IMPROVEMENTS IN STEAM ROCK DRILLS
Year: 1884

page_text: COMPLETE SPECIFICATION.
and in
I, HERBERT JOHN ALLISON, of the firm of Allison Brothers, of 52 Chancery
Lane, London, in the County of Middlesex, Patent Agents, do hereby declare the
nature of my Invention for "IMPROVEMENTS IN STEAM ROCK DRILLS
what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement, reference being had to the
accompanying Drawings forming part of this Specification.
My Invention relates to steam rock drills which comprise a steam cylinder and
reciprocating piston and piston-rod carrying a drill, steam passages for distributing
the steam in the cylinder to reciprocate the piston, a valve-chest and a steam-
moved valve therein, constructed and arranged to co-operate with the piston in
governing said passages, together with suitable mechanism to feed the drill to its
work; the work designed to be done by the machine being that of striking a
succession of blows with the drill by the reciprocation of the piston.
As the efficiency of this machine is in proportion to the force of the blows struck
and the rapidity of the reciprocation of the piston, it is important that the piston
should move to the end of its working stroke with as little obstruction as possible
from the steam introduced into the cylinder to effect the return stroke. To the
extent that steam is introduced before the piston reaches the limit of its working
stroke, the force of the blow struck is lessened by the "cushioning" of the piston
on the steam,
In this class of rock drills as ordinarily constructed, such "cushioning "necessarily
takes place in practice, by reason of the variation in the length of the working
stroke which results from the variation of the point of the collision of the drill
with the rock, and the want of uniformity in the feed of the drill.
It is necessary that by the time the piston reaches the termination of its shortest
practical stroke it shall have performed its part of the work of causing the
introduction into the cylinder of the steam which is to effect the return stroke;
otherwise, at that point the piston would stop. But when, as is the case in drills
as heretofore made, the uncovering of the inlet port to the cylinder takes place
simultaneously with the said action of the piston, at the end of its shortest working
stroke, the piston in all longer strokes will necessarily be met at all points, between
its shortest and longest strokes, by the incoming steam, and the force of its blows

page_text: will be diminished in proportion to the amount of steam thus prematurely
introduced.
The objects of my Invention are (while securing in any event the introduction
of steam to effect the return of the piston, after its shortest working stroke,) to
prevent the introduction of steam and the consequent "cushioning" of the piston
when larger working strokes are made; also to combine with the said obviating of
the "cushioning" of the piston at the end of its working stroke, the use of steam
expansively; and also the confining in the upper end of the cylinder of the residual
stenm therein, after the exhaust, and the compression of the same by the upward
stroke of the piston, whereby the compressed steam serves as a
cushion" to assist
in arresting the piston, and then by its re-expansion assists in impelling the piston
in its working stroke.
"
I obviate the "cushioning" of the piston at the end of its working stroke by
making the passage through which the steam passes, by means of which the valve
is shifted to admit steam to the cylinder to effect the return stroke of the piston,
of suitably small cross-area or conducting capacity, to so limit the rate of trans-
mission of steam through it, that there will necessarily occur between the opening
of said passage, at the end of the shortest practical working stroke of the piston,
and the actual shifting of the valve to open the inlet passage to the cylinder, a
determinate delay, for the purpose of allowing the piston to complete longer strokes
by the time the said passage is opened. I combine with the said constricted steam
passage, the inlet port to the upper end of the cylinder, governed by the piston, and
so located relatively thereto that the steam is cut off by the piston before it reaches
the limit of its downward or working stroke, whereby the steam is used expan-
sively during the remainder of said working stroke. I arrange and locate the
exhaust port of the upper end of the cylinder, so that it is closed by the return
stroke of the piston soon after the commencement of that stroke, the steam being
thus confined in the upper end of the cylinder until the piston makes both its
upward and downward strokes and again opens the exhaust port.
