IMPROVEMENTS IN STEAM ENGINES
Year: 1874

page_text: LETTERS PATENT to James Scott Rawlings, of Birmingham, in the
County of Warwick, Mechanical Engineer, for the Invention of
Twin
Sealed the 6th April 1875, and dated the 21st October 1874.
PROVISIONAL SPECIFICATION left by the said James Scott Rawlings
at the Office of the Commissioners of Patents, with his Petition,
on the 21st October 1874.
I, JAMES SCOTT RAWLINGS, of Birmingham, in the County of
Warwick, Mechanical Engineer, do hereby declare the nature of
the said Invention for "IMPROVEMENTS IN STEAM ENGINES," to be as
follows:-
My Invention has reference to the parts of steam engines which have
for their object the reversing of the engine and the working of the
engine expansively, and consists of the arrangements or combinations of
parts herein-after described, whereby the reversing and the working of

page_text: the engine expansively are effected more conveniently than by the
mechanism ordinarily employed for those purposes.
I mount the excentric by which the valves are worked on a secondary
hollow or tubular shaft driven by toothed gearing from the crank shaft
instead of mounting the said excentric on the crank shaft as usual. The
said hollow shaft is divided transversely between parts on which the
toothed wheel and the excentric are respectively situated. The two
parts of the hollow shaft are connected together by means of a helically
groved bolt or quick threaded screw engaging in a concave screw formed
in the interior of the hollow shaft. That part of the grooved bolt :
engaging in one part of the hollow shaft has right-handed screw threads,
and that part engaging in the other part of the said hollow shaft has
left-handed screw threads. The concave screws in the two parts of the
hollow shaft are similarly formed. So long as the screwed bolt has no
sliding motion in the hollow shaft it simply gears together, the two 1
parts of the shaft partaking of their motion of rotation. When, however,
the said screwed bolt is advanced in one or other direction in the hollow
shaft the part of the shaft carrying the excentric is made to perform a
partial rotation independently of the rotation communicated by the
toothed gearing, and the position of the excentric relative to the crank is a
changed, and by this change of the relative positions of the excentric and
crank the rate of expansion is changed or the direction of the engines

page_text: and steam admitted, so that the piston follows in the same direction,
moving with it the middle valve; this continues until the eduction and
induction ports are closed which takes place when the centres of the
valvo are coincident; this is their normal position, a position of
equilibrium to -which they always tend. The screwed bolt is then at
thic other extremity and the excentric is in advance of the crank.in the
other direction.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said James Scott Rawlings in the Great Seal Patent
Office on the 16th April 1875.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JAMES
SCOTT RAWLINGS, of Birmingham, in the County of Warwick, Mechanical
Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twenty-first day of October, in the
year of our Lord One thousand eight hundred and seventy-four, in the
thirty-eighth year of Her reign, did, for Herself, Her heirs and suc-
cessors, give and grant unto me, the said James Scott Rawlings, Her
special license that I, the said James Scott Rawlings, my executors,
administrators, and assigns, or such others as I, the said James Scott
Rawlings, 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 James Scott Rawlings, 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 James Scott Rawlings, do hereby
declare the nature of the said Invention, and in what manner the

