IMPROVEMENTS IN INDICATORS USED FOR ASCERTAINING THE POWER OR STEAM ENGINES
Year: 1875

page_text: vention of "IMPROVEMENTS IN INDICATORS USED FOR ASCERTAINING THE
POWER OR STEAM ENGINES"
PROVISIONAL SPECIFICATION left by the said Edward Thomas Darke
at the Office of the Commissioners of Patents, with his Petition,
on the 25th October 1875.
I, EDWARD THOMAS DARKE, of No. 1, Brecknock Crescent, Camden
Road, in the County of Middlesex, do hereby declare the nature of the
said Invention for "IMPROVEMENTS IN INDICATORS USED FOR ASCERTAINING THE
POWER OF STEAM ENGINES," to be as follows:-
This Invention has for its object improvements in indicators used for
ascertaining the power of steam engines. These indicators as is well
known consist of spring drums which are caused to rotate partially to
and fro in unison with the motion of the piston of the engine. The
spring drum receives a paper on which a tracer marks, and the tracer

page_text: moves in accordance with the varying pressure of the steam in the
cylinder during the stroke. Thus a diagram is traced on the paper
from which the power of the engine is calculated.
The spring drum has to be connected with a moving part of the
engine having a suitable length of stroke by a string which is wound
around the drum. At present the string has to be connected and
disconnected each time a diagram is taken. These troublesome operations
it is one of the objects of my Invention to avoid; for this purpose I
attach to the drum a ratchet, and I provide a pawl to work with it.
This ratchet and pawl retain the drum when it is not required to
operate. As the engine continues to work the string falls slack at each
return stroke of the piston, the ratchet and pawl preventing the spring
drum from following and winding up the slack as it otherwise would in
consequence of the tension which has been put upon the spring. When
a diagram is to be taken the movement of the marker to bring it into
contact with the paper causes the pawl to be tripped, and the drum
then at once commences to move in unison with the engine. The
removal of the tracer from the surface of the paper after the diagram
has been taken permits the pawl again to fall into the teeth of the
ratchet. If preferred the pawl may be controlled by hand.
It is obvious that in place of a ratchet and pawl other equivalent
instruments may be employed.
In order to simplify the construction of the instrument I cast in one
piece with the cylinder the bracket or table upon which the paper
drum
is carried, I connect the piston of the instrument against which the
steam acts with the pencil or marker by an arrangement of links which
forms a modification of the instrument known as the pantagraph, it
consists of links forming a jointed parallelogram with two short and two
long sides, one of the long side links is prolonged at one end a short
distance and is carried upon a fixed centre, whilst the side link jointed
to its opposite end is prolonged and made to carry a pencil or marker,
the point of which aligns with the fixed centre and the centre of the
joint which couples together the two other sides of the parallelogram.
This latter joint is coupled to the end of the piston rod.
In place of the fixed centre being at the end of the prolongation of
one of the longer links, as above described, this prolongation of the link
may be jointed to the piston rod, whilst the joint to which the piston
rod was, as previously described, attached is made the fixed centre.

page_text: In either case any desired ratio of movement may be provided for
between the stroke of the piston and that of the pencil or point upon
the paper.
In order that the adjustment of the length of the string may be more
readily effected I employ a clip having an eye in it at one end to receive
a string which makes the connection with the moving part of the
engine. At the other end of the clip is an eye through which a loop in
the string of the indicator is passed. The loop is passed round the stem
of a button with a screw stem or shank, the loop is then drawn to the
position required and the button is screwed down upon it so as to
clamp it.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Edward Thomas Darke in the Great Seal Patent
Office on the 25th April 1876.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, EDWARD
THOMAS DARKE, of No. 1, Brecknock Crescent, Camden Road, in the
County of Middlesex, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twenty-fifth day of October, in the
year of our Lord One thousand eight hundred and seventy-five, in the
thirty-ninth year of Her reign, did for Herself, Her heirs and suc-
cessors, give and grant unto me, the said Edward Thomas Darke, Her
special license that I, the said Edward Thomas Darke, my executors,
administrators, and assigns, or such others as I, the said Edward
Thomas Darke, my 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 "IMPROVEMENTS IN INDICATORS USED FOR ASCERTAINING THE
POWER OF STEAM ENGINES," upon the condition (amongst others) that I,
the said Edward Thomas Darke, my executors or administrators, by an
instrument in writing under my, or their, or one of 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

