Abstract:
A pressure cap for openings in tanks, in particular in automobile radiators, has an outer cap component which is provided with a locking element that can be connected to the tank&#39;s neck, and provided with a handling element rotatably mounted in relation to said locking element, and furthermore provided with a coupling insert which is anti-rotationally mounted in the handling element and which can be axially engaged in and disengaged from the locking element to allow a releasably non-rotational connection between the locking element and the handling element. The pressure cap is furthermore provided with a valve assembly containing a valve body that can be axially moved back and forth, for releasing and blocking flow connections between the inside and the, outside of the tank depending on the pressure prevailing inside the tank. To create an anti-rotation means directly governed by and in time and sequence with the conditions prevailing inside the tank, it is provided that the engaging and disengaging movement of the coupling insert is derived from the pressure-dependent axial movement of the valve body of the valve assembly.

Description:
TECHNICAL FIELD 
   The present invention relates to a pressure cap for openings in tanks, in particular in automobile radiators, with an outer cap component which is provided with a locking element that can be connected to the tank&#39;s neck. The pressure cap is also provided with a handling element rotatably mounted in relation to the locking element, with an anti-rotation means provided with a coupling insert. The coupling insert is held non-rotatably in the handling element and can be axially moved back and forth, for the releasable anti-rotational connection of the locking element and the handling element. Included also is a valve assembly containing a valve body that can be axially moved back and forth for releasing and blocking flow connections between the inside and the outside of the tank depending on predetermined values of the pressure prevailing inside the tank. 
   BACKGROUND OF THE INVENTION 
   In such pressure caps for openings in tanks, in particular in automobile radiators, which are known from published international application, WO 95/32904, the movement of the coupling insert between the handling element and the locking element of the outer cap component is controlled by the temperature via a memory spring. In such cases, the memory spring lies inside the inner cap component on the side of the valve assembly that faces away from the inside of the tank. It was found that this remote arrangement of the memory spring causes problems and delays in measuring the temperature prevailing inside the tank, which leads to less than satisfactory results in activating and deactivating the anti-rotation means. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is to improve a pressure cap of the above kind for openings in tanks, in particular in automobile radiators, such that an anti-rotation means can be created which is directly governed by and in time and sequence with the conditions prevailing inside the tank. 
   To achieve this object for a pressure cap for openings in tanks, in particular in automobile radiators the axial engaging and disengaging movement of the coupling insert is derived from the pressure-dependent axial movement of the valve body of the valve assembly. 
   Thus, the anti-rotation means can be activated and deactivated substantially without time delay and directly by deriving the movement directly from the valve body depending on the pressure prevailing inside the tank. Since the pressure inside the tank directly affects the respective valve body of the valve assembly, there is also a direct effect on the activation and deactivation of the anti-rotation means. 
   In one preferred embodiment of the present invention, an axial first compression spring is provided between the valve body and the coupling insert. A guidance element is also provided between the valve body and the coupling insert whose one end sits on the valve body and whose other end can be axially moved in relation to the coupling element and engages in same. The axial first compression spring is held between the guidance element and the coupling element, with the guidance element being axially movable and coupled with the coupling insert in the direction of the effect of the first compression spring. A second compression spring is also provided between the guidance element and the inner cap component, wherein axially extending teeth are provided on the outer circumference of the coupling insert and on the inner circumference of the locking element are provided. In this preferred embodiment, the anti-rotation means is activated by transmitting the movement via a compression spring, while the return to its deactivated position is accomplished by a combination of compression spring and traction mechanism. 