page_text: same is to be performed, to be particularly described and ascertained
in and by the following statement thereof, that is to say:-
My Invention has reference to the parts of steam engines which have
for their object the reversing of the engine and the working of the
engine expansively, and consists of the arrangements of parts herein-
after described, whereby the reversing and the working of the engine
expansively arc effected more conveniently than by the mechanism
ordinarily employed for those purposes.
I mount the eccentric by which the valves are worked on a secondary
or tubular shaft driven by toothed gearing from the crank shaft instead
of mounting the said eccentric on the crank shaft as usual. The said
hollow shaft is divided transversely between the parts on which the
toothed wheel and the eccentric are respectively situated. The two
parts of the hollow shaft are connected together by means of a helically
grooved bolt or quick threaded screw engaging in a concave screw
formed in the interior of the hollow shaft. That part of the grooved
bolt engaging in one part of the hollow shaft has right-handed screw
threads, and that part engaging in the other part of the said hollow
shaft has left-handed screw threads. The concave screws in the two
parts of the hollow shaft are similarly formed. So long as the screwed
bolt has no sliding motion in the hollow shaft it simply gears together,
the two parts of the shaft partaking of their motion of rotation. When,
however, the said screwed bolt is advanced in one or other direction in
the hollow shaft the part of the sliaft carrying the eccentric is made to
perform a partial rotation independently of the rotation communicated
by the toothed gearing and the position of the eccentric relative to the
crank is changed, and by this change of the relative positions of the
eccentric and crank the rate of expansion is changed or the direction of
the engines working is reversed.
The motion of the screwed bolt may be effected directly by hand or
automatically by a governor or by a steam cylinder and piston in
combination with a hand lever or a governor.
When I employ a steam cylinder for this purpose I connect the
screwed bolt to the piston and arrange the valves of the said stcam
cylinder as follows:-The face and ports of the cylinder and the hand
valve arc of the ordinary kind, but between the hand valve and the

page_text: rod and receives a corresponding motion but of shorter range. This
valve consists of a flat plate having ports similar to those of the cylinder,
only somewhat less. When the piston is at one end of the cylinder the
screwed bolt is at one extremity of its stroke, and the eccentric has a
position in advance of the crank in onc direction. If the hand valve is'
then moved to the other extremity of its stroke the exhaust is opened
and steam admitted, so that the piston follows in the same direction,
moving with it the middle valve; this continues until the eduction and
induction ports are closed, which takes place when the centros of the
valves are coincident; this is their normal position, a position of
equilibrium to which they always tend. The screwed bolt is then at the
other extremity and the eccentric is in advance of the crank in the other
direction

page_text: the part carrying the eccentric e to perform a partial rotation inde-.
CZ³
pendently of the rotation communicated by the spur wheel c. By the
partial rotation communicated to the part d² of the shaft by the sliding
therein of the bolt the angular position of the eccentric relative to the
crank is changed, and by this change of the relative positions of the
eccentric and crank the degree of expansion or cut off at which the
şteam is worked is changed; or when the eccentric e has moved from its
extreme position on one side of the crank to its extreme position on the
other the direction of the engine's working is reversed.
The shaft may be operated upon either by hand or automatically by
a governor. In large engines however I prefer to operate upon the boltƒ
by means of a separate small steam cylinder and piston in combination
with a hand lever or governor, and I have represented in the accom-
panying Drawings the arrangement of the said steam cylinder and piston
and parts connected therewith put into operation by a hand lever. i is
the steam cylinder; h is the piston; g, the piston rod connected to the
end of the bolt f. By means of the hand lever operating through
the connecting rod k³, weighted shaft m, lever n, and connecting links
motion is given to the slide valve p and steam is admitted through the
port q into the steam cylinder i between the upper side of the piston
and the cover end of the cylinder. The pressure of this steam moves
the piston in the direction of the arrow, the bolt ƒ being moved through
a liko distance in the same direction, and the position of the eccentric e
relative to the crank thereby changed, as herein-before described.
The greater expansion of the steam or the complete reversal of the
engine's motion is effected according as the piston is. moved through a
part or the entire length of the cylinder . For preserving the piston h
in equilibrium in that part of the cylinder to which it has been brought
I employ a supplementary plate valve sliding between the ordinary
slide valve p and the ports q, q, of the steam cylinder i. This plate
valve is connected to and moves with the piston / through the medium
of the rods and links t, t, t, to the last of which the rod of the plate
valve is connected. The plate valve always moves in the same
direction as the piston h but has a shorter stroke. In order the better
to explain the action of the steam cylinder i and piston / I remark that
when the said piston his at the cover end of the cylinder or occupies
the position represented in Figure 2 the engine works at full steam, that
is, the steam is not worked expansively; and when the piston is at the

