These descriptions and illustrations of the Lancashire boiler are of
general value, owing to the fact that very many exhaustive tests and
experiments upon steam economy have been made and permanently recorded
in connection with this form of steam generator.
In the GALLOWAY form of boiler the flue is sustained and stiffened by
the introduction of numerous conical tubes, flanged at the two ends and
riveted across the flue. These tubes, a sketch of which are given in
fig. 18 (_a_), are in free communication with the water of the boiler,
and besides acting as stiffeners, they also serve to increase the
heating surface and to promote circulation.
[Illustration: Figs. 19, 20.]
The illustration (figs. 18, 19 and 20) give all the principal details
of a Lancashire boiler fitted with Galloway tubes. Fig. 18 represents a
longitudinal section and figs. 19 and 20 shows on a large scale an end
view of the front of the boiler with its fittings and also a transverse
section. The arrangement of the furnaces, flues, and the Galloway tubes
is sufficiently obvious from the drawings. The usual length of these
boilers is 27 feet, though they are occasionally made as short as 21
feet.
The minimum diameter of the furnaces is 33 inches, and in order to
contain these comfortably the diameter of the boiler should not be
less than 7 feet. The ends of the boiler are flat, and are prevented
from bulging outwards by being held in place by the furnaces and flues
which stay the two ends together and also by the so-called gusset stays
_e_, _e_. In addition to the latter the flat ends of the boiler have
longitudinal rods to tie them together; one of these is shown at _A_,
_A_, fig. 18.
The steam is collected in the pipe _S_, which is perforated all along
the top so as to admit the steam and exclude the water spray which may
rise to the surface during ebullition. The steam thence passes to the
stop valve _T_ outside the boiler and thence to the steam pipes to the
engines.
There are two safety valves on top of the boiler on _B_ (fig. 18),
being of the dead weight type described hereafter, and the other, _C_,
being a so-called low water safety valve. It is attached by means of a
lever and rod to the float _F_, which ordinarily rests on the surface
of the water. When through any neglect, the water sinks below its
proper level the float sinks also, causing the valve to open, thus
allowing steam to escape and giving an alarm. _M_ is the manhole with
its covering plate, which admits of access to the interior of the
boiler and _H_ is the mud hole by which the sediment which accumulates
all along the bottom is raked out. Below the front end and underneath,
the pipe and stay valve are shown, by which the boiler can be emptied
or blown off.
On the front of the boiler (fig. 19) are shown, the pressure gauges,
the water gauges and the furnace door; _K_ is the feed pipe; _R_, _R_,
a pipe and cock for blowing off steam. In the front of the setting are
shown two iron doors by which access may be gained to the two lower
external flues for cleaning purposes.
In the Lancashire boiler it is considered advisable to take the
products of combustion, after they leave the internal flues, along the
bottom of the boiler, and then back to the chimney by the side. When
this plan is adopted the bottom is kept hotter than would otherwise be
the case, and circulation is promoted, which prevents the coldest water
from accumulating at the bottom.
The Galloway (or Lancashire) boiler is considered the most economical
boiler used in England, and is being introduced into the United States
with success. The long traverse of heat provided (three turns of about
27 feet each) contributes greatly to its efficiency.
It may be useful to add the following data relating to this approved
steam generator, being the principal dimensions and other data of the
boiler shown in fig. 18:
Steam pressure, 75 lbs. per sq. inch.
Length, 27 feet.
Diameter, 7 feet.
Weight, total, 15-1/2 tons.
Shell plates, 7/16 inch.
Furnace diameter, 33 inches.
Furnace Plates, 3/8 inch.
End plates, 1/2 inch.
Grate area, 33 sq. feet.
Heating surface:
In furnace and flues 450 sq. feet.
In Galloway pipes, 30 „
In external flues, 370 „
----
850 sq. feet.
We have thus detailed step by step the improvement of the steam boiler
to a point where it is necessary to describe at length the locomotive,
the marine, the horizontal tubular and the water tube boilers, which
four forms comprehend ninety-nine out of one hundred steam generators
in use in the civilized world at the present time.