page_text: calendar months next and immediately after the date of the said
Letters Patent.
NOW KNOW YE, that I, the said Edward Thomas Darke, do hereby
declare the nature of the said Invention, and in what manner the
same is to be performed, to be particularly described and ascertained
in and by the following statement thereof, that is to say :-
This Invention has for its object improvements in indicators used for
ascertaining the power of steam engines. These indicators as is well
known consist of spring drums which are caused to rotate partially to
and fro in unison with the motion of the piston of the engine. The
spring drum receives a paper on which a tracer marks, and the tracer
moves in accordance with the varying pressure of the steam in the
cylinder during the stroke. Thus a diagram is traced on the paper from
which the power of the engine is calculated.
The spring drum has to be connected with a moving part of the engine
having a suitable length of stroke by a string which is wound around
the drum. At present the string has to be connected and disconnected
cach time a diagram is taken. These troublesome operations it is one
of the objects of my Invention to avoid. For this purpose I attach to
the drum a ratchet, and I provide a pawl to work with it. This ratchet
and pawl retain the drum when it is not required to operate. As the
engine continues to work the string falls slack at each return stroke of
the piston, the ratchet and pawl preventing the spring drum from
following and winding up the slack as it otherwise would in consequence
of the tension which has been put upon the spring. Or as I prefer a
spring pulloy separate from the drum may be applied, in which case the
pulley remains at work and takes up the slack of the cord whilst the
drum is held stationary. When a diagram is to be taken the movement
of the marker to bring it into contact with the paper causes the pawl to
be tripped, and the drum then at once commences to move in unison
with the engine. The removal of the tracer from the surface of the
paper after the diagram has been taken permits the pawl again to fall
into the teeth of the ratchet. If preferred the pawl may be controlled
by hand.
It is obvious that in place of a ratchet and pawl other equivalent
пици.
It is obvious that in place of a ratchet and pawl other equivalent

page_text: piece with the cylinder the bracket or table upon
which the paper drum
is carried. I connect the piston of the instrument against which the
steam acts with the pencil or marker by an arrangement of links which
forms a modification of the instrument known as the pantagraph. It
consists of links forming a jointed parallelogram with two short and two
long sides. One of the long side links is prolonged at one end a short
distance and is carried upon a fixed centre, whilst the link jointed to its
opposite end is prolonged and made to carry a pencil or marker, the
point of which aligns with the fixed centre and the centre of the joint
which couples together the two other sides of the parallelogram. This
latter joint is coupled to the end of the piston rod.
In place of the fixed centre being at the end of the prolongation of
one of the longer links, as above described, this prolongation of the link
may be jointed to the piston rod, whilst the joint to which the piston
rod was, as previously described, attached is made the fixed centre.
In cither case any desired ratio of movement may be provided for
between the stroke of the piston of the indicator and that of the pencil
or point upon the paper.
In order that the adjustment of the length of the string may be more
readily effected I employ a clip having an eye in it at one end to receive
a string which makes the connection with the moving part of the engine.
At the other end of the clip is an eye through which a loop in the string
of the indicator is passed. The loop is passed round the stem of a
button with a screw stem or shank, the loop is then drawn to the
position required, and the button is screwed down upon it so as to
clamp it.
In order that my said Invention may be most fully understood and
readily carried into effect, I will proceed to describe the Drawings here-
unto annexed.
DESCRIPTION OF THE DRAWINGS.
Figure 1 is a front elevation partly in section of an indicator con-
structed according to my Invention; and Figure 2 is a side elevation of
the same. a, a, is the cylinder; b, the nozzle by which it is adapted to
the engine which it is desired to test; c is the spring box and d the
bracket or table on which the paper drum is carried. The parts a b c

