856,750. Tanks. SILLEY, H. A. J., and UNTHANK, D. G. Sept. 11, 1959 [July 2, 1958], No. 21238/58. Class 69 (1). A collapsible tank has walls which are straight sides in plan and has a rigid bottom 1 and rigid top 4 connected together by side walls 8 capable of being folded into a plurality of superposed pleats and one or a number of rigid frames 9 connected with the side walls to establish the outer fold lines of the pleats, the vertical alignment of the bottom 1, top 4 and the frames 9 being maintained by pairs of folding members 10, the two members 11, 12 of each pair being hinged together at 13 and hinged respectively at 15 to the two adjacent frame members 9 or to the top 4 or bottom 1, with the hinge axes 13, 15 normal to the general plane of the adjacent wall of the tank so that the folding members fold and unfold in vertical planes parallel to the general plane of the adjacent wall of the tank. The top 4 has an edge frame 6 and the bottom 1 has an edge frame 3. The frames 3, 6 and 9 are formed of H-section bar so that in the collapsed condition of the tank the parts of each pair of folding members 10 are accommodated in spaces formed by registering recesses in adjacent parts of the frames 3, 6 and 9. A short section of the central web of the H-section bars is removed as shown at 14 (Fig. 4) so that the connection of the levers 11, 12 may be effected at 15. Stops 27 are provided on the outer ends of the levers 11, 12 for engagement with the webs of the H-section bars at one side of the gaps 14 to limit the extent to which the folding members 10 can be unfolded so that the axes of the pivots 13, 15 do not become aligned. Compressible thickening members 19 are provided on the walls of the tank for pressure engagement with the edges of the folding members 10 in the extended condition of the tank and rubbing engagement with the edges of the members 10 during an early part of the movement of the tank towards the collapsed condition. Ropes 24 with tension spring inserts 25 (Fig. 5) extend across the interior of the tank between flexible anchorages 26 provided on the required inner fold lines 20 of the tank walls. Alternatively, freely movable weights are provided in the tank, each connected through a plurality of flexible members with anchorages on the walls of the tank located on the desired inner fold lines of the walls of the tank.