IMPROVEMENTS IN STEAM ENGINES AND BOILERS
Year: 1860

page_text: LETTERS PATENT to William Macnab, of Greenock, in the County of
Renfrew, North Britain, Engineer, for the Invention of "IMPROVEMENTS
IN STEAM ENGINES AND BOILERS,"
Sealed the 20th November 1860, and dated the 26th September 1860.
PROVISIONAL SPECIFICATION left by the said William Macnab at the
Office of the Commissioners of Patents, with his Petition, on the
26th September 1860.
I, WILLIM MACNAB, of Greenock, in the County of Renfrew, North
Britain, Engineer, do hereby declare the nature of the said Invention of
"IMPROVEMENTS IN STEAM ENGINES AND BOILERS," to be as follows, that is
to say:-
This Invention relates to improvements in the arrangement or construction
of the parts of steam engines and boilers, more particularly, though not
exclusively, designed for marine propulsion.
A set of engines for driving the screw propeller constructed with the present
improvements comprises two direct-acting inverted "low-pressure "cylinders,
arranged above and in the line of the shaft, and acting upon separate cranks
disposed at about the angle of 120° from each other. In the space between
the two low-pressure cylinders there are placed two comparatively small
"high-pressure" cylinders, the piston rods of which are connected to a single
crosshead, and this to a third crank disposed at angles of 120° from the other
two. Each low-pressure cylinder is controlled by a separate valve, whilst a
single valve, by preference, of the piston class acts for the two high-pressure
[Price 8d.]

page_text: cylinders, and the space otherwise unoccupied of the casing between the two
low-pressure cylinders and enclosing the two high-pressure cylinders is used
as a kind of reservoir for the steam on its way from the high-pressure to
the low-pressure cylinders. The valves are of course actuated to correspond
with the positions of the respective cranks. The low-pressure cylinders and
intermediate casing are provided with steam jackets.
The improvements in boilers are applicable to those of the " haystack
form. In carrying them out the interior of the lower or furnace part of the
boiler is made with an inner cylindrical water space, the inside of which space
communicates with the flue space, being separated by the water space from
the furnaces, which last occupy less proportionate radial depth than hitherto.
From the furnaces the gases pass up between the external water space and
the inner water space, into which the lower ends of vertical water tubes are
secured, and pass across these tubes towards the centre. The space containing
these tubes is, as it were, partitioned off from the centre or flue tubes, either
by a cylindrical water space connecting the internal tube plates, of which
there are three, and having apertures for the gases some distance below the
roof or upper tube plate of the outer or water tubes, or by a ring of water tubes,
having their upper ends fixed into the circular tube plate forming the bottom
of an upper central water space projecting downwards. From this tube plate
flue tubes pass up to the top of the boiler to give egress to the gases, the
central tube or flue being by preference made large enough to admit a man
into the interior. The object of this arrangement is to obtain greater
heating surface, combined with strength, and to prevent the gases from
taking so direct a course to the funnel, as is the case in ordinary boilers of this
class. The upper or flue tubes also serve to dry or superheat the steam.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said William Macnab in the Great Seal Patent Office on
the 25th March 1861.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
MACNAB, of Greenock, in the County of Renfrew, North Britain, Engineer,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-sixth day of September, in the year of our
Lord One thousand eight hundred and sixty, in the twenty-fourth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me,

page_text: the said William Macnab, Her special licence that I, the said William Macnab,
my executors, administrators, and assigns, or such others as I, the said
William Macnab, my executors, administrators, and assigns, should at any
time agree with, and no others, from time to time and at all times thereafter
during the term therein expressed, should and lawfully might make, use,
exercise, and vend, within the United Kingdom of Great Britain and Ireland,
the Channel Islands, and Isle of Man, an Invention for "IMPROVEMENTS
IN STEAM ENGINES AND BOILERS," upon the condition (amongst others) that
I, the said William Macnab, my executors or administrators, by an instrument
in writing under my, or their, or one of their hands and seals, should particu-
larly describe and ascertain the nature of the said Invention, and in what
manner the same was to be performed, and cause the same to be filed in the
Great Seal Patent Office within six calendar months next and immediately
after the date of the said Letters Patent.
NOW KNOW YE, that I, the said William Macnab, do hereby declare
the nature of my said Invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the
following statement in writing, reference being had to the accompanying
Drawings,and to the letters and figures marked thereon, that is to say:-
My said Invention relates to improvements in the arrangement or con-
struction of the parts of steam engines and boilers, more particularly, though
not exclusively, designed for marine propulsion.
And in order that my said Invention may be properly understood and
carried into effect, I have hereunto appended two Sheets of explanatory
Drawings, representing examples of my improved engines and boilers.
. A set of engines for driving the screw propeller is shown in Sheet 1 of the
Drawings as constructed with theimprovements, Figure 1 being a longitudinal
vertical section, Figure 2 a transverse vertical section, and Figure 3 a hori-
zontal section. The arrangement comprises two direct-acting inverted "low-
pressure" cylinders A', A, placed above and in the vertical plane of the shaft
B, and acting upon separate cranks C1, C2, disposed at about the angle of 120
degrees from each other. The "low-pressure" cylinders A', A², are placed
rather further apart than in ordinary arrangements of like class, and in the
space between there are placed two comparatively small "high-pressure
cylinders D1, D2, lying in a transverse vertical plane, or one on each side of the
vertical plane of the shaft B. The piston rods E1, E2, of these two "high-pres-
sure" cylinders 1, D2, are fixed to a single crosshead F, which is connected to a
third crank G, disposed on the shaft B at angles of 120 degrees from the other
two cranks C¹,C. The "low-pressure" cylinders A1, A2, receive steam by means
"

