Air-lock

Chamber having two doors, one opening into a cai on or compartment containing compre ed air, and the other communicating with the outer atmosphere. The outer door being open, workmen enter the air-lock; it is then closed and the compre ed air slowly admitted until the inner door can be opened, when the workmen enter the cai on. The greatest air pre ure in which men can work is ab. 45 lbs. per sq. inch above the atmosphere, corresponding to a depth of about 100 feet below the water surface. The figure shows a pneumatic pile with an air-lock at the top.