I will now proceed to describe a steam rock drill embodying my Invention, and in
doing so I shall for convenience designate the movement made by the piston in
delivering its blows as the down or "working" stroke, and its movement in the
opposite direction as its up or "return" stroke. The end of the cylinder towards
which the piston moves on its working stroke, I shall call the lower end, and the
opposite end, the upper end. I shall designate as the lower end of the valve and
valve-chest that to which the steam is admitted to shift the valve for opening the
inlet port to the lower end of the cylinder, and the opposite, the upper end; and
the movement of the valve towards the lower end of the valve-chest I shall call
the downward movement, and the reverse, the upward movement.
I desire it to be understood that I do not confine myself, in all its parts, to the
machine herein represented and described, it being obvious that the devices and
mechanism which I employ to effect the objects attained by my present Invention,
may be employed in steam rock drills and analogous machines differing in many
other respects from the one here shown and described.
The accompanying Drawings illustrate a steam rock drill embodying my
Invention.
Figure 1 is a side elevation.
Figure 2 is a transverse section through the line x, x, on Figure 4.
Figures 3, 4, 5 and 6 are longitudinal sections taken through the line y, y, on
Figure 2, respectively showing the piston, in elevation, in various positions. For
clearness of illustration the lower portions of Figures 3, 4, 5 and 6 represent as in
a vertical plane that portion of the line y, y, which extends obliquely upward from
the centre of the cylinder, and then horizontally outward through the nozzle which
is for connection with the steam pipe.
Figure 7 illustrates a modification in the form of the valve, and in the arrange-
ment of the steam passages from the cylinder to the valve-chest, which permits the
employment of a piston-valve, having but one circumferential groove.

page_text: Figure 8 is a modification showing an arrangement of steam passages adapted
for the employment of a piston-valve having three circumferential grooves.
Figure 9 is a longitudinal section showing a modification in the arrangement of
the steam inlet passages to the valve-chest, by which direct communication is had
between the steam-chest and the valve-chest.
Figure 10 is a detached part of the machine, embracing the valve-chest and
valve, a broken part of the piston and the steam passages communicating with the
valve-chest, showing a modification hereinafter fully described.
Figure 11 is also a detached part of the machine, embracing the middle portion
of the cylinder and piston, the valve-chest and the valve, and the passages for
distributing steam to the cylinder, illustrating a modification of devices embodying
my Invention hereinafter described.
A is the cylinder and B is the piston which is elongated sufficiently to afford space
for a steam chamber in its middle portion, and also to perform the functions of
opening and closing the steam ports hereinafter described. C is the piston-rod
which carries the drill, or other tool, and D is the spiral rod for effecting the
rotation of the drill. The middle portion of the piston is circumferentially grooved,
and the annular space E between the grooved portion of the piston and the wall of
the cylinder serves as a steam-chest to receive steam through the nozzle E¹ which
projects from the side of the cylinder, as shown. F is a valve-chest connected with
the side of the cylinder, as shown; and G is a single cylindrical valve fitted to
work in a correspondingly shaped chamber in said chest; and said valve is operated
by steam introduced into said chainber by ports leading from the steam-chiest E.
h is the inlet port communicating between the upper end H of the cylinder and
the upper end of the valve-chest, and also opening into the cylinder at a point
where it will communicate with the steam-chest E, when the piston is at the end
of its upward stroke, as seen in Figure 5. is a port also communicating between
the interior of the cylinder A and the valve-chest F near its upper end, opening
into the cylinder at a point where it will be uncovered and communicate with the
steam-chest E when the piston has reached, in its upward movement, the position
shown in Figure 4; and will be closed by the piston, in its downward movement,
thereby cutting off the steam from the upper end of the cylinder, before the piston
has reached the limit of its downward stroke. In the Drawing this cut-off is
represented as taking place at about half-stroke. But it is obvious that the position
of the inner mouth of the port h³ may be varied.
is the exhaust port leading from the valve-chest.
i is a steam passage
communicating between the lower end J of the cylinder and the valve-chest, and
this passage serves both as an inlet and outlet port. I is a port communicating the
cylinder and the valve-chest, and so located that it will be uncovered by the piston
and communicate with the steam-chest E when the piston is in the position shown
in Figure 6.