   In another preferred embodiment of the present invention, has a movement-transmitting element between the valve body and the coupling insert, whose one end adjoins the valve body and whose other end adjoins the coupling insert. The coupling element and the end of the movement-transmitting element which faces the former have mutually adjoining fingers which engage in axial recesses of the locking element. The coupling element is acted upon by a compression spring which is supported on the inside of the handling element are provided. In this preferred embodiment, the anti-rotation means is activated by a rigid movement transmission from the valve body to the coupling insert, while the return to its deactivated non-rotational position is accomplished via a counter-compression spring. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further details of the invention are provided in the following description in which the invention is explained in detail with reference to the drawings, where: 
       FIG. 1  is a longitudinal section through a pressure cap for an automobile radiator with a pressure-relief/vacuum valve assembly and an anti-rotation means in closed, i.e. non-activated initial position, according to a first preferred embodiment of the present invention; 
       FIG. 2  is a view that corresponds to that in  FIG. 1 , but showing a position while pressure is building up inside the tank; 
       FIG. 3  is a view that corresponds to that in  FIG. 1 , but showing a position after the pressure inside the tank exceeds the first threshold value but before it reaches a second threshold value; 
       FIG. 4  is a view that corresponds to that in  FIG. 1 , but showing a position after the pressure inside the tank exceeds a third threshold value which constitutes the safety limit; 
       FIG. 5  is a view that corresponds to that in  FIG. 1 , but showing a position after normal pressure is reached inside the tank and before the anti-rotation means is returned to its deactivated position; 
       FIG. 6  is a longitudinal view of a pressure cap for an automobile radiator with a pressure-relief/vacuum valve assembly in closed initial position and with an engaged non-rotation means according to a second preferred embodiment of the present invention; 
       FIG. 7  shows the pressure cap as in  FIG. 6  in a position at a slight overpressure inside the tank and with the anti-rotation means deactivated; 
       FIG. 8  shows the pressure cap as in  FIG. 6  in a position after the pressure inside the tank exceeds a first threshold value; 
       FIG. 9  shows the pressure cap as in  FIG. 6  in a position after the pressure inside the tank exceeds a second threshold value and dynamic pressure prevails; 
       FIG. 10  shows the pressure cap as in  FIG. 6  when the pressure inside the tank has exceeded a third threshold value which constitutes the safety limit. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Pressure cap  111 ,  211  shown in the drawings by example of two embodiments for a tank such as an automobile radiator has an outer cap component  110 ,  210  which is provided with a handling, element or handling means  112 ,  212  to whose locking element  113 ,  213  (shown here as a screw-on element) an inner cap component  114 ,  214  with a pressure-relief/vacuum valve assembly  115 ,  215  is rotatably suspended. When in use, the pressure cap  111 ,  211  is fixed or screwed to a radiator neck (not shown). Inner cap component  114 ,  214  protrudes from the radiator neck into the inside of the radiator. An O ring  116 ,  216  seals the inner cap component  114 ,  214  against the wall of the radiator. In the two-piece outer cap component  110 ,  210 , the cap-like handling means  112 ,  212  is axially fixed to the screw-on element  113 ,  213 , although it can be rotated in circumferential direction. When there is normal pressure inside the radiator, this rotatability is blocked by an axially movable coupling insert  180 ,  280  for screwing and unscrewing pressure cap  111 ,  211 . 
   In the embodiment shown in  FIG. 1 to 5 , the pressure-relief part of the valve assembly  115  is designed in two steps. In a first overpressure step, it has the function of preventing the radiator from boiling dry, and in a second overpressure step it prevents damage to the radiator system due to excessive overpressure. The pressure-relief part of the valve assembly  115  is provided with a single valve body  117 , which is axially movable inside the inner cap component  114  between two end positions. Valve body  117  has a contoured ring seal  118  with an axially acting sealing surface arrangement  120  and a radially acting sealing surface arrangement  121 . Valve body  117  is axially biased toward the inside of the tank by means of a compression spring  122  which is supported by the inner cap component  114 . 
   Inner cap component  114  is designed in two parts, namely an inner element  125  and an outer main element  126  which is suspended in the screw-on element  113  of outer cap component  110  and in which the fixed inner element  125  is sealed. Inner element  125  has the approximate shape of a hood with an axial opening in the hood floor  128  by whose inside one end of compression spring  122  is supported. At approximately the level of the lower end of the outer cap component  110 , the outer circumference of inner cap component  114  is provided with escape openings  129 . Between the inner element  125  and the main element  126 , an O ring  124  is provided to ensure a tight connection. 
