Year: 1886

page_text: I, LEONARD JENNETT TODD, of 67 Walford Road, South Hornsey, in the County
of Middlesex, Engineer, do hereby declare the nature of this invention to be as
follows:-
This invention relates to steam-engines of the type in which live steam is
distributed by means of a valve or valves to passages communicating with the
extremities of the cylinder; and, having performed its work in actuating the
piston, escapes from the cylinder by way of a central exhaust port, admission to
which is controlled by the piston itself. Such engines possess the advantage of
permitting variations to be made in the lead and cut-off of the steam-admission
valve without affecting the action of the exhaust. It is also possible in such
engines to maintain the temperature of the cylinder extremities and passages at a
degree corresponding with that of the live steam; these parts not being subjected
to the serious cooling influence which the expanded steam exerts in ordinary
engines during its return flow.
My improvements in such engines consist, first, in specially proportioning the
cylinder relatively to the average initial steam pressure and to the stroke of the
piston, with the object of avoiding excessive back pressure after the exhaust port
has been closed by the piston and the undischarged contents of the cylinder com-
pressed by the return stroke of the piston; and secondly, in means for effecting
the economical distribution of the steam for automatically varying the cut-off, or
for reversing the direction of rotation when the nature of the work to which the
engine is applied so requires.
In determining the cylinder capacity of a double-acting engine constructed
according to this invention, I add to the length of stroke & depth of piston such
an amount of clearance at each end of the cylinder that the volume of this clearance
bears the same ratio to the volume swept through by the piston as the ultimate
steam pressure bears to the initial steam pressure. Thus, when using high pressure
steam & a considerable degree of expansion, the clearance is moderate; but when
using low pressure steam, or when the total expansion is effected in two or more
cylinders, the amount of clearance is comparatively large. By these means the
undischarged contents of the cylinder, having been compressed by the return stroke

page_text: of the piston, acquire a pressure closely approximating that of the initial steam
pressure.
For effecting the distribution of the steam to the extremities of the cylinder
alternately, I employ a slide-valve constructed by preference in two parts con-
nected together but placed at a distance asunder, the cylinder passages being
correspondingly shortened. Upon the back of this valve, an expansion valve of a
similar description may be arranged; both valves being actuated in the usual
manner by eccentrics or other suitable appliances.
When it is desired to vary the steam admission automatically according to the
resistance to be overcome by the engine, I mount piston-valves upon the back
of the bi-part expansion valve; these piston valves being connected by links
extending from opposite sides of a rocking shaft operated by the governor spindle.
Both sides of the piston-valves being exposed to the steam pressure, they are in
equilibrium and are readily acted upon by the governor.
When it is required to render the direction of rotation of the engine reversible,
I employ a double ported valve, which may be formed in two parts as before
described and which is actuated by an eccentric or its equivalent set at right angles
to the crank. When so arranged, the valve will present two openings in each part,
one or the other of the openings in each part being uncovered by a pair of hand-
moved slides applied to the back of the said valve. When one pair of openings
in the valve is exposed, the admission of steam to the cylinder is suitably timed
for operating the crank in one direction; but when the other pair of openings in
the valve are brought into use, the steam admission is so timed as to operate the
crank in the reverse direction of rotation. The lever whereby the directing slides
are moved may be notched back from its extreme position, whereby the steam is
cut off earlier; or it may be placed at mid-stroke and the steam shut off from
both ends of the cylinder as in ordinary practice. If desired, an expansion valve
may be interposed between the main valve and the pair of directing valves, in
which case the double passages previously referred to will be formed in such
expansion valve. Two valves, for forward and backward motion respectively, may
be substituted for the double ported valve, the directing slides before described
being employed to bring one or the other of these valves into operation.
When a pair of engines of the kind herein before referred to are coupled together
to work cranks at right angles, the admission valves to each cylinder may be
actuated direct from the crosshead appertaining to the other cylinder.
When the total expansion of the steam is effected in two or more cylinders
worked successively, the cylinder or cylinders in which the steam is finally
expanded is constructed on the mid-cylinder-exhaust principle and as herein before
described; whilst the cylinder or cylinders in which the steam is first expanded
may be either of the same type or of the ordinary type in which the exhaust
escapes from the extremities of the cylinder.

