The Locomotive - Lighthouse Survival Blog

50 THE L O C O 31 U T I ^' E , [April,
thick; and au examinatiou of the detached tube-end showed that it had l)een expanded
with a Prosser expander, the tool that had been used being evidently designed for a
finch head. For the benefit of those who may be unfamiliar with the Prosser
expander, we may say that it consists of series of pieces shaped like A in Fig. 2, and
arranged in a circle around a central pin. This central pin is tapering, and when the
expander has been put in position in the tube, tlie segments are set out forcibly against
the tube by driving in the \nn. In this way the end of the tube is turned over against
the head, and the tube is expanded so as to fit the tube-hole tightly. The tube is also
enlarged slightly ju;;t inside the head. When the expander has been set out against the
tube sufficiently in one position, the pin is drawn out and the tool is sliifted slightly and
Fig. 2.— ILLUSTRATI^'G the Actiux of the Prossek Expander.
driven auaiii. In the better boiler shops tubcr-ends are mostly rolled, nowadays, and
except in special cases where the rolling operation is not convenient, the Prosser expander
is used very little.
Fig. 2 illustrates what happens when, as in the case under consideration, the tubes
are expanded with a Prosser tool tliat is too small for the JieaJ. The projection B, that is
intended to enlarge the tube just inside the head, and which ought to just clear the
liead on the inside, does not clear it, but forces the metal of the tube against tlie inner
edge of the head, so that the tool and tube sheet act like the two blades of a pair of
shears. The inevitable result is, that the tube is badly strained at this point, or, if the
tool is new and sharp and the work carelessly done, it may even be sheared in two. At
all events, the tube is pretty sure to be so badly strained that its strength is destroyed,
and sooner or later it will give trouble.
In the present instance the trouble was no doubt aggravated by the fact that the
boiler was fed directly over the fire-slieet. The lower tubes were subjected to the chilling
action of the feed-water, and must have contracted violently at times, and experienced