. The steam-engine and other heat-motors . f the center X and of thelength of the arm XA may be readily determined from the valvediagram. The student should draw a number of complete diagrams,including the indicator-cards to scale, keeping in mind that thesteam- and exhaust-laps are constant (Fig. 177). Lay off nega-tively an angular advance DO A. With the maximum throw ofthe eccentric OA (4xOA, Fig. 176) as a diameter construct onOA (and OA produced) valve-circles. With steam-laps OC andexhaust-lap OH construct steam- and exhaust-lap circles. With a 342 THE STEAM-ENGINE AND OTHER HEAT-MOTORS.
. The steam-engine and other heat-motors . f the center X and of thelength of the arm XA may be readily determined from the valvediagram. The student should draw a number of complete diagrams,including the indicator-cards to scale, keeping in mind that thesteam- and exhaust-laps are constant (Fig. 177). Lay off nega-tively an angular advance DO A. With the maximum throw ofthe eccentric OA (4xOA, Fig. 176) as a diameter construct onOA (and OA produced) valve-circles. With steam-laps OC andexhaust-lap OH construct steam- and exhaust-lap circles. With a 342 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. center on OX produced if necessary (to the right in this case) anda radius XA=4:XA (Fig. 176) construct an arc AffF. Join 0and any point / and construct on Of and on an equal pro-longation valve-circles; they will be the valve-circles for the newthrow and new angular advance. Note the effect on— 1. The crank-angle of admission. 2. The amount of steam-lead. 3. The point of cut-off. 4. The crank-angle of exhaust-opening and Fig. revs, per minute, width ofexhaust-lap 0, L/R=6; center X Fig. 178.—Diagram from a 12X12 engine. port 1, length of port 9, steam-lap f abouL which the eccentric swings is distant 14 from the center of the 179.—Diagram from Straight-Line engine llX14. 275 revs, per minute, width of port f, length of port, If crank end, If head end; exhaust-lap, crank end fj, head end \Y) eccentricity varies from l|f to 2\\ steam lead —.04 at quarter cut-off. (Kleins Steam-engine.) 5. The crank-angle and piston position of exhaust-closure. 6. The work of compression. 7. Note the effect of choosing the center X above andbelow the line OX. 8. Note the effect of sliding the eccentric in guides so thatthe center of the eccentric moves in a vertical line through A, REVOLUTION CONTROL. 343 9. Note the position of the point X in the diagram and onthe fly-wheel. 10. Note the effect of interchanging the position of thefixed and movi
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