Abstract:
A sterilization container has a valve arrangement that remains open in a venting phase and is then closed before a pressure difference is compensated for at a predetermined differential pressure. The valve remains closed until the container is opened for the purpose of withdrawing and using the sterilized instruments contained therein. The valve is actuated through a snap disk arrangement, the snap disks of which vault gradually into opposite directions at predetermined temperatures, thereby effecting a defined valve control. The snap disk arrangement is provided in a thermally isolated housing, which prevents a premature back-switching of certain snap disks that could be caused by a cooling-off as a result of the evaporation of condensate.

Description:
BACKGROUND 
     The invention relates to a sterilization container having a valve arrangement which permits a media exchange inside a sterilizer right into the vacuum drying phase and closes in the last ventilation phase, so that the vacuum prevailing at this instant in the container interior is maintained and the container remains hermetically sealed, the valve arrangement having a valve body subjected to the flow pressure. 
     Such sterilization containers, as described, for example, in DE 41 11 075 C2, have the advantage that the material to be sterilized can be kept in the container for a prolonged period without the risk of contamination, since the external atmospheric pressure keeps the container hermetically closed until ventilation is effected at random. The valve body is under spring preloading, which keeps the valve in the open position until the pressure in the sterilizer increases in the last ventilation phase and presses the valve body onto its valve seat, as a result of which the vacuum prevailing in the container at the moment of closing is maintained. 
     In the valve arrangement, however, the valve body must be reliably prevented from being pressed onto the valve seat prematurely by the inflowing steam, since otherwise no reliable sterilization could take place and the container could even possibly implode. It has been found that the spring preloading of the valve body in the open position cannot reliably prevent premature closing in particular when this valve body subjected to the pressure of the flow medium has a considerable surface extent. The risk of premature closing is there, depending on the load, due to the high inflow velocities. The greater the amount of material to be sterilized which is in the container, the greater is the steam consumption required in the same time. The sterilizer is subjected to a pressure increase controlled with respect to time, i.e. the pressure increases constantly in the environment of the container, and it also penetrates into the container, in which case immediate condensation takes place (gaseous-liquid phase transition releases heat). Accordingly, the container must be “resupplied” with steam, but this steam immediately condenses again, until the heating achieved by constant condensation leads to a situation in which steam can no longer condense. 
     Thus, if an empty container is sterilized, hardly any more steam is required on the “inside” as on the “outside” (in order to reach 134° C.): the valve is then not substantially loaded with flow pressure. 
     If a load is sterilized, substantially more steam is “consumed” on the inside—depending on the total weight and the heat capacity of the load: thus substantially more steam—in the same time predetermined by the sterilizer—must therefore [lacuna] through the valve gap than in the empty state. In the case of larger loads, there is therefore the risk of slamming. 
     In the sterilization containers of the generic type, the valve control is expediently effected via at least one temperature sensor with hysteresis behavior. This temperature sensor may be provided with a snap-disk arrangement, as described in DE 41 11 075 C2. Such a sterilization container, after opening, and after removal of the sterile material, is again available for a renewed sterilization operation without manual valve actuation being necessary. In order to ensure this, the temperature sensor, after removal of the sterilization container from the sterilizer, must automatically switch back again into the original state. In temperature sensors having a snap-disk arrangement, the switching-back is effected by the hysteresis behavior of the thermobimetal. The temperature sensors with snap disks, but also other temperature sensors, are therefore designed in such a way that the switching-back is effected within a temperature range in which the vacuum valve controlled by the sensor is reliably closed, i.e. the switching-back must not be effected before completion of the ventilation phase. In snap-disk arrangements, a temperature of 30 to 50° C. is generally assumed as switch-back temperature, i.e. a temperature which is normally not achieved until after removal from the sterilizer and after cooling of the sterilization container to room temperature. 
     However, it has been found that these switching temperatures of preferably 35 to 40° C., under certain circumstances, may already be reached during a drying phase inside the sterilizer. This premature cooling may occur during the sterilization of heavy steel loads, since these steel loads produce very large condensate quantities, as a result of which the sensor arrangement may be wetted with condensed steam. If vacuum drying now starts, condensate is re-evaporated, resulting in energy consumption and cooling at those locations where evaporation of the moisture occurs. If such cooling is effected in the region of the temperature sensors, the end of the sterilization operation is simulated, and premature switching-back may be effected, which would result in incorrect switching of the vacuum valve. 