page_text: of separate valves H', H2, whilst a single valve I, by preference of the piston
class, distributes the steam to the two "high-pressure" cylinders D¹, D³. A
casing J, extending from one "low-pressure" cylinder A¹ to the other A2,
encloses the two "high-pressure" cylinders, and the valves and valve passages,
and the otherwise unoccupied space of this casing constitutes a kind of
reservoir for the steam on its way from the "high-pressure" to the "low-
pressure" cylinders. The valves are actuated by eccentrics in the ordinary
way, these being of course arranged to correspond with the positions of the
respective cranks. The intermediate casing J is shown as formed with jacket
spaces for steam direct from the main boilers or from auxiliary boilers, and
the "low-pressure" cylinders A1, A2, are also by preference formed with similar
jacket spaces, although this by mistake has not been shown in the Drawing.
Although inverted cylinders are herein-before described, it will be obvious
that my improved mode of combining "bigh-pressure" and "low-pressure"
cylinders is applicable with cylinders arranged horizontally or in other
positions.
In the Drawings the arrangements for condensing the steam are not
shown, and with reference to them I would merely remark, that whilst
various modifications of condensing apparatus may be used, I prefer those
described in the Specifications of British Letters Patent granted to me, and
bearing dates 21st April 1860 (No. 1001), and 27th June 1860 (No. 1557).
My present improvements in boilers are applicable to those of the "hay-
stack" form, and are represented on Sheet 2 of the accompanying Drawings,
Figure 4 being a vertical section, Figure 5 a half plan, and Figures 6, 7,
and 8 horizontal half sections, as at the lines 6-6, 7-7, and 8-8, in
Figure 4.
In this arrangement the furnace bars A, placed radially (or otherwise),
occupy an annular space surrounding an inner cylindrical water space B, the
inside C of which communicates with the flue spaces. The furnace is
surrounded by an outer cylindrical water space D, and the fire gases pass up
between this external water space D and the upper outwardly bulging
portions 6 of the inner water space B. The fire gases next impinge upon an
annular series of vertical water tubes E, having their lower ends secured in an
annular tube plate E, forming the horizontal top of the inner water space B, b,
the gases passing inwards across the tubes towards the centre of the boiler.
The upper ends of the tubes E are fixed in an upper annular tube plate G,
joined to the internal shell of the outer water space D, and to an inner
cylindrical shell H, returning downwards to a circular tube plate I, whilst a
ring of tubes J extend from the outer edge of this tube plate 1, down to the

page_text: inner part of the lower tube plate F. A kind of annular chamber K is thus
formed, in which the fire gases act upon the tubes E and the surrounding
water spaces, finding egress from the chamber by the comparatively con-
tracted spaces between the inner ring of tubes J. These tubes J are taken
advantage of for the passage through them of vertical tie rods L, connecting
the crown M of the boiler to the lower inner water space B; or, instead of
the tubes J, an annular water space may be made to connect the parts,
openings being formed through it for the passage of the fire gases. These fire
gases finally pass up a number of flue tubes N extending from the tube plate I
to the crown M, the centre one of these tubes being by preference made
sufficiently large to admit a man into the interior. In order to secure a
complete circulation of the water in this boiler it is provided with four external
pipes or ducts P, into the upper ends of which the water enters near the
surface level. The water, descending by the ducts P, re-enters the boiler by
three branches from each duct, two branches Q in each case communicating
with the bottom of the outer cylindrical water space D, and the third branch R
communicating with the bottom of the inner water space B.
This improved arrangement of boiler has the advantage of possessing
increased heating surface combined with strength, whilst the fire gases are
prevented from taking so direct a course to the funnel as in ordinary boilers
of this class. The upper or flue tubes N also serve to dry or superheat the
steam.
Having thus particularly described my said Invention, and the manner in
which the same is or may be used or carried into effect, I have to state that I
do not restrict myself to the precise details herein described or delineated, but
that what I consider to be novel and original, and claim as the Invention
secured to me by the herein-before in part recited Letters Patent, is,
First, the combining of "high-pressure" and "low-pressure" cylinders,
substantially in the manner herein-before described.
Second, the constructing or arranging of the parts of haystack boilers,
substantially as herein-before described.
In witness whereof, I, the said William Macnab, have hereunto set
my hand and seal, this Twenty-third day of March, in the year of
our Lord One thousand eight hundred and sixty-one.
WILLIAM MACNAB. (L.S.)