CERTAIN IMPROVEMENTS IN STEAM ENGINES
Year: 1867

page_text: LETTERS PATENT to George Holcroft and William Nathan Dack, both
of the City of Manchester, Engineers, for the Invention of "CERTAIN
IMPROVEMENTS IN STEAM ENGINES."
Sealed the 29th May 1868, and dated the 11th December 1867.
PROVISIONAL SPECIFICATION left by the said George Holcroft and
William Nathan Dack at the Office of the Commissioners of Patents,
with his Petition, on the 11th December 1867.
. We, GEORGE HOLCROFT and WILLIAM NATHAN DACK, both of the City of
Manchester, Engineers, do hereby declare the nature of the said Invention
for "CERTAIN IMPROVEMENTS IN STEAM ENGINES," to be as follows:-
The first part of our Invention relates to an improved piston; secondly, to
an improved stop or other valve; thirdly, to an improved equilibrium slide
valve; fourthly, to certain improved expansion gears for cutting off the steam
in proportion to the load; fifthly, in placing a circular or segmental expansion
valve within the steam valve; and, lastly, to the governor by which the
variations in the speed of the engine are made to act on the expansion gear
above referred to, or on the steam or expansion or throttle valve.
Our improved piston consists in turning a screw or spiral recess in the body
of the piston, and screwing the metallic packing into the said recess; the
packing is held by stops or by a cover.

page_text: Our improved stop or other valve consists in dispensing with the usual
wings in the seating or valve, and guiding the valve by a shank, to which the
spindle is connected by a bush or otherwise.
Our improved equilibrium slide valve consists in surrounding the valve by
a loose frame or sides which support the back plate, with recesses corre-
sponding to the ports; or the back plate may be supported by ribs on the
cylinder or steam chest. A cut-off or expansion valve on a steam valve may
be balanced by surrounding it with a loose frame or ribs cast on the steam
valve, on which is a back plate fixed to the steam valve, the back plate
having recesses corresponding to the ports or otherwise.
Our improved expansion valve is moved to and fro on and by the slide
valve, and the traverse of the expansion valve is regulated by bushes through
which the spindle or coupling rod of the expansion valve passes; one of
these bushes has a right and the other has a left-handed thread; these bushes
are actuated by a pinion into which a rack moved to and fro by the governor
gears. By this arrangement any variation in the speed of the engine causes
the bushes to approach or recede from each other, consequently the bushes
act sooner or later on shoulders on the expansion valve spindle or coupling
rod, and thus vary the cut off of the steam in the proportion required.
A modification of our expansion gear consists in varying the position of the
eccentric or cam or other equivalent by which the expansion valve is worked,
by forcing a screw or other equivalent into a bush to which the eccentric or
other equivalent is connected. The bush has a spiral groove into which a
key enters, and causes the eccentric or other equivalent to move either
forward or backward. The screw or other equivalent is forced into or out of
the bush by mechanism actuated by the governor. In this arrangement the
expansion valve can either work on the back of the slide valve or on an
intermediate face plate between the expansion and steam valves.
Another modification of our expansion gear consists in varying the position
of a taper or spiral cam or rollers acting on fixed cams by means of a screw
or wedge, or other agent actuated by the governor. The cam or rollers
working the steam or expansion valve is released from a differential stop by a
second cam or eccentric, so that it can be moved to and fro by the governor,
and it is held again by a spring or balance weight against the differential stop,
the position of which is regulated by the governor.
Expansion valves may be worked by a cam or eccentric against the action
of a spring or weight. The expansion valve is connected to or disconnected
from the cam or eccentric by a catch or other agent which is actuated by a

