III. HIGH-PRESSURE COMPRESSORS.
B. High-duty Apparatus.-
1. Compressors with no Refrigeration.-When no means of cooling is employed, compressors cannot be advantageously used except for low pressures, and at velocities so far reduced that the heat developed by the compression may be dissipated as fast as generated. It is rarely that a pressure above 2 at. mospheres can be reached, working at high speed, as dry air compressed to this degree attains a temperature of 165° Fahr.; or 3 atmospheres work. ing at low velocity as the final temperature of air compressed under this pressure exceeds 266° Fahr.
The Sachs compressor (Fig. 147) is an example. In this case the
motor (at Vieille Montagne) is an 8-horse-power hydraulic wheel.
The useful effort applied to the compressor is 6-horse power,
the remainder being otherwise utilized. The piston acts in horizontal
cylinder directly on the air. The three inlet-valves at one end
of the cylinder open into the atmosphere; the three delivery-valves
in the other end open into chambers which communicate with a cast-iron
tube placed parallel to the cylinder. On this is a safety-valve
and the connection for the air-conduit. Dimensions and data:
Absolute air-pressure, a atmospheres; volume of air furnished
at this pressure, 47 cubic feet. Air-cylinder. Diameter of piston,
9.7 inches; stroke, 85.8 inches; useful volume of cylinder, 2,730
cubic inches; revolutions per minute, 45; theoretic volume delivered
per minute, 143 cubic feet. As compression is not carried to
a high degree, the heat generated causes no difficulty.