IMPROVEMENTS IN DOUBLE ACTING STEAM ENGINES
Year: 1884

page_text: I, JAMES POLLARD LEA of Handsworth in the County of. Stafford Engineer do
hereby declare the nature of the said invention for "IMPROVEMENTS IN DOUBLE
ACTING STEAM ENGINES" to be as follows:-
My invention has for its object improvements in direct acting steam engines by
which I am enabled to economize the steam and also the room occupied by such
engines to a considerable extent indeed obtain practically the same effect with
one cylinder as is obtained in ordinary work with two cylinders. I will describe
my invention as applied to an engine which would act as a compound engine with
one cylinder:
First I use a piston made in such a manner that the back end is reduced in size
and continued in its reduced state sufficiently long to go through the end of the
cylinder so as to act like a piston rod to the piston itself. This reduced projecting
guide piece has a suitable outside casing fitted to the end of the cylinder or cast with
it in which it slides and in which it may be kept steam tight with rings or a gland
and packing in a stuffing box.
This projecting piece may be of such a diameter as to leave any ratio of pro-
portion in area between the front and back of the piston, indeed the back of the
piston is merely an annular space. The Steam passages are so arranged with the
steam valve that the front or largo end of the piston is the only end which can
communicate with the atmosphere direct. Thus when the steam has been used at
the back or annular end to expansively or otherwise force the piston to the front
the valve is so moved as to carry the steam already used at the back to the front of
the piston which is larger in area than the annular space and thus the piston is
brought back. When new steam is admitted to the back of the piston the front
is open to the atmosphere or to the condenser. Thus the back or annular end is
never open to the atmosphere or condenser and the projecting piece and outside
casing may take the place of the slide and slide bars.

page_text: JAMES POLLARD LEA of Handsworth in the County of Stafford, Engineer, do
hereby declare the nature of the said invention for "IMPROVEMENTS IN DOUBLE
ACTING STEAM Engines” and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement that is to
say-
My Invention has for its object improvements in double acting steam engines by
which I am enabled to economize the steam used and the room occupied by such
engines and to expand the steam to a considerable extent yet simplicity of con-
struction is one of the principal features and I am therefore enabled to produce
engines occupying but little space and to work economically at a small cost.
In order that my invention may be more clearly understood and more readily
carried into practice I have appended hereunto a sheet of drawings in which,―
Figure 1. is a sectional elevation of a vertical engine.
Figure 3. is a plan of the same engine.
Figure 2. is a sectional elevation of the same engine but shewing an alternative
arrangement of the valve gear.
Figure 4. is an alternative section of a slide valve.
Figure 5. is a diagram shewing the setting of the valve.
Figures 6 are details of the gland at the open end of the cylinder.
I will describe my invention as applied to an engine which would act as a
compound engine with one cylinder.
I use a piston C made with the back C¹ reduced in size and continued. in its
reduced state sufficiently long as shown to go through the upper end A¹ of the
cylinder A which is shewn by preference in two pieces with tho faced joint, a², for
the convenience of casting and fitting through the upper and lower parts may be
cast in one when desired. This extension C¹ of the of the piston C acts as the
piston rod to the piston C having the reduced end A' of the cylinder A to form a
guide in which it slides and in which it may be kept steam or air-tight with a
gland and packing as shewn by Figures 4 and 6 or with metallic spring packing
rings made preferably of Phosphor-Bronze and in addition to them one or moro
grooves may be turned in the outer portion of the part C of the piston C and
when desirable to reduce friction the projecting part C of the piston may be
reduced in diameter as shewn between points C and C³, to any desirable or
convenient extent and the recess so formed may be filled or partially filled with
any suitable substance which is a bad conductor of heat. The part A of the
cylinder A may be of such diameter as to leave any desired ratio of proportion in
arca between the front and back of the piston, indeed at the back of the piston is
merely an annular space, the passages o, p, and n are so arranged with the valve k,
that the front or large end of the pisten C is the only end that can communicate
with the atmosphere to liberate the pressure of steam or air or other fluid or gas.
I will now follow out the action of the, say, steam, for a single revolution of the
engine the action being similar in the case of using compressed air.-The steam is
admitted through the pipe m into the valve chest containing the valve k, thence
into the annular space or what I have called the back of the piston. This valve is
placed upon a spindle to which the lever i is attached. The end of this lever
receives a reciprocatory motion through the connecting rod, f, bent lever g, and
coupling rod h, from the crank e, thus giving to the valve a reciprocating and
partly rotary motion. The steam having been admitted by the valve, k, through
the passage o, into the annular space formed between A and C, acts upon an

