The Locomotive - Lighthouse Survival Blog

68 THE LOCOMOTIVE. [May,
diameter of the dome, and we proceed to consider the objections to the seven-inch hole
and the series of three-quarter-inch holes. The most obvious objection to tliese is, that
in such cases the interior of the dome is quite inaccessible for inspection and repairs.
We hold that the best solution of the dome-opening problem is to make the opening
elliptical, 11" x 15", and to securely rivet to it a manhole frame (see Fig. 1). This makes
the interior of the dome quite accessible, preserves a considerable portion of the shell,
and so stiffens what remains as to materially increase its efficiency.
In old boilers where the dome is of considerable size compared with the shell, say
30" in diameter on a 48'' cylinder, one or two stay bolts may be put across it as shown in
Fig. 3. This construction is not recommended for new boilers, but it is often serviceable
where the dome of a boiler already in use gives trouble by leakage along the joint where
it is riveted to the boiler. The same object may likewise be attained by the construction
shown in Fig. 4, which represents two bars of tee-iron riveted securely to the shell.
Fig. 4. — Arrangement of Tee-iron for Stiffening the Shell.
These bars should be made as long as possible, — that is, they should extend around the
boiler shell until they almost touch the sides of the dome. This stiffens the shell admir-
ably, and while we consider the manhole frame better for a new^ boiler, the tee-irons
may perhaps be more readily applied to an old boiler which shows distress around the
dome. It may also be well to say in this place that when the opening in the shell is less
than the diameter of the dome, small drip-holes should be provided close to the dome at
the lowest points on the sides (at the points corresponding to B and C in Fig. 3), to
allow the water of condensation to flow back into the boiler.
We have next to consider the connection of the dome to the shell. Usually the
dome is flanged and fastened to the shell by a single row of rivets. In our ojDinion, this
is not good practice, as the joint between the dome and the shell is subjected to very
trying strains. In the first place, it will be seen that this joint has to withstand the upward
pressure of the steam against the head of the dome. This brings a tensile .strain
on the rivets, which tends to strip off their heads; and rivets are much weaker when the
strain comes on them in this way than when it is entirely of the nature of a shear, as in
""