74 of the indicator element in such a way that they remain connected only by means of a connecting line 85 with the indicator element and for this reason are elastically arranged on the same in this case each locking element on its free end possesses a widened portion which carries a bearing area 86 externally the transitional region between the first stage 78 and the second stage 79 of the through bore 77 in the sealing plate 74 is constructed in the form of an inclined plane 87 which in its configuration corresponds to the bearing surface 86 of each locking element 80 81 82 83 the lower rim 78 of the indicator element 76 is supported upon the helical spring 71 which in turn is supported on the first cylindrical element 68 that is why the helical spring 71 presses from below against the detector element 76 which would pass through the through bore 77 in the sealing plate 74 if the bearing surfaces 86 of the locking elements 80 81 82 83 were not bearing against the inclined plane 87 in the sealing plate 74 and would thus hold back the indicator element 76 the locking elements 80 81 82 83 are in this case when the compressed air bottle is in the filled state prevented from swivelling inwardly and from releasing the indicator element 76 since the indicator element 76 is constructed in a hollow cylindrical fashion and the second cylindrical element 69 is inserted into the.