fig1 to 3 illustrate a three - part filter unit , which is denoted overall by reference numeral 10 and is mounted on a lid 12 of a sterile container ( not shown in more detail ). the filter unit 10 comprises a holding frame 14 , which can be connected to the lid 12 , a filter element 16 , which can be placed into the holding frame 14 and connected to the latter , and a cover 18 which can be connected to the holding frame 14 . the holding frame 14 comprises a cover plate 20 which has an octagonal external contour and also has a circular opening 22 surrounded by an encircling inner rim 24 . an encircling outer rim 26 adjoins the octagonal outer contour of the cover plate 20 , so that a hollow profile which is substantially u - shaped in cross section is formed . four identical cylindrical sleeves , serving as mounting bushes 28 , are inserted into the cover plate , in each case offset by 90 ° in the circumferential direction , which sleeves , at their end remote from the cover plate 20 , have an annular flange 30 facing inward and running parallel to the cover plate 20 . between the mounting bushes 28 are disposed four identical slots 32 , which extend over an angular range of approximately 45 ° and are partially covered by a projection 34 , which is formed integrally with the cover plate 20 and is adjoined by an integrally formed , resilient latching lug 36 which faces in the circumferential direction , which can be moved to a slight extent perpendicular to the cover plate 20 and , on a side facing away from the cover plate 20 , has a small spherical projection ( not shown ). the projection 34 and the latching lug 36 cover approximately 40 % of the slot 32 in the circumferential direction starting from one end of the slot 32 . furthermore , the inner rim 24 is provided with four radial projections 38 , which are distributed symmetrically over the circumference , extend in the circumferential direction , project radially inward and extend over an angular range of approximately 40 °. on one side , the radial projections 38 are extended by latching tongues 40 which protrude in a parallel offset manner and can be moved to a slight extent perpendicular to the cover plate 20 . a free rim contour 27 , facing away from the cover plate 20 , of the outer rim 26 is partially curved and configured so as to correspond to an inner surface ( not shown in more detail ) of the lid 12 , so that it is possible to realize positively locking placement of the holding frame 14 against the lid 12 . the filter element 16 comprises two clamping disks 42 and 43 , which have an inner ring 45 and 49 , respectively , in each case connected via eight radially extending webs 46 and 50 , respectively , to an outer ring 44 and 48 , respectively . four holding webs 54 , which are disposed in a cross shape and centrally carry a centering projection 56 , pass through the inner ring 45 of the clamping disk 42 . between the clamping disks 42 and 43 there is a sterile filter 52 which completely covers the annular opening 58 delimited by the outer rings 44 and 48 . the two clamping disks 42 and 43 and the sterile filter 52 are fixedly connected to one another , for example by adhesive bonding or ultrasound welding , and form a single unit . the external diameter of the annular filter element 16 corresponds to the internal diameter of the opening 22 of the holding frame 14 and can therefore be inserted into this opening 22 . to connect the filter element 16 to the holding frame 14 , the outer ring 48 is provided with four receiving grooves 60 , which are distributed symmetrically over the circumference and are open to the radially outer side . in each case one lateral end of the receiving groove 60 is closed off by a groove end wall 62 . the filter element 16 is inserted into the holding frame 14 in such a manner that the four receiving grooves 60 engage between those regions of the inner rim 24 which are provided with the radial projections 38 . a radially protruding outer annular flange 64 of the outer ring 48 in this position is supported on the radial projections 38 . the filter element 16 is then rotated until the groove end wall 62 comes to a stop against the end edge 39 of the radial projection 38 engaging in the receiving groove 60 . in this connection position of the holding frame 14 and the filter element 16 , the projections disposed on the latching tongue 40 penetrate into corresponding recesses 66 at the open end of in each case one side wall 61 of the receiving groove , resulting in latching locking of the connection position . furthermore , the outer ring 48 is provided with an annular groove 68 which is open in the direction facing away from the outer ring 44 and into which a sealing ring 70 is inserted . the filter unit 10 is closed off by means of the cover 18 , which has an octagonal baseplate 72 which corresponds to the outer contour of the cover plate 20 and is provided with a central bore 74 for introduction of the centering projection 56 . a circular surface region 76 is provided with slots 78 of different lengths in each case running parallel in quarter - circle sectors , so that webs 80 remain between the slots 78 , protruding as extensions running obliquely , approximately at an angle of 60 °, relative to the baseplate 72 . obliquely running web regions form aperture covers 81 that in each case completely cover the slots 78 , so that obliquely extending passages 82 are formed in each case . direct passage through the slots 78 perpendicular to the baseplate 72 is not possible . four symmetrically distributed retaining projections 86 , which are l - shaped in cross section , extend over an angular range of approximately 30 ° and one free limb of which , at one of its ends , has a bore 88 running perpendicular to the baseplate 72 , project from an underside 84 of the baseplate 72 . the cover 18 is connected to the holding frame 14 in the following way : the cover 18 is introduced , by means of the retaining projections 86 , into regions of the slots 32 which are not covered by projections 34 , until the underside 84 of the baseplate 72 bears against the cover plate 20 . rotation of the cover 18 in the clockwise direction causes the free limbs of the retaining projections 86 to engage behind the projections 34 until an end side 87 of the retaining projection 86 comes to a stop at an end edge 33 of the slot 32 . in this closure position , a hemisphere 37 disposed on the latching lug 36 penetrates into the bore 88 and locks the closure position of the cover 18 and of the holding frame 14 . the securing of the holding frame 14 to the lid 12 is explained in conjunction with fig2 . on the lid 12 , adjacent to a circular aperture ( not shown ), on its inner side there are disposed four substantially cylindrical holding bolts 90 protruding perpendicularly away from the lid 12 . the mounting bushes 28 of the holding frame 14 are pushed over the holding bolts 90 , so that the annular flanges 30 engage against the inner side of the lid 12 , surrounding the holding bolts 90 . each holding bolt 90 is surrounded by a coil spring 92 , which on one side is supported against the annular flange 30 and on the other side is supported against an annular flange 94 of a cover 96 which has a central bore 97 , the internal diameter of which corresponds to the external diameter of the holding bolt 90 . the cover 96 is ultrasonically welded or adhesively bonded to the holding bolt . this mounting arrangement makes it possible for the entire filter unit 10 to be lifted off the inner side of the lid 12 counter to the prestress of the coil springs 92 . this occurs , for example , if a sterile container with a filter unit 10 disposed thereon is introduced into a sterilizer and acted on by pressurized hot steam . the pressure surrounding the sterile container is in this case higher than the pressure in the interior of the container , so that the entire filter unit 10 lifts off the lid 12 and opens up an additional flow path for hot steam to flow in . this prevents the sterile container from being deformed by the action of excessive pressure differences . if the externally acting pressure drops again , the filter unit 10 is preloaded onto the inner side of the lid 12 by means of the coil springs 92 . the sealing ring 70 , in this closed position , engages against a corresponding sealing projection 98 of the lid 12 , so that gas exchange is then only possible through the sterile filter 52 into the interior of the sterile container . on account of this resilient mounting , the entire filter unit 10 simultaneously also performs the function of a pressure - relief valve .
the invention relates to a sterile container , especially for receiving and containing surgical instruments or material in sterile conditions , comprising a receiving area formed by a container bottom and container walls , a lid for sealing the receiving are , and a gas exchange opening which can be sealed by a sterile filter maintained in a filter holder . in order to simplify replacement of the sterile filter and to simplify the production of the lid , the sterile filter and filter holder form a filter unit and the filter holder is mounted on the lid .