. The steam-engine and other heat-motors . g off BCifrom X. Project XY on any parallel line below the diagram and obtainXY , the length of the card; lay off XZ to obtain the line of novolume or clearance line. Lay off the absolute pressures 40 + 15pounds and 15+2 pounds and obtain the steam admission andback-pressure lines ZB and C8. Project B to Is and draw theisothermal expansion curve BT>n; project C\ the position of thepiston when the exhaust closes, and obtain 6 and draw the isother-mal curve of compression CCf. Find the points of steamadmission and exhaust-opening and sketch in the ex
. The steam-engine and other heat-motors . g off BCifrom X. Project XY on any parallel line below the diagram and obtainXY , the length of the card; lay off XZ to obtain the line of novolume or clearance line. Lay off the absolute pressures 40 + 15pounds and 15+2 pounds and obtain the steam admission andback-pressure lines ZB and C8. Project B to Is and draw theisothermal expansion curve BT>n; project C\ the position of thepiston when the exhaust closes, and obtain 6 and draw the isother-mal curve of compression CCf. Find the points of steamadmission and exhaust-opening and sketch in the expectedcurves. On a parallel line lay of 12 = *ieam lead; 13 = width ofport; 26 = the width of valve = steam and exhaust lap + widthof port. To draw the valve in its extreme right-hand position lay off34 = the overtravel and then 47 is the width already found. It isevident that 79 ought to be at least as wide as the other port whichis exhausting through 79. If the valve is thrown into its extreme 102 THE STEAM-ENGINE AND OTHER HEAT-MOTORS,. Fig. 72. VALVE-DIAGRAMS AND SLIDE-VALVES. 103 left-hand position it should go about an eighth of an inch beyond8. This prevents the formation of a ridge at that point. Ex. 30. If the data given in the above problem had been for thecrank end, draw the indicator-card. Ex. 31. Assume the indicator-card found in Ex. 30 for the headend and draw the crank end of the valve. Ex. 32: Suppose that the eccentric in Ex. 30 was insecurely fast-ened and slips backwards (or ahead) some 30°, draw the is the effect on steam admission and cut-off, exhaust-openingand compression? Ex. 33. Diminish the throw of the eccentric J in Ex. 30, andalso increase the angular advance 30g. Draw the card. Ex. 34. Draw the indicator-card for the crank end of Ex. 29 ifthe valve-stem is made \ too long. There is another form of the Zeuner diagram that is frequentlyseen. In this form, instead of using a negative angular advance,a negative rotation of the crank is used
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