     SUMMARY 
     The object of the invention is therefore to ensure reliable vacuum sealing of any desired loads of the sterilization container, even of heavy steel loads. 
     According to a feature of the present invention, a stop prevents a valve body from closing, and is disabled before or during a venting phase through pressure differentiations. This feature overcomes the above mentioned load- or process-related condensation problems. 
     According to another feature of the present invention, a temperature sensor is prevented from premature cooling through screening. This feature addresses the above mentioned load- or process-related condensation problems or the problems associated with the premature cooling of the temperature sensor. 
     The thermal screening also produces reliable screening against moistening due to condensate dripping down and leads to insulation, as a result of which the existing temperature sensors follow the saturated-steam curve in a virtually ideal manner, i.e. cooling to room temperature is effected essentially by convection alone. Instead of the arrangement of the temperature sensors from above/outside on the valve body, the sensors are shifted into the interior of the gas space of the bellows. This results in perfect screening against moistening due to condensate dripping down. 
     The complete sensor, after switch-on is effected, is now also shut off in a gas-tight manner with respect to the bellows space. The recoil temperature of 95° C. prevails in the sensor space at this instant, so that the temperature sensor cannot continue to cool down inside the sensor space (evaporation can no longer take place); the sensor space itself “conserves” a comparatively high temperature of 95° C. during the entire drying. As a result, it becomes possible to carry out the vacuum drying for as long as desired in a vacuum which is as low as desired without the recoil temperature being reached prematurely inside the sensor space. As a result, premature undesirable switching of the sensor is reliably prevented. 
     According to a preferred embodiment, which is explained in more detail with reference to the drawing, the temperature sensor preferably provided with snap disks is shifted into the interior of the gas space of a bellows, which results in perfect screening against moistening and heat. In this case, measures are taken which direct the ventilation through the temperature final control element. 
     This results in the advantage that any desired load of the sterilizer can be dried for as long as desired without the described premature cooling of the temperature sensors being able to lead to a malfunction. 
     In sterilization technology, work is carried out at different sterilization temperatures of, for example, either 120° C. or 134° C. The sterilization containers have hitherto been equipped with temperature sensors which were adapted only to one of the two common sterilization temperatures and in which malfunctions could not be ruled out if sterilization was carried out with an unmatched steam temperature. 
     The object of the invention is therefore to also provide a sterilization container having a valve arrangement which reliably carries out the desired switching operations and irrespective of the steam temperature at which sterilization is carried out. 
     This object is achieved by providing two snap-disk temperature sensors in a snap-disk stack, each having different temperature behaviors. The present invention also features a design and arrangement of the snap disks as provided in the exemplary embodiment described below with reference to the drawing. 
     The valve arrangement according to the invention may be arranged at any location in the sterilization container, i.e. in the lid or on the side walls of the trough. However, the valve is preferably arranged at the lowest point at the bottom of the trough in such a way that, during the sterilization operation, during which the vacuum valve is open, the condensate water can thus flow off. The draining of condensate therefore permits drying of the container contents without the need for energy-consuming re-evaporation of the condensate. Only in this way does it become possible to produce sterilization containers without having to take into account the thermal conductivity or heat capacity of the material used, so that, for example, containers made of plastic may also be used. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention are described below with reference to the drawing, in which: 
         FIG. 1  shows a vertical section of a sterilization container designed according to the invention; 
         FIG. 2  shows a view of the trough of the sterilization container according to  FIG. 1  (in the right-hand part as viewed from above, in the left-hand part as viewed from below); 
         FIG. 3  shows a detail, drawn on an enlarged scale and designated by X in  FIG. 1 , of the lid seal; 
