The Locomotive - Lighthouse Survival Blog

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PUBLISHED BY THE HARTFORD STEAM BOILER INSPECTION AND INSURANCE COMPANY.
\i.\\ Series- Vol. XV. BARTFORD, CONK, AUGUST, 1894. No. 8.
Hand-Hole Guards.
I; sometimes happens that a boiler manufacturer who has paid great attention to
the more important parts of his boilers, fails to give due consideration to the small
things about them that occasionally give trouble. One of these "small things" is the
hand-hole guard: and as very little is said about this comparatively insignificant item
in the books, we propose to offer a few words of advice about it in the present article.
The simplest form of guard that we know of is shown in Fig. 1 ; and this form, in
our opinion, is also the best one for general use that has vet been proposed. It is often
made unnecessarily heavy, but as this does not interfere with its efficiency, one could
only object to the extra weight on a;sthetical grounds; aud it is hardly necessary to say
that aesthetics and such muudane things as hand-hole guards have no business with each
Fig. 1. — Common Two-Legged Guard.
other, anyway. Moreover, it is better to have the guards too heavy than too light,
because they will then be less liable to injury from burning.
The only strain that comes on a hand-hole guard is that which is put upon it at the
outset in screwing up the nut so as to make the gasket tight. The steam pressure, by
compressing the gasket, tends to relieve the strain on the guard, rather than to increase
it. So far as strength is concerned, therefore, the two-legged form of guard is quite
satisfactory. In days when boilers were made with |-inch iron heads, aud gaskets were
much harder than those now in use, it was found that when a two-legged guard was used,
the head would sometimes spring enough to cause a slight leakage around those parts
of the hand-hole that were furthest from the legs of the guard. A four-legged guard
like that shown in Fig. 2 was therefore favored by many builders, and it was held that
this form would prevent the plate from springing sensibly. If the four legs rested
equally on the head there can be no doubt that this would be the case; but it is readily
seen that it is no easy matter to secure this condition. If the head and the guard were
carefully planed, or •'surfaced.*'' the bearing of the legs could be made practically per-
fect : but
in actual practice we should find, in most cases, that two of the legs took all