IMPROVEMENTS IN STEAM ENGINES
Year: 1875

page_text: LETTERS PATENT to Robert Duncan, of Madeley, in the County of
Salop, Gas Engineer, for the Invention of "IMPROVEMENTS IN STEAM
ENGINES."
PROVISIONAL SPECIFICATION left by the said Robert Duncan at the
Office of the Commissioners of Patents, with his Petition, on the
10th May 1875.
I, ROBERT DUNCAN, of Madeley, in the County of Salop, Gas
Engineer, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN STEAM ENGINES," to be as follows:-
My Invention consists of the improvements herein-after described in
steam engines, which said improvements are especially applicable to
direct acting steam pumps, but are also applicable to steam engines of
other constructions.
My improvements relate principally to the valve mechanism of the
said steam engines.

page_text: I will describe my Invention in connection with a direct acting steam.
pump, the steam cylinder and pump cylinder of which are situated
horizontally. On the upper side of the steam cylinder a steam chest is
cast, in which chest are two small cylinders situated respectively at the
opposite ends of the said chest. Pistons herein-after called valve pistons
work in the said small cylinders, the said valve pistons being connected
together by a rod. An arm fixed laterally to the said connecting rod of
the valve pistons engages with the principal slide valve, which receives its
motion from the motion of the said valve pistons, which are actuated as
herein-after explained.
The said principal slide valve and the valve ¡pistons arc situated side
by side in the valve chest. The said principal slide valve by its motion
opens and closes the steam and exhaust ports of the steam cylinder in
the usual way.
Steam is admitted to the backs of the valve pistons by means of a
secondary slide valve working upon the upper faces of the small
cylinders in the valve chest, in which faces are the requisite steam and
exhaust ports. This secondary slide valve takes its motion from a rod
working through a stuffing box in the valve chest. This rod is parallel
to the main piston rod of the steam cylinder, and is rigidly connected
thereto by a cross arm, so that it travels with and has the same motion
as the said main piston rod.
The rod working the secondary valve is provided with lugs or tappets
at the required distance apart, which lugs or tappets give the required
sliding to-and-fro motion to the secondary valve.
The action of the parts is as follows:-As the main piston in the
steam cylinder approaches the end of its stroke in one direction, the rod
by which the secondary slide valve is worked changes the position of the
said secondary valve. By this change of position steam is admitted to
the back of that one of the valve pistons in the steam chest which had
been open to the exhaust, and the one upon which steam had last acted
is put in communication with the exhaust. The position of the valve
pistons is thereby reversed, and by the action of the lateral arm on the
rod of the valve pistons, the position of the principal slide valve is
reversed. The piston of the steam cylinder moves to the opposite end
of the said cylinder, on approaching which the secondary slide valve is
first operated upon, and through its motion the valve pistons and
'

page_text: principal slide valve have their positions severally reversed, thereby
producing the reverse motion of the main piston.
In order to work the steam expansively, I adopt the following
arrangement of parts:-Two small or expansion valves adjustable by
screws are fitted to work through and are carried by the principal slide
valve. These expansion valves are worked by the rod which works the
secondary slide valve herein-before described, the said rod having an arm
on one side which acts on a projection made on a second rod carried on
the back of the principal slide valve. This second rod is connected with
a third rod, the ends of which are bent into a suitable figure to lift up
and press down the said expansion valves, by working through eyes
formed at the tops of the stems of the said valves.
The parts of the bent rod which act immediately on the expansion
valves are capable of being adjusted to a greater or less distance apart,
so as to cut off the steam at any required position of the stroke of the
piston of the steam cylinder.
The exhaust steam passes to a condenser which consists of an enlarge-
ment in the pipe up which the stream of water is raised by the pump.
The pipe conveying the exhaust steam enters the side of the enlarged
part and communicates with a valve seat in the axis of the said enlarged
part. A valve on the valve seat opening upwards permits of the
introduction of the exhaust steam, but prevents the passage of water
into the exhaust steam pipe. The exhaust steam is condensed by the
ascending stream of water, and an exhaust or vacuum is produced,
which by the removal of atmospheric pressure from the exhaust side of
the piston in the steam cylinder, is equivalent to a like increase in the
pressure of the steam..
In applying the expansion gear described to a steam engine giving a
rotatory motion to a shaft, I work the two cut off valves through the
main slide valve, by means of levers which receive motion from the said
main slide valve, the latter being worked in the usual manner.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Robert Duncan in the Great Seal Patent Office on
the 9th November 1875.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ROBERT
DUNCAN, of Madeley, in the County of Salop, Gas Engineer, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Tenth day of May, in the year of our
Lord One thousand eight hundred and seventy-five, in the thirty-eighth
year of Her reign, did, for Herself, Her heirs and successors, give and
grant unto me, the said Robert Duncan, Her special license that I, the
said Robert Duncan, my executors, administrators, and assigns, or such
others as I, the said Robert Duncan, 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,"
upon the condition (amongst others) that I, the said Robert Duncan,
my executors or administrators, by an instrument in writing under
my, or their, or one of their hands and seals, should particularly
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 Robert Duncan, do hereby declare
the nature of the said Invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the
following statement thereof, that is to say:-
My Invention consists of the improvements herein-after described in
steam engines, which said improvements are especially applicable to
direct acting steam pumps, but are also applicable to steam engines of
other constructions.
My improvements, relate to the valve mechanism of the said steam
engines.