         FIG. 4  shows a side view of the valve, inserted into the bottom of the trough, in the open position; 
         FIG. 5  shows a sectional view, drawn on an enlarged scale, of the valve-control device in the position according to  FIG. 4 ; 
         FIG. 6  shows a perspective view of the cover plate, carrying the control members, of the valve-control device; 
         FIG. 7  shows a perspective view of the outlet seal of the valve-control device; 
         FIG. 8  shows a view of the valve body shifted into the open position against a stop; 
         FIG. 9  shows, on an enlarged scale, a view corresponding to  FIG. 8 ; 
         FIG. 10  shows the valve-control device in a view after a temperature increase to a first temperature (of, for example, 115° C.); 
         FIG. 11  shows the valve-control device in a sectional view during a temperature increase after reaching a second temperature (of, for example, 117° C.); 
         FIG. 12  shows a sectional view of the valve-control device after a cooling phase; 
         FIG. 13  shows a sectional view of the valve in the closed position; 
         FIG. 14  shows a sectional view of a second embodiment of the valve-control device in an operating position according to  FIG. 5 ; 
         FIG. 15  shows a sectional view of the valve-control device according to  FIG. 14  in the valve closed position according to  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , the sterilization container consists of the trough  10  and the lid  12 . The trough has a sloping bottom  14  and an encircling base frame  16 . A sealing ring  18  of L-shaped cross section is arranged between the top rim of the trough  10  and the lid  12  ( FIG. 3 ). This sealing ring, with its inwardly pointing leg, is captively inserted into an encircling groove  20  of the lid  12  and effects a seal downward and outward. The sealing ring  18  accordingly has positive locking in the horizontal, so that adhesive bonding need not be effected, but rather the seal can be exchanged on the spot without any effort. Even if the seal “sticks” slightly to the trough after prolonged mounting, the positive locking enables the lid to be removed without the seal being released from the latter. The seal has a double sealing seat: end-face contact on the one hand (especially at first—when the container is not under vacuum but is only closed with the fasteners), but, when the pressure force is increased (when the pressure difference builds up), specific displacement of the seal into the cavity, enclosed in an encircling manner, in such a way that the vertical surfaces also become tight. 
     In the deep-set center section, the trough  10  has perforation holes  22  which serve for the media exchange and the outflow of the condensate. A valve arrangement  24  is provided in this center region of the container bottom  14 , this valve arrangement  24  having a sealing ring  26  which interacts with an annular valve seat  28  which is formed by the bottom of the trough and lies outside the perforation holes  22 , so that the container contents are sealed off from the outside atmosphere after the valve  26 ,  28  has been closed. The sealing ring is carried by a valve plate subjected to the flow pressure and forms the valve body together with this valve plate. 
     As can be seen from  FIG. 1 , the trough bottom  14  has, in the region of the valve arrangement  24 , a conical wall section  30  with the perforation holes  22 . It is designed in such a way that the valve arrangement can be accommodated above the base area of the base frame  16 . Formed in the central flat section  32  is a hole  34  into which a valve cap  36  is inserted from below, this valve cap  36  consisting of a rotationally symmetrical high-grade-steel part and being mechanically secured to the wall section  32  by means of a rotary-lock fastener  38  and by means of a circlip  40 . The rotary-lock fastener  38  is an oval rotatable fastener which is held on the valve cap by means of the circlip  40 . After the rotary lock  38  is turned by 90°, the valve cap  36  is arrested on the trough bottom. Latching is effected by raised heads  42 . A valve-cap flange  44  running under the flat section  32  is welded all-round at the bottom in a gas-tight manner to an axially compressible bellows  46 . An outwardly directed annular flange  48  at the lower end of the bellows  46  is welded via an intermediate ring  52  to the valve plate  50  made of high-grade steel. The valve plate  50  carries the sealing ring  26  at its outer periphery. A baffle plate  54  running conically outward and downward under the perforation holes  22  is put onto the valve plate, so that condensate dripping out of the perforation holes  22  is diverted outward and does not collect on the valve plate  50 . The valve sealing ring  26  is made of an elastomer, e.g. silicone, and is adhesively bonded or vulcanized in place on the valve plate  50 . 
