IMPROVEMENTS IN STEAM ENGINES
Year: 1880

page_text: LETTERS PATENT to John Crawford Stevenson and John Bennett Price, both
of Preston, in the County of Lancaster, for an Invention of "IMPROVEMENTS
IN STEAM ENGINES."
PROVISIONAL SPECIFICATION left by the said John Crawford Stevenson
and John Bennett Price at the Office of the Commissioners of Patents on the
9th January 1880.
•
JOHN CRAWFORD STEVENSON and JOHN BENNETT PRICE, both of Preston, in the
County of Lancaster. "IMPROVEMENTS IN STEAM ENGINES."
This Invention of improvements in steam engines has reference to expansion
valve gear in which a variable "cut off" is produced by the governor disengaging
the rods or catch levers of the expansion valves from a sliding block operated by an
eccentric additional to that which works the main valves, such disengagement
taking place sooner or later, according to the load on the engine. The object of
our Invention is to render the apparatus sensitive and enable the disengagement to
be promptly effected. The sliding block is suitably mounted and jointed at one
end to a rod operated by the expansion valve eccentric, from which the block receives
a to and fro motion. The upper side of the block we provide with a double groove
to receive the ends of the rods or catch levers connected to the two expansion
valves which, with the respective main valves, are arranged at each end of the
cylinder. The bottom of each groove we provide with a notch with which
corresponding projections on the lower sides of the expansion valve rods or catch
levers come in contact alternately at the commencement of each stroke, as will be
well understood, the expansion valves being kept open until the rods or catch
levers are raised by the tappet levers below, and disengaged or released from the
notches in the sliding block, when the expansion valve will be closed. The tappet
evers we mount one near each end of the sliding block on axes or fulcra, the
tappets projecting inwardly or towards the centre of the block, and the arms
pointing downwards. We arrange the governor rod midway of the stroke of the
liding block in suitable stationary guide bearings, in which it is able to move
[Price 6d1

page_text: upward and downward; also we connect it midway between the bearings by
jointed arms or links to the lower ends of the respective tappet levers. When the
engine is at rest the links connecting the governor rod with the tappet levers will
be in a borizontal position, and consequently the tappet lever arms distended, but
as the speed of the engine increases the governor rod will be raised and the tappet
lever arms drawn in. Thus the position of the double joint on the governor rod
relatively to the positions of the ends of the tappet lever arms will determine the
point of the stroke at which the expansion valve rods or catch levers will be
disengaged and the "cut off" effected, whilst the to and fro motion of the sliding
block past the governor rod will give to the tappet levers the necessary motion for
raising the expansion valve rods or catch levers at the desired point.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said John Crawford Stevenson and John Bennett Price in the Great
Seal Patent Office on the 5th July 1880.
า
JOHN CRAWFORD STEVENSON and JOHN BENNETT PRICE, both of Preston, in the
County of Lancaster. "IMPROVEMENTS IN STEAM ENGINES."
This Invention of improvements in steam engines has reference to expansion
.valve gear in which a variable "cut off" is produced by the governor disengaging
the catch rods of the expansion valves from a sliding block operated by an
eccentric additional to that which works the main valves, such disengagement
taking place sooner or later according to the load on the engine. The object of our
Invention is to render the apparatus sensitive, and enable the disengagement to be
promptly effected.
In the accompanying Drawings, Fig. 1 shows in side view our Invention as it
may be applied to a horizontal cylinder; Fig. 2 is a side elevation (partly in
section); and Fig. 3 a cross section shewing details of our improved "cut off"
nechanism. In Fig. 1, A, A, are the valve or steam chests, one shewn with the
cover removed, and the other with the cover on; C, the main valve, and D, the
expansion valve. The expansion valves with their respective main valves are
arranged at each end of the cylinder as shewn. Air vessels E, E, are provided for
the purpose of cushioning the "cut off" stroke of the expansion valves, which is
effected by means of spiral springs; F, F, are the valve spindles; G, G, bell-crank
levers jointed at their upper ends to the valve spindles F, F, and at their lower
ends to the catch rods a, a; b is a sliding block moving between V slides c, c,
(see Fig. 3), and jointed at one end to a rod d operated by the expansion valve
eccentrics from which the block b receives a to and fro motion. The upper side of
the block is provided with a double groove e, e, (see Fig. 3) to receive the ends of
the catch rods a, a, connected to the two expansion valves. The bottom of each
groove e we provide with a notch f, with which corresponding projections f¹ on the
lower sides of the expansion valve catch rods a, a, (see Fig. 2) come in. contact
alternately at the commencement of each stroke, as will be well understood; the
expansion valve D being kept open until the rods a, a, are raised by the tappet
levers g, g, below, and disengaged or released from the notches f. f, in the sliding
block 6, when the expansion valve D will be closed. The tappet levers g, g, we
mount one near each end of the sliding block b on axes or fulcra h, h, the tappets
projecting inwardly or towards the centre of the block, and the arms pointing
downwards. We arrange the governor rod i midway of the stroke of the sliding
block in the stationary guide bearings j, j, in which it is able to move upward and
downward; also we connect it midway between the bearings by jointed arms or
links k, k, to the lower ends of the respective tappet levers g, G.
When the engine
is at rest, the links k, k, connecting the governor rod with the tappet levers will be
in a horizontal position, and consequently the tappet lever arms distended; but as
the speed of the engine increases the governor rod i will be raised, and the tappet
lever arms drawn in. Thus the position of the double joint on the governor rod
relatively to the positions of the ends of the tappet lever arms will determine the
point of the stroke at which the expansion valve rods a, a, will be disengaged and
the "cut off" effected, whilst the to and fro motion of the sliding block b past the
governor rod i will give to the tappet levers g, g, the necessary motion for raising
the expansion valve catch rods a, a, at the desired point. Means are provided for
shortening or lengthening the catch rods a, the governor rod i, and the links k, as
may be required for purposes of adjustment.
Having described the nature of our said Invention, and explained in what

page_text: manner the same is to be or may be performed or carried into practical effect, it is
to be noted that no claim is made generally to the use of grid-valves or notches or
tappets; but that what we consider to be novel and original, and therefore claim as
the Invention secured to us under the Letters Patent herein before in part recited is,
effecting the disengagement or disconnection from the operating eccentrics of the
expansion valves by the use, in conjunction with the catch rods of those valves and
a sliding block, of tappet levers carried by such block and connected to a governor,
substantially as and for the purpose herein above described.
In witness whereof, we, the said John Crawford Stevenson and John Bennett
Price, have hereunto set our hands and seals, this Third day of July, in the
year of our Lord One thousand eight hundred and eighty.