page_text: differential stop or motion regulated by the governor, thereby allowing it to
be closed by the action of the spring or weight, and to cut off the steam
according to the load.
Our improved expansion gear may be modified by making the expansion
valve and the steam valve cylindrical, the former being within the latter; the
cut off is varied by arresting the motion of the expansion valve, and this is
again effected by the governor moving a rack gearing into a pinion, the boss
of which forms a nut for right and left handed screws acting on shoulders on
the rod which stops the expansion valve while the steam valve continues its
traverse. Instead of the rack and pinion above referred to the connection
from the governor may be made by levers or other equivalents.
Our improvement in governors consists in the combination of a weight to
counterbalance the centrifugal force of the balls with arms crossing each
other, and suspended to centres above the point of intersection of the arms.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said George Holcroft and William Nathan Dack in the Great
Seal Patent Office on the 10th June 1868.
TO ALL TO WHOM THESE PRESENTS SHALL COME, we, GEORGE
HOLCROFT and WILLIAM NATHAN DACK, both of the City of Manchester,
Engineers, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Eleventh day of December, in the year of our Lord
One thousand eight hundred and sixty-seven, in the thirty-first year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto us,
the said George Holcroft and William Nathan Dack, Her special license
that we, the said George Holcroft and William Nathan Dack, our executors,
administrators, and assigns, or such others as we, the said George Holcroft
and William Nathan Dack, our 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 "CERTAIN IMPROVEMENTS IN STEAM ENGINES," upon the condition (amongst
others) that we, the said George Holcroft and William Nathan Dack, our
executors or administrators, by an instrument in writing under our, or their,

page_text: or one of our or 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 we, the said George Holcroft and William
Nathan Dack, do hereby declare the nature of our said Invention, 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) :-
The first part of our Invention relates to an improved stop or other valve;
secondly, to an improved equilibrium slide valve; thirdly, to certain im-
proved expansion gears for cutting off the steam in proportion to the load, and
lastly, to placing a circular or segmental expansion valve within the steam
valve.
(
And in order that our Invention may be fully understood and readily
carried into operation we will proceed to describe the three accompanying
Sheets of Drawings, reference being had to the figures and letters marked
thereon.
On Sheet 1, Figure 1 is a transverse section, and Figure 2 a plan of our
improved stop valve. The improvement consists in dispensing with the usual
wings in the seating or on the valve; and in guiding the valve by a shank, to
which the spindle is connected by a bush or otherwise. a, is the body of the
valve box; a', the lid; a, the seating, and b, the valve, which is connected to
the spindle b¹ by the bush b and the pins which pass through the bush and the
boss of the valve; this spindle fits loose in the boss of the valve, and on it is
a screw taking into a square nut 6 let into the lid a¹, consequently as the
spindle is turned round by the hand wheel b the valve is opened or closed.
This improvement is not only applicable to stop valves as shewn, but to every
description of valves for steam or other fluid.
Figure 3 is a transverse section of one of our improved equilibrium slide
valves; Figure 4 is a longitudinal section; Figure 5 a plan, and Figure 6 a
plan of the back plate of the same.
Our improvement consists in supporting the back plate of the valve by ribs
cast on the cylinder or steam chest. c is the cylinder to which are cast the
ribs c¹ between which the valve d works; d¹ is the back plate having recesses
corresponding to the ports. The back plate d¹ is held down on the ribs c¹ by
the spring c which presses against the inside of the lid of the steam chest,
and the back plate is prevented moving endwise by the projections d³; or the

