Compressed Air Work And Diving 1909

64 COMPRESSED AIR WORK. lubricated, would have been forceel home by the tongues. Thus it was quite impossible for an accident to take place through the carelessness of the men working the air valves. The bueket was hoisted by a 5-ton electrically driven crane. The lid of the door was suspended (see Fig. 12) from the jib head of the crane by two chains. As the bueket was hoisted out of the chamber, taking the lid with it, the bueket was attached to the lid by two short chains, which, when the bueket was inside, were bunched up on the lid out of the way. By this means the shell of the bueket was held up when the bueket was lowerecl and the bottom opened and the excavatccl material tippeel into hoppers to be taken out to sea. The caissons were built in situ on overhanging timber caps or cantilevers marked ff in the diagram, Fig. 13. The method of lowering was as follows. Tresties were erected on each side of the caissons, on which were placed four box girders 3 ft. high and 1 ft. 6 in. wide. At each of the four points of support the top and bottom flanges were cut away to allow the sixteen suspeneling links to pass through. Between each pair of links was placed a 150-ton hydraulic ram. On the top of each ram were small cross sfirclers and these took the weight of the caisson by means of two 2-in. diameter turneel pins which passeel through holes in the suspeneling links which had been clrilled every 18 in. The stroke of the rams was 2 ft. They were connected up to two hånd pumps and in such a way that the four along one side could be shiit off or opened out together, or the four at each end. This was to enable the caisson to be kept straight with- out too great a load being put on any one pair of links. The rams could also be shiit off singly or in pairs. In lower- ing, the first operation was to insert pins at bb and then raise the rams a fcw inches until the holes cc in the links