page_text: I will describe my Invention in connection with a direct acting steam
pump, the steam cylinder and pump cylinder of which are stuated hori-
zontally. On the upper side of the steam cylinder a steam chest is cast,
in which chest are two small cylinders situated respectively at the opposite
ends of the said chest, or they may be situated at the middle of the chest.
Pistons herein-after called valve pistons work in the said small cylinders,
the said valve 'pistons being connected together by a rod, a slot in the
said rod receiving a projection on the principal slide valve or an arm
fixed laterally to the said connecting rod of the valve pistons engages
with the principal slide valve which receives its motion from the motion
of the said valve pistons, which are actuated as herein-after explained.
The said principal slide valve and valve pistons are situated one over
the other or side by side in the valve chest. The principal slide valve,
by its motion, opens and closes the steam and exhaust ports of the steam
cylinder in the usual way.
Steam is admitted to the backs of the valve pistons by means of a
secondary slide valve, working upon the upper faces or sides of the small
cylinders in the valve chest, in which faces or sides are the requisite
steam and exhaust ports. This secondary slide valve takes its motion
from a rod working through a stuffing box in the valve chest. This rod
is parallel to the main piston rod of the steam cylinder, and is rigidly
connected thereto by a cross arm, so that it travels with and has the
same motion as the said main piston rod.
The rod working the secondary valve is provided with a lug or tappet,
which gives the required sliding to-and-fro motion to the secondary
valve. The valve pistons are cushioned by the exhaust steam, and are
thereby prevented from striking the ends of their cylinders.
The action of the parts is as follows:-As the main piston in the
steam cylinder approaches the end of its stroke in one direction, the rod
by which the secondary valve is worked changes the position of the' said
secondary valve. By this change of position steam is admitted to the
back of that one of the valve pistons in the steam chest which had been
open to the exhaust, and the one upon which steam had last acted is
put into communication with the exhaust. The position of the valve
pistons is thereby reversed, and by the action of the projecting arm on
the main valve or the lateral arm on the rod of the valve pistons, the
position of the principal slide valve is reversed. The piston of the steam

page_text: cylinder moves to the opposite end of the said cylinder, on approaching
which the secondary valve is first operated upon, and through its motion
the valve pistons and principal slide valve have their positions severally
reversed, thereby producing the reverse motion of the main piston.
In order to work the steam expansively, I adopt the following arrange- à
ment of parts:-Two small or expansion valves adjustable by screws
are fitted to work through and are carried by the principal slide valve.
These expansion valves are worked by the rod which works the secondary
slide valve herein-before described, the said rod having an arm on one
side, which acts on a projection made on a second rod carried on the 1
back of the principal slide valve. This second rod is connected with a
third rod; the ends of which are bent into a suitable figure to lift up
and press down the said expansion valves by working through eyes
formed at the tops of the stems of the said valves.
The parts of the bent rod which act immediately on the expansion
valves are capable of being adjusted to a greater or less distance apart
só as to cut off the steam at any required position of the stroke of the
piston of the steam cylinder.
Having explained the nature of my Invention I will proceed to
describe with reference to the accompanying Drawing the manner in 2
which the same is carried into effect.
Figure 1 represents in transverse vertical section, and Figure 2, in
longitudinal vertical section, a direct acting steam pump provided with
valve mechanism constructed according to my Invention.
Figure 3' is a plan of the valve mechanism, the cover of the steam 2
chest being removed, and Figure 4 is a longitudinal vertical section of
the secondary slide valve and the small cylinders in which the valve
pistons work. The section, Figure 2, is taken on the line A of Figure 1,
and the section, Figure 4, is taken on the line B of Figure 1.
Figure 5 represents in end elevation a modification of the arrangement 3
represented in Figures 1, 2, 3, and 4.
Figure 6 represents in longitudinal section an arrangement for
cushioning the valve pistons, and Figure 7 represents in longitudinal
section a part of the valve mechanism Figures 1, 2, 3, and 4, and
exhibits my arrangement for working the steam expansively.
3

