has to
be made in the design for maintaining the circulation of water through
the tubes. (For "flash" boilers see MOTOR VEHICLES, and for domestic
hot-water boilers HEATING.)

Lancashire.

_Tank Boilers._--Of large stationary boilers the forms most commonly
used are those known as the "Lancashire" boiler, and its modification
the "Galloway" boiler. These boilers are made from 26 to 30 ft. long,
with diameters from 6-1/2 to 8 ft., and have two cylindrical furnace
flues which in the "Lancashire" boiler extend for its whole length
(see fig. 3). The working pressure is about 60 lb. per sq. in. in the
older boilers, from 100 lb. to 120 lb. per sq. in. in those supplying
steam to compound engines, and from 150 to 170 lb. where triple
expansion engines are used. In some cases they have been constructed
for a pressure of 200 lb. per sq. in. The furnace flues are usually
made in sections from 3 to 3-1/2 ft. long. Each section consists of
one plate bent into a cylindrical form, the longitudinal joint being
welded, and is flanged at both ends, the various pieces being joined
together by an "Adamson" joint (fig. 1.). It will be seen that these
joints do not expose either rivets or double thickness of plate to the
action of the fire; they further serve as stiffening rings to prevent
collapse of the flue. In most of these boilers the heating surface is
increased by fitting in the furnace flues a number of "Galloway"
tubes. These are conical tubes, made with a flange at each end, by
means of which they are connected to the furnace plate. They are so
proportioned that the diameter of the large end of the tube is
slightly greater than that of the flange of the small end; this
enables them to be readily removed and replaced if necessary. These
tubes not only add to the heating surface, but they stiffen the flue,
promote circulation of the water in the boiler, and by mixing up the
flue gases improve the evaporative efficiency.

[Illustration: FIG. 1.--Adamson Joint.]

In the "Galloway" boiler the two furnaces extend only for about 9 or
10 ft. into the boiler, and lead into a large chamber or flue in which
a number of "Galloway" tubes are fitted, and which extends from the
furnace end to the end of the boiler. A cross section of this flue
showing the distribution of the Galloway tubes is shown in fig. 2.
When boilers less than about 6-1/2 ft. in diameter are needed