Abstract:
A filter holder, for a sterilization container ( 1 ), has a wall area ( 5 ) with ventilation openings ( 7 ), through which an exchange of air takes place between the interior space of the sterilization container and the surrounding area, covered by a filter sheet ( 10 ) to form a sterile barrier, sterilizing air entering the interior space. The filter sheet is held on the wall area ( 5, 6 ) by an air-permeable pressing disk. A holding pin ( 20 ), with a mounting hole ( 34 ), by which the pressing disk ( 12 ) can be pressed against the wall area in the axial direction ( 41 ), can be attached to a mounting pin ( 11 ), which is stationary relative to the wall area. The holding pin ( 20 ) is connected with the mounting pin in a pressed position via a detachable positive-locking connection ( 19, 51 ). The connection can be secured by an adjusting sleeve ( 21 ) mounted displaceably on the holding pin.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. §119 of German Utility Model Application DE 20 2013 007 581.3 filed Aug. 23, 2013, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a filter holder for a sterilization container, which container is provided in a wall area or in a plurality of wall areas with ventilation openings, through which an exchange of air takes place in the closed state between the interior space of the sterilization container and the surrounding area, wherein the ventilation openings are covered by means of a filter sheet to form a sterile barrier, which brings about sterilization of the air entering the sterilization space through the ventilation openings, wherein the filter sheet is held on the wall area by an air-permeable pressing disk. 
     BACKGROUND OF THE INVENTION 
     Sterile containers, also called sterilization containers, comprise, as a rule, a box-shaped, lower container part and a container cover that can be placed tightly thereon. Such sterilization containers are known to be used to sterilize medical devices. The complete sterilization container is heated, as a rule, during the sterilization process, so that a diverse overpressure develops within the container. To make it possible to reduce this overpressure, such sterilization containers are provided in a wall area or in a plurality of wall areas with ventilation openings, through which the exchange of air with the surrounding area takes place. 
     To bring about sterilization of the entering ambient air especially during the cooling phase, during which ambient air enters the sterilization container for pressure equalization, such sterilization containers are usually equipped with a so-called sterile barrier. An air-permeable filter sheet, which fully covers the ventilation openings, is used as a sterile barrier in some embodiment variants. Various constructions, in which an air-permeable pressing disk is used to hold the filter sheet, are known in the state of the art for fixing such a filter sheet in the wall area of the ventilation openings tightly and sealingly. 
     Reference should be made in this connection, for example, to DE 20 2010 009 925 U1. A frame element, which has a ring-shaped design and is arranged stationarily in the area surrounding the ventilation openings within the corresponding wall area, is used in this constructions. The pressing disk has various perforations in this construction, so that the pressing disk itself is likewise permeable to air. A flat spring, which is provided with bayonet connection elements, is provided in this construction to hold the pressing disk or for pressing against the filter sheet placed on the inner wall in the area of the ventilation openings. The flat spring can be meshed and unmeshed with correspondingly associated bayonet connection elements of the frame element by means of these bayonet connection elements. Furthermore, the flat spring can be rotated about a common central axis of rotation in relation to the pressing disk, and the pressing disk is held in the frame element nonrotatably during the rotary adjustment of the flat spring. 
     Thus, a plurality of components are used in this construction to press the filter sheet stationarily against the inner wall of the wall area with the ventilation openings. 
     Furthermore, another construction, in which the pressing disk presses the filter sheet on the top side by means of special locking connections via a ball catch connection, is known from DE 20 2011 001 772 U1. The pressing disk is designed as a round disk in this construction and has a circular locking groove on the outside, with which the pressing disk can be brought lockingly in connection with locking elements. 
     These locking elements are arranged for this in the circumferential area of the ventilation openings and thus of the mounted pressing disk in a uniformly distributed pattern. Each locking element is designed as a separate component and arranged stationarily in mounting holes of ring segments projecting axially over the wall area extending at right angles to the wall area. 