page_text: The same letters of reference indicate the same parts in the several
Figures of the Drawing.
I will first describe the arrangement represented in Figures 1, 2, 3,
and 4; a is the main steam cylinder, and b, the piston of the same;
c, d, are the ports by which steam and exhaust are alternately admitted
to and removed from either end of the steam cylinder, and fis the
exhaust passage; e is the steam chest on the upper side of the steam
cylinder a, steam being admitted at 9 into the steam chest in the usual
way. In the said steam chest e are two small cylinders h, i, in which
two valve pistons h³, ², respectively work; k is the principal slide valve
which receives its motion from the motion of the valve pistons ², ³, the
said principal valve & being connected to the valve pistons ³, ³, by the
projection, on the said valve k engaging in a slot in the connecting
rod of the valve pistons (see Figure 2). By the motion of the
principal slide valve k, the ports c and d are alternately put into
communication with the steam chest e and exhaust passage fin the
usual way.
On the side of the small cylinders h, i, is a secondary slide valve m
for admitting steam at the proper times, to and removing the exhaust
from the backs of the valve pistons ², 2, (see Figure 4). The small
cylinders, i, are provided with steam and exhaust ports p, P, whereby
the said small cylinders are by the motion of the secondary slide valve
m put into communication with the steam chest e and with the exhaust
passage f. The secondary slide valve m is worked by the rod q passing
through a stuffing box in the steam chest, the said rod q being rigidly
connected to the main piston rod by the cross arm *, so that the rod q
travels with and has the same motion as the rod of the said main steam
piston. The rod q is not directly connected to the secondary slide valve
m, but is connected thereto by the cross arm n (see Figure 1).
On the rod q is a tappet q2 (see Figure 4), which by the motion of the
said rod q alternately strikes the projections m³, m³, on the secondary
valve m, and gives a to-and-fro motion to the said valve m, and thereby
admits steam to the back of one of the valve pistons ² or 2, and conveys
exhaust steam from the back of the other valve piston in the small
cylinders h, i.
The action of the several parts is as follows:-As soon as the main
steam piston in the steam cylinder a, making its stroke in the direction

page_text: of-the arrow, Figure 1, approaches the bottom end of the said cylinder a,
the tappet on the rod q acting on the projection m² of the secondary
slide valve m, changes the position of the said secondary slide valve m,
as illustrated in Figure 4, and steam is now admitted to the back of the
valve piston ³, and the back of the valve piston h² is opened to the
exhaust pipe f. By the action of the steam on the back of the valve
piston **, it moves in the direction of the arrow on the said valve piston
and the position of the valve pistons 2, 3, is thereby reversed. This
reversed motion of the valve pistons is communicated through the arm
k to the principal slide valve k, and the position of the said valve k is
thereby reversed. Steam is now admitted to the bottom end of the
cylinder a, and the piston 6 makes its stroke in a direction contrary to
that indicated by the arrow, and as the said piston 6 approaches the
cover end of the cylinder the action described of the several valves again
takes place and their positions are severally reversed, thereby producing
the reverse motion of the main piston b, and so on.
It will thus be seen that the supplementary valve m changes its
position at each stroke of the main piston and before any change is
made in the position of the main valve k, so that the two valves never
change together, the change in the one being the cause of the change in
the other, whereby any dead point or stopping place and consequent loss
of power in the arrangement is prevented.
'
To prevent the valve pistons h², ³, striking the ends of their cylinders
h, i, exhaust steam may be cushioned by the arrangement of parts
represented in Figure 6. For this purpose I arrange the exhaust ports
in the small cylinder, so that the exhaust port is closed by the valve
piston passing the said port before the said valve piston has reached the
end of its stroke, whereby the exhaust steam left in the cylinder is pre-
vented from escaping into the exhaust passage, and serves as a cushion
to the said valve, piston and prevents the latter striking the end of its
cylinder. In the said Figure 6 the exhaust port of the cylinder / is
marked h³, and the steam port * and the exhaust port of the cylinder i
is marked ³, and the steam port is marked **.
It will be seen by an examination of the Drawing, that the exhaust
port has been closed by the advance of the valve piston ³, and the
exhaust steam has been cushioned between the said valve piston &² and
the end of the cylinder i, the steam port being closed by the end of

