Compressed Air Work And Diving 1909

96 COMPRESSED AIR WORK. The cast-iron lining was built up in rings, 23 ft. om- side 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 tapereel and measured 12.25 in. along the outside circumference, and 12.6014 in. along inside of flanges. This necessitated. t\ o special segments, marked b on plan, one on each side the key piece. These special segments measured 6 ft. 5.9948 in. alonc the outside circumference. All the other segments, a on plan, were interchangeable, 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 useel 011 curve cincl for keeping the tunnel true to line and gradient. In order to enable 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 cill bolt holes were spéicecl the same distance apart. The key piece also, when measured along the same line, was equ<il in length to the distance between two bolt holes. 1 he distance of each end bolt hole from the end of each segment was, of course, half the pitch. If a.t any time the cast-iron lining was found to be getting out of position, a, tapereel ring' was introduced, with the wiclest part at any point in the last ring which niight be required to correct the er ror. It will be noticed that the space left for caulking at the encls of the flanges is shaped so as to form a key.