e is a port communicating between the lower end of the valve-chest and the
cylinder, and located, as shown, so as to be controlled by the portion of the piston
below its circumferential groove; and G¹is an exhaust port communicating between
the lower end of the valve-chest and the cylinder, the same also being controlled
by the said lower portion of the piston. The valve-chest is internally circum-
ferentially grooved forming internal annular steam spaces into which the outer
mouths of the ports h², i and I respectively open; the portions of the interior wall
or face of said chest, not included in said annular grooves, constituting the valve-
seats of the cylindrical portions of the valve G. The said valve G is formed, as
before stated, of a single cylinder of metal, circumferentially grooved, as shown,
the cylindrical parts fitting with steam-tight joints into the said valve-seats.
heads h, h, of the valve-chest, at either end, against which the ends of the valve
abut, project into the chest with reduced diameters, thus respectively providing
steam-spaces in the valve-chest at the ends of the valve, when it is in contact with
said heads, which communicate respectively with ports e, h and G'.
The
E' is a longitudinal groove or recess in the cylinder, communicating with the

page_text: steam-chest formed in the cylinder at E, and into which opens the steam supply
pipe E that communicates with the boiler. This groove E permits the circum-
ferential groove in the piston, and of course the piston itself as well as the cylinder,
to be made considerably shorter than it would otherwise have to be in order to
maintain constant communication between the pipe E¹ and the steam-chest, and
yet permit the piston to have the requisite length of stroke.
The operation of the said machine is as follows: Assuming the parts to be in the
position shown in Figure 3, the steam entering through the steam-chest E will pass
through the port I into the passage i, through the annular space g into the lower
end J of the cylinder, and through the piston upward. When the piston thus
begins its upward movement, the steam from steam-chest E is acting against the
lower end of the valve G and holding it in the position shown in Figure 3, the
exhaust port G¹ being closed. As the piston moves upward it will first close
the port e, then the port I, cutting off steam from the lower end of the cylinder,
and also open the exhaust port Ğ¹. When it has reached the position shown in
Figure 5, the piston will uncover the inner mouth h³ of the port h and thereby
admit steam into the upper end of the valve-chest, whereby the valve will be
thrown downward into the position shown in Figures 5 and 6, thus closing the
communication through the annular space between the ports I and i, and opening
communication through the annular space between i and ¹, thus closing the inlet
port to the lower end of the cylinder, even when the port I is opened by the piston,
and opening the channel for exhaustion from the lower end of the cylinder. By the
uncovering of said port ho, steam is also admitted into the upper end H of the
cylinder. The piston will now begin its downward movement, and closing
successively the inner mouths of the ports h and h² thereby cuts off the steam from
the upper end of the cylinder. Then as it continues its downward movement it
will uncover the port I; but as the communication between I and i is at the
moment closed, steam is not then admitted to the lower end of the cylinder through
said port . The piston next uncovers the port e, after closing the port G³, steam
being thus admitted to the lower end of the valve-chest, through said port e, and
operating to throw the valve upward, the steam at the upper end of the valve-
chest being at the moment exhausting through ports h' and h, the upper end H of
the cylinder and the exhaust port H₁; and by said upward movement of the valve
communication is opened between I and i, and steam is again admitted into the
lower end of the cylinder.
Now, it will be observed that the port e is uncovered some time before the
piston has reached the limit of its downward stroke and that if steam were at that
moment admitted into the valve-chest at full pressure, so as to reverse the valve,
steam would be thereby admitted into the lower end of the cylinder, and the
piston, during the remainder of its stroke, would be "cushioned" against the
steam, thus impeding the movement of the piston and diminishing the force of
the blow of the drill.
To obviate this result I make the inlet port e of small diameter so that the
steam will be admitted into the lower end of the valve-chest so slowly that it will
not reverse the valve until the piston has had time to move from the point where
it uncovers the port e, to the limit of its downward movement in the cylinder.
