Twentieth century hand-book for steam engineers and electricians, with questions and answers .. . ithout havingdone any useful work except to merely fill the spacedevoted to clearance. On the other hand, if theexhaust valve is closed before the piston completesthe return stroke, the steam then remaining in thecylinder will be compressed into the clearance spaceand can be deducted from the total volume which,without compression, would have been exhausted atthe terminal pressure. Figs. 79 and 8o, which are reproductions of diagramstaken by the author while adjusting the valves on a16 x 42 in. co
Twentieth century hand-book for steam engineers and electricians, with questions and answers .. . ithout havingdone any useful work except to merely fill the spacedevoted to clearance. On the other hand, if theexhaust valve is closed before the piston completesthe return stroke, the steam then remaining in thecylinder will be compressed into the clearance spaceand can be deducted from the total volume which,without compression, would have been exhausted atthe terminal pressure. Figs. 79 and 8o, which are reproductions of diagramstaken by the author while adjusting the valves on a16 x 42 in. corliss engine, will serve to graphically DIAGRAM ANALYSIS 237 illustrate this point. Fig. 79, which was the first oneto be taken, shows no compression. The point ofadmission at A is plainly defined by the square cornerat the extreme end of the stroke. The clearance of FIGURE 79. this engine is 4 per cent, of the volume of the pistondisplacement. The engine being 16 in. bore by 42 , the piston displacement is found by the follow-ing calculation: Area of piston, sq. in. x stroke,. FIGURE 80. 42 in. = cu. in. The volume of clearancespace is equal to cu. in. x .04 = cu. in.,which divided by 1,728 = .195 cu. ft. By reference to Fig. 80, taken after adjusting the 238 ENGINEERING valves for compression, it will be noticed that thesteam is there compressed to 37 lbs., the compressioncurve beginning at C and ending at B. There istherefore compressed during each stroke a volume ofsteam equal to .195 cu. ft. at a pressure of 37 , or 52 lbs. absolute. One cubic foot of steam at 52 lbs. absolute pressureweighs .1243 lbs., and .195 cu. ft. will weigh .1243 = .0242 lbs. The engine was running at 70 R. P. M., or 140strokes per minute. Thus, according to Fig. 80, thetotal weight of steam compressed and doing usefulwork during one hour, and which without compressionwould have passed out through the exhaust pipe, isequal to .0242 x 140 x 60 = 2
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