. The steam-engine and other heat-motors. oint on thecurve from the other asymptote. Suppose that we have theasymptotes CB and CD and any point a of the curve. Througha draw several radiating lines similar to aabb. Only one is drawnto avoid confusion. Lay off bbf equal to aa; b in each will 70 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. be a point of the curve. Any of the points b will serve as adid for finding other points. The same method of constructionwill serve on the compression curve FE. f The Point of Cut-off.— The term cut-off as applied tosteam-engines, although somewhat indefinite, is u
. The steam-engine and other heat-motors. oint on thecurve from the other asymptote. Suppose that we have theasymptotes CB and CD and any point a of the curve. Througha draw several radiating lines similar to aabb. Only one is drawnto avoid confusion. Lay off bbf equal to aa; b in each will 70 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. be a point of the curve. Any of the points b will serve as adid for finding other points. The same method of constructionwill serve on the compression curve FE. f The Point of Cut-off.— The term cut-off as applied tosteam-engines, although somewhat indefinite, is usually con-sidered to be at an earlier point in the stroke than the beginningof the real expansion line. That the cut-off may be defined inexact terms for commercial purposes, as used in steam-enginespecifications and contracts, the Committee recommends that,unless otherwise specified, the commercial cut-off, which seemsto be an appropriate expression for this term, be ascertainedas follows: Through a point showing the maximum pressure. EC Fig. 46.—Four-valve Engine. Slow-speed Commercial Cut-cff=—^ during admission draw a line parallel to the atmospheric the point on the expansion line near the actual cut-offdraw a hyperbolic curve. The point wheie the£e two lines inter-sect is to be considered the commercial cut-off point. The per-centage is then found by dividing the length of the diagrammeasured to this point by the total length of the diagram andmultiplying the result by 100. The principle involved in locating the commercial cut-offis shown in Figs. 46 and 47, the first of which represents a dia-gram from a slow-speed Corliss engine, and the second a dia-gram from a single-valve high-speed engine. In the latter casewhere, owing to the fling of the pencil, the steam line vibrates, t See Trans. A. S. M. E. Standard Rules. *? CURVES AXD THE WORK OF EXPAXSIOX. 71 the maximum pressure is found by taking a mean of the vibra-tions of the highest point. The com
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