   Floor  131  of main element  126  of inner cap component  114  has a coaxial flow-through opening  132  which forms a connection between the inside of the tank and the inside of the interior cap component  114 . Flow-through opening  132  is coaxially surrounded by an annular lug  133  whose free annular face forms a sealing seat  134  for the axial sealing surface arrangement  120  of contoured ring seal  118  of valve body  117 . An annular space  136  remains between the outer circumference of annular lug  133  and the inner circumference of main element  126 . Above that annular space  136 , between the lower annular face of inner element  125  and a recess in the main element  126  of inner cap component  114 , an annular insert is accommodated which contains a U shaped throttle channel  139  or forms such a channel with its adjacent components. In the embodiment shown, the U shaped throttle channel  139  is provided in a place on the circumference of inner cap component  114 . Throttle channel  139  has two radial channel parts arranged at an axial distance:  141  (adjacent to inner element  125 ) and  142  (adjacent to the recess in main element  126 ), which are connected by an axial channel part  143  located between the associated inner circumference section of main element  126  and the associated outer circumference section of annular insert  138 . Here, the channel parts  141 ,  142  and  143  are formed by radial or axial grooves cut into the annular insert  138 . 
   One-part valve body  117  has a radially stepped main part  146  in axial direction, which carries the contoured ring seal  118 , and on which—facing away from the contoured ring seal  118 —sits a guidance element  147  which is hollow cylindrical and engages in the hollow coupling insert  180 . Compression spring  122  is supported on a radial outer shoulder of main part  146  of valve body  117 . 
   On the inner surface of the stepped outer circumference of valve body  117 , the contoured ring seal  118  is fastened. Seen in cross section, the axial sealing surface arrangement  120  of contoured ring seal  118  is vault-shaped and has a radially outer sealing surface  151 , a radially central sealing surface  152  and a radially inner sealing surface  153 . The radially inner sealing surface  153  interacts with a vacuum valve body  171 , which will be described below, while the radially central sealing surface  152  in rest position bears on the sealing seat  134  of inner cap component  114  and the radially outer sealing surface  151  lies on the floor of annular space  136 . On the other hand, the radial sealing surface arrangement  121  has two sealing surfaces  156  and  157  arranged at a certain axial distance, between which a cut-out  158  is provided. The upper sealing surface  156  as well as the lower sealing surface  157 , which turns into the radially outer sealing surface  151 , are sealingly adjoining the inner wall  161  which is formed as a sealing seat, and/or  162  of main element  126  of interior cap component  114  or annular insert  138 . 
   One inner end of guidance element  147  sits on the outer surface of the inside shoulder of valve body  117 , while its other end extends into the centered through-hole of coupling insert  180 . Coupling insert  180  and guidance element  147  are mutually rotatable and can slide axially toward each other. As  FIG. 1  shows, the axial slidability is limited by the adjoining shoulders  181 ,  182  such that guidance element  147  and coupling insert  180  always engage each other. Guidance element  147  is designed as a sleeve whose outer circumference at the inner end facing valve body  117  is stepped to form contact shoulders for an axial spring coupling means. The spring coupling means has a first inner pressure coil spring  183  which is arranged with bias between coupling insert  180  and guidance element  147 , and a second outer pressure coil spring  184  whose one end is supported by guidance element  147  and whose other end is supported by inner element  125  of inner cap component  114 . These two pressure coil springs  183  and  184  are surrounded by pressure coil spring  122  which acts upon valve body  117 . 
   The axially slideable coupling insert  180 , whose lower end, which overlaps guidance element  147 , passes through a central through-hole of inner element  125  of inner cap component  114 , has an outer end with a larger diameter. As shown in  FIG. 1 , this end lies within a recess  186  of a radial flange  187  of screw-on element  113  and within a centered ring flange  188  which protrudes axially toward the inside. Coupling insert  180  is non-rotationally connected to the axial flange  188  on the handling means  112 , for example through intermeshing peripheral teeth. In the initial position shown in  FIG. 1 , the coupling insert  180  is also non-rotationally connected with the radial flange  187  of screw-on element  113 , also via peripherally and axially extending tooth arrangements (not shown). In this manner, the handling means  112  and the screw-on element  113  are non-rotatably connected with each other in circumferential direction, such that the pressure cap  111  can be screwed on and off the neck (not shown) of a tank with handling means  112 . 
   In the centre of valve body  117 , an opening  166  is provided which is on the side facing the inside of the radiator is closed by the vacuum valve body  171  of valve assembly  115 . Main part  172  of vacuum valve body  171  protrudes through central opening  166 , and its end section is acted upon by a compression spring  167  which is supported at one end by a shoulder of main part  172  and at the other end by the outer surface of the inner shoulder of valve body  117 . In this manner, the annular sealing seat  173  of vacuum valve body  171  is sealingly adjoining the radially inner sealing surface  153  of the axial sealing surface arrangement  120  of contoured ring seal  118  of valve body  117 . 
