Compressed Air Work And Diving 1909

64 COMPRESSED AIR WORK. lubricated, would have been forcecl 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 bucket was hoisted by a 5-ton electrically driven crane. The lid of the cloor was suspended (see Fig. 12) from the jib head of the crane by two chains. As the bucket was hoisted out of the chamber, taking the lid with it, the bucket was attacheel to the lid by two short chains, which, when the bucket was inside, were bunched up on the lid out of the way. By this means the shell of the bucket was held up when the bucket was lowered and the bottom opened and the exeavated 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 foliows. Tresties were erected on each side of the caissons, 011 which were placecl 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 suspending links to pass through. Between each pair of links was placecl a 150-ton hydraulic ram. On the top of each ram were small cross girders and these took the weight of the caisson by means of two 2-111. diameter turned pins which passeel through holes in the suspending links which had been drilled every 18 in. The stroke of the rams was 2 ft. They were connected up to two hanel pumps and in such a way that the four along one side coulcl 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 coulcl also be shut 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