. Machinery for metalliferous mines : a practical treatise for mining engineers, metallurgists and managers of mines. e, and at a high temperature ; the pistoncontinuing to i, where it then begins the return stroke. The discharge valve now having closed we have the volume (a e)filled with compressed air, which expands to the point (j), and as l82 MACHINERY FOR METALLIFEROUS MINES. Air delivered bt/double St3ge Comp^ the volume is small, and the velocity slow, we may assume that theexpansion follows the isothermal curve, since the piston and cylinderend are at this time at a high temperature, a
. Machinery for metalliferous mines : a practical treatise for mining engineers, metallurgists and managers of mines. e, and at a high temperature ; the pistoncontinuing to i, where it then begins the return stroke. The discharge valve now having closed we have the volume (a e)filled with compressed air, which expands to the point (j), and as l82 MACHINERY FOR METALLIFEROUS MINES. Air delivered bt/double St3ge Comp^ the volume is small, and the velocity slow, we may assume that theexpansion follows the isothermal curve, since the piston and cylinderend are at this time at a high temperature, and impart their heat succeeding strokes the fresh air taken in is only the volume (j li) instead of a b, and thecapacity for taking in fresh air isnow only 85 per cent, of thewhole cylinder volume. This decrease in volume, how-ever, is not accompanied by a lossof power, since work equivalentto the area (a i j) is given backby the air in the clearance space,and therefore the only loss isin capacity; the work performedduring the cycle is now measured)y the space (b G H 1 j). Owing to the heat generated. n: C IK l^olume of free Air dra tf/n in when Single Stage Compressord d° dj^ L. P. Volume d Fig. 124.—Am Card Illustrating Compound Compressor. during compression, the air at h nearly always shrinks to the point (k)before it can be utilised in the motor, the measure of work thusdissipated being the area (b c h k d). We will now consider double stage compression, using the samecylinder as before for the first stage. The air is drawn in till the piston reaches b, when it is compressedalong the adiabatic curve as before, but only to the point (g), whereit passes into an intermediate cooler on its way to the other piston moves on to L, the end of its stroke. The same clearnessas before (fl) now contains air at 365 lb. instead of 90 lb. absolutepressure, which expands as before isothermally to the point (m), causinga loss in capacity of only 4] per c
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