Sealing mechanism for a double-lid seal structure
BACKGROUND OF THE INVENTION 
     The invention relates to a sealing mechanism for a double-lid system allowing a contamination-free transfer of radioactive or toxic substances from one container to another. 
     A double-lid system of this type is presented and described in German Pat. No. 20 47 538. As shown therein, a drum is initially pressed against the chamber flange in such a manner that simultaneously the flange-type seal of the drum is engaged with the flange of the chamber and the outer rim of the drum lid is engaged with the chamber lid seal. The drum lid and the chamber lid are then coupled together and the locking mechanism of the drum lid is released. The chamber lid and drum lid can then be lifted as a unit and brought into the chamber, allowing the transfer of substances from the chamber to the drum or vice versa. After completion of the transfer, the chamber and drum are both sealed and the chamber lid and drum lid are separated from each other. The purpose of this system is, above all, to prevent the chamber and drum lid outer surfaces, which are exposed to the atmosphere, from becoming contaminated in the process. Thus, the chamber seal and the drum seal must each carry out two different functions. Their radially outer regions should be engaged with the inner and outer surfaces, respectively, of the chamber flange; at the same time, their radially inner regions should hold the rim of the drum lid firmly between them. Problems, due, for example, to tolerances, may arise however. If the rim of the drum lid is somewhat too thick, the chamber flange seal will be impaired; if it is somewhat too thin, it will not be pressed against the seals sufficiently and will not seal properly. 
     The object of the invention is to improve the sealing machine of this kind of double-lid system in such a way that the chamber lid seal and the drum seal fully retain their sealing capability with respect to both the chamber flange and the rim of the drum lid during all operations, in spite of the occurrence of geometric or material deviations (tolerances) of the interacting parts. 
     SUMMARY OF THE INVENTION 
     In a seal structure for a double-lid seal system associated with a containment for handling toxic materials and a drum adapted to be mounted thereon for transferring toxic materials between the containment and the drum, a first seal member is disposed on said containment around an opening therein and a second seal member is disposed on a rim of said drum and extending around the opening in the drum. The containment opening has a containment lid engaging the first seal member from within and the drum has a lid engaging the associated second seal from without and also abutting the first seal when the drum is mounted to said containment. Means are provided for selectively engaging the drum lid with the drum or with the containment lid in such a manner that any space between the containment lid and the drum lid is sealed to prevent contamination of their outer surfaces. The second seal member has an annular closed gas chamber formed therein adjacent the drum lid rim so as to provide resiliency for safe sealing engagement with the drum lid. In order to accommodate the rim of the drum lid, the drum seal is preferably provided with a recess somewhat shallower than the thickness of the rim of the drum lid. This allows the radially inner region of the drum seal abutting the rim of the drum lid to be compressed to a greater extent than the radially outer region, both regions, however, having approximately the same attainable sealing force. Variations in the thickness of the rim of the drum lid or in the elasticity of the seals can thereby be accommodated without impairing proper operation of the seal. 
    
    
     SHORT DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partially sectional view of a double-lid system for transferring radioactive substances between a drum and an airtight chamber; 
     FIG. 2 shows an enlargement of detail A of FIG. 1; and 
     FIG. 3 shows detail A just before the chamber lid and drum lid are placed on the chamber flange and the drum seal, respectively. 
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     As shown in FIG. 1, the double-lid system comprises essentially a chamber lid 1 and a drum lid 2, which constitute the upper and lower lids, respectively. The chamber lid 1 is provided at its circumference with a chamber lid seal 3, of which the radially outer region 3a (FIG. 2) rests on a sealing surface 5a of the flange 5 which encloses the chamber opening, said sealing surface being situated in the interior of the chamber. At its opening the drum 6 is provided with a flange-type drum seal 7, of which the radially outer region 7a is biased against the chamber flange 5 sealing surface 5b situated outside the chamber 4. The outer rim 2a of the drum lid 2 is engaged between the radially inner region 3b of the chamber lid seal 3 and the radially inner region 7b of the drum seal 7. A locking piece 2b of the drum lid 2 is unlatched from a fastening groove 6a of the drum 6 in the position shown. A grabbing hook 1a of the chamber lid 1 is adapted to simultaneously grab a knob 2c of the drum lid 2 for pulling it toward the chamber lid 1, thereby causing the rim 2a of the drum lid 2 to abut the inner region 3b of the chamber lid seal 3. 
     FIG. 2 shows further that the radially inner region 7b of the drum seal 7 with the rim 2a of the drum lid disposed thereon is provided with a closed annular cavity 7c providing an air cushion with oval cross-section. The inner region 3b of the chamber lid seal 3 has a recess 3c of a depth corresponding to the thickness of the chamber flange 5. 
     As can be seen from FIG. 3, the region 7b of the drum seal 7 accommodate the rim 2a of the drum lid 2 in an annular recess 7d of a depth somewhat smaller than the thickness of the rim 2a of the drum lid 2. 
     As the chamber lid 1 and the drum lid 2 are together lowered into place (see FIG. 3), the rim 2a of the drum lid 2 first contacts the region 7b of the drum seal 7, this region having a greater elasticity due to the air cushion 7c. Further lowering of the lids compress the seal region 7b (FIG. 2) until the region 3a of the chamber lid seal 3 abuts the sealing surface 5a of the flange 5. The drum lid 2 can then be secured to the drum 6 by the locking piece 2b in the known manner and released from the chamber lid 1 by unlatching the grabbing hood 1a. The sealed and locked drum 6 can then be safely separated from the chamber 4 and removed. 
     It is noted that, with the arrangement according to the invention, the drum lid outer surface, although being taken into a contaminated chamber when being removed from the drum, is never exposed to contamination and remains uncontaminated upon removal of the drum from the chamber.