page_text: the cover of the spring box. The piston rod is coupled with a system of
pantagraph levers having a fixed fulcrum at upon a standard which
can turn freely around the spring box c, or the standard
structed and carried in the way shown at Figures 2*.
may be con-
o is a coiled
The spring
plan of the
The Figures 3 show to an enlarged scale the way in which the piston
rod is coupled with the pantagraph levers. The Figures 4 show to the
same scale the joint at ; the Figures 5 show one of the intermediate
joints; and the Figures 6 show the end of the lever which holds the
metallic or other pencil i. The bracket or table d carries a pin or
axle k, it passes through the disc and clamps it down to the table d,
the axle receiving a thumb nut ', as is clearly seen in Figure 7, which
is a section of the parts around the axle ; ' is a pin entering a recess
in the table to prevent the disc turning; m is a ring carrying the
pulleys m' to guide the cord, by which from a moving part of the steam
engine motion is given to the paper drum of the indicator. The ring m
can when the thumb nut is slack be turned around the disc to
accomodate itself to any direction of the cord, and the ring when set as
required can be clamped by tightening the nut. n is the pulley upon
which the cord is wound, it is able to turn on the axle k;
spring within the pulley n which connects it with the disc.
acts in the direction of the arrow on Figure 8 (which is a
pulley ) and tends to hold the stop n' on the under side of the pulley,
in the position in which it is shown, resting against the stop on the
disc. When the cord is unwound from the pulley the spring is coerced,
and as soon as the strain on the cord is relaxed the spring turns the
pulley and prevents the cord falling slack, which is the object the
spring o is intended to serve. p is the carrier for the paper drum, it is
mounted so as to be able to turn upon the axle k, and it is attached by
a coiled spring q to a collar
the axis. The spring q tends to
turn the carrier of the paper drum in the direction indicated by the
arrow in Figure 9; this Figure is a plan partly in section of the instru-
ment, and in it the carrier is shown locked in opposition to the spring
by the pawl entering between the ratchet teeth formed upon the
carrier at p. 2 is a stop upon the upper side of the pulley n. When
the pawl is lifted the spring q turns the drum carrier until the stop 1³
upon the under side of the carrier takes the position shown by the dotted
lines in Figure 9, resting against the stop 2. If the pulley n be turned
by the action of the cord connected to the engine whilst the parts are in
this position the pulley will take the drum carrier with it, and when the
fixed to

page_text: pull on the cord is relaxed the drum carrier will return with the pulley
by the action of the springs o and q. When however the pawl » is
allowed to fall into the teeth p' the drum is held, but the pulley "
continues to play. 8 is the paper drum, the paper is lapped around it
in the usual way, the drum fits on to the drum carrier and a notch and
pin prevent it moving. The pawl is mounted on a stud t and is pressed
towards the teeth by a spring fixed to the outside of the cylinder a.
On the pawl there is also a nib 2, and there is a shoulder ³ formed on
the piece to act against the nib, so that the act of turning the piece h
around the spring box c into a position to bring the pencil i against the
paper lifts the pawl out of the teeth and sets the drum free to move in
unison with the engine; similarly moving the pencil away from the
paper allows the pawl to drop into the teeth and the motion of the
drum is arrested so that the diagram may be examined, and the drum
can be removed from the carrier, repapered, and replaced ready to tako
another diagram. To be able to do this without disturbing the con-
nection of the instrument with the engine is a great convenience
obtained by the construction of indicators according to my Invention.
Figure 10 is an elevation, and Figure 11 is a sectional plan of an
arrangement in which the pawl is controlled independently of the
movement of the pencil to and from the paper. The pawl has a
surface formed upon it; this surface extends across the pawl from one
side to the other of the axis about which it turns. The spring & presses
on this surface, and when in the position shown by full lines it holds
the pawl to the ratchet teeth, but the spring which is held in the clips a¹
can be slidden around tho cylinder into the position indicated by the
dotted lines, and it then tends to raise the pawl off the teeth. is a
button fixed on the spring by pressure on the button; the spring is
moved from one position to the other. The spring x is not sufficiently
strong to raise the pawl when the spring 7 is acting against it, but
immediately the pawl is relieved from this pressure by the tension of the
cord around the pulley the spring is able to raise the pawl and the
paper drum commences to work without shock or jerk, which in the
other arrangement can only be avoided by care in liberating the pawl at
the proper moment.
Figures 12 show the clip which I use to connect the cord, a portion
of which is wound upon the pulley " with another cord attached to a
reciprocating part of the engine. The cord on the pulley " is attached

page_text: to the eye t, and the cord from the engine is passed double through the
eye u and over the screw pin v. The latter cord when it has been drawn
to the proper length is secured by screwing down the pin until it clips
the cord.
What I claim is the construction of indicators in such manner that
the motion of the paper drum may be arrested and started at the
pleasure of the operator without interfering with the connection with
the engine by means of a pawl or equivalent instrument resisting the
tendency of the spring to rotate the paper drum.
I also claim the combination of the standard h, piston rod e¹, the
system of levers 7, and the pencil or marker i.
I also claim the construction of indicators, substantially as described
and illustrated in the annexed Drawings, either with or without the
pawl and parts in connection therewith, for controlling the motion of
the paper drum.
I also claim the means of adjusting the length of the cord for con-
veying motion from the engine to the paper drum by the use of the
instrument shown at Figures 12.
In witness whereof, I, the said Edward Thomas Darke, have here-
unto set my hand and seal, this Twenty 21st day of April in the
year of our Lord One thousand eight hundred and seventy-
six.
EDWARD THOMAS DARKE. (L.S.)