184 THE SECOND-CLASS ENGINEER.
the indicator-diagrams (Figs. 15 and 16) were taken
from a locomotive-cylinder 18 inches diameter, 24
inches stroke; steam-ports 13 by 2 inches; exhaust-
port 13 by 3 inches; lap of valve outside 11 inch;
inside inch. Each figure shows three diagrams for
periods of admission, respectively 16, 11%, and 7 inches
of the stroke, the terminations of which, and of the
expansions, are pointed off on the figures. For the
first figure, the speed of piston was 240 feet per minute;
for the second, 770 feet per minute. The wire-drawing
at the lower speed was obviously nothing; at the
higher speed, the pressure fell 3 lbs., 12 lbs., and
D
Figs. 15 and 16.-Indicator-Diagrams.
25 lbs. below the initial pressure, before the steam was
cut off: doubtless explained by the fact that, in the
three cases, the travel of the valves was respectively
4, 3, 37 inches; and the maximum opening of the
port was 1, nearly, and inch. It was found,
however, that, in the third case, with the shortest
admission, the steam-line was practically straight and
parallel to the atmospheric line, at speeds of piston up
to 450 feet per minute. In inferiorly arranged engines,
with short lap and short travel of valve, wire-drawing
is considerably greater than in the example just illus-
trated. With the same sizes of cylinders, a -inch