page_text: I, LEONARD JENNETT TODD, of 67 Walford Road, South Hornsey, in the County
of Middlesex, Engineer, do hereby declare the nature of this invention and in what
manner the same is to be performed, to be particularly described and ascertained in
and by the following statement:-
This invention relates to steam-engines of the type in which live steam is
distributed by means of a valve or valves to passages communicating with the
extremities of the cylinder; and, having performed its work in actuating the
piston, escapes from the cylinder by way of a central exhaust port, admission to
which is controlled by the piston itself. Such engines possess the advantage of
permitting variations to be made in the lead and cut-off of the steam admission
valve without affecting the action of the exhaust. It is also possible in such
engines to maintain the temperature of the cylinder extremities and passages at a
degree corresponding with that of the live steam; these parts not being subjected
to the serious cooling influence which the expanded steam exerts in ordinary
engines during the return flow.
My improvements in such engines consist, first, in specially proportioning the
cylinder relatively to the average initial steam pressure and to the stroke of the
piston, with the object of avoiding excessive back pressure after the exhaust port
has been closed by the piston and the undischarged contents of the cylinder com-
pressed by the return stroke of the piston; and secondly, in means for effecting
the economical distribution of the steam, for automatically varying the cut-off, or
for reversing the direction of rotation when the nature of the work to which the
engine is applied so requires.
In determining the cylinder capacity of a double-acting engine constructed
according to this invention, I add to the length of stroke and depth of piston such
an amount of clearance at each end of the cylinder that the volume of this clearance
bears the same ratio to the volume swept through by the piston as the ultimate
steam pressure bears to the initial steam pressure. Thus, when using high pressure
steam and a considerable degree of expansion, the clearance is moderate; but when
using low pressure steam, or when the total expansion is effected in two or more
cylinders, the amount of clearance is comparatively large. By these means, the
undischarged contents of the cylinder, having been compressed by the return stroke
of the piston, acquire a pressure closely approximating that of the initial steam
pressure.
For effecting the distribution of the steam to the extremities of the cylinder
alternately, I employ a slide-valve constructed by preference in two parts con-
nected together but placed at a distance asunder, the cylinder passages being
correspondingly shortened. Such an arrangement is represented in Figure 1 of the
accompanying drawings, the same being a longitudinal section of the cylinder of a
mid-cylinder-exhaust engine constructed according to this invention.
A is a
double-acting piston working in a cylinder B provided centrally with apertures b

page_text: communicating with an exhaust passage b¹ and outlet b². 63 63 are steam passages
leading from the steam ports 6 which are by preference duplicated and in con-
junction with which a bi-part steam admission valve C works, the steam ports a
herein being also duplicated to correspond with the cylinder ports bt. Within the
steam-chest D and upon the back of the valve C an expansion valve E similarly
constructed in two parts connected together, is arranged. The valves D and E are
actuated in the usual manner by eccentrics or other suitable appliances. For non-
reversing engines and when each member of the bi-part main valve C is provided
with a single inlet-port as shewn, each member of the bi-part expansion valve E
should be formed with a single steam passage instead of with duplicate passages as
represented.
When it is required to render the direction of rotation of the engine reversible,
and when the main valve is formed in two parts, each part being provided with
a passage or opening communicating with each cylinder-passage respectively,
I duplicate the passages through the valve and employ one pair of passages for
working the engine in one direction and the other pair for working the engine in
the other direction of rotation. When an expansion valve is applied, I form the
duplicate passages in that valve instead of in the main valve. The latter combi-
nation is illustrated in Figure 1. e e¹, e e¹ are the duplicate passages through the
expansion valve E. In conjunction with each pair of passages e e¹ is arranged a
reversing slide F, the latter being connected by means of rods ff to a lever f¹
mounted on a rocking shaft f' actuated from the exterior by means of a hand-
lever in the usual manner. In the position of the lever f¹ illustrated in Figure 1,
the reversing handle is in mid-gear and steam is entirely shut off from the cylinder;
but upon the lever f¹ being moved into its extreme position in one direction, the
passages e e through the bi-part expansion slide E alternately admit steam to the
main slide C and thus to the cylinder, the passages el e¹ being covered by the
reversing slides F F. In the opposite extreme position of the reversing_handle
and lever f¹, the passages e¹ el are utilised and e e are closed by the slides F F.
When the passages or openings ee (which, as before explained, may be formed
in the main valve when an expansion valve is not employed) are exposed, the
admission of steam to the cylinder is suitably timed for operating the crank in one
direction; but when the other pair of passages or openings el el are brought into
use, the steam admission is so timed as to operate the crank in the reverse direction
of rotation. The lever whereby the directing slides F F are moved may be notched
back from its extreme position, whereupon the steam is cut off earlier; or it may
be placed at mid-stroke and the steam shut off from both ends of the cylinder.
Two valves, for forward and backward motion respectively, may be substituted for
the double passaged valve; directing slides being employed for bringing either the
one or the other of these valves into operation.
"
This arrangement of reversing valve gear when applied to my improved mid-
cylinder-exhaust steam engine cylinders, possesses many advantages over the
ordinary "link motion or similar mechanism for altering the direction of rotation.
By its means the steam can be cut off at the very earliest point in the stroke of
the piston whether the engine be running forwards or backwards. Thus steam can
be expanded many times in a single cylinder, irrespective of direction of rotation,
and without altering either the Lead, the Exhaust or the Compression. And as my
improved mid-cylinder-exhaust steam engine is less subject than ordinary engines
to initial condensation of the entering steam there accrues as a general result a
decided advantage in respect of economy.
When it is desired to vary the steam admission automatically according to the
resistance to be overcome by the engine, I mount piston valves upon the back of
the bi-part expansion valve; these piston valves being connected by links
extending from opposite sides of a rocking shaft operated by the governor-spindle.
Both sides of the piston valves being exposed to the steam pressure, they are in
equilibrium and are readily acted upon by the governor. Such an arrangement is
indicated in the upper part of Figure 2 which represents in longitudinal section a