page_text: back plate may be supported by a loose frame or sides as shewn in Figures 7
and 8; in these views the loose frame. c rests on the cylinder or steam chest,
and the valve d moves to and fro within the frame.
On Sheet 2, Fig. 9 is an end elevation of the principal parts of a steam
engine to which our improved expansion gear is applied, and Fig. 10 is a
plan in section of the same. c is the cylinder; d, the slide valve; and f, the
expansion valve which rests upon and is moved to and fro by the slide valve d.
The slide valve is worked as usual by an eccentric or tappet, and it is provided
with the usual ports for the admission and exhaust steam. The expansion
valve is connected by lock nuts to the spindle f¹, which is provided with the
taper shoulders and f'; between these shoulders the spindle f¹ passes through
the bushes g and g'; the former has a right-hand thread on its circumference,
and the latter a left-hand thread; both these bushes are screwed into a fixed
bracket, and they are connected by a key and groove to the tube g³ shewn best
in Fig. 11, which represents a section of a modification of this part of our
Invention. Upon the tube g₁ is keyed the pinion g³ into which the rack h
gears; this rack is connected to and moves to and fro by the governor, con-
sequently as the speed of the engine varies according to its load the rack h
causes the pinion g³ to turn round either in one direction or the other. On
referring to Fig. 10 it will be seen that the valve d, in addition to the ordinary
admission and exhaust ports, has also the passages d³ and the expansion
valve is provided with the ports f' and passages f; by this means the steam
is admitted and cut off simultaneously at two points.
The mode of operation is as follows: As long as the engine is working at
its proper speed and the governor balls revolve in the same plane, the valve
d in working to and fro carries the expansion valve f with it and the shoulders
f and coming alternately in contact with the ends of the bushes g and g¹
arrest the motion of the expansion valve while the slide valve completes its
stroke, but as soon as the speed of the engine increases the governor balls
in expanding move the rack h in the direction of the arrow, thereby causing
the pinion to turn partly round and to unscrew the bushes g and g¹ partly out
of their bracket; by this means the distance between the ends of the bushes is
increased and the shoulders and fare brought sooner in contact with them
consequently the motion of the expansion valve is arrested and the steam cut
off earlier than before. On the other hand, when the load on the engine
increases and the speed is reduced, the rack his moved in the contrary direc-
tion, the bushes and g¹ are screwed into their bracket and the shoulders f
and are brought later in contact with the ends of the bushes, thereby

page_text: increasing the quantity of steam admitted to the cylinder. In Fig. 11 the
shoulders and f³ are replaced by discs containing washers of leather or other
yielding material, and the ends of the bushes g and g¹ are also provided with
discs; by this means the noise or shock of the shoulders is avoided.
Fig. 12 represents a section of a slide valve with a passage at the back of
the ordinary exhaust port, by which arrangement the steam is exhausted from
the cylinder at two points, as shown by the arrows, thereby facilitating the
escape of the exhausted steam; by this means the least possible amount of lap
on the steam side of the valve may be given while the proper amount of
exhaust passage is obtained, thereby carrying the steam when necessary to the
fullest extent before the expansion valve is closed.
Fig. 13 represents a modification of our improved expansion gear in this
view; the spindle f.of the expansion valve is provided with two inclines; the
governor is connected to the crank h¹ fixed to the screwed bush g, and this
bush is connected to the bush g' by gearing; both the bushes and g¹ are
connected to the block g which has also two inclines on its lower surface
corresponding to those on the spindle f. By this arrangement, when the
speed of the governor varies, the block g³ is raised or lowered, thereby varying
the cut off as above described. The bushes g and g¹ are shewn with right and
left handed screws, but by the application of intermediate gearing they may be
made either both with right-hand screws or both with left-hand screws.
Fig. 14 represents another modification of our improved expansion gear. In
this view de is the eccentric for working the ordinary slide valve d, and f¹ is
an eccentric for working the expansion valve. The eccentric do is fixed to
the shaft and the end of this shaft is screwed at i'; on this screw fits the
bush i, the position of which is regulated by the governor either by the rack
hgearing in the pinion g³ to raise or lower the differential stop f shewn in
section in Fig. 18; this stop acts on the forked lever f which takes into a
groove in the bush j, or the bush can be raised and lowered in any other
convenient manner. The bush j is connected by a key and groove to the boss
of the eccentric fº. In the end of the shaft i is screwed the screw k, to which
is fixed the spur pinion ¹ gearing into the pinion fitting on a stud passing
through the top of the bush j; to the pinion is fixed the star wheel l¹ acting
against a fixed stop piece. When the engine is at work the star wheel l' and
consequently the bush ; are turned round a portion of a revolution at every
revolution of the crank shaft, thereby screwing the bush i partially off the
screw and releasing the differential stop f, the governor is then at liberty to
act on the pinion g³. If the speed of the engine is too great the differential

