III. HIGH-PRESSURE COMPRESSORS.
B. High-duty Apparatus.-
7. Hydraulic Piston-Compressors.-An example of this type is the improved Sommeiller compressor used in the tunneling of Mont Cenis, as shown in Fig. 154.
The two cylinders of each compressor are isolated, and each has
its own piston, only one of the faces of which (that in contact
with the water, and which, by the intermediation of the latter,
acts on the air) is concealed, while the other is easily accessible
in the pump-body in which it moves. The piston is very long,
so that it guides itself. The valves consist of four circular
leaves of leather with metallic backing, resting on an inclined
bronze seat. These are disposed, two by two, along the vertical
column of the compressor, as shown in the engraving. The upper
ones are the inlet-valves, and take air from a cylindrical iron
envelope which communicates with the atmosphere. The lower valves
open into a water-box, and serve for the introduction of water
to replace that entrained by the compressed air. The delivery-valve
is of bronze, and conical. Dimensions and data: Absolute air-pressure,
7 atmospheres; volume of air furnished at this pressure by the
two compressors connected to a single hydraulic wheel, 68.4 cubic
feet. Motor, hydraulic wheel, 216 inches in diameter, and 163.8
inches in breadth, discharging 35.3 cubic feet of water per second,
under a head of 216 inches. Direct crank-connection. Compressor:
Piston-diameter, 23.4 inches; stroke, 58.5 inches; useful volume
of cylinders, 14.9 feet; number of turns per minute, 8 ; theoretic
volume of air delivered at this velocity, 476.55 cubic feet.
Final temperature of air on leaving compressors, 104° Fahr.