Compressed Air Author:Frank Richards Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: acl is but 27 lbs., or only 76 per cent of the former. The comparison should, however, be reversed. The adiabatic mean effective pressure is 131 per cent of t... more »he isothermal mean effective pressure : 27 : 3S-36 : : 1 '. M1, and this 31 per cent is, of course, the additional, or, as we might say, the unnecessary, power employed, assuming iso- thermal compression to be attainable. Neither of these compression-lines, ab or ac, is possible in practice. Air cannot be compressed without losing some of its heat during compression, so that the actual compression-line must always fall within or below the line ab. On the other hand, it is equally impossible to abstract all the heat from the air coincidently with the appearance of that heat, so that the actual compression-line must always fall outside or above the line ac. The best air-compressor practice of to-day is very near the line ao, or the mean of the adiabatic and the isothermal curves. The actual line is generally above this, and seldom below it. It would be impossible to produce a line exactly coincident with this in practice. If we produced a line giving the same mean effective pressure as ao, it would probably run above ao for the first half of the stroke, and perhaps a little below it at the last. If the compression were two-stage or compound,—that is, if it were done in two or more cylinders instead of in one,—there would of course be breaks in the continuity of the compression-curve. The mean effective pressure for the line aol is about 31.5 lbs., or still nearly 17 per cent in excess of the M.E.P. for the line acl. As aol represents exceptionally good practice, the loss of power for the average practice in air-compression, independently of the friction of the machinery, may be put at 20 per cent. Lest some impatien...« less