AIRLOCKS ON CAISSONS FOR ADMITTING AND REMOVING MATERIAL.
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The cocks admitting pressure from within, or allowing the same to escape, were made of small bore, to prevent any one from making this change too quickly, as this would not be unaccompanied by risk of injury to the person exposed to it. One man was seriously injured by the india-rubber joint of one door suddenly giving way and exhausting the pressure in an instant of time, instead of taking from one and half to two minutes. Fortunately, the subject was a strong and healthy person, and well accustomed to high-pressure work, otherwise the result might have been fatal. As it was, there was considerable bleeding from the nose, the mouth, and the ears, and some pains in the limbs. The lock for admitting or removing material was different in construction. (See Figs. 40, 41, 42, 43, 44, 45.) The principal portion of it was also a part of the 3 ft. 6 in. air-shaft closed at top and bottom by a sliding door. A recess was left at each end for these doors to enter into when drawn open. and there was a further recess which contained the winding drum for lifting and lowering the buckets. The sliding doors were worked by horizontal hydraulic rams, but could, in the absence of water pressure, be moved by rack and pinion and handwheel. By an interlocking arrangement of simple construction it was impossible to open both doors at once, a contingency which would have been fatal to the men working in the air-chamber below. The winding drum was driven by a worm and wormwheel outside the lock, and actuated by a pair of ordinary reversible engines, the main shaft which carried the drum being provided with air-tight glands at both ends where passing the sides of the air-lock. A chain passed round the drum and over a snatchblock suspended
