Compressed Air Work And Diving 1909

EAST RIVER TUNNELS. 93 pressure and water not balance at the bottom of the screen, the water as it rose would compress the air and thus bring about a balance. Shoulcl also the emergency lock happen to get half full of water, this woulcl not interfere with its working, or add to the clanger in any way. 7 o prevent the air from escaping between the tail of the shield and the cast-iron lining, segmental plates were fixed to the back of the rams round the top half of the shield. Except when an iron ring was being- erected, these were kept pushed out against the flanges of the lining, and as they were made to fit quite close to the shield, and to almost touch each other at the encls, they practically completely closed the Space between the cast- iron lining and the tail of the shield clown to the level of the bottom of the safety screen. This space was also kept pugged up with clay. There were twenty-seven of these rams, and each had an effective area of 54.7 sq. in. With a water pressure of 3 tons to the square inch this gave a force on the back of the shield of very nearly 4,500 tons. These rams had a piston arrangement inside, which was in constant communication with the pressure, and which actecl as a pull back. When the pressure, therefore, was taken off, the rams went home automatically. This arrangement is a great improvement upon the ordinary one, which is, to have a ram of smaller diameter fixed in the head of the large ram. This forces the ram home by pushing against the cast-iron lining, but the small ram has then to be pushed home by hånd. Also a copper flexible known as the “pull back” has to be connected up each time to each ram separately, and all this takes up a lot of time. Another feature of these shields is the hoods, which came out 3 ft. in front of the cutting edge and ex-