     The locking elements are formed from an approximately cylindrical housing block, which is provided with a radial hole extending at right angles. A locking ball, which meshes (engages) radially inwardly with the locking groove of the pressing disk in the mounted state, is received in the radial hole adjustably in a spring-loaded manner. The housing block of the locking element is fixed stationarily in the respective mounting hole, for example, by means of a spring-type straight pin. 
     It is advantageous according to the devices of DE 20 2010 009 925 U1 and DE 20 2011 001 772 U1 that the pressing disk can be pressed onto the filter sheet without the pressing disk having to be rotated for fixation relative to the filter sheet, as this is known from the state of the art for previous constructions. 
     However, as it was already mentioned above, these constructions for holding the pressing disk have very complicated designs. The handling of the bayonet connections is also relatively unfavorable in DE 20 2010 009 925 U1, because the flat spring must first be aligned concentrically with the frame element and in the circumferential direction with its bayonet connection elements with the bayonet connection elements of the frame element for establishing these connections manually in order to be subsequently able to be rotated relative to the frame element. 
     It is additionally necessary in the subject of DE 20 2011 001 772 U1 to provide the pressing disk with a radially extending grip part, which must be located at a spaced location from the wall area of the sterilization container in order to make it possible to reach behind it. It shall be achieved by means of this grip part that the fingers can reach behind the pressing disk, so that the locking connections between the pressing disk and the locking balls can be released in a simple manner. The locking connections can be released by themselves in unfavorable cases in case of an impact on the container cover. 
     SUMMARY OF THE INVENTION 
     The basic object of the present invention is accordingly to design, based on the above-mentioned state of the art, a filter holder for a filter sheet (filter element) such that said filter holder can be handled in an extremely simple manner and it cannot, with certainty, be released by itself. 
     The object is accomplished according to the present invention with a filter holder for a sterilization container, which container is provided in a wall area or in a plurality of wall areas with ventilation openings, through which an exchange of air takes place in the closed state between the interior space of the sterilization container and the surrounding area, wherein the ventilation openings are covered by means of a filter sheet to form a sterile barrier, which brings about sterilization of the air entering the sterilization space through the ventilation openings, wherein the filter sheet is held on the wall area by an air-permeable pressing disk. A mounting pin, which projects over the wall area and is stationarily in connection with the wall area, is provided in the wall area of the ventilation openings. A holding pin is provided with a mounting hole, by which the pressing disk can be pressed against the wall area in the axial direction. The holding pin is able to be attached to the mounting pin, by the holding pin being in connection in its pressed state with the mounting pin via a detachable positive-locking connection. The positive-locking connection is able to be secured by means of an adjusting sleeve mounted displaceably on the holding pin. 
     Provisions may be made, according to further features of the invention, for the positive-locking connection between the mounting pin and the holding pin to comprise a circular locking groove of the mounting pin and a plurality of holding balls arranged in a radial through hole of the holding pin. The holding balls in the through holes are designed such that they can be radially adjusted from a neutral position, in which they are not in connection with the locking groove of the mounting pin, into a blocked position in which they mesh with the locking groove. 
     Further, provisions may be made according to further features of the invention for the adjusting sleeve to have a through hole for being pushed on the holding pin. The through hole has, in through hole end areas pointing towards the mounting pin, a circular, radial expansion, which is located in an upper, neutral axial position of the adjusting sleeve on the holding pin in the area of the holding balls and whose diameter is selected to be such that the holding balls can be moved radially into their neutral position, for the through hole with its holding balls, which has a smaller diameter, to be able to be brought into functional connection during an axial adjustment of the adjusting sleeve on the holding pin into its securing position such that the holding balls can be brought through the through hole into their blocked position, in which they protrude into the mounting hole of the holding pin and mesh with the locking groove of the mounting pin. 
