IMPROVEMENTS IN STEAM ENGINES AND IN FURNACES
Year: 1851

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, DAVID
MAIN, of Beaumont Square, in the County of Middlesex, Engineer, send
greeting.
WHEREAS Her present most Excellent Majesty Queen Victoria, by Her
Royal Letters Patent under the Great Seal of the United Kingdom of Great
Britain and Ireland, bearing date at Westminster, the Eleventh day of
September, One thousand eight hundred and fifty-one, in the fifteenth year of
Her reign, did, for Herself, Her heirs and successors, give and grant unto
me, the said David Main, my exors, adñors, and assigns, Her especial
license, full power, sole privilege and authority, that I, the said David
Main, my exors, adñiors, and assigns, or such others as I, the said David
Main, my exors, adññors, or assigns, should at any time agree with, and no
others, from time to time and at all times during the term of years therein
expressed, should and lawfully might make, use, exercise, and vend, within
England, Wales, and the Town of Berwick-upon-Tweed, and in the Islands of
Guernsey, Jersey, Alderney, Sark, and Man, and also in all Her said
Majesty's Colonies and Plantations abroad, my Invention of "IMPROVEMENTS IN
STEAM ENGINES AND IN FURNACES;" in which said Letters Patent is contained
a proviso that I, the said David Main, shall cause a particular description
of the nature of my said Invention, and in what manner the same is to be
performed, by an instrument in writing under my hand and seal, to be
enrolled in Her Majesty's High Court of Chancery within six calendar
months next and immediately after the date of the said in part recited Letters
Patent, as in and by the same, reference being thereunto had, will more fully
and at large appear.

page_text: NOW KNOW YE, that in compliance with the said proviso, I, the said
David Main, hereby declare that the nature of the said Invention, and in
what manner the same is to be performed, are fully described and ascertained
in and by the present Specification thereof, being had to the Drawings hereunto
annexed, that is to say:-
Firstly, my Invention consists of an improved steam engine, to which I
give the name of the "Duplex Compensating Engine," because it consists of
a pair of engines so disposed and combined that every single stroke of each
piston produces, with the help of a like single stroke of its companion pistons,
two revolutions of a working shaft, (say, for example, a screw shaft,) and
because any strain which either engine might exert on the crank shaft is
so counteracted or neutralised that the dead weight of the moving parts is all
that the shaft bearings have to sustain. Figure 1 exhibits a front elevation
of this engine, as applied on. board. a ship, and .Figure 2 a ground plan.
A' and A' are the two cylinders or engines with the respective air pumps and
other appendages; and B', B; the bed plates or foundations to which they are
fixed; which are secured to the beams and kelson of the ship; sufficient space
is left between the two engines for the slide valve, gear, and pumps. D is the
driving shaft, which has its bearings in bed plates, and is placed lengthways of
the ship, but across the two engines, having four cranks, two of which for one
engine are placed at right angles to two cranks from the other engine. E'is
a second or supplementary shaft, from which the slide valves and bilge and
feed pumps are worked: This shaft is supported on bearings overhead, and
lies in the same direction as the other, only with a lead of about one eighth or
three eighths of a revolution in advance. The cap of each piston rod is con-
nected by two rods a, a, with the short arm of a lever L, the long arm of
which is connected by a vertical rod (V) with the lower crank shaft D.
When the engines are set to work the two piston rods ascend together, and
the centres of their caps describe a line equal to the stroke of the piston,
which line may be considered as the base of a triangle, the other two sides of
which would be represented by the connecting rods (a, a,) when at the end of
the top and bottom strokes, so that when the piston has ascended to the half
stroke the lever L will have passed out a distance equal to the difference
between the vertical height of the supposed triangle and the length of the
rods a, a; and so also, that when the piston has completed its top stroke the
lever L will have resumed its original position; consequently, when the piston
has made one ascent the lever L will have both gone out and come in; or in
other words, while the piston has made one single stroke the lever will have
made one double stroke, and produced. by its connection with the crank shaft

