Compressed Air Work And Diving 1909

96 COMPRESSED AIR WORK. The cast-iron lining was built up in rings, 23 ft. out- sicle diameter, 21 ft. 2 in. inside flanges, and 2 ft. 6 in. wide, with eleven segments and key piece to each ring (Fig. 15c). The key piece was tapered and measured 12.25 in- along the outside circumference, and 12.6014 in. along inside of flanges. This necessitatecl t\ -o special segments, marked b 011 plan, one 011 each side the key piece. These special segments measured 6 ft. 5.9948 in. along the outside circumference. All the other segments, a on plan, were interchangeLible, and measured 6 ft. 5.6489 in., and their encls were radial to the centre line. The faces of all flanges were machined, and special tapered segments were usecl on curve and for keeping the tunnel true to line and gradient. In orcler to enablc joint to be broken, segments A and b were made the same length when measured along a line passing through the centre of the bolt holes, and all bolt holes were spaced the same distance apart. The key piece also, when measured along the same line, was equal in length to the distance between two bolt holes. The distance of each end bolt hole from the end of each segment was, of course, half the pitch. If at any time the cast-iron lining was found to be getting out of position, a tapered ring was introduced, with the widest part at any point in the last ring which might be required to correct the error. It will be noticecl that the space left for caulking at the encls of the flanges is shaped so as to form a key.