     To adjust the adjusting sleeve on the holding pin in a defined manner, provisions may be made according to further features of the invention for the holding pin to have in its outer jacket surface an L-shaped groove, which forms a vertical section extending in parallel to the central longitudinal axis of the holding pin and a horizontal section extending at right angles thereto, for providing in the side wall of the adjusting sleeve a through hole, into which a fixing pin can be stationarily inserted, and for the fixing pin to pass through the side wall radially to the inside in the mounted state and to mesh with the L-shaped groove, for the adjusting pin to be able to be brought from its neutral upper axial position into its lower securing position axially along the vertical section and to be subsequently able to be caused to mesh with the horizontal section by a relative rotation in relation to the holding pin with its fixing pin into an axially nondisplaceable locking position. The adjusting sleeve and the holding pin are, furthermore, captively in connection with one another due to this design, so that when the adjusting sleeve is “raised,” the holding pin is also “raised” at the same time via the fixing pin, which is in connection with the L-shaped groove thereof. Operation is considerably simplified hereby. 
     Further, provisions may be made according to further features of the invention for the holding pin to have in its upper end area a continuous through hole extending at right angles, in the radially outer end areas of which locking balls are provided, which are pressed radially outwardly by means of an axial compression spring, and for the through hole of the adjusting sleeve to have a circular fixing groove in its axially upper end area, and for the axial arrangement of the through hole in the holding pin and the axial arrangement of the fixing groove in the through hole of the adjusting sleeve to be selected to be such that the locking balls lockingly mesh with the fixing groove in the upper, neutral axial position of the adjusting sleeve. The upper, neutral axial position of the adjusting sleeve relative to the holding pin is secured due to this embodiment, so that an unintended adjustment of the adjusting sleeve in the axial direction is prevented from occurring. 
     The locked position of the adjusting sleeve on the holding pin is secured by the embodiment according to further features of the invention. Provisions are accordingly made for the through hole of the adjusting sleeve to have two mutually diametrically opposed milled recesses axially above their fixing groove and for the circumferential positions and the axial position of the milled recesses of the adjusting sleeve relative to the locking balls of the holding pin are selected to be such that the locking balls lockingly mesh with the milled recesses after the axial adjustment and rotation of the adjusting sleeve into the locked position thereof. 
     It is achieved through the embodiment according to further features of the invention that when the adjusting sleeve is raised together with the holding pin, the pressing disk is also raised at the same time. Furthermore, when the holding pin is placed on the mounting pin, the pressing disk is inevitably placed in its correct position on the filter sheet or in the area of the ventilation openings, so that the pressing disk does not need to be separately aligned in advance. Provisions are thus made for the pressing disk to be stationarily in connection with the holding pin. 
     It is achieved due to the embodiment according to further features of the invention that the holding pin may co-rotate during a relative rotation of the adjusting sleeve relative to the holding pin to release or establish the positive-locking connection, which contributes to reliable operability of the device according to the present invention. Accordingly, provisions are made for the mounting pin to have in its end area located towards the wall section a radially expanded profile web with holding surfaces arranged uniformly distributed on the circumference and for the mounting hole of the holding pin to have in its end area located towards the wall section a bearing profile, with which the holding pin meshes nonrotatably in its pressed position with the holding surfaces of the profile web. 
     Due to the embodiment of the filter holder according to the present invention, comprising the pressing disk, the mounting pin, the holding pin with its adjusting sleeve and the corresponding positive-locking connection, extremely simple handling is achieved during the replacement of a filter sheet. Thus, the complete filter holder can be detached by a simple rotary and axial motion and fixed again correspondingly in the opposite direction. 
