Scientific American Supplement, No. 520, December 19, 1885 by Various
page 62 of 123 (50%)
page 62 of 123 (50%)
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Fig. XABCX is an ideal indicator card, taken from a cylinder, imagined to
be 600 feet long, in which the piston, making one stroke per minute, has therefore a piston speed of 600 feet per minute. Divide this card into any convenient number of ordinates, distant _dx_ feet from each other, writing upon each the absolute pressure measured upon it from the zero line XX. By way of example, let the diameter of the cylinder be 29.59 inches, and let the back pressure from all causes be 7 pounds uniformly throughout. It will be represented by the line b_{1}, b_{2}, etc. This quantity subtracted from the pressures p_{1}, p_{2}, etc., leaves the remainder (p-b) upon each ordinate, which remainder represents the net pressures which at that point may be applied to produce external power. If, now, A is the area of the piston, then the external power (d W) produced between each ordinate is: To any convenient scale, upon each ordinate, set off the appropriate power as calculated by this equation (1). A(p-b)dx dW = --------------. (1.) 33,000 There will result the curve _w, w, w_, determining the power which at any point in the diagram is to be regarded as a gain, to be carried to the credit side of the account. It is evident that, so long as the gains from expansion exceed the losses from expansion, it is profitable to proceed with expansion, but that |
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