When the piston in its downward movement has uncovered the port e the
condition is thereby established in which the valve will certainly be reversed
eventually. If by collision of the drill-tool with the rock, the piston should be
arrested immediately after the port e is opened, there will be a momentary pause
before the piston will begin its upward movement; the pause being for the time
required for sufficient steam to pass through the port e to reverse the valve; and it
is intended that this space of time shall be equal to the space of time occupied by
the piston in moving from the inner mouth of the port e to the limit of any strokes
beyond that point. Thus, in proportion as the feed is less excessive, and the
length of the stroke of the piston is extended, the duration of the said pause is
decreased, until the stroke reaches the limit of motion in the cylinder, when the

page_text: reversal of the valve occurs, and the introduction of steam into the lower end of
the cylinder takes place, simultaneously with the termination of the stroke, and
the piston begins its upward movement immediately after the blow is delivered.
The port e is intended to open into the cylinder at a point where it will be reached
and uncovered by the piston under the most excessive feed ordinarily practiced, so
that the opening of said port at the termination of the working stroke will at all
I find that
times be assured under the greatest practical variations of feed.
locating the inner opening of this port so that the piston will move, after opening
it, about one and three-quarter inches, before reaching the limit of its movement
in the cylinder, will provide sufficiently for variation of feed for practical purposes,
while avoiding under all circumstances the premature introduction of the steam
into the lower end of the cylinder.
In order to attain the above named result it is necessary that the area of cross-
section, or conducting capacity of the passage e should bear a certain relation to
the weight, diameter and length of stroke of the valve G, and also to the velocity
of the piston and the distance it moved from the point where it uncovers the
port e to the limit of its stroke in the cylinder. The following statements of the
proportions which are found to give satisfactory results in an ordinary working
drill of the usual dimensions, will enable a skilled mechanic to adapt the size of
In such a machine in
the port e to variations in the dimensions of the machine.
which the diameter of the piston is three and one-eighth inches, the entire stroke
six and one-half inches, and, after opening the port e, one and three-quarter inches,
striking four hundred to four hundred and twenty blows per minute, under a
pressure of seventy pounds per square inch above the atmosphere, and the diameter
of the valve is one and a sixteenth inch, its weight seventeen ounces, and
its stroke five-eighths of an inch, the diameter of the passage e is about five
thirty-seconds of an inch.
It is obvious that the same result will be attained by enlarging the inlet port e
and constricting the exhaust port of the opposite end of the valve-chest. If, when
the steam should be let in full pressure to one end of the valve, this pressure
should be balanced by equal steam pressure at the opposite end, the valve would
not, of course, be shifted until the pressure at said opposite end was reduced so
far that the overbalancing pressure at the one end was sufficient to overcome the
inertia and friction of the valve. The effect therefore is the same whether the
exhaust is immediate and the inlet gradual, or the inlet is immediate and
the exhaust gradual; and, it is furthermore obvious, that both the inlet and
exhaust may be gradual, the restriction of both such ports together being equal to
the restriction of either one, when the entire effect of the gradual admission or
exhaustion of the steam is to be accomplished by the restriction of one alone.
The modification of the valve and exhaust port by which the said gradual
exhaust may be accomplished is shown in Figures 8 and 10, and consists in making
the exhaust he of the port h³, in Figure 10, of small diameter or cross-area, and the
port e of large diameter as shown therein. The mouth hª should preferably be so
located relatively to the inner mouth of the port e that it will be uncovered
simultaneously therewith, and simultaneously with the exhaust port H¹, as shown
in said Figures. By this arrangement the steam is let in so that it would shift
the valve G immediately upon the opening of said port e were it not for the
pressure of the steam at the upper end of the valve-chest. In order to adapt the
valve G to the desired modification of the valve-chest-exhaust shown in said.