page_text: other end of the cylinder the engine similarly works at full steam, the.
rotation of the principal shaft being in the opposite direction. When
the piston is at the middle of the cylinder i the engine is at rest, and
when the piston is on either side of the middle position the steam works
expansively, the rotation of the engine being in opposite directions as
the piston h is on opposite sides of the middle of the cylinder.
1
The hand lever k is provided with a spring bolt, which drops into.
depressions in the curved bar and retains it in the position to which it.
may be brought. When the hand lever k is at one end of its stroke it
brings the piston / to one end of the cylinder, and when the said hand.
lever is at the other end of its stroke it brings the piston / to the other.
end of the cylinder. When the hand lever is brought into an inter-
mediate position it brings the piston k into an intermediate position.
9
. These positions of the piston / are determined by the hand lever k in-
the following manner :-When the hand lever k is brought, for example,
to the middle of its path it moves the slide valve p to the middle of its
path, and the port 7 in the plater being uncovered steam enters through
the port of the cylinder to the upper or cover side of the piston. The
piston h is thereby made to move towards the middle of the cylinder i,
the motion of the piston effecting motion in the same direction of the
plater, and at the moment when the piston / has arrived at the middlo
of the cylinder i the plate has so far advanced upon the slide valve p.
that the port in the plate is again closed and steam shut off from
the cover side of the piston h. The opening and closing of the port re
whereby steam has been admitted into or shut off from the cover end of
the cylinder, has been accompanied by a like action with respect to the
ports, the closed end of the cylinder, and the exhaust.
If by the momentum of the parts or other cause the piston / has
passed beyond the point at which it was desired it should become,
stationary, and for which position the hand lever and slide valve have
been brought into the proper positions, the restitution of the piston to
its proper position is immediately effected as follows:-The carrying of
the plater beyond the position necessary to close the port ² so as to shut
off the steam opens communication between the said port and the
exhaust, and also by a similar action opens the port ³ to the steam when

page_text: a reverse motion of the piston h is brought about and an equilibrium is
thus established on the said piston h. In other words in whatever
direction the piston h is moved from that which is the properly arranged
position it is brought back to that position, and can only be at rest and
in equilibrium in that position. By the action described the position of
the hand lover & determines the position of the slide valve p. The
position of the slide valve p determines the position in which alone the
piston / can be in equilibrium in the cylinder i, and the position of the
piston determines the position of the eccentric e relative to the crank x,
and thereby determines the working of the engine at full steam, or at
any degree of expansion or cut off, and also the direction of the rotation
of the principal shaft of the engine.
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,―
First. The construction and combination of parts herein-before described
and illustrated in the accompanying Drawings for effecting any required
expansive working of the engine, for reversing the direction of the
engine's rotation and for bringing the engine to rest, that is to say,
mounting the eccentric, by which the valves of the engine are worked,
upon a supplementary hollow or tubular shaft made in two parts and
driven by toothed gearing or other gearing from the principal shaft, the
said two parts of the supplementary shaft being geared together and
made to take any desired angular position with respect to one another
by means of a sliding grooved bolt or screw, the grooves or threads of
which are right and left handed respectively, and work in corresponding
hollow screws or threads in the two parts of the supplementary hollow
shaft, substantially as described and illustrated.
Secondly. The construction and arrangement of parts herein-before
described and illustrated in the accompanying Drawings for working the
said sliding grooved bolt or screw, whereby the position of a hand lever
is made to determine through a steam cylinder and piston the position of a
the said grooved bolt or screw, and thereby to bring about any required

page_text: expansive working of the steam or the required direction of the engine's
rotation or to bring the engine to rest.
In witness whereof, I, the said James Scott Rawlings, have here-
unto set my hand and seal, this Thirteenth day of April, in
the year of our Lord One thousand eight hundred and seventy-
five.
Witness,
GEORGE SHAW.
JAMES SCOTT RAWLINGS. (L.S.)