Présentation de l'éditeur
To find the terminal pressure divide the initial pressure by the ratio of expansion. EXAMPLES team of 75 pounds gage pressure is expanded to six times its original volume. What will its pressure be? A gage pressure of 75 pounds is 75-{-15=90 absolute, approximately, and90-1-6= 15 pounds absolute or zero gage. To find the initial pressure multiply the terminal pressure by the ratio of expansion. EXAMPLE In an engine cylinder steam is expanded to 4.5 times its volume at cut-off, the pressure at the end of the stroke being 18 pounds absolute. What is the initial pressure? 4.5X18=81 pounds absolute, or 81 15=66 pounds gage. In Fig. i leto xrepresent the absolute zero of pressure ando A the zero of volume. Suppose we have a volume of steam proportional to AB or oI at 120 pounds absolute. If it is exF lG. I. FIG. 2. panded to twice its original volume its volume will be represented by the line o2 and its pressure will be 120-7-2=60 pounds. Setting off 60 pounds on the 2d ordinate we have the point a as representing its pressure at this volume. If it is expanded to three times its original size its volume will be bounded by the ordinate 3and on this ordinate we set off the pressure 120-4-3=40 pounds, locating the point b. Locating in the same manner the points cd ef g, representing the pressures at successive volumes, we find that if joined together they form a curve which constantly approaches, but never reaches the zero line. Wre can locate as many points on this curve as we like. For instance, when the volume has expanded to y2 the pressure will be 120-1-1.5=80 pounds, which set off on the corresponding ordinate gives us the point h.
(Typographical errors above are due to OCR software and don't occur in the book.)
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