page_text: By this
stop will be pushed out, thereby moving the bush ; and turning the
eccentric to the position required for cutting off the steam sooner; the
contrary action takes place when the engine is running too slow.
arrangement the cut off can be varied to the full stroke of the piston, whereas
in the arrangements previously described the cut off will be limited to the full
throw of the eccentric. We wish to observe here that cams may be used
instead of the eccentrics d and fº.
Figures 15, 16, and 17 are three views of another modification of our
improved expansion gear, in which an ordinary tappet or Cornish or double
beat valve is worked by a cam or eccentric. c is the cylinder; f, the valve
rods; m, the levers fixed to the upright bars m', which are provided below
with antifriction bowls, and are moved by the taper cams or eccentrics n fixed
to the shaft n; this shaft is turned by the fly wheel shaft or other convenient
part of the engine. The springs o are connected below to a fixed bracket
and above to the links o' jointed to the short arms of the levers p, the long
arms of which are connected by a slot and stud to the upright bars m¹. The
rod h from the governor is jointed to the horizontal arm of the elbow lever q,
the vertical arm of which is jointed to the horizontal bar q¹; the arms q are
jointed to this bar, and the forked end of these arms take into grooves in the
antifriction bowls bearing upon the cams n. Near the centre of the bar q' is
the saddle q³, which is caused to press on the bar q', when the valves are open
by the action of the springs o, thereby preventing the bar q¹ moving laterally
when the bowls fall on the taper cams. When the valves are closed the
weight of the valves and rods acting on the levers p extend the springs o, and
release the saddle q3 off the bar q', which is then at liberty to be moved
laterally by the action of the governor; by this means the antifriction bowls
are brought on to the different parts of the taper cams, and the valves are
allowed to close either earlier or later according to the load. In some cases
weights or other equivalents may be applied in lieu of the springs o.
Figure 18 is a modification of the arrangement above described. In this
view the taper cam n acts as before on a bar connected to the valve, and the
pressure on the shoulder of the spindle f is released to allow the governor
to act on the pinion g3 by means of a rack or other equivalent by the cam n³,
the rod of which is connected to the short arm of the elbow lever r, the
spindle being connected at f to the longer arm of the said lever. The
shoulder is held up against the end of the screwed bush g by the spring f.
When the cam n lifts the shoulder out of the end of the bush g by over-
coming the action of the spring f (during this time the taper cam n is not

page_text: acting on the steam valves) the governor is at liberty to alter the position of
the screwed bush g, and by this means when the cam n has acted on its rod
the spring brings the shoulder against the end of the bush g, thereby
holding the cam n in the position corresponding to the load on the
engine.
:
Figure 19 represents a combination of the apparatus shewn in Figures 16
and 18. In this arrangement the horizontal bar g¹ acts as before described on
the rollers of the upright bars m', and the elbow lever q is again connected to
the governor by the slotted rod h*. The spindle f is jointed to the elbow
lever q, and is provided with a shoulder P, screwed bush g, and spring f',
as shewn in Figure 18; the pinion g" is also connected to the governor by the
rack h. The mode of operation is as follows:-When the upright bars m¹ are
lifted by the cams n, the rollers against which the cams act have a tendency
to slip down, thereby pressing the bar q' in the direction of the arrow; to
prevent this the shoulder is followed up by the screwed bush g, which is
turned partly round by the rack h acting on the pinion g³.
On Sheet 3, Figure 20 is a section, and Figure 21 a plan of another
modification of our improved expansion gear. In this arrangement the valve
boxes of the cylinder c are connected by side pipes as usual. The slide
valves d, d, are connected by the valve rod de; these valves are worked as
usual by an eccentric or tappet. The cut off or expansion valves are con-
nected by the spindle f, and these valves are balanced by the back plates
bearing upon loose frames or on ribs cast on the slide valves d, as described
in reference to Figures 3, 4, 5, 6, 7, and 8. The back plates f
have recesses corresponding to the ports and passages in the valves d. To
the valve rod d is fixed a plate with catches d, and through this plate pass
the studs with antifriction bowls do and d¹¹; these bowls are acted upon by
the taper cams s, which are connected together by the double elbow lever s¹,
and to the governor by the rod h. To the spindle are jointed the two
catches foresting upon the catches do, and the end of the spindle f¹ is acted
upon by the springs and f". The mode of operation is as follows:-
brings the bowl d" against one of the cams & the bowl
rides up the cam and causes the stud of the bowl to raise the corresponding
catch f; the spring then forces the spindle f¹ and the cut-off valves / in
the direction of the arrow, thereby shutting off the steam; the contrary action
takes place when the valves d are working in the opposite direction, and the
bowl comes against its taper cam, and as the position of the taper cams s
is varied by the governor, it is evident that the cut off is regulated according
When the valve rod d

