6 and 7 so that the end plates 8 and 9 overhang the principal member 5 provided in the overhanging segments 10 are through holes 11 for arranging connecting or tie rods 12 the end plates 8 and 9 are usefully embodied identically in terms of size such that the through holes 11 of the mutually opposing end plates 8 and 9 are congruent and permit the arrangement of each tie 15 rod 12 in order to assure positionally correct assembly of the end plates to the principal member 5 a groove 13 is provided on the side of the end plates 8 and 9 facing the principal member 5 for the edge 14 of the open ends 6 and 7 when the end plates 8 and 9 are assembled such that the ends 6 and 7 are closed the edge 14 of the principal member 5 engages the groove 13 of each end plate and thereby assures positionally correct assembly with the principal member 5 this arrangement also assures precisely aligned mutually correct positioning of the through holes 11 for installing the tie rods 12 three tie rods 12 are provided around the circumference of the end plates 8 9 one tie rod 12 approximately intersects the center longitudinal axis 48 of the pressure container 1 in an extension of the pressure piece over the opening apparatus.