   In the rest position (initial operating position) shown in  FIG. 1 , when there is no overpressure inside the tank yet, any flow connection between the inside and the outside of the tank is closed by the fact that all sealing surfaces  151  to  153  of the axial sealing surface arrangement  120  of contoured seal  118  of valve body  117  sealingly adjoin the corresponding sealing seats  136 ,  134 ,  173  of inner cap component  114  or vacuum valve body  171 . In other words, at contoured ring seal 118  of valve body  117  as well as on the underside of vacuum valve body  171 , the normal (ambient) pressure in the form of the air cushion above the liquid coolant prevails through flow-through opening  132 . 
   When the pressure inside the tank rises to a certain level above normal pressure, but below a first threshold, the unscrew protection means of pressure cap  111  is activated. As shown in  FIG. 2 , valve body  117  is moved upward, such that the contoured ring seal  118  with its central sealing surface  152  is lifted off sealing seat  134 . Thus, the effective surface acted upon by overpressure, which until then was formed only by the underside of vacuum valve body  171 , is enlarged by the inner axial surface of the contoured ring seal  118 . This enlarged effective surface means that a greater force is acting upon valve body  117  while the pressure remains the same, resulting in greater lift for the valve body. Due to the lift movement of valve body  117 , which however does not yet open throttle channel  139 , against the effect of the first pressure coil spring  183  and the second pressure coil spring  184 , the guidance element  147  is initially displaced axially in relation to coupling insert  180 . Since this lift movement biases the first pressure coil spring  183  which is supported by coupling insert  180 , coupling insert  180  is axially displaced. This axial outward movement of coupling insert  180  in the direction of Arrow A and up to an inner stop on the underside of handling means  112  causes the end of coupling insert  180  with the larger outer diameter to disengage from the teeth on screw-on element  113 . This disengagement of coupling insert  180  has the effect that the handling means  112  idles in relation to screw-on element  113 , such that above a certain defined overpressure (in this case, for example, 0.3 bar), pressure cap  111  can no longer be unscrewed. 
   If the pressure inside the tank increases further, i.e. above the predetermined first threshold value (e.g. 1.4 bar), valve assembly  115  of pressure cap  111  reaches the operating state shown in  FIG. 3  according to which valve body  117  continues to lift against the effect of its compression spring  122 , and the contoured ring seal  118  moves into the range of annular insert  138 , such that the two radial sealing surfaces  156  and  157  of the radial sealing surface arrangement  121  of contoured ring seat  118  of valve body  117  are below/above the radial channel parts  141  and  142  and thus open throttle channel  139  on both sides. In this state, in which the unscrew protection means remains activated, an equilibrium has occurred between the effect of the pressure inside the tank and the counter effect of compression spring  122 . Thus, the first flow connection between the inside and the outside of the tank is open, which leads from flow-through opening  132  via the U-shaped throttle channel  139  to the escape openings  129 . This means that air can flow outside from the air cushion above the liquid coolant and compensate or reduce the overpressure. If this reduces the overpressure below the first threshold value, valve body  117  is again moved to sealingly adjoin the axial sealing seat  134  of inner cap component  114 . 
   If on the other hand, the pressure inside the tank continues to rise during or after the escape of the air cushion, and if this causes liquid coolant to reach the underside of contoured ring seal  118  and vacuum valve body  171 , the fact that throttle channel  139  is very narrow (e.g. a cross section measuring only a few hundredths of a millimeter), causes the coolant to back-up at the entrance to the lower radial channel part  142  of throttle channel  139 , and therefore causes dynamic pressure on the full-surface undersides of contoured ring seal  118  and vacuum valve body  171 . This dynamic pressure leads to an axial movement of valve body  117  against the effect of compression spring  122 , such that in this state (e.g. of 1.4 bar), throttle channel  139  is closed again (in a manner not shown) at upper channel part  141  by the upper radial sealing surface  156  of contoured ring seal  118 . The unscrew protection means continues to be activated. This prevents the discharge of liquid coolant. If the pressure inside the tank is reduces through cooling and the liquid coolant is returned, valve body  117  can also be returned under the effect of its compression spring  122 , such that throttle channel  139  opens again and the pressure can be reduced further. 