page_text: the secondary slide valve m. The same action takes place on the reverse
motion of the secondary slide valve m.
My arrangement for working the steam expansively is best seen in
Figure 7. It is also represented in Figures 1 and 2; r, s, are the
expansion valves carried by the principal slide valve k, and capable of
rising and falling in the said valve. The upper ends of the said valves
r, 8, are furnished with loops or eyes marked 72, 82. The expansion
valves 7, 8, are worked by the rod t, through the rod q, which also
works the secondary slide valve m, the said expansion valve rod t being
connected to the rod q through the cross arm u, as seen in Figure 1.
Connected to the rod is a bar w, having inclines or projecting parts
v, x, upon it of a shape proper to work through the eyes or loops 72, 8²,
of the expansion valves r, s, and lift up and press down the said valves.
When the main piston 6 has reached that position of its stroke at which
it is required to cut off the steam to the steam cylinder a, the rod t has
been moved by means of the rod q and cross arm 2, see Figure 1, to
such a position that the incline x is withdrawn from the eye of the valve
8, in which it was engaged, and presses down the said valve so as to
close the steam port d. By the continued motion of the rod t in the
same direction, the other incline v enters the eye of the other expansion
valve, and lifts the said valve as seen in Figures 2 and 7, so that when
the position of the ports is reversed by the motion of the principal slide
valve k, the steam port c is clear for the admission of steam to the
opposite side of the piston.
When the principal slide valve k makes its motion in the opposite
direction in the manner herein-before described the expansion valve s is
lifted, and the expansion valve is pressed down by the respective
inclines x, v, as will be understood by an examination of Figure 7. The
steam may thus be cut off at the required position of the stroke of the
main piston by adjusting the position of the inclines v, x, on the
bar w.
Figure 8 shows in longitudinal section; Figure 9, in plan; and
Figure 10, in elevation, an arrangement for controlling the length of
stroke of the main valve by a crank and rod. The crank is carried off

page_text: On applying the expansion gear described to a steam engine giving a
rotary motion to a shaft I work the two cut-off valves r, s, through the
main slide valve k by means of levers, which levers receive motion
from the said main slide valve, the latter being worked in the usual
manner.
In the modification, Figure 5, the small cylinders h, i, and the prin-
cipal slide valve k, instead of being arranged one over the other, as in
Figures 1 and 2, are arranged side by side, the valve pistons working in
the said small cylinders h, i, being connected to the principal slide valve
by the lateral arm on the said valve pistons. The secondary slide
valve m for working the said valve pistons is situated over the small
cylinders h, i, instead of on the side, and the secondary slide valve m,
and the expansion valves 7, 8, are worked from the central rod q. ·
I prefer to use the arrangement of parts represented in Figures 1 and
2, as the width of the steam chest is much reduced, and great compact-
ness of the parts is secured.
Having now described the nature of my Invention, and the manner in
which the same is to be performed, I wish it to be understood that I do
not limit myself to the precise details herein described and illustrated,
as the same may be varied without departing from the nature of my
Invention; but I claim as my Invention of improvements in steam
engines,―
Firstly. Actuating the principal slide valves of steam engines by
means of a pair of reciprocating valve pistons working in short cylinders
in the steam chest, the said short cylinders being provided with steam
and exhaust ports, and a secondary slide valve operated from the rod of
the main steam piston for admitting steam to and cutting off steam from
the said valve pistons, the several parts being constructed, arranged, and
working substantially as herein-before described and illustrated in the
accompanying Drawing; also, the arrangement of parts described and
illustrated for cushioning the valve pistons, and preventing them striking
the ends of their cylinders.
Secondly. The construction and arrangement of the expansion valves,
herein-before described and illustrated in the accompanying Drawing for
cutting off the steam at any required position of the stroke of the main
steam piston, and the combination of parts herein-before described and

page_text: illustrated for working the said expansion valves from the rod of the
main steam piston.
In witness whereof, I, the said Robert Duncan, have hereunto
set my hand and seal, this Thirtieth day of October, in the
year of our Lord One thousand eight hundred and seventy-
five
Witness,
HENRY BARKER CARTWRIGHT,
Cashier,
Madeley Wood,"
Salop.
ROBERT DUNCAN. (L.S.)