IMPROVEMENTS IN BOILERS AND VALVULAR MECHANISM FOR STEAM ENGINES
Year: 1862

page_text: PROVISIONAL SPECIFICATION left by James Robert Napier and William
John Macquorn Rankine at the Office of the Commissioners of Patents,
with their Petition, on the 21st November 1862.
We, JAMES ROBERT NAPIER, Engineer and Shipbuilder, and WILLIAM JOHN
MACQUORN RANKINE, Civil Engineer, both of Glasgow, in the County of
Lanark, North Britain, do hereby declare the nature of the said Invention
of "IMPROVEMENTS IN BOILERS AND VALVULAR MECHANISM FOR STEAM ENGINES," to
be as follows, that is to say:
This Invention comprises improvements in the arrangement or construction
of boilers for supplying steam to motive power engines, and improvements in
the valvular mechanism for regulating the admission of the steam to such
engines, the improvements in boilers being carried out under various
modifications.
Oue modification of steam boiler comprised in the present Invention is
designed more particularly, although not exclusively, for steam of high pressure
for marine engines. The boiler consists of four vertical cylindrical shells with
hemispherical tops, and furnaces are formed in the lower parts of two of these
shells. The furnace spaces are at their upper parts each gradually contracted
into a flue, which is bent into a horizontal direction somewhat below the water
surface line, and which crosses into one of the two shells having no furnace.
In each of these shells the flue is bent downwards, and expands into a chamber
traversed by vertical tubes having the water inside them, and the fire gases
pass downwards through this tube chamber and off by a flue or up-take rising

page_text: up centrally between the four shells or boilers. Instead of the flue first rising
upwards from each furnace, the furnace and its shell may be constructed to
deliver the fire gases directly and horizontally into the flue crossing into the
other shell, and this latter with its tube chamber may be extended downwards
considerably below the furnace shell, a fan or other known means being
employed to start or insure a proper draught.
In another modification the four shells or boilers are made to unite at their
upper parts in a single steam dome, covering them all, and through the centre
of which the up-take passes.
According to other modifications the boiler may consist of only two shells,
one a furnace shell and the other a descending flue tube chamber shell, or the
boiler may consist of more than two pairs of shells.
In a further series of modifications the boiler may consist of one, two, or
more cylindrical boilers disposed horizontally, there being formed in each
cylindrical body a longitudinal furnace space, which is separated by a vertical
Jongitudinal partition of fire-brick or other suitable material from a chamber
traversed by tubes having the water inside them. By an opening at the
upper part of the partition the fire gases cross from the furnace space into the
tube chamber, in which latter they descend, passing from the bottom of
the chamber to a central or external up-take. With a cylindrical body
of sufficient length furnaces may be arranged to be fired from both ends
thereof.
The improvements in valvular mechanism relate to that class which contains"
a double slide and a link motion. In an arrangement embodying the improve-
ments the slide next the valve seat is moved by a pair of eccentrics and a link
motion in the ordinary manner, and the position of those two eccentrics on the
shaft is fixed with reference to the exhaust only, so as to make it begin and
end at the instants most suitable for efficient exhaustion of the steam without
regard to the admission or cut-off. The admission of the steam takes place
through a pair of openings in the first slide. The cut-off is effected by means
of a second slide behind the first slide. This second slide consists of one plate
with an opening in the middle, or of two connected plates with an opening
between them, the two endmost edges of which opening overlap the openings
of the first slide inwards to the extent required for the lap necessary, in order
to produce the expansive working. The second slide is moved by means of a
third eccentric fixed on the shaft in such a position that the centres of the
three eccentrics form a triangle, whose acute angles at the centres of the
forward and backward eccentrics respectively are equal to the angular advance
necessary to produce the admission and cut-off required in full forward and

page_text: full backward gear respectively. The expansion is varied by means of the
link motion in the ordinary way, and thus two disadvantages are avoided
at the same time, on the one hand, the disadvantage of the common
link motion with a single slide of cushioning too much steam at high grades
of expansion; and on the other hand, the disadvantage of previous compound
slide valve motions of requiring more complex mechanism to regulate them
than the ordinary link motion. Cranks or other mechanical equivalents may
be substituted for the eccentrics.