page_text: effective arca equal to the dillerence in areas between the lower portion of cylinder A
and the upper portion A', and drives the piston C inwards.
When Chas traversed any desired part of its instroke-the valve gear being of
course arranged to the desired cut off-the valve, k, cuts off the steam from tho
passage o; the steam already admitted expanding as C continues its instroke.
Just before or at the completion of this instroke the valve, k makes a com-
munication between the passages o and p and the steam at once becomes common
to the under as well as the upper side of the piston, the pressure per square inch,
being of course the same on each side.
The effective area of the bottom of the piston C is however greater than the
upper or annular space and the piston tends to move outwards. When Chas
moved a certain distance outwards the communication between the passages o
and is cut off by the valve and the steam above the piston in the annular
space is compressed and the steam behind the piston is expanded as C moves
outwards The valve now opens the passage p to the exhaust outlet, n, thus
allowing the expanded gas or vapour to escape from the underpart of the piston
either into a condenser or into the atmosphere. Now when has nearly or quito
completed its upstroke, . opens the passage, o, and again admits a new supply of
steam or compressed air-as the case may be-into the annular space, the opera-
tions before described being repeated. During the instroke of C the passage p
remains open to the exhaust outlet n until after the valve has cut off the steain
or compressed air from entering the annular space when p is closed until the valve k
again makes the communication between passages o aud p.
Motion is given through the connecting rod f. from the crank e to the lever g;
the spindle r, to which the lever is fastened receives a partially rotative and
reciprocatory movement. The slide valve may be placed directly on this spindle,
but where this arrangement is undesirable the valve may be placed in any con-
venient position on another spindle which has its axis parallel to that of spindle r.
The movement of r may be transmitted (amplified or diminished in extent) to the
valve spindle by any suitable arrangement of levers and coupling rods such as
the shorter arm of lever g. the coupling rod h, and the lever i. To whatever extent
the movement of the valve-spindle is varied, its pendulous motion is exactly
synchronous with that of the spindle . The connecting rod f is of suitable
length proportionate to the stroke of the engine. On the length of the lever, g.
viz: from the centre of pin, 8. to the centre of spindle r and on the position of r,
the angular movement of the valve depends.
A little distance before the crank pin reaches its top dead centre, the slido valvo
is just beginning to admit steam to the annular space and in whatever position the
lever g is at that moment it must occupy exactly the same position when the crank
pin reaches the point at which steam is cut off, and therefore the straight line
joining the points representing these two positions of the crank pin forms the
base of an isosceles triangle the sides of which are equal in length to that of
the connecting rod f. The centre of spindler may be situated at any point (from
which it is workable) in a circle struck with a radius equal in length to that of
lever g. from the apex of this triangle. The position of may thus be adjusted
as to allow of considerable variation of the valve movement and in distributing the
steam or compressed air. The points of admission and cut off being fixed and the
valve gear arranged accordingly, the point at which the exhaust commences is
dependent upon that when the exhaust closes, or "vice versa ;" and so the point at
which communication between the two ends of the main cylinder begins is dependent
on that when it ceases and "vice versa." The beginning and end of the exhaust or
the commencement and close of communication between the ends of the cylinder
may be taken as the bases for designing the valve gear instead of the points of
admission and cut off. When from either of these data the valve gear is arranged
and the point of cut off ascertained the areas of the lower portion of the cylinder A
and its upper portion A¹ may be made such as to allow the steam or compressed
air to be expanded to the required degree.

page_text: Without in anyway altering the principle or idea of this method of actuating
the slide valve the connecting rod, f, may be attached to the connecting rod of the
engine instead of to the crank pin as before described. The principal effect of this
is to lessen the angular traverse of the lever, g, for instance figure 2 is the sectional
elevation of an engine having its valve gear so arranged; and it also has the motion
of its slide valve in the direction of a straight line instead of semi-rotary as before
described. The drawing speaks for itself. A slot is formed on the shorter arm of
lever, g, and in it the pin of the valve rod h, engages. Instead of this arrangement,
connection between g and may be made by a coupling red or link.
Figure 4 shews a modification of the passages and a suitable construction of the
slido valve which is ported so that the operations as previously described shall be
duly performed.
In Figure 6. c is a form of suitable gland adjustable by means of the studs and
nuts b, b,. The space a, formed by the trunk and gland c, is filled with hemp,
asbestos, or other suitable packing. The connecting rod d works through a slot
in the gland, c.
In figuro 4 the plain part R works through the stuffing box S, and gland T and
is packed in the ordinary manner.
Figure 5. is a diagram of the valve motion a, a¹ is the line of direction of motion
of trunk piston a,, j, is the path of the crank pin revolving in the direction of the
arrow. At the point of admission to the annular space the position of the crank
pin is represented by b; at the cut off by d'; at the beginning of communication
between the two ends of main cylinder by b¹; at the close of this communication
by d; at the commencement of the exhaust by c, and at its close by c'; ap. I P
fp represent the respective positions of the valve lever corresponding to these
points hp and i p. are the angular limits of the valve travel, n, is the passage
leading to the annular space, m, to the main cylinder; is the exhaust outlet.
The valve is shown in its position when the crank pin is at 6 or d¹.
Another method of working the engine is that the annular space may be con-
stantly open to the pressure and the valve gear arranged to admit into expand in,
and exhaust from the main cylinder behind the piston only.
There are a number of ways in which these engines may be worked without
departing from the essential features of my invention such for instance as the
coupling of two or more cylinders radiating from one shaft with valve motion
complete to act on one crank pin, or a number of cylinders or engines placed, side
by side to act on one crank shaft with as many throws as there are cylinders would
greatly economize room. In cither of these cases the valve motion of one cylinder
may be actuated from the crank pin or connecting rod of either of the other
cylinders.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed; I declare that what
I claim is,―
The improvements in double-acting steam or other engines of the cylinder A
and trunk piston C forming the annular space on one side with the increased area
on the opposite side actuated in the manner substantially as herein set forth.
Dated this 3rd day of October 1884.
GEORGE BARKER,
Agent for the Applicant,
77, Colmore Row, Birmingham.