. The steam-engine and other heat-motors. ing of futureI value. One should remember that questions may arise other t See Trans. A. S. M. E. Standard Rules. 64 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. than those of present interest. It is much better to have toomany than too few data after the test is over. It is advisable to make notes of special circumstances such asthe end of the cylinder which is represented by the card, thesize of pipes and ports, pressures at the boiler and at the throttle,description of the boiler and special incidents and a locomotive diagram note the speed
. The steam-engine and other heat-motors. ing of futureI value. One should remember that questions may arise other t See Trans. A. S. M. E. Standard Rules. 64 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. than those of present interest. It is much better to have toomany than too few data after the test is over. It is advisable to make notes of special circumstances such asthe end of the cylinder which is represented by the card, thesize of pipes and ports, pressures at the boiler and at the throttle,description of the boiler and special incidents and a locomotive diagram note the speed from the time elapdngin passing mile-posts, the position of the link and throttle, thecharacter and number and weight of cars drawn, the grade, thesize and position of the blast orifice, character of the coal andquantity burned, amount of water taken on. In marine work take data that may be of value from theships log. Fig. 37 is an indicator-diagram from a non-condensing enginein good condition. In most steam-engines it is desirable that. Fig. 37. the crank-pin revolve at uniform speed. We shall find thatthis necessitates a very irregular motion of the piston. As thelatter approaches the end of the stroke it slows down, comingto absolute rest at the end of its stroke, since it must reverse STEAM-ENGINE INDICATOR AND ITS CALIBRATION. 65 its motion. On the return stroke the speed increases to a pointnear mid-stroke and then decreases as before. The card showsthat the valve commences to open for steam just before thepiston finishes the preceding stroke, at A, so that when the pis-ton is actually on the dead-center and instantaneously atrest the valve is open—the amount is called lead—and admit-ting steam. The pressure against the piston rises rapidly andremains constant as long as the opening of the port is the piston is half-way between B and C the port has itsmaximum opening and the valve starts on its return to closethe port. With a diminishing port opening
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