     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 
         FIG. 1  is an embodiment variant of a sterilization container, comprising a lower container part as well as a container cover; 
         FIG. 2  is a perspective bottom view of the container cover of the sterilization container from  FIG. 1 ; 
         FIG. 3  is a perspective partial view of a wall area of the container cover from  FIG. 2  in a bottom view in the area of ventilation openings with a mounting pin as well as with a lock nut, which can be arranged stationarily centrally in the area of the ventilation openings; 
         FIG. 4  is an exploded perspective view of a pressing disk shown in a partial section together with a holding pin as well as with an adjusting sleeve: 
         FIG. 5  is the holding pin from  FIG. 4  in a perspective bottom view; 
         FIG. 6  is a sectional view VI-VI of the adjusting sleeve from  FIG. 4 ; 
         FIG. 7  is a perspective sectional view in the central area of the pressing disk with the holding pin mounted and with the adjusting sleeve from  FIG. 4  attached; 
         FIG. 8  is a perspective sectional view of the wall section with the ventilation openings of the container cover with the mounting pin mounted as well as with the pressing disk attached on this together with the holding pin that is stationarily in connection with the pressing disk and with the adjusting sleeve attached; 
         FIG. 9  is the view from  FIG. 8  with the adjusting sleeve in its active securing position; and 
         FIG. 10  is a sectional view of the wall section of the container cover from  FIGS. 1 and 2  in the area of the ventilation openings thereof with the pressing disk locked. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings in particular,  FIG. 1  shows as an example a sterilization container  1 , which has a box-shaped design in this exemplary embodiment and has a lower container part  2 . A container cover  3  is placed tightly on this lower container part  2 , and said container cover is held in this attached position by means of two container closures  4 , but only the “front” container closure  4  is visible in  FIG. 1 . 
     Further, it can be seen in  FIG. 1  that the container cover  3  has two wall areas  5  and  6  in the present exemplary embodiment, which are provided with a plurality of ventilation openings  7  each. The ventilation openings  7  of the wall area  6  are shown in the bottom view in  FIG. 2 . 
     The two wall areas  5  and  6  with their ventilation openings  7  differ in that the ventilation openings in the second wall area  6  are covered by a cover plate  8 . This cover plate  8  is located at a vertically spaced location from the wall area  6 , so that ambient air can flow through the ventilation openings  7  visible from  FIG. 2 . 
     Furthermore, it is seen in  FIG. 1  that a flat lock nut  9 , whose significance will be explained in more detail below, is provided centrally within the ventilation openings  7  of the wall area  5 . 
     The ventilation openings  7  are used for “pressure equalization” within the closed sterilization container  1  during operation. Thus, such a sterilization container  1  is used, as was mentioned already in the introduction to the specification, for example, to sterilize surgical instruments. The surgical instruments are placed for this purpose into the sterilization container  1 , the container cover  3  is placed on the container part  2  and closed tightly. The sterilization container  1  is heated, as a rule, during the sterilization process, so that an overpressure develops within this sterilization container  1 . The air now flows through the ventilation openings  7  from the inside to the outside for pressure equalization. 
     The sterilization container  1  is cooled again after the sterilization operation, so that ambient air flows through the ventilation openings  7  into the sterilization container  1  in the opposite direction. To prevent contamination within the container or of the sterilized medical instruments for hygienic reasons, a so-called sterile barrier is provided, which is in the form of a filter sheet  10  in the embodiment variant shown and is shown as a separate component in  FIG. 2 . 
     As can be seen further from the bottom view of the container cover  3  in  FIG. 2 , a mounting pin  11 , which is screwed into a corresponding threaded hole of the wall area  6  of the container cover  3 , which said threaded hole is not visible in  FIG. 2 , is provided centrally in the wall area  6  or in the area of the ventilation openings  7 . The cover plate  8 , which is screwed onto a threaded section, which protrudes on the top side above the wall section  6  of the container cover  3 , is used in the area of the container cover  3  to secure this mounting pin  11 . 
     After the mounting pin  11  has been positioned, the filter sheet  10  can be placed on same in the area of the ventilation openings  7 . As is shown for the wall area  5  in  FIG. 2 , a pressing disk  12 , which is braced on the top side against the filter sheet  10  via a special holding device  13  in the exemplary embodiment shown, is subsequently placed on the filter sheet  10 . The holding device  13  thus forms a filter holder together with the pressing disk  12  for stationarily holding the filter sheet  10  in the area of the ventilation openings  7 . 
