j PISTON AND CRANK EFFORT DIAGRAMS 323 
_ piston at the middle of the forward stroke? Compute the horse-power of this 
_ engine when the speed is 80 revolutions per minute. 
__ &, Indicator d ms from the cylinders of a horizontal tandem compound 
_ steam-engine are given in Fig. 502. Diameter of H.P. cylinder, 24 inches, 
Diameter of L.P. cylinder, 46 inches. Stroke of pistons, 6 feet. Diameter of 
LIN [Hel YI | 
FRONT. | BACK. 
_f 
oN 
Pe i 
fg ; 
me ied et ee = mies 
-rod AB, 5jinches. Diameter of piston-rod CD, 4? inches. Construct 
on a straight base 4 inches long the combined piston effort diagrams for the 
forward and return strokes, showing the combined effort on the two pistons per 
square inch of the back of the low-pressure piston. Effort scale, 1 inch to 
30 Ibs. Compute the horse-power of this engine when the speed is 50 revolu- 
tions per minute. 
3. The piston of an engine, and all the parts rigidly connected to it, weigh 
400 Ibs., and the stroke is 20 inches. The crank shaft makes 150 revolutions 
r minute. Assuming an infinite connecting-rod, determine the difference 
ween the total effective pressure on the piston and the thrust on the cross- 
head pin, (a) at the beginning of the stroke, (b) at 5 inches from the beginning 
of the stroke. 
"4 In a steam-engine the piston at the beginning of its stroke is exposed to 
a total pressure of 2000 lbs., but the inertia is such that the thrust of the piston- 
rod at the cross-head is only 1600 lbs. The speed of the engine is now raised 
until it becomes half as great again as before, while the pressure is unchanged: 
what is the thrust of the piston-rod ? [{Inst.C.E.] 
‘ 5. In the engine referred to in Exercise 2, the total weight of the recipro- 
; cating yet 6700 Ibs. The length of the connecting-rod is 15 feet, and the 
speed of the crank shaft 50 revolutions per minute. Construct on a stroke base 
; 4 inches long the diagram of accelerating force per square inch of the back of 
the low-pressure piston, the force scale to be 1 inch to 30 lbs, 
6. In a direct-acting steam-engine the stroke is 2 feet. the connecting-rod 
4 feet long, the piston 14 inches diameter, the weight of the reciprocating oe 
300 Ibs., and the revolutions 180 per minute. At the commencement of the 
down stroke the difference of pressure per square inch on the two sides of the 
— is 40 Ibs. (acting downwards) ; at the end of the down stroke the difference 
10 lbs. (acting upwards). Find the effective pressure transmitted to the crank 
pin in these positions. Ifthe steam pressure remained unaltered, at what speed 
would the engine have to run in order to make the effective pressure at the end 
of the stroke zero, and what would then be the effective pressure at the commence- 
ment of the stroke? (U.L.] 
“7. Construct the polar and rectangular diagrams of crank effort for a direct- 
acting steam-engine in which the effective pressure on the piston is 50 Ibs. per 
ware inch throughout each stroke, and determine the coefficient of fluctuation 
of energy, (a) assuming an infinite connecting-rod, (6) taking the length of the 
connecting-rod § times the length of the crank. 
: 8. To the left of Fig. 503 are shown the piston effort diagrams for a direct- 
steam-engine, the pressures being in lbs. per square inch. Construct the 
acting t 
and rectangular gy of crank effort, and find the coefficient of 
Saati of energy, also the ratio of the maximum torque to the mean torque 
yo tere wee Ce ee Se 
tell “le a ee 