   If, on the other hand, the pressure inside the tank continues to rise, valve body  117  is lifted further against the action of compression spring  122  when an upper (safety) threshold (e.g. of 2 bar) is exceeded, such that axial escape channels  169 —situated in certain circumferential sections in the wall of annular insert  138  and of the inner element  125  of inner cap component  114 —are opened which are connected to escape opening  129  and thus with the outside of the tank ( FIG. 4 ). In that state, the upper channel part  141  remains closed as before. This upper end position of valve body  117  is limited by the compressed compression springs  122 ,  183  and  184 . The unscrew protection means remains activated. This means that the said overpressure can be reduced via a second flow connection, after which valve body  117  can be returned through the various operating states by compression spring  122 , as shown in  FIG. 5 . 
     FIG. 5  also shows a possible short-term state of the unscrew protection means when valve body  117  has returned to its initial position and when the handling means  112  was rotated while the activation of the unscrew protection means was activated. In that case, it could have happened that the teeth of coupling insert  180  are not exactly above the tooth spaces of screw-on element  113 . To return the unscrew protection means from its activated state into its deactivated state, as shown in  FIG. 1 , it is enough to give handling means  112  a short turn, which has the effect that the second pressure coil spring  184 , which is under considerable bias, moves guidance element  147  down against the direction indicated by Arrow A. This releases the inner first compression spring  183 , while the outer ring shoulder  181  of guidance element  147  adjoins the inner ring shoulder  182  of coupling insert  180  and carries the latter along against the direction indicated by Arrow A, such that the coupling connection between handling means  112  and screw-on element  113  engages again and becomes effective. Thus, the exact operating position shown in  FIG. 1  is reached, and pressure cap  111  can be safely unscrewed from the neck of the radiator. 
   Valve assembly  115  assumes the initial position shown in  FIG. 1  when the pressure inside the radiator ranges between a vacuum threshold and a very slight overpressure threshold of (in this case) less than 0.3 bar. Such pressure conditions prevail, for example, in a vehicle that was parked for a long period, or when the vehicle is driven while the coolant inside the radiator is sufficiently cooled by the headwind and/or the fan. If the vehicle is parked after a long drive, the pressure may rise inside the radiator causing the contents of the radiator (air, water or water vapour) to flow into valve assembly  115 . If as a result of this after-heating effect, the coolant volume expands so much that it exceeds the volume of the radiator, this necessarily leads to a discharge of coolant. This undesirable effect is prevented in the manner described above. If in this operating state, the pressure in the cooling system continues to rise in an uncontrolled fashion, leakages and other detrimental effects due to excessive demands on the radiator and/or its hose connections must be prevented. Such effects are prevented through the second valve step as shown in  FIG. 4 , where the radiator pressure is limited to a predetermined safety threshold value. 
   If in case of an operating state as shown in  FIG. 1  there is a vacuum inside the radiator, and this vacuum falls below a predetermined vacuum threshold value, the sealing seat  173  of vacuum valve body  171  is lifted off the radially inside sealing surface  153  of contoured ring seal  118  of valve body  117  toward the inside of the radiator. Vacuum pressure valve  171  is lowered against the bias of compression spring  167 , such that a third flow connection (not shown) is opened between the inside and the outside of the radiator. 
   According to the embodiment shown in  FIG. 6 to 10 , the pressure-relief valve of valve assembly  215  is designed in two parts, and its function is to prevent (in a first overpressure step) the radiator from boiling dry, and (in a second overpressure step) to ensure protection against damage to the radiator system due to excessive overpressure. The pressure-relief part of valve assembly  215  inside inner cap component  214  has a first valve body  217 , a second valve body  218 , and a third valve body  219 . The first valve body  217  is arranged in the direction of the outside of the cap above the second valve body  218 , while the third valve body  219  is accommodated coaxially within the second valve body  218 . 