       FIG. 3  shows for this a partial sectional view of the wall area  5  with the ventilation openings  7 . It can be recognized that an internal screw thread, into which a threaded pin  15  of the mounting pin  11  can be screwed, is provided centrally in the area of the ventilation openings  7 . The axial length of this threaded pin  15  is selected here to be such that this threaded pin passes through the wall area  5  in the mounted state. The lock nut  9  can be correspondingly screwed onto this threaded pin  15 , so that the mounting pin  11  is arranged stationarily in the wall area  5 . To make it possible to screw the lock nut  9  onto the threaded pin  15  in a tightly seated manner, said lock nut has, on the whole, three flat wrench contact surfaces  16  arranged uniformly distributed on the circumference in the exemplary embodiment being shown. 
     Further, it can be recognized from  FIG. 3  that the mounting pin  11  has, in its end area located towards the threaded pin  15 , a radially expanded profile web  17 , which forms a plurality of flat holding surfaces  18  distributed uniformly on the circumference. In the opposite end area of this profile web  17 , the mounting pin  11  has a circular locking groove  19 , which has an approximately partly cylindrical cross-sectional shape. 
     As was already mentioned in connection with  FIG. 2 , the holding device  13  can be detachably placed on this mounting pin  11  in the mounted state. 
       FIG. 4  shows for this a partial perspective view of the pressing disk  12  from  FIG. 2  together with a holding pin  20  and with an adjusting sleeve  21 . This holding pin  20  and the adjusting sleeve  21  together form the holding device  13  mentioned in connection with  FIG. 2  for the pressing disk  12 . The pressing disk  12  has a plurality of perforations  22 , so that an air flow can flow correspondingly through these. The pressing disk  12  is provided centrally with an internal screw thread  23 , which is limited on the top side by means of a radially inwardly protruding stop web  24 . 
     Corresponding to the diameter of this stop web  24 , the holding pin  20  has a vertically upwardly projecting cylindrical bearing section  25 . 
     In the lower end area of this bearing section  25 , the holding pin  20  forms a radially projecting, circular mounting web  26 , which is provided with a corresponding external screw thread  27  (not shown explicitly in the drawing). For mounting in the pressing disk  12 , the holding pin  20  can be passed with its cylindrical bearing section  25  through the stop web  24  and can be caused to stationarily mesh by its external screw thread  27  with the internal screw thread  23  of the pressing disk  12 . 
     Further, it can be seen in  FIG. 4  that the cylindrical bearing section  25  of the holding pin  20  has, in its jacket surface in the front left area, an L-shaped groove  28 , which has a vertical section  29  towards the upper end area, which said vertical section extends in parallel to the central longitudinal axis  30  of the bearing section  25  or of the holding pin  20 . The L-shaped groove  28  forms a horizontal section  31  extending at right angles in the lower end area of this vertical section  29 . 
     Further, it can be recognized from  FIG. 4  and also from the bottom view of the mounting pin  20  in  FIG. 5  that a through hole  32  is provided in the free end area of the bearing section  25 . This through hole  32  is used to receive two locking balls, between which an axial compression spring is provided, as this will be explained in more detail below. 
     In the area located towards the mounting web  26 , the bearing section  25  has a total of three mounting holes  33  ( FIG. 5 ), which are used to receive a fixing element in the form of a locking ball, as this will be explained in more detail below. 
     Further, it can be recognized from  FIG. 5  that the holding pin  20  has a central mounting hole  34 , with which this holding pin  20  can be placed fittingly onto the mounting pin  11  from  FIG. 3 . Further, this mounting hole  34  in the axial end area of the mounting web  26  is provided with a bearing profile  35 , with which the holding pin  20  can be placed fittingly onto the holding surfaces  18  of the profile web  17  of the mounting pin  11 . The holding pin  20  can thus be arranged on the mounting pin  11  secured against rotation in the mounted state. 
     Further, it can also be seen in  FIG. 5  that two grooves  36 , which are used to firmly tighten the holding pin  20  in the internal screw thread  23  of the pressing disk  12 , are arranged in the area of the mounting web  26  on the underside in the front surface of said mounting web. 