page_text: high-pressure cylinder G fitted with bi-part main valve H, bi-part expansion
valve K, and a pair of governor-controlled piston valves L L; said high-pressure
cylinder G being worked in conjunction with a low-pressure cylinder M of the
mid-cylinder-exhaust type. Steam is distributed to the latter from the intermediate
receiver N by means of the valve P.
When the total expansion of the steam is effected in two or more cylinders
worked successively, the cylinder or cylinders in which the steam is finally expanded
is constructed on the mid-cylinder-exhaust principle and as herein before described.
The cylinder or cylinders in which the steam is first expanded may either be of the
mid-cylinder-exhaust type or of the ordinary type. Any number of either of
such types of cylinders may be used, to enable the steam to be expanded on either
the Double, the Triple, the Quadruple or other principles of expansion, as may be
desired. The essential characteristic of this feature of my invention is that the final
or lowest pressure cylinder of any such compound engine, is constructed on the
mid cylinder-exhaust plan; and in those compound engines in which there are two
or more lowest pressure cylinders worked with equally low-pressures, I construct
each of such lowest pressure cylinders on this mid-cylinder-exhaust plan.
In the construction represented in Figure 2, the cylinder G in which the steam
is first expanded may, if preferred, be of the mid-cylinder-exhaust type instead of
the ordinary type as there shewn. Or the arrangement of cylinder or cylinders
for the first expansion or expansions may be otherwise varied as already described.
The lowest pressure cylinder of a compound engine is always the most important
in an economic sense, as heat which escapes any higher pressure cylinder may
afterwards be partly intercepted by the lowest pressure cylinder; but heat which
escapes the lowest pressure cylinder is entirely lost to the engine. And as my
improved mid-cylinder-exhaust cylinder is less subject to initial condensation of
the entering steam than ordinary cylinders, and as the low temperature of the
final exhaust has less cooling effect upon it than usual, it intercepts heat and uses
it more beneficially than ordinary lowest pressure cylinders do. And therefore
the application of such a cylinder, as the final or lowest pressure cylinder of a
compound engine, becomes economically advantageous.
Having thus particularly described and ascertained the nature of this invention
and in what manner the same is to be performed, I claim :-
=
First The improved construction of mid-cylinder-exhaust steam engine pro-
vided with a double passaged valve or valves in combination with an adjustable
shut-off valve or valves substantially as herein described; the arrangement being
such that either the passages adapted for a forward or for a backward direction of
rotation may be brought into use.
Second-Conducting the final expansion of the steam in a compound engine in
a cylinder or cylinders of the mid-cylinder-exhaust type.
Third In a compound engine, the combination of cylinders and valve gear
substantially as described with reference to Figure 2 of the accompanying
drawings.