page_text: beneath D two revolutions of that shaft. It is true that the short end of
the lever L passes through a space but equal to one half of the stroke
of the piston rod; yet, it must be observed, on the other hand, that simul-
taneous with this action of the lever there is a similar action taking place with
the lever of the other or opposite engine, therefore the spaces passed over
by the short ends of the two levers are jointly equal to the traverse of the
piston. As before stated, the cranks on the upper shaft E should be set from
th to ths of a revolution in advance of the others; but I may observe, that
the latter position is the preferable one, as then the two engines will nearly
balance one another. It is further deserving of remark, that from the manner
in which the levers (L, L,) act, that is to say, from the one lever always
rising while the other is falling, this must necessarily have the effect of
equalizing the strain on the crank shaft, and abstracting as little as may be
from the working efficiency of the engine. The slide valves are worked by an
equilateral motion, by which means the weight of the valves are just over-
balanced by the weight of the excentric rods, &c., and so throughout great.
care has been taken that every strain or thrust shall be effectually counter-.
balanced or counteracted, and that the two engines shall work in perfect.
unison. The advantages of this system of construction are briefly these:-
First, that the working shaft to which it is desirable to give the utmost speed
possible revolves twice as fast as the moving parts of the engine themselves,
and with a proportionate diminution of tear and wear. Second, that the
whole power of the steam is transmitted to the working shaft without throwing
any strain on the shaft bearings. Third, that the entire weight of the
machinery is thrown low in the vessels, so much so that in ships of war the.
whole may be under the water line. Fourth, that the working parts of these
engines work vertically, and thus better ensure their uniform wear. And lastly,.
that all the parts are easily accessible for purposes of repair or replacement.
Secondly, my Invention consists of a modification of the duplex compen-
sating engine before described, which may be considered preferable to it
wherever no great power is required and saving of space is an object.
Figure 3 is an elevation, and Figure 4 a plan of this modification. In this
case there are only two cranks placed at right angles on the driving shaft, and
the duplex motion is given out by rods and levers from each side of the piston
rod caps,
instead of the opposing force being given from the piston rod caps of
the opposite cylinders. The air pumps have each a stroke, which is a portion
of the stroke of the piston, and the bilge and feed pumps are connected to the
cross head of the air pumps while the slide valves are worked from a short
shaft over the crank or driving shaft. The space which an engine of this

page_text: description will occupy in the length of the ship need not much exceed the
diameter of the cylinder.
Thirdly, my Invention consists of an adaptation of the duplex engine before
described, where motion is required to be given to the two shafts, as, for
instance, where there are two screws or wing propellers employed, one under
each quarter of a ship. Figure 5 is an elevation, and Figure 6 a plan of
this modification, Figure 5 shewing two screw or other propellers. In this
case the two cylinders are laid horizontally while the air pumps are fixed
vertically; and the working points are composed of two connecting rods B, B,
working from the ends of the piston cross head as a centre, and connected by
their two ends direct to the two crank shafts; the two shafts again are so
connected as to revolve in opposite directions, causing the centre of the con-
necting rods to move in a straight line which coincides with the path of the
piston cross head, thereby superseding entirely all necessity for parallel motion
or guides. The air pumps, it will be observed, are worked by means of the com-
bined motion of the revolving cranks and the stroke of the piston. Or, instead
of two connecting rods, one only might be employed, working through a crank
and connected with the air pump cross head by guides, or otherwise. This
description of engine may be made with one connecting rod working through
a trunk cylinder, and in this case the air pump cross head might be contained
in guides.
Fourthly, my Invention consists of an improved method of fitting the shafts
where two screw or wing propellers are employed, one under each quarter of
a ship. Figure 7 is a longitudinal plan exhibiting the details of this proposed
arrangement. The shafts are contained in strong cases or trunks B of
wrought iron, carried through the ship's quarters, and extended sufficiently aft
to support the screws S, S, in the fine run of the ship or concave sweep imme-
diately before the rudder D. These trunks are worked into the framework
of the ship, and not only firmly supported internally by cross stays, but con-
nected to each other by diagonal bracing so as to resist effectually any strain
which may be given out by the engine in working the screws or other
propellers, and at the points where they come through the ship they are fitted
inside with stuffing boxes C, C. Or, instead of the preceding arrangement, the
crank of each shaft may be carried out through the ship's quarter as far as
the screw, and supported at the outer end by a wrought-iron bracket E, with
arms. The shafts may be made to disengage from the engines, or draw back
in the usual way, and the screws or other propellers may be shipped or
unshipped through apertures in the quarters, or lowered and hoisted over the
counter by suitable apparatus.