     Further, it can be seen in  FIG. 4  that the adjusting sleeve  21  forms a central through hole  40 , which has an inner fixing groove  42  at an axially spaced location from its upper front surface in the direction of arrow  41 . 
     In the upper end area, the adjusting sleeve  21  has a radially expanded, profiled actuating web  43 , which is used for the simplified operation of the adjusting sleeve  21 . In the area between the inner fixing groove  42  and the upper front surface or in the area of this actuating web  43 , the through hole  40  is provided with a milled recess  44 , diametrically opposed to which a second milled recess  44 , which is not recognizable in  FIG. 4 , may be arranged. 
     This milled recess or these milled recesses  44  is/are used during operation to fix a preset, relative angular position of the adjusting sleeve  21  relative to the holding pin  20 . The milled recesses  44  will be overlapped with the through hole  32  in this position, so that the locking balls arranged in the through hole  32  under spring loading will come to mesh with these milled recesses  44 . 
     Further, it can be recognized from  FIG. 4  that the adjusting sleeve  21  has a through hole  46  in its cylindrical side wall  45 . 
     As can be recognized from the sectional view of the adjusting sleeve  21  in  FIG. 6 , a fixing pin  47 , which is seated stationarily in the through hole  46  in the mounted state and, as this is shown by broken lines in  FIG. 6 , protrudes into the through hole  46 , can be caused to mesh with this through hole  46 . This fixing pin  47  is inserted after attaching the adjusting sleeve  21  to the holding pin  20  and meshes in the mounted state with the L-shaped groove  28  or with the vertical section  29  or horizontal section  31  thereof as desired. It is thus achieved that the adjusting sleeve  31  is adjustable, on the one hand, limited to the holding pin  20  in the axial direction of the double arrow  48  and is likewise rotatable to a limited extent in the direction of the double arrow  49 . The fixing pin  47  can be pressed, soldered or bonded into the through hole  46 . A “clamping” threaded connection is also conceivable, so that the fixing pin  47  cannot become detached by itself in the through hole, which is designed as a threaded hole in this case. 
     Concerning the preassembled state of the pressing disk  12 , of the holding pin  20  and of the adjusting sleeve  21 ,  FIG. 7  shows an enlarged partial view of these components in the central area of the pressing disk  12 . 
     It can be recognized from  FIG. 7  that the adjusting sleeve  21  with its through hole  40  is attached to the cylindrical bearing section  25  of the holding pin  20 . The adjusting sleeve  21  with its actuating web  43  is now located above the upper front surface  37  of the cylindrical bearing section  25 . The above-mentioned two locking balls  50  shown in  FIG. 7  mesh with the circular locking groove  42  of the adjusting sleeve  21  in this “neutral” position of the adjusting sleeve  21  relative to the holding pin  20 . The neutral, axial relative position of the adjusting sleeve  21  relative to the holding pin  20  is thus secured. 
     Further, it can be recognized from  FIG. 7  that the fixing pin  47  is arranged in the through hole  46  in a tightly seated manner and meshes with the vertical section  29  of the L-shaped groove  28  in the upper end area thereof. The adjusting sleeve  21  is thus fixed in this position against rotation against the holding pin  20  based on the functional connection of the fixing pin  47  with the vertical section  29  of the L-shaped groove  28 . 
     Further, one of the three radial through holes  33  of the bearing section  25  from  FIG. 5 , in which a corresponding holding ball  51  is arranged, can also be recognized from  FIG. 7 . Further holding balls  51  are correspondingly inserted into the other two through holes not recognizable in  FIG. 7  as well. 
     In this axial relative position of the adjusting sleeve  21  in relation to the holding pin  20 , this holding ball  51  (or locking balls) is (are) located in an axial area of a radial expansion  52  of the through hole  40  of the adjusting sleeve  21 , which is arranged in the lower end area of the adjusting sleeve  21 , as this can also be recognized especially from the sectional view in  FIG. 6 . The holding ball  51  (or holding balls) can thus be moved radially to the outside until this comes into contact with this radial expansion  52  on the inside and does not protrude into the mounting hole  34  of the holding pin  20  any longer. 