     This sealing ring could also be put on the valve seat  28  on the bottom of the trough. The valve plate  50  has a vent opening  56 , which is closed by a sealing disk  58 , which is pressed on in a sealing manner by a leaf spring  60  welded to the valve plate  50 . These parts act as a check valve which permits venting of the valve interior space, i.e. of the space inside the bellows  46 . Inside the space enclosed by the bellows  46 , a bowl  62  provided with an internal thread is welded in place on the valve plate  50 . The base of this bowl  62  has a center opening  64  which is in alignment with a ventilation opening  66  in the valve plate  50 . This ventilation opening  64 ,  66  is covered by an outlet sealing disk  68 , which lies on the base of the bowl  62  and is designed according to  FIG. 7 . It has two openings in the form of segments of a circle, between which the web covering the ventilation opening  64 ,  66  lies. 
     The annular wall  72 , provided with an external thread, of a lid  74  is screwed into the internal thread of the bowl  62 . The lower annular end face of the annular wall  72  is restrained in a sealing manner against the rim of the outlet sealing disk  68 . This sealing disk  68  accordingly has a double function by virtue of the fact that, on the one hand, it closes the ventilation opening  64 ,  66  when there is internal positive pressure in the valve and, on the other hand, it seals the parts  62 ,  72  screwed to one another. 
     The lid  74  has a center hole  76  with a recess for a sealing ring  78 . The ventilation of the valve interior space is effected via this center opening. Welded in place on the lid  74  is a spring-steel plate  80 , from which a blocking spring  82  is stamped and, in the manner which can be seen from  FIG. 6 , is bent in such a way that it overlaps a cutout  84  of the disk  80 , this cutout  84  lying above the center opening  76  of the lid. This blocking spring  82 , designed as a leaf spring, carries a blocking pin  86  which is notched in a V-shape and prevents the slamming of the valve by flow pressure, as will be described in detail further below. The blocking pin  86  is connected to the leaf spring  82  via a press-in pin  88 , which projects downward into the center opening  76  and interacts with a polished valve ball  90 , the valve seat of which is formed by the sealing ring  78 . 
     The housing formed by bowl  62  and lid  74  and enclosing the temperature sensor forms, together with the valve cap  36  and the bellows  46 , thermal screening for the temperature sensor and prevents ingress of condensate dripping down and thus premature switching of the snap-disk temperature sensor. This could be realized with only one snap-disk type which keeps the valve open, closes the valve when the control temperature “hot” is reached (venting via the check valve) and only then opens again—protected by the insulated fitting—after sealing (vacuum) and cooling of the container have been effected (in order to prepare the valve for the next use). 
     The following switching temperatures of the temperature sensor, for example, would be conceivable: 
     134° C. during heating/30–50° C. during cooling: this valve would “function” during every sterilization program which reaches 134° C. 
     Disadvantage: it would not operate if, for example, a 120° C. program is run (for it would of course then never switch “ON”). 
     120° C. during heating/30–50° C. during cooling: this valve would function in a 120° C. program, and also to a limited extent in a 134° C. program, although involving risks: if the valve closes at 120° C., a further pressure increase in the gas space of the bellows is no longer possible (only its venting . . . ); but it is not until 120° C. that a pressure of 2.1 hPa prevails (saturated-steam curve). If a container is now sterilized in a 134° C. program, a further pressure increase to 3.2–3.4 hPa is effected. This pressure increase (difference is 1.1–1.3 hPa) would compress the bellows, and could therefore not penetrate into the container, with the result that either the correct sterilization conditions are not reached inside the container or that the container does not withstand the pressure difference and implodes. 
     134° C. and 120° C. programs are the two standard temperature levels in hospital sterilization. A user therefore ought to have different valves (for 120° C. or 134° C. level) and also to attach or exchange these valve before use. This is conceivable, but awkward and susceptible to errors. The snap-disk arrangement described below avoids this disadvantage by the valve being designed in such a way that it can be used at all the common sterilization levels. 
     The valve ball  90  is carried by a high-grade-steel disk which runs convexly upward in a spherical segment shape and to which it is welded. This high-grade-steel disk  92  retains its shape irrespective of temperature and pressure changes and is displaced merely within the space defined by the annular wall  72  by interacting with the snap disks described below. These snap disks are made of thermobimetal and are characterized in that they switch over into their opposite curvature state at a predetermined heating temperature and, affected by hysteresis, snap back during cooling at a lower switching temperature. In  FIG. 5 , the snap disks described below are depicted in their curvature state which they assume at room temperature. The snap disk  94  adjacent to the high-grade-steel disk  92  is curved in the opposite direction to the steel disk  92  and is upwardly concave. This snap disk  94  typically has the following switch-over temperatures: 
     during heating, the snap disk  94  snaps over from the concave position into the convex position at 115° C. During cooling, it snaps back from the convex position into the concave position at 95° C. 
