Improvements in the Construction and Working of Mid-cylinder- exhaust Steam Engines.
Year: 1892

page_text: •
Date of Application, 8th Mar., 1892
Complete Specification Left, 8th Dec., 1892-Accepted, 14th Jan., 1893
PROVISIONAL SPECIFICATION.
Improvements in the Construction and Working of Mid-cylinder-
exhaust Steam Engines.
I. LEONARD JENNETT TODD, of 25, Brooke Road, Stoke Newington, in the
County of Middlesex, Engineer, do hereby declare the nature of this invention to
be as follows:-
This invention relates to single- or double-acting engines of the kind referred to
in the Specification to Letters Patent granted to me A.D. 1886, No. 2132, and con-
sists in means whereby the starting of such engines is facilitated.
In engines of the mid-cylinder-exhaust type, the depth of the piston (in' double-
acting engines) is nearly equal to half the length of the cylinder; so that, soon after
the piston commences its return stroke, it operates to cut off the exhaust. During
the remainder of the stroke, the steam or other fluid in front of the piston is sub-
jected to compression, considerable resistance to the further advance of the piston
resulting. After the engine has been fairly started and a good vacuum is obtained,
the body of steam or other fluid compressed is reduced to comparatively small pro-
portions, and the resistance due to compression correspondingly diminished.
According to my improved inode of construction, I provide a valve or valves
adapted for manual operation and so arranged as to enable the engine to be worked
at starting with a terminal exhaust. After the engine has been set to work and a
good vacuum is available, the communication between the terminal ports (or port,
in the case of a single-acting engine) and the exhaust passage is closed; the exhaust
thereupon taking place exclusively through the mid-cylinder ports.
The valves for effecting the objects described may be arranged in passages formed
in the body of the cylinder and communicating, by way of the main slide-valve,
between the ordinary inlet passages and the exhaust passage; or a single valve may
be placed in such a manner as to control' admission to the exhaust passage. Or,
with engines having independent admission and emission valves, as on the Corliss
system, the latter are provided with means whereby they may, when descried, be
tripped out of gear and remain closed; the exhaust thenceforward taking place
exclusively by way of the mid-cylinder-exhaust ports.
Dated the 8th day of Mouch ear
G. G. M. HARDINGHAM,
191, Fleet Street, London, E:C., Chartered Patent Agent.
COMPLETE SPECIFICATION.
Improvements in the Construction and Working of Mid-cylinder-
exhaust Steam Engines.
I, LEONARD JENNETT TODD, of 25, Brooke Road, Stoke Newington, in the
County of Middlesex, Engineer, do hereby declare the nature of this invention
nd in what manner the same is to be performed to be' particularly described' and
scertained' in and by the following statement:
This invention relates to single- or double-acting steam engines of the kind
eferred to in the Specification to Letters Patent granted to me No. 2,132,
A.D. 1886, and consists in means whereby the starting of such engines is facilitated.
In the accompanying drawings,
Fig. is a longitudinal section of the cylinder of a double-acting mid-cylinder-
xhaust steam engine constructed according to my invention;