   The first valve body  217 , which is designed in two parts, has a radially inner valve body part  265  approximately in the shape of a valve disk, and a radially outer valve body part  266 . These two parts overlap at the edge, whereby the radially inner part sits on the radially outer valve body part. On the side of the two valve body parts  265 ,  266  facing toward the inside of the radiator, an annular membrane seal  221  is arranged which is provided with sealing surfaces facing axially inward. The radially outer stepped valve body part  266  of the first valve body  217 , on a side facing away from the inside of the radiator, is acted upon by a recoil spring  222  whose end facing away from the first valve body  217  is supported by a spring plate  223  which in turn is supported by inner cap component  214 . The radially outer valve body part  226  of the first valve body  217  is biased in the direction of the inside of the radiator by means of recoil spring  222 . Above the radially outer flat sealing edge  268  of membrane seal  221  sits the radially outer valve body part  226  on a first annular sealing seat  224  of the second valve body  218 . The radially inner valve body part  265  of first valve body  217  has a central recess  237  whose annular limiting edge is surrounded by the inner part of membrane seal  221 . Toward the inside of the radiator, this radially inner U shaped sealing edge  267  of membrane seal  221  forms a sealing surface for a vacuum valve  257  still to be described. On the side of the outer edge, the inner valve body part  265  bears on the inner edge of the radially outer valve body part  266  of first valve body  217 . 
   The radially inner valve body part  265  is provided near its radial outer edge with an axially protruding annular rim  269  on which a guidance sleeve  271  sits which is rotatable in relation to valve body  265 . The inner end of guidance sleeve  271  is curled over and overlaps annular rim  269  radially inside. Bearing on the other axial end of guidance sleeve  271 , which end is formed by single one-piece protruding fingers  272 , is coupling insert  280  under the effect of a compression spring  281  which is supported on the inside of handling element  212  of outer cap component  213 . Coupling insert  280  has a disk  285  which is proved with axially downward extending finger-shaped claws whose cross section corresponds to fingers  272  of guidance sleeve  271 . When no pressure prevails inside the radiator, as shown in  FIG. 6 , fingers  272  of guidance sleeve  271  as well as claws  282  of coupling insert  280  engage in axial recesses  273  of locking element  210  of outer cap component  213 . Furthermore, coupling insert disk  285  is provided axially toward the outside, i.e. facing away from claws  282 , with protruding claws  283  which grip in positive connection between axially directed circumferential teeth  284  of handling means  212 . The inwardly directed claws  282  lie on a radially inner ring, while the axially outward-pointing claws  283  lie on a radially outer ring. In the initial or normal position shown in  FIG. 6 , a non-rotational connection exists via coupling insert  280  between handling element  212  and locking element  210  of outer cap component  213 , such that pressure cap  211  can be screwed to and unscrewed from the neck (not shown) of a radiator. 
   The one-piece second valve body  218  has a hood part  226  whose free face is provided with the first sealing seat  224 , and a concentric and hollow-cylindrical receptacle part  227  pointing from floor  228  of hood part  226  to the inside of the radiator for the third valve body  219 . The outer circumferential side of floor  228  between hood part  226  and receptacle part  227  is provided with a flange in whose circumferential groove a second ring seal in the form of an O ring  231  is accommodated. O ring  231  is provided with a second sealing seat  232  which is formed by a collar rim on inner cap component  214 . This collar ring  232  is formed between a hollow-cylindrical upper part of inner cap component  214  (of greater inside diameter and accommodating the first valve body  217  and the hood part  226  of second valve body  218 ) and a lower part of inner cap component  214  (of smaller inside diameter and surrounding the receptacle part  227  of second valve body  218 ). In this lower section, the inner cap component  214  is provided with an axial opening  233 . The radially outer valve body part  266  of the first valve body  217  with sealing ring  268  of the first annular seal  221  is pressed by recoil seal  222  against the first sealing seat  224  of the second valve body  218 , whose second ring seal  231  in turn is pressed against the second sealing seat  232  on inner cap component  214 . 
   Located between the underside of first ring seal  221  and the upper side of floor  228  of the second valve body  218  is a cylindrical chamber  234  whose outer circumference is constant in axial direction between floor  228  and the underside of the first ring seal  221 . Chamber  234  is in communication in the middle via a hole  236  in floor  228  with a recess  237  in the second valve body  128 . In a conical section arranged at one free end of receptacle part  227 , recess  237  enters the axial opening  233  of inner cap component  214 . Between hole  236  and recess  237 , the second valve body  218  is provided with a shoulder which is facing toward the inside of the radiator and holding a third flat ring-shaped seal  239 . 