     Adjacent to the snap disk  94  is a further snap disk  96  having a switching characteristic which is different from the switching characteristic of the snap disk  94 . The fitted position of the snap disk  96  corresponds to that of the snap disk  94  and it bears convexly upward in full-face contact with the snap disk  94 . The thermobimetal snap disk  96  typically has the following switching temperatures: during heating, it snaps over from the concave position into the convex position at 117° C. During cooling, it snaps back from the convex position into the concave position at 35 to 50° C. 
     Adjacent to the snap disk  96  is a further high-grade-steel disk  98  which is of upwardly concave design and corresponds to the curvature of the inserted snap disks; it does not change its shape, only its position. 
     Adjacent to the high-grade-steel disk  98  is a snap disk  94 A curved convexly upward and having the same switching characteristic as the snap disk  94 . Adjacent to this snap disk  94 A is a snap disk  96 A which is likewise curved convexly upward and has the same switching characteristic as the snap disk  96 . The snap disk  96 A is supported by a further dimensionally stable high-grade-steel disk  99  which is curved convexly upward and corresponds in its curvature exactly to the curvature of the snap disks. This high-grade-steel disk is provided with holes for improving the steam inlet and is supported at the peripheral rim on the outlet sealing disk  68 . The intermediate ring  52  forms a shim for providing a distance between the annular flange  48  of the bellows  46  and the valve plate  50  and is connected to these parts in each case in a gas-tight manner by welding, adhesive bonding or screwing. 
     In the drawing, for the sake of clarity, in each case only the snap disk determining the function is shown. In practice, it may be expedient to use in each case a plurality of identical snap disks fitted in the same direction. 
     The function of the valve arrangement  24  is described below with reference to  FIGS. 4 to 13 : 
     The position of the snap disks which is shown in  FIGS. 4 and 5  is maintained during heating up to 115°. At 115° C., the snap disks  94  and  94 A switch over into their opposite curvature position according to  FIG. 10 . The overall height and thus the position of the valve ball  90  does not change in the process. 
     When the second switch-over temperature of 117° C. is reached, the snap disks  96  and  96 A additionally switch over into their opposite curvature position, as can be seen from  FIG. 11 . The overall height of the stack and the position of the valve ball  90  remain unchanged, so that the valve ring  26  remains lifted from its valve seat  28 , i.e. the valve remains open, so that the media exchange can continue to be effected without hindrance. 
     According to the invention, measures are taken in order to hold the valve in the open position even when, during the sterilization operation, a flow pressure loads the valve body formed by the valve plate  50 , this flow pressure attempting to close the valve against spring preloading.  FIGS. 8 and 9  show that a pressure acting on the valve plate  50  from the bottom upward has displaced the valve plate and the parts carried by it only until the blocking pin  86  held in the inclined position by the spring  82  strikes the step  100  of the valve cap  36 . This stop position can be seen from  FIGS. 8 and 9 . A flow gap between the valve seat  28  and the valve ring  26  is also maintained in this position, so that the media exchange can continue to take place without hindrance. Slamming of the container is therefore reliably prevented, so that any desired loads can be sterilized in sterilizers which are as fast as desired without it being possible for the container to be destroyed. 
     During the cooling phase, the snap disks  94  and  94 A switch over into the position according to  FIG. 12  at about 95° C., whereas the curvature of the snap disks  96  and  96 A still remains unchanged. This results in expanding of the snap-disk stack and thus in lifting of the valve ball  90 , which in this position according to  FIG. 12  bears against the sealing ring  78  and closes off the valve space from above. During its upward movement, the ball  90  has lifted the blocking pin  96  via the press-in pin  88  and, as can be seen from  FIG. 12 , straightened it up, so that the blocking pin can run freely into the valve cap  36 . During the pressure drop in the sterilizer, the external pressure progressively decreases relative to the internal pressure in the container and in the valve space, and pressure compensation is effected via the valve  26 ,  28 , which is still open, it being possible for the pressure compensation inside the valve chamber to be effected via the check valve  58  or the vent opening  56 . Further evaporation—and thus vacuum cooling—inside the temperature sensor can now no longer occur, so that premature, undesirable switching of the sensor is reliably prevented. 
