inserted fittingly into the holding flange  18  of the frame element  15 , whereby the projections  46  mesh with the insertion expansions  19  in a fitting manner or with little play. 
         [0051]    For this, it should be noted here that the flange elements  21  defining the respective mounting groove  20  downwards in their thickness correspond approximately to the thickness of the pressure washer  36 . I.e., in the state of the pressure washer  36  fully inserted into the frame element  15  fixed to the wall element  3 , this pressure washer  36  is held nonrotatably by its projections  46  by means of the flange elements  21  defining the insertion expansions  19 . 
         [0052]    Further, it is evident from  FIG. 7  that the pressure washer  36  has a central through hole  47 , which, in the mounted state, runs coaxially to the central through hole  42  of the spring washer  35 . 
         [0053]    Further, the enlarged detail VIII of the pressure washer  36  from  FIG. 7  in drawing  FIG. 8  shows that on the bottom side the pressure washer  36  is provided with a ring groove  48 , in which a sealing ring  49  is mounted circumferentially. With this sealing ring  49 , the pressure washer can be placed tightly onto a filter sheet placed in the wall area  4 . 
         [0054]    The spring washer  35  from  FIG. 6  preferably has a slight arch in the center, directed towards the pressure washer  36 , so that in the mounted state this presses in a spring-elastic manner against the pressure washer  36  under slight prestress. 
         [0055]      FIG. 10  shows a partial top view of the wall element  3  with a fully mounted filter unit  55 . It can be seen that the frame element  15  is placed on the wall element  3  and completely surrounds the wall area  4  in a ring-shaped manner. The radial outer centering elements  26  are mounted with extremely little play in the circumferential ring groove  6  of the wall element  3 . Furthermore, as a suggestion, it can be seen from  FIG. 10  that the radially inward protruding holding flanges  28  mesh with the respectively assigned locking slots  10  of the ring groove  6 . 
         [0056]    Furthermore, it can be seen that the spring washer as well as the pressure washer  36  are located in the frame element  15 . In this mounted position shown in  FIG. 10 , the openings  37  and  45  of the spring washer  35  and of the pressure washer  36  are arranged congruently. It can be seen that the projections  38  of the spring washer  35  in this mounted state are arranged in the circumferential direction offset to the projections  45  of the pressure washer  36  meshing with insertion expansions  19  and mesh in a positive-locking manner with the respective mounting groove  20 . The radial projections  46  of the pressure washer  36  are thus mounted in a fitting manner in the associated insertion expansions  19  of the frame element  15 , so that the pressure washer  36  is arranged in the frame element in a nonrotatable manner. 
         [0057]    The spring washer  35  was rotated for locking in the direction of arrow  23 , so that its radial projections  38  mesh in an axially fixed manner with the respectively assigned mounting groove  20  of the insertion expansions  19 . 
         [0058]    Furthermore, it can be seen from  FIG. 10  that the openings  37  and  45  are arranged in the area of the gas-exchange openings  5  of the wall area  4  and these gas-exchange openings  5  are at least approximately fully released. 
         [0059]      FIG. 10  does not show the filter sheet located between the pressure washer  36  and the wall area  4 , so that the gas-exchange openings  5  can correspondingly be seen. 
         [0060]    Furthermore, it is evident from  FIG. 10  that the gripping part  40  on the top side is mounted on the spring washer  35 , so that the spring washer  35  can be rotated via this gripping part  40  in a simple manner for “locking” and “unlocking.” 
         [0061]    For this,  FIG. 11  shows a sectional view XI-XI from  FIG. 10 . It can be seen that the gripping part  40  is mounted in a fixed manner on the top side on the spring washer  35 . The pressure washer  36  is arranged between the spring washer  35  and the wall element  3  or its wall area  4 . On the top side, the sealing ring  49  lies tightly on the filter sheet  50 , which can be seen as a suggestion. Here the filter sheet  50  completely covers the gas-exchange openings  5 . 
         [0062]    Furthermore, the frame element  15 , with its lower ring land  25 , meshes with the ring groove  6  of the wall element  3 . For this,  FIG. 12  shows an enlarged detail XII from  FIG. 11 . It can be seen that the frame element  15  is mounted in a fitting manner in the ring groove  6  with its radially outwardly protruding centering elements  26  of the ring land  25 . The radially inwardly protruding holding flange  28  of the circumferential ring land  25  meshes with the respectively assigned locking slot  10  in a fixed manner. 
         [0063]    Furthermore, it can be seen from  FIG. 12  that the filter sheet  50  is mounted between the pressure washer  36  and the wall element  3  or wall area  4 . Here the sealing ring  49  presses axially against the filter sheet  50 , so that this lies tightly on the wall element  3 . Accordingly, the radial projection  38  of the spring washer  35  meshes with the assigned mounting groove  20  of the frame element  15 , so that the pressure washer  36  with its sealing ring  49  is pressed against the filter sheet  50 . Thus, due to the spring-elastic design of the spring washer  35  and also of the sealing ring  49 , a sealing of the wall area  4  with the placed filter sheet  50  is especially produced against the frame element  15 . 
         [0064]    Furthermore,  FIG. 13  shows in an exemplary manner an enlarged view XIII from  FIG. 11 , from which can be seen especially the manner in which the gripping part  40  is fastened to the top side of the spring washer  35 . The gripping part  40  is fastened to the spring washer  35  by means of two mounting screws  60  and  61 . Accordingly, these two mounting screws  60  and  61  project through the through holes  41  and  42  already mentioned in regard to  FIG. 6 . Furthermore, a centering pin  62 , which represents a common axial connection for the spring washer  35  and the pressure washer  36  and accordingly projects in the central through holes  42  and  47  thereof, is screwed into the gripping part  40 . This centering pin  62  is designed in its length in such a way that it furthermore meshes with a central hole  64  of the wall area  4  and accordingly also projects through the filter sheet  50 . Thus, by means of this centering pin  62 , the filter sheet  50 , pressure washer  36  and spring washer  35  are held rotatably concentric to the ring groove  6  and thus to the frame element  15  meshing with this ring groove  6 . The filter sheet  50  here covers the gas-exchange openings  5  in the wall area  4  of the wall element  3  and is held on the surface of the wall area  4  by the pressure washer  36 , which can likewise be seen in  FIG. 3 . 
         [0065]      FIG. 14  shows in an exemplary manner an embodiment variant of a hand lever  65  that is provided for establishing and canceling the bayonet connection between the frame element  15  and the wall element  3 . For this, the hand lever  65  has, on the bottom side, two contact pins  66  and  67  arranged in pairs, which can be meshed in a positive-locking manner with the positive-locking elements  16  and  17  ( FIG. 3 ) arranged on the top side in the frame element  15 . Furthermore, it can be seen from  FIG. 14  that the hand lever  65  has on the inside at least one gripping element  68 , by means of which the correspondingly necessary torque can be applied for establishing the bayonet connection or for canceling the bayonet connection. 
         [0066]    While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.