     Furthermore, it can be recognized from  FIG. 7  that the holding pin  20  with its external screw thread  27  of its mounting web  26  meshes with the internal screw thread  23  of the pressing disk  12  in a stationary manner. 
     The pressing disk  12  with the holding device  13  comprising the holding pin  20  and the adjusting sleeve  21  can be placed in this preassembled state onto the mounting pin  11  according to  FIG. 3 . Furthermore,  FIG. 7  also shows the axial compression spring  60 , by which the two locking balls  50  arranged in the end area of the through hole  32  extending at right angles are pressed radially outwardly under prestress. 
       FIG. 8  shows the view from  FIG. 7  with the pressing disk  12  of the holding device  13  in the state in which it is placed on the mounting pin  11 . The mounting pin  11  is screwed into the wall section  5 , and the lock nut  9  is screwed stationarily onto the threaded pin  15  of the mounting pin  11  on the underside. The mounting pin  11  is fixed nonrotatably on the wall area  5  in this mounted state of the mounting pin  11  in the wall area  5 . 
     Further, it can be recognized that the holding ball  51  is located in the axial area of the circular locking groove  19  of the mounting pin  11  in this state in which the pressing disk  12  with the holding device  13  is placed “loosely” on the mounting pin  11 . In this attached state, the holding pin  20  meshes with the holding surfaces  18  of the profile web  17  of the mounting pin  11  in a positive-locking manner and hence nonrotatably by its bearing profile  35 , which can be recognized as a suggestion only in  FIG. 8 . Thus, the pressing disk  12  is also held nonrotatably in the wall area  5  based on the stationary threaded connection with the holding pin  20 . 
     Further, it can be recognized from  FIG. 8  that the filter sheet  10  shown as a separate component in  FIG. 2  is arranged between the pressing disk  12  and the wall area  5 . Furthermore, it can also be recognized from  FIG. 8  that a sealing ring  55  is provided under the filter sheet  10 . 
     Reference should briefly also be made in this connection to the view in  FIG. 3 , from which it can be recognized that a mounting groove  56 , in which a second sealing ring, which is not shown explicitly in  FIG. 3 , is provided in the mounted state, is arranged in the outer circumferential area of the ventilation openings  7 . To receive the sealing ring  55  from  FIG. 8 , the wall area  5  likewise has a circular mounting groove  57  in the area located radially within the ventilation openings  7 . 
     To now press the pressing disk  12  at least slightly against the surface of the filter sheet  10  and especially to achieve a sealing action of the sealing ring  55 , the adjusting sleeve  21  can be adjusted manually downwardly in the direction of arrow  41 . The holding ball  51  (or holding balls) now enters (enter) the radially tapered through hole  40  from the area of the radial expansion  52  of the through hole  40 , so that an adjusting motion of the holding ball  51  is brought about in the radial direction indicated by arrow  58 . The holding ball  51  is thus pressed inevitably into the circular locking groove  19 , as a result of which adjusting forces are, in turn, generated in the direction of arrow  41 . Since a total of three such holding balls  51  are provided in the through holes  33  recognizable in  FIG. 5 , uniform pressing of the pressing disk  12  is brought about via these holding balls  51  and the locking groove  19  in the direction of arrow  41 . 
     The fixing pin  47  “slides” along the vertical section  29  of the L-shaped groove  28  during this adjusting motion in the direction of arrow  41 . When the “lower” end position of the adjusting sleeve  21  is reached, this fixing pin  47  is located in the axial area of the lower horizontal section  31  of the L-shaped groove  28 . The fixing pin  47  can thus now be caused to mesh with the horizontal section  31  to fix this axial securing position of the adjusting sleeve  21  by rotating same in the direction of arrow  59  into its fixing position. 