Figures 8 and 10, the said valve is provided with an additional circumferential
groove h, forming an additional cylindrical port h³; and the steam-spaces in the
valve-chest, the port h² and the main inlet port h are so arranged that when the
valve G is thrown down, steam is let into the upper end H of the cylinder A from
the steam-chest E through the port h², the steam-space surrounding the annular
groove h' and the inlet port h; and when the valve is thrown up it closes the
outer mouth h' of the port h and cuts off the steam, the lower branch h¹ acting

page_text: only to admit steam to the upper end of the valve-chest to impel the valve
downward.
Another modification, within the spirit of my Invention, is shown in Figure 9.
In the machine there shown I establish, by suitable passages K, K¹, communication
between the steam supply pipe E¹ and both ends of the valve-chest. The exhaust
passages from the lower end of the said valve-chest, and, if preferred, from both
ends thereof, are governed by the piston. Under these conditions, with both
exhaust passages closed, it is apparent that the valve would remain at rest, and
that it would be reciprocated by the alternate opening of the exhaust at the
opposite ends of the valve-chest. Now, if either the inlet passage K to the
lower end of the said chest, or the exhaust passage at its opposite end were
constricted as before described, the upward movement of the valve, after the
commencement of the movement of the steam through such constricted passage,
would be delayed until the gradual increase of pressure upon the valve should be
sufficient to overcome the weight and inertia of the valve, as herein before specified.
When these open steam passages K, and K' are employed, the head h of the lower
end of the valve-chest should not be tapered but should fill the chest so that when
the valve abuts against it, it will leave substantially no steam-space in this end of
the valve-chest. Then the passage for the exhaust through G can be made by a
small groove in the under side of the head which projects into the valve-chest, as
shown in Figure 9.
The modification shown in Figure 11, represents both the inlet to the lower end
of the valve-chest, and the exhaust passages from the upper end of said chest,
constricted, so that jointly they will retard the transmission of steam by the agency
of which the valve is shifted to admit steam to the lower end of the cylinder, so
that a delay occurs in the shifting of the valve as hereinbefore described. It is
obvious that with this arrangement both said passages should be suitably
constricted so as to produce conjointly substantially the same result in retarding
the transmission of steam as will be produced by the constriction of either one
alone, when the entire effect of the gradual admission of steam, to move the valve,
is to be accomplished by the constriction of one.
The inner mouth of the port 2 is located relatively to the piston, as described
and shown, so that it will be closed and the steam cut off by the piston before
the latter has reached the limit of its downward stroke, preferably at about
half stroke, whereby, during the remainder of the stroke, the steam is used
expansively.
I find that by preventing the "cushioning" of the piston in its downward
stroke, I can use steam expansively, as described, and obtain equal efficiency, and
the drill will do as much work, as when steam at full-stroke is used with the
cushioning" that necessarily takes place when steam is let into the lower end of
the cylinder at the termination of the shortest practical stroke of the piston.
I thus economize in the use of steam.
"
His the exhaust port of the upper end of the cylinder opening through the
wall thereof, and which is controlled by the upper cylindrical portion of the piston,
and said port is located as shown in the Drawings, where it will be uncovered by
the piston only momentarily when the piston is at, or near, the limit of its
downward stroke, being covered and closed by the piston at all other times.
Now it is obvious that upon the closing of the exhaust port H¹ by the piston in
its upward stroke, the residual steam then remaining in the upper end of the
cylinder will be confined therein, and during the remainder of the said upward
stroke will therefore by gradually compressed, and its elastic resistance will
contribute to arrest the movement of the piston, thus contributing a "cushion" for
the piston; and that thereby there will also be stored up in said compressed steam
a part of the energy expended in propelling the piston in said upward stroke; and
the energy thus stored up will be re-expended in assisting in propelling the piston
in the downward or working stroke. By this operation the said residual steam is,

page_text: without the loss of energy expended in its compression utilized to furnish a
"cushion" for assisting to arrest the rapid movement required of the piston in its
upward stroke, thus obviating the necessity for the employment of live steam for
this purpose. It is evident that I thus further economize in the use of steam.
