Wrought iron is said to expand 1/150,000 of an inch for each degree of
heat communicated to it; to make the calculation take the length of the
pipe in inches, multiply it by the number of degrees between the normal
temperature it is required to attain when heated, and divide this by
150,000. Suppose the pipe is 100 feet long, and its temperature zero,
and it is desired to use it to carry steam at 100 pounds pressure—equal
to a temperature of 338 degrees—multiply 100 feet by 12 to reduce it
to inches, and by 338, the difference in temperature; divide this by
150,000, and the result will be 2.7 inches, which would be the amount
of play that would be required, in this instance, in the expansion
joint.
[Illustration: Figs. 153 and 154.]
Figs. 153 and 154 show a properly designed arrangement of steam
connections for a battery of boilers. To the nozzles, risers are
attached by means of flanges, and from the upper ends of these risers
pipes are led horizontally backwards into the main steam pipe. In this
horizontal pipe, the stop valves, one to each boiler, are placed. These
valves should have flanged ends as shown, so that they may be easily
removed, if repairs become necessary, without disturbing any other
portion of the piping. Unlike the engraving, the valve C should be
arranged in another position: the stem should, of course, be horizontal
or nearly so, in order that the valve may not trap water.
By this arrangement it will be seen that the movements of the boilers
and the piping itself are compensated for by the spring of the pipes.
The height of the risers should never be less than three feet, and when
there are eight or ten boilers in one battery, they should be, if room
permits, six to eight feet high, and the horizontal pipes leading to
main steam pipe should be ten or twelve feet or more.