   The third valve body  219 , which is designed, for example, as a rotational part with a stepped circumference in axial direction, is accommodated with axial movement in recess  237  of second valve body  218 . The third valve body  219  has a neck area  241  of smaller diameter which is movable in hole  236  and within the third annular seal  239 , and it also has a shoulder region  242  whose slanted shoulder forms a third annular seal  243  assigned to the third annular seal  239  on second valve body  218 , and it also has a cylindrical ventral region  244  which is supported in a manner not shown in detail by the inside wall of conical section  238  of the second valve body  218 . For this purpose, within recess  237  a second compression spring  246  is provided whose one end is supported by a shoulder between the shoulder region  242  and the ventral region  244 . The third valve body  219  is biased in the direction of the inside of the radiator by the second compression spring  246 . Between the ventral region  244  of the third valve body  219  and in inner circumference of recess  237  of the second valve body  218  there is an annular gap  247  of very narrow width, i.e. only a few hundredth of a millimeter wide. As are hole  236  and chamber  234 , the annular gap  247  is part of a first flow connection  250  between the inside and the outside of the cap. A second glow connection  251  bypasses the outer circumference of second valve body  218  (see  FIG. 10 ). 
   In the centre of the radially inside valve body part  265  of first valve body  217  there is an opening  256 , whose side facing the inside of the radiator is closed by vacuum valve body  257  of valve assembly  215 . The main part  258  of vacuum valve body  257  protrudes through central opening  256  in whose end section it is acted upon by a third compression spring  259  which is supported at one end by a shoulder of main part  258  and at the other end by the outer surface of the radially inner valve body part  265 . In this manner, the annular sealing seat  261  of vacuum valve body  257  is sealingly adjoining the underside of the radially inner sealing edge  267  of the first ring seal  221  of the first valve body  217 . Sealing seat  261  of vacuum valve body  257  lies radially inside the first sealing seat  224  of second valve body  218 , while the latter lies radially outside the second sealing seat  232  of inner cap component  214  and the latter in turn lies radially outside the third sealing seat  243  on the third valve body  219 . All sealing seats  224 ,  232 ,  243 ,  261  point axially outward, while all sealing seats surfaces  221 ,  231 ,  239  point axially inward. 
   In the initial operating position shown in  FIG. 6 , in which the pressure inside the radiator has not yet exceeded a first threshold value, the first flow connection  250  is closed by the sealing contiguity of the first annular or membrane seal  221  of first valve body  217  to the first sealing seat  224  of second valve body  218 . In other words, in chamber  234  and thus on the underside of the first ring seal  221  of first valve body  217 , the pressure inside the radiator in the form of the air cushion above the liquid coolant prevails through annular gap  247 . The second flow connection  251  along the outer circumference of second valve body  218  is closed by the sealing contiguity of the second seal  231  of second valve body  218  to the second sealing seat  232  of inner cap component  214 . 
   If the pressure inside the radiator increases to a certain point above the normal or ambient pressure, but below a first threshold value for pressure inside the radiator, the unscrew protection means of pressure cap  211  is activated. As shown in  FIG. 7 , the radially inner valve body part  265  of first valve body  217  is moved upward, while the second valve body  218  remains in its sealing position. Furthermore, the radially outer valve body part  266  of first valve body  217  remains in its sealing position in relation to the second valve body  218 . The membrane annular seal  221  allows this relative movement between the radially inner valve body part  265  and the radially outer valve body part  266  because this seal has a meandering shape between its two sealing edges  267  and  268 . As the radially inner valve body part  265  moves outward in the direction of Arrow A, it carries along guidance sleeve  271  which in turn moves coupling insert  280  against the effect of compression spring  281  while its fingers  272  push the axially inward-directed claws  282  out of recesses  283  in locking element  210 . This axial movement comes to an end when the inner shoulder of guidance sleeve  271  strikes against locking element  210 . This disengagement of coupling element  280  from locking element  210  of outer cap component  213  has the effect that handling element  212  idles in relation to locking element  210 , such that starting at a predetermined overpressure (in this case, for example, 0.3 bar) pressure cap  211  can no longer be unscrewed from the radiator&#39;s neck. 