The various parts of the machine described, by which this compressing the
residual steam is effected, are susceptible of modification without departing from
this feature of my Invention which consists in the devices by which the residual
steam, remaining in the upper end of the cylinder after the exhaust port is closed,
is compressed in said upper end of the cylinder during the remainder of the
upward stroke of the piston, and being thus compressed is utilized to assist in
arresting the upward stroke of said piston, and in propelling the piston in its
return or downward stroke.
From the foregoing description it will be clearly understood that the essential
feature of my Invention is, together with suitable means for transmitting steam by
the agency of which the valve is shifted to open the inlet port to the lower end of
the cylinder (which are brought into operation when the piston reaches the point
of limit of the shortest working stroke that in practice it is intended to be
permitted to make,) the described means and method whereby such transmission
of steam is so controlled and limited, that between the commencement of such
transmission and the actual shifting of the valve, there shall necessarily occur
a determinate delay for the purpose of enabling the piston to make its longer
working strokes before the steam is, by the shifting of the valve, introduced into
the cylinder to effect the return stroke of the piston; such control and limitation
being effected by making the passage for such transmission of said steam of small
cross-area or conducting capacity, relatively to the diameter, weight and length of
stroke of the valve, the velocity of the piston, and the difference between its
shortest and longest working strokes, as described. The said described constriction
of the said passage is a necessary condition; but it is obviously not essential that
the precise devices herein described for introducing the steam into the said
constricted passage, (whether it be the inlet or the exhaust,) at the termination of
the shortest practical working stroke of the piston, should be employed. Any
other suitable devices for that purpose, adapted to the general structure and parts
of the machine may be used. Also that my Invention provides for the use of
steam expansively in conjunction with the said non-cushioning of the piston at the
end of its downward stroke; and also for the use of the steam remaining in the
upper end of the cylinder, after the exhaust, to form by its compression by the
upward stroke of the piston, a "cushion" to arrest the piston, and to assist in its
downward stroke.
It will be understood that my Invention is applicable to other machines
analogous to steam rock drills, in which the work done is the striking of a
succession of blows by the reciprocation of a piston, impelled by steam or other
elastic fluids.
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:-
First. In a steam rock drill, or analogous machine, in which the length of its
working strokes is liable to variation, the combination with a steam-moved valve
governing the inlet port to the lower end of the cylinder, of a passage, (whether
the inlet or exhaust passage) communicating with the valve-chest for the trans-
O mission of steam by the agency of which the valve is shifted to introduce steam to
the lower end of the cylinder, said passage being suitably constricted, as described,
to so limit the transmission of steam that, between the commencement of the
movement through it of the steam by which the valve is shifted, and the actual
shifting of the valve, there shall necessarily occur a determinate delay in which
5 the piston may move beyond the point of the shortest working stroke which in
practice it is intended to be permitted to make, and make its longer strokes,

page_text: as described, by the time steam is introduced into the lower end of the cylinder, as
and for the purpose specified.
Second. The method of decreasing the steam cushioning in the working stroke
of the piston of a rock drill, or analogous machine, liable to make strokes of
variable length, which consists in the application, at the time the piston reaches its
shortest practical working stroke, of a gradually increased steam pressure to the
stean.-moved valve governing the inlet port to the lower end of the cylinder,
whereby, between the beginning of said pressure and the shifting by it of the
said valve, there shall necessarily occur a determinate delay, as and for the
purpose specified.
Third. In a steam rock drill, or other analogous machine, the steam-moved
valve governing the distribution of steam to the cylinder, and the inlet and
exhaust passages to and from said valve, one of said passages, at one end of the
valve-chest, being constricted, as described, relatively to the corresponding passage
at the other end of said chest, whereby the valve has a slow motion in one
direction, and a quick motion in the opposite direction, as and for the purpose
described.
.