     This fixed fixing position of the adjusting sleeve  21  with its fixing pin  47  can be recognized in the perspective sectional view shown in  FIG. 9 . It can also be recognized in this view that the locking ball  50  meshes with the milled recess  44  of the through hole  40  of the adjusting sleeve  21  and is held in this meshing position by the axial compression spring  60 . The second locking ball  50  correspondingly meshes with the second milled recess not recognizable in  FIG. 9 . This meshing position of the second locking ball  50  with the second milled recess  44  is indicated by broken lines in  FIG. 10 , because this is not “actually” recognizable in  FIG. 10  based on the section orientation from  FIG. 9 , because this is located “in front of” the plane of the drawing sheet. 
     As can also be determined from  FIG. 9 , the fixing pin  47  meshes with the horizontal section  31  of the L-shaped groove  28 . Based on the positive-locking connection of the mounting pin  11  with the holding surfaces  18  of the profile web  17  with the inner bearing profile  35  of the holding pin  20 , the holding pin  20  is likewise fixed nonrotatably relative to the wall section  5  on the mounting pin  11 . It is thus ensured that the holding pin  20  cannot co-rotate during the rotary adjusting motion of the adjusting sleeve  21  in the direction of arrow  59 . 
     Based on the meshing of the two locking balls  50  with the corresponding milled recesses  44  of the adjusting sleeve  21 , the adjusting sleeve  21  is secured in this “locked” position. 
     Further, it can be determined from  FIG. 10  that the holding ball  51 , three of which are arranged distributed uniformly on the circumference, meshes with the locking groove  19  of the mounting pin  11 . This locking ball  51  is supported at the inner wall of the through hole  40  of the adjusting sleeve  21 , so that the locked position of the holding pin  20  is fixed securely together with the pressing disk  12 . For example, the sealing ring  55  is compressed at least slightly in the wall area  5  in this fixed position, so that an optimal sealing action can be achieved here, as this can be recognized from  FIG. 10 . 
     By a correspondingly opposite rotary motion against arrow  59  from the locking position shown in  FIGS. 10 and 9  and subsequently raising the adjusting sleeve  21  against arrow  41 , the adjusting sleeve  21  with its radial expansion  52  will again reach the axial area of the locking balls  51 , so that these are adjustable against arrow  58  radially outwardly until they come into contact with the inner wall of the radial expansion  52 . The axial path of adjustment of the adjusting sleeve  21  to the holding pin  20  against arrow  41  is defined now by the axial length of the vertical section  29  of the L-shaped groove  28 . Due to the radial adjusting motion of the holding balls  51 , the positive-locking connection between these holding balls  51  and the locking groove  19  of the mounting pin  11  is eliminated, so that the entire holding device  13  is lifted off together with the cover disk  12  that is stationarily in connection with this and the filter sheet  10  located under it can be replaced. 
     It can be easily imagined that based on the special embodiment, especially of the holding device  13 , the pressing disk  12  can be mounted and removed in an extremely simple manner. For mounting, the pressing disk  12  is ultimately placed simply on the mounting pin  11  together with the holding device  13  until the holding surfaces  18  of the profile web  17  come to mesh with the bearing profile  35  of the holding pin  20  in a positive-locking manner. Since a connection of this holding pin  20  with the mounting pin  11  is now achieved, which connection rotates in unison, the pressing disk  12  is likewise arranged on this nonrotatably in relation to the wall section  5 . This position can be fixed in a very simple manner by subsequently adjusting the adjusting sleeve  21  in the axial direction indicated by arrow  41  and subsequent rotation in the direction of arrow  59 . The pressing disk  12  can, in turn, be lifted off from the filter sheet  10  in a very simple manner by correspondingly reversing these motions, so that the filter sheet can be replaced in a simple manner. 
     Based on the fixation of the pressing disk  12  via the holding surfaces  18  of the profile web  17  of the mounting pin  11  and the bearing profile  35  of the holding pin  20 , the pressing disk  12  is fixed nonrotatably relative to the wall section  5  and hence to the filter sheet  10 , so that damage, especially during the mounting of the filter sheet  10 , is ruled out with certainty. 
     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.