The Locomotive - Lighthouse Survival Blog

138 THE LOCOMOTIVE, [September,
added to 19.1 gives 19.7, which is the number of Vjraces that would be required if 100
lbs. were the allowable pressure. For a boiler on which only 75 lbs. are allowed, -j^/^ of
this number of braces will be sufficient,— that is, ^Vo (o^" three-quarters) of 19.7, which
is 14.8. Hence 15 braces will be sufficient on a boiler of this size and design, running
at a pressure not exceeding 75 lbs. to the square inch.
When the proper number of braces is known, the next step is to distribute them as
equably as possible over the area to be stayed (i. e., the segment shown by the dotted
lines in Fig. 7). As the arrangement will vary with the number of braces, it will not
be possible to give any general rule for it, except the one above,— namely, to cover the
segment to be braced as equably as possible. Fig. 8 shows the head of a 66-inch boiler,
with 86 3-inch tubes. The distance from the top of the tubes to the top of the shell is.
28|^ inches. For 100 pounds pressure, Table II calls for 17.4 braces. The cut shows nine-
Fig. 8. — Distribution of the Braces.
short off, with nothing to indicate how it was
inferred that the original construction was faulty.
teen braces, as i1^ is a little easier
to distribute nineteen bracesequably,
than eighteen. The
rivet-holes for securing the braces
to the head are shown by the little
circles, and the segment to be
braced is shown by the dotted
lines. It will be noticed that the
braces are arranged along four
concentric circles, the innermost
circle being represented by twa
braces, the next one by four, the
next by six, and the outermost by
seven. The style of brace in-
tended to be used on this head
is shown in Fig. 9. It is the
old-fashioned " crow-foot," which
we believe to be the best form of
brace yet proposed, if it is forged
up without a weld, and carefully
made. We have found
many braces of this style broken
done, leaving it to be reasonably
Braces are often secured to the heads of boilers by angle irons. When this is done,
we recommend the arrangement of angle iron shown in Figs. 10 and 11. Fig. 10
shows the pieces riveted to the heads above the tubes (of which only the upper row is
shown in the cut) in a radial position. By making this disposition of them we are en-
abled to use a straight brace, and the resulting pull on the brace is more direct than it
would be with the brace in any other position. (The small circles in Fig. 10 represent
the rivets. The braces are attached to the web of the tee irons, letween the rivets, as
shown in Fig. 11.) We recommend the J. iron, as shown, in preference to L iron. The
± irons should be of the best quality obtainable, 4x4x|^ inches. The rivet-holes in
their flanges, both for the attachment of the J. iron to the head and for the attachment
of the brace to the ± iron, and also the rivet holes in the boiler-head, should be
drilled, not punched. This makes a much better job. Fig. 12 shows the form of brace
recommended for use with the foregoing arrangement of ± irons. These braces should