Fourth. In a steam rock drill, or other analogous machine in which the length
of the working stroke is subject to variation, the combination with the main piston
and a valve governing the inlet port to the lower end of the cylinder, of a passage
for the transmission of steam by which said valve is actuated, said passage being
constricted as and for the purpose described, and an inlet passage to the upper end
of the cylinder so arranged that it is closed before the piston reaches the limit of
its downward stroke, as described, and for the purpose specified.
Fifth. In a steam rock drill, or other analogous machine, the combination of the
cylinder, elongated circumferentially grooved piston, the steamn moved valve and
the valve-chest, with the steam passage h opening at one end into the upper end
of the cylinder, and at the other end into a branch passage ' controlled by the
piston, said branch passage opening at one end into the upper end of the valve-
chest, and at the other end into the cylinder, whereby steam is introduced from
the steam-chest into both the upper end of the cylinder and the upper end of the
valve-chest, substantially as and for the purpose described.
Sixth. In a steam rock drill, or analogous machine, having the cylinder, the
elongated circumferentially grooved piston, and the described means for distributing
the steam to the cylinder, the combination with the piston of an inlet passage to
conduct steam from the circumferential chamber in the piston, to be distributed to
the upper end of the cylinder, said passage being governed by the piston, and
located relatively thereto, as described, so that the piston in its downward stroke
closes said passage before reaching its termination, whereby the steam is used
expansively during a portion of the downward stroke, as specified.
Seventh. In a steam rock drill, or analogous machine, the cylinder, the elongated
circumferentially grooved piston, the described circumferentially grooved steam-
moved valve in the described valve-chest, and the steam passages or ports located
relatively to each other and to the piston and valve, as described, whereby, while
said valve operates to control the distribution of steam to the ends of the cylinder,
the piston operates directly as a cut off to the inlet ports, as specified.
Eighth. The combination in a steam rock drill, or analogous machine, of the
cylinder, the elongated circumferentially grooved piston, the valve-chest and single
valve, with the steam inlet port I and the exhaust passage i, and the passage i
which serves both as an induction and eduction port for the lower end of the
cylinder, substantially as and for the purpose specified.
-Ninth. The cylinder provided with the longitudinal groove E' and the supply-
pipe E communicating therewith, and the elongated piston provided with the
circumferential groove forming a steam-chest in the cylinder communicating with
said groove E², as and for the
purpose described,

page_text: Tenth. In combination with a steam-moved valve, means for introducing live
steam into one end of the valve-chest, while the other end of the valve-chest is in
communication with the end of the main cylinder containing expanded steam,
whereby the valve is moved by the excess of the pressure of live steam acting
upon one end thereof, over the pressure of expanded steam acting upon the other
end thereof as described.
Eleventh. In a steam rock drill, or other analogous machine, the cylinder and
piston, the described passages for distributing the steam to the cylinder, and the
steam-moved valve governing, in co-operation with the piston, said passages,
together with the exhaust port leading from the upper end of the cylinder,
governed by the piston, and located relatively thereto, as described, so that the
residual steam remaining in the upper end of the cylinder, after the exhaust, is
confined therein, while the piston makes its upward stroke and until, on its
working stroke, the exhaust is again opened, whereby the steam in its compression
assists in arresting and terminating the upward stroke of the piston, and by its
re-expansion assists in propelling the piston in its downward stroke.
Twelfth. In a steam rock drill comprising the main cylinder and piston, the
steam-moved valve, the described passages for distributing steam to the cylinder
and valve-chest and exhausting steam therefrom, the combination with the piston
governing the exhaust ports from the valve-chest, and the steam-moved valve
governing the inlet port to the lower end of the cylinder, of the inlet passages to
the valve-chest that establish open communication between the ends of the
cylinders and the live steam supply, the said inlet passage leading to the lower end
of the valve-chest being of comparatively small cross-area, or conducting capacity,
whereby there necessarily occurs a determinate delay between the opening of the
exhaust at the upper end of the valve-chest and the shifting of the valve to open
the inlet port to the lower end of the main cylinder, as and for the purposes
specified.
naind this 11th day of March 1884