III. HIGH-PRESSURE COMPRESSORS.
A. Low-duty Apparatus.-
2. Hydraulic Compressors.-The compressor used in the mines
of Perseberg, Sweden (Fig. 146), is connected with and actuated
by the pumping-engine. It consists of two vertical cylinders
connected by a cast-iron bed below, and carrying a valve-box above.
In one of the cylinders is the piston which , surrounded by water,
causes the liquid at each stroke to rise in one vessel and descend
in the other. In order to facilitate the descent of the piston,
a cross-head is attached to the piston-rod from the arms-bars
extend down on each side and below the apparatus. These bars
sustain a counterweight which equilibrates the water in the second
cylinder. Simple flap-valves of leather backed with metal are
employed. The inlet-valves are counterweighted. The dimensions
and data are as follows: Absolute air-pressure, 2.5 atmospheres;
volume of air furnished at this pressure, 32.1 cubic feet. Compressor
(double-acting): Diameter of piston, 15.6 inches; stroke, 85.8
inches; useful volume of cylinder, 10 cubic feet; number of double
strokes per minute, 4; theoretic volume de. livered at this velocity,
80 cubic feet.