     As soon as the pressure in the sterilizer increases again in the last ventilation phase, the bellows is compressed to an increasing extent as a result of the pressure difference which builds up and the valve  26 ,  28  is closed, in which case the blocking pin  86 , as can be seen from  FIG. 13 , can run into the interior of the valve cap  36 . During this operation, the bellows  46  is compressed. This closed position of the valve  26 ,  28  is maintained during the further cooling and also after removal of the sterilization container from the sterilizer, since a vacuum is maintained in the interior of the sterilization container and the atmospheric pressure keeps the valve closed. By appropriate dimensioning of the valve gap or of the bellows (cross section and spring rate), the level of the trapped vacuum can be varied within wide limits. 
     During cooling to their switching temperature (e.g. 35 to 50° C.), the snap disks  96 ,  96 A snap over into their opposite curvature position, as a result of which the valve ball  90  is lifted from its seat. In the process, the valve space is ventilated via the ventilation opening  66 , but the container interior space is not ventilated. The valve arrangement itself remains in the closed position until the atmospheric pressure can penetrate into the sterilization container via an additional ventilation valve, not shown in the drawing, and a filter connected upstream of the latter. As a result of the spring action of the bellows  46  and due to gravitational force, the valve arrangement then returns into the position according to  FIGS. 4 and 5 , and the sterilization container can be used for the next sterilization operation without manual manipulation. 
     A further exemplary embodiment is shown in  FIGS. 14 and 15 . The function of the valve arrangement shown here corresponds essentially to the function in the case of the embodiment shown according to  FIGS. 1 to 13 . The valve arrangement is modified compared with the exemplary embodiment described above inasmuch as a second ball valve is arranged instead of the outlet sealing disk  68 . This ball valve consists of a valve-seat ring  104  which is inserted into the ventilation opening  66 , is secured by a disk  102  and interacts with a valve ball  106  which is welded to the convexly curved high-grade-steel disk  99 . This disk  99  is preloaded by springs  108 , as a result of which the valve ball  106  is lifted from its seat. Further springs  110  act on the top high-grade-steel disk  92 , as a result of which the valve ball  90  is preloaded in the open position. This causes the ventilation opening  66  to be constantly open while the valve is open. It is not until switch-over is effected into the position according to  FIG. 15 , which corresponds to the position according to  FIG. 12 , that the ventilation opening is closed. The difference compared with the first exemplary embodiment accordingly consists in the fact that, after the switching of the snap disks, the snap-disk housing is completely shut off in both directions. 
     LIST OF DESIGNATIONS 
     
         
           10  Trough 
           12  Lid 
           14  Sloping bottom 
           16  Base frame 
           18  Sealing ring 
           20  Groove 
           22  Perforation holes 
           24  Valve arrangement 
           26  Sealing ring, valve ring 
           28  Valve seat 
           30  Conical wall section 
           32  Flat section 
           34  Hole 
           36  Valve cap 
           38  Rotary-lock fastener 
           40  Circlip 
           42  Heads 
           44  Valve-cap flange 
           46  Bellows 
           48  Annular flange 
           50  Valve plate 
           52  Intermediate ring 
           54  Baffle plate 
           56  Vent opening 
           58  Sealing disk 
           60  Leaf spring 
           62  Bowl 
           64  Center opening 
           66  Ventilation opening 
           68  Outlet sealing disk 
           70  Openings 
           72  Annular wall 
           74  Lid 
           76  Center opening 
           78  Sealing ring 
           80  Spring-steel plate 
           82  Blocking spring 
           84  Cutout 
           86  Blocking pin 
           88  Press-in pin 
           90  Valve ball 
           92  High-grade-steel disk 
           94 ,  94 A Snap disk 
           96 ,  96 A Snap disk 
           98  High-grade-steel disk 
           99  High-grade-steel disk 
           100  Step 
           102  Disk 
           104  Valve-seat ring 
           106  Valve ball 
           108  Springs 
           110  Springs