II. MEDIUM-PRESSURE COMPRESSORS.
A. Low-duty Apparatis.-
3. Compressors for Bridge-Foundations-These are mainly
employed for forcing air into bridgecaissons. The disposition
of the Cail compressor used at Kehl Bridge is the plan for Fig.
143. The rods of the cylinders are connected. The compressing
cylinder is at the base of an iron box, so that the intermediate
space between its outer periphery and the box may be filled with
water. In this box also are the aspiration and compression valves.
The dimensions, etc., are as follows: Absolute air-pressure,
3.5 atmospheres; volume furnished at this pressure, 60 cubic feet.
Motor: Diameter of piston, 12.5 inches; stroke, 23.6 inches;
fly-wheel, 6.5 feet in diameter; steam-pressure, 75 lbs. Compression
cylinder: Diameter of -piston, 15.7 inches; stroke, 23.6 inches;
use. ful volume of cylinder, 4,561 cubic inches; revolutions per
minute, 40; theoretic volume generated per minute, 213 cubic feet.
The caissons of the East River Bridge, New York City, were supplied
with compressed air by six steam-engines driving two single-acting
compressors, with cylinders 14.9 inches in diameter by 13.7 inches
stroke. See CAISSONS.