page_text: Fig. 2 being a side elevation showing the mechanism used for enabling both
supplementary valves to be actuated simultaneously by hand.
Fig. 3 represents the application of my, invention to a single-acting mid-cylinder-
exhaust steam engine.
Fig. 4 illustrates a modified form of double-acting engine in which only one
exhaust valve controlled by a single supplementary valve is employed.
Fig. 5 shows an engine on the "Corliss" system embodying the present
invention;
Fig. 6 being a side elevation, drawn to a smaller scale, representing the means I
prefer to use for moving the exhaust valves continuously and actuating them
simultaneously.
In engines of the mid-cylinder-exhaust type, the depth of the piston (in double-
acting engines) is nearly equal to half the length of the cylinder; so that, soon
after the piston commences its return stroke, it operates to cut off the exhaust.
During the remainder of the stroke, the steam or other fluid in front of the piston is
subjected to compression; considerable resistance to the further advance of the
piston resulting. After the engine has been fairly started and a good vacuum
obtained, the body of steam or other fluid compressed is reduced to comparatively
small proportions, and the resistance due to compression correspondingly
diminished.
In carrying out my invention in the manner illustrated in Fig. 1, I provide, in
addition to the ordinary slide A B, supplementary valves C and D adapted for
manual operation and so arranged as to enable the engine to be worked at starting
with a terminal exhaust. After the engine has been set to work and a good vacuum
is available, the communication by way of the slide A B between each of the
terminal ports p and q and the exhaust passager is closed; the exhaust thereupon
taking place exclusively through the mid-cylinder ports s. In Fig. 1, the valve C
is shown closed and the valve D open, but this is merely for illustrative purposes,
as in actual working both valves open and close together. Communication between
the port p and the passage p', and between the port q and the passage may be
opened or closed simultaneously by moving the lever T (Fig. 2); the valves C
and being connected by a rod t. In the single-acting engine illustrated in Fig. 3,
N is the slide-valve and O the supplementary valve; being the port, p³ the
passage leading from the port by way of the valves and N to the exhaust
passage r', and s¹ the mid-cylinder ports.
Instead of valves for effecting the objects described arranged in passages formed
in the body of the cylinder and leading from the ports as represented in Figs. 1
and 3, a single valve F placed in such a manner as to control admission by way of
the ports p and q and the slide-valve E to the exhaust passage r, as shown in
Fig. 4, may be employed. Or, with engines having independent admission and
emission valves, as on the "Corliss" system, the latter are provided with means
whereby they may, when desired, be tripped out of gear and remain closed; the
exhaust thenceforward taking place exclusively by way of the mid-cylinder-
exhaust ports.
In the mid-cylinder-exhaust "Corliss " engine illustrated in Fig. 5, U and V are
the admission-valves, and G and H the exhaust-valves. The latter, instead of being
tripped out of gear after the starting of the engine, may be operated by the
mechanism shown in Fig. 6. The rod t connects the valves G and H in such a
manner that, when one valve is turned in one direction, the other valve is turned
in the opposite direction. The valve H is coupled by a rod L to a sliding block
mounted in a link J pivoted on the pin K. The link J is caused to vibrate by an
eccentric I on the crank-shaft W. The rod L is united by a bar m to the arm M'
of the lever M M'. When the sliding block is in its highest position, as shown,
the valves G and H are opened and closed in the ordinary way. When, however,
the lever M M has been moved so as to bring the block into its lowest position, the
valves G and H only turn to a very slight extent-not sufficiently to allow of
the exhaust taking place otherwise than through the mid-cylinder ports <.
This

page_text: slight rocking movement of the valves prevents their becoming set fast in their
seats.
The distributing valve or valves, as also those designed for occasional use, may
be of any suitable pattern; those shown in the drawings being given merely by
way of example. Other mechanism than that illustrated may also be employed for
operating the supplementary valves.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I claim :-
:-
1. The improved method of constructing and working steam engines of the mid-
cylinder-exhaust type, substantially as described with reference to Figs. 1, 3 and 4
respectively of the accompanying drawings, and whereby, for the purpose of
facilitating the starting of such engines, communication may be temporarily opened,
by way of the slide-valve, between a terminal passage (which in regular working
may be the steam-inlet passage) and the steam-outlet.
.
2. The improved method of constructing and working steam engines of the mid-
cylinder-exhaust type substantially as described with reference to Fig. 5 of the
accompanying drawings, and whereby, for the purpose of facilitating the starting
of such engines, communication may be temporarily opened, by way of an exhaust
valve, between a terminal port or passage and the steam-inlet.
3. A mid-cylinder-exhaust steam engine provided with a terminal exhaust
passage for use in starting the engine, and with means for cutting off such passage
when the engine is in regular work, substantially as herein described.
Dated the 8th day of December 1892.
G. G. M. HARDINGHAM,
191, Fleet Street, London, E.C., Chartered Patent Agent.