   If the pressure inside the radiator continues to rise, i.e. above the first predetermined first threshold value (such as 1.4 bar), valve assembly  215  reaches the operating state shown in  FIG. 8  in which—due to the increased pressure inside the radiator the radially outer sealing edge  268  of the first ring seal  221  of the radially outer valve body part  266  of first valve body  217  lifts against the effect of its first compression spring  222  off the first sealing seat  224  of second valve body  218 , thus opening the first flow connection  250 , such that air from the air cushion above the liquid coolant can flow outside and thus compensate or reduce the overpressure. Due to the overpressure prevailing in chamber  234 , the second ring seal  213  of second valve body  218  continues to be pressed against the second sealing seat  232  of inner cap component  214 . If this reduces the overpressure again below the first threshold value, the radially outer valve body part  266  again becomes sealingly adjacent to second valve body  218 . The anti-rotation means remains activated as before. 
   If on the other hand, the pressure inside the radiator continues to rise even during or after the air cushion escapes, and if this causes liquid coolant to reach the underside of the second and third valve body  218 ,  219 , the fact that the annular gap  247  is very narrow causes the liquid coolant to back up at the entrance to annular gap  247  and thus dynamic pressure at the full-surface underside of third valve body  219 . This dynamic pressure causes the axial movement of third valve body  219  against the effect of its second compression spring  246 , at whose end the third sealing seat  243  of third valve body  219  adjoins the third ring seal  239  of second valve body  218  and closes the first flow connection  250  (see  FIG. 9 ). 
   The closing of the first flow connection  250  between the second and third valve body  218 ,  219  causes the pressure in chamber  234  to drop to a point below the said threshold value, such that the radially outer valve body part  266  of first valve body  217  is moved toward the second valve body  218  under the effect of the first compression spring  222 . This state is also shown in  FIG. 9 . If the cooling of the vehicle&#39;s radiator causes the pressure inside the radiator to drop and the liquid coolant to return again, the third valve body  219  is returned under the effect of its second compression spring  246 , such that the first flow connection  250  in this region is opened again, as shown in  FIG. 6 . 
   If on the other hand, the pressure inside the radiator continues to rise and the threshold value that constitutes the upper safety limit is exceeded, the second valve body  218  is lifted against the pressure of the first compression spring  222  bearing on the radially outer valve body part  266  of first valve body  217  is lifted off the second sealing seat  232  on inner cap component  214 , such that the second flow connection  251  is opened and the said overpressure can be reduced (see  FIG. 10 ). The anti-rotation means remains to be activated. This allows the said overpressure to be reduced via the second flow connection, after which the valve bodies can be returned via the different operating states by the different compression springs and coupling insert  280 , as shown in  FIG. 6 . 
   If the lower claws  283  of coupling insert  280  are radially offset in relation to recesses  274  in locking element  210 , it is enough to turn handling element  210  to bring claws  282  and recesses  273  to mesh again, such that the tightened compression spring  281  returns the coupling element into the activated position against the direction indicated by Arrow A. 
   Valve assembly  215  is returned to the initial position shown in  FIG. 6  only when the pressure inside the radiator ranges between a vacuum threshold value and a first overpressure threshold value. Such pressure conditions prevail, for example, when a vehicle is parked for a long period of time or when the vehicle is driven while the coolant inside the radiator is sufficiently cooled by the headwind and/or the fan. If the vehicle is parked after a long drive, the pressure may rise inside the radiator causing the contents of the radiator (air, water or water vapour) to flow into valve assembly  215 . If as a result of this after-heating effect, the coolant volume expands so much that it exceeds the volume of the radiator, this would necessarily lead to a discharge of coolant. This undesirable effect is prevented as described above when the valve assembly is in the operating state shown in  FIG. 7 to 9 . If in this operating state, the pressure in the cooling system continues to rise in an uncontrolled fashion, leakages and other detrimental effects due to excessive demands on the radiator and/or its hose connections must be prevented. These effects are prevented through the second valve step as shown in  FIG. 4 , where the radiator pressure is limited to a predetermined safety threshold value. 
   If there is a vacuum inside the radiator, and if this vacuum falls below a predetermined vacuum threshold value, sealing seat  261  of vacuum valve body  257  is lifted off the underside of the radially inside sealing edge  267  of the first ring seal  221  of first valve body  217  toward the inside of the radiator. Vacuum pressure valve  257  is lowered against the bias of third compression spring  259 , such that a flow connection (not shown) is opened between the inside and the outside of the radiator.