page_text: to the load on the engine. In some cases weights or other equivalents may
be used instead of the springs f and f".
In Figures 22 and 23 we have shewn a vertical and horizontal section of
our improved circular or segmental cut-off valve placed within the steam
valve. In these views is the outer casing or valve box; d is the circular
steam valve fixed to the spindle d³, and the circular expansion valve fixed
to the spindle f. The valves are shewn in the position they occupy when
the exhaust is open; the valve d is turned partly round by an eccentric or
tappet, and the position of the valve is regulated according to the load by
any of the improved expansion valve gears, above described, or otherwise.
The expansion valve may be balanced by the back plate f", which is screwed
to the steam valve d, and is provided with recesses corresponding to the ports
in the steam valve; the circular steam valve may be balanced in the same
manner.
Having thus stated the nature of our Invention, and described the manner
of performing the same, we declare that we claim,-
First. The improved stop or other valve shewn in Figures 1 and 2, whereby
the usual guide wings are dispensed with.
Secondly. The improved mode of supporting the back plate of balanced
steam valves, as shewn and described in reference to Figures 3 to 8.
Thirdly. The various improved expansion gears for cutting off the steam
in proportion to the load, as shewn and described in reference to Figures 9
to 21.
Fourthly. The application to expansion gears of the screwed bushes g and g³,
connected to the governor, and acted upon directly by it, as described.
Fifthly. The application to expansion and slide valves of the extra ports
and passages marked d, f, and f³, as shewn in Figures 10 and 12, whereby
the expansion valve is made to cut off the steam more suddenly
than heretofore.
Sixthly. The application of the extra exhaust passage in the slide valve, as
shewn in Figure 12, whereby the usual lap or cover of the valve may be
reduced and the requisite amount of exhaust attained.
Seventhly. The use and application of the screw i¹, shewn in Figure 14,
whereby the position of the eccentric for working the cut off valve is varied in
relation to that of the eccentric for working the slide valve.
Eighthly. The particular application of springs or weights or other equiva-
lents to expansion gear, as shewn in Figures 15, 16, and 17.
Ninthly. The application of the differential stop to expansion gears, as
shewn and described in reference to Figs. 14 to 19.

page_text: Tenthly. The application of springs or weights or other equivalents to a
separate cut-off valve on the back of the steam valve, as shewn and described
in reference to Figures 20 and 21.
Elevently. The application of a balanced expansion valve to a slide valve,
as shewn and described in reference to Figs. 20 and 21.
And, lastly. The improved circular or segmental steam and cut-off valve,
shewn and described in reference to Figures 22 and 23, and the mode of
balancing the same.
In witness whereof, we, the said George Holcroft and William Nathan
Dack, have hereto set our hands and seals, the Ninth day of June, One
thousand eight hundred and sixty-eight.
GEO. HOLCROFT. (L.S.).
WILL. N. DACK. (L.S.)