page_text: Fifthly, my Invention consists of a method of working the air and other
auxiliary pumps of steam engines at one half the velocity of the engines
themselves by means of a helical wheel, represented in Figure 8 (an eleva-
tion), and Figure 9 (a plan). I accomplish this by causing the working
shaft to actuate the pumps through the medium of rollers travelling or rolling
on the peripheries of a peculiarly shaped wheel A. The periphery of this
wheel is a geometrical helix or volute, the curve of which recedes regularly in
the course of one revolution from the point nearest to the centre to that part'
which is most distant from it, and again in the course of another complete
circuit returns to the point nearest to the centre; and the helices of the two
pumps are so adjusted that as one pump finishes its stroke the other shall be
just commencing its stroke. Farther, the one pump is connected by a lever
with the other, so that the one shall assist in the return stroke of the other;
that is to say, the ascent of the one pump is made to correspond with the
descent of the other. In this way the air pump may be worked at a moderate
speed, as compared with the speed of the working shaft; and supposing this
arrangement to be applied to any direct acting engine with one condenser, one'
pump would be always in action, and the cylinder always playing into a con-
denser in a course of constant exhaustion, working consequently with great
energy, as the pumps would work at only half the velocity of the steam pistons;
the steam pistons would in fact be thus set free as it were from the usual.
encumbrance of the air pumps, and a range would be given to the speed of
direct acting steam engines much greater than has been hitherto accomplished
in connection with condensing engines.
Sixthly and lastly, my Invention consists of two several improvements in
furnaces, which are respectively represented in Figures 10, 11, 12, and 13,
of the Drawings annexed, the first of these improvements being relative
to that description of furnaces in which revolving fire bars' are employed,
and consists in forming on the side of each fire bar a projection m
(Figures 12 and 13), which fits into a corresponding recess n in the next or
adjoining bar, so that any number of such bars may be interlocked with one
another, and form an endless chain. The second of these furnace improve-
ments consists of an improved mode of regulating the feed, whereby the fuel
is heated or partially coked before it is admitted into the furnace. A, A,
(Figures 10 and 11,) is a hopper which has a valve or hinge flap at B. C, a
dead plate at the mouth of the furnace on which the coals fall from the
hopper. When the furnace is to be stoked the hinge flap is closed by a
lever D, which stops the descent of the coals, while at the same time it leaves
an opening through which to stoke the furnace. E is an eye-hole through.

page_text: which to inspect the state of the furnace from time to time, and F a lever by
which the entire hopper-flap, &c. may be,lifted-up when it is required to draw.
the fire or remove clinkers.
And having now, described the nature of, my said Invention,, and; in what
manner the same is to be performed,, I declare that the Improvements which 5
I claim are as follows:-
First, I claim the duplex. compensating engine herein-before described, in
the peculiar combination and disposition of parts of which the same, consists,.
that is to say, in so, far as regards the arrangements whereby the power of
the engine is transmitted to the crankshaft, and that shaft is caused.to make 1
two revolutions for each stroke of the pistons, and whereby also all strain on
the crank shaft bearings is prevented, or nearly, so.
:
A
Second, I claim the modification of the preceding engine, represented in
Figures. 3 and 4, and before, described.
Third, I claim the direct acting engine, represented in Figures 5 and 6, and 1
before described;, in so far as regards the arrangements whereby it is adapted:
to the working of two screws, or wing propellers under the quarters of.
vessels, and the mode of working. the air, pump by means of the combined,
motion of the crank shaft, and the stroke of the piston...
Fourth, I claim, the methods of fitting the shafts for screws or other wing 2
propellers, represented in Figure 7, and before,described.
Fifth, I claim the method of working the air and other auxiliary pumps of
steam engines at one half the speed of the engines themselves by means of
helical, wheels, as represented in Figures 8 and 9, and before described...
And sixth, I claim the two several improvements, in furnaces, represented in 2
Figures, 10, 11, 12, and 13, and before described..
In witness whereof, I, the said David Main, have hereunto set my hand
and seal, this Eleventh day of March, in the year of our Lord One
thousand eight hundred and fifty-two..
DAVID (L.s.) MAIN. 3
AND BE IT REMEMBERED, that on the Eleventh day of March; in the
year of our Lord 1852, the aforesaid David Main came before our, said Lady
the Queen' in Her Chancery, and acknowledged the Specification "aforesaid,
and all and every thing therein contained and specified, in form above written.
And also the Specification aforesaid was stamped according to the tenor of 3
the Statute made for that purpose.
Enrolled the Eleventh day of March, in the year of our Lord One thou-