IMPROVEMENTS IN OR ADDITIONS TO STEAM ENGINE INDICATORS
Year: 1877

page_text: LETTERS PATENT to Henry Lea, of Birmingham, in the County of Warwick,
Consulting Engineer, for the Invention of "IMPROVEMENTS IN OR ADDITIONS
TO STEAM ENGINE INDICATORS."
Sealed the 13th July 1877, and dated the 26th February 1877.
PROVISIONAL SPECIFICATION left by the said Henry Lea at the Office of
the Commissioners of Patents on the 26th February 1877.
HENRY LEA, of Birmingham, in the County of Warwick, Consulting Engineer.
"IMPROVEMENTS IN OR ADDITIONS TO STEAM ENGINE INDICATORS."
In ordinary steam engine indicators the pencil of the instrument is made to
describe on a surface of paper a figure or diagram, from which may be ascertained
amongst other things the mean pressure per square inch of the steam upon the
piston of the steam engine throughout the stroke of the said piston. The said
mean pressure per square inch and the area and speed of the piston being known, a
simple calculation shows the indicated horse power which the piston received from
the steam when the particular diagram in question was taken.
The work done by the engine is sometimes so regular that a single diagram will
represent with sufficient accuracy the power exerted by the steam during a period
of several minutes or hours, but in most cases the action of the steam is very
irregular, and in such cases the diagrams may vary so rapidly that it becomes im-
possible to ascertain correctly what total power the steam has exerted for any
period other than that during which any particular diagram or diagrams was or
were taken.
One method of ascertaining the mean pressure per square inch from a diagram
drawn by the indicator is to measure by means of the planimeter the area in
square inches contained within the outline of the diagram, and then to divide the
area thus found by the length of the diagram in inches. The result gives the mean

page_text: height of the diagram in inches, and the mean height may be converted into the
mean pressure by multiplying it by the pressure of steam in pounds per square
inch required to raise or depress the pencil of the indicator one inch above or below
its normal position.
By my Invention the process of drawing separate diagrams to be afterwards
measured in detail is dispensed with, and instead thereof the indicator is caused to
measure the area of every diagram during its formation, and to add that area to the
sum of the areas already recorded. A cumulative result is thus obtained, extending
over any desired length of time, and far more accurate than can be had from
separate diagrams, be they ever so numerous.
My Invention has for its object to construct and arrange the parts of the said
instruments for indicating and registering, so that they shall register continuously
the areas of the diagrams:
My said Invention consists essentially in combining, in' the manner herein-after
described, registering or recording mechanism with the indicator so as to obtain
without calculation a direct delineation of the work performed by the steam engine.
To the cylinder of an ordinary indicator I attach a lever pivotted at one end upon
a fixed stud so as to be moved in a vertical arc by the piston rod of the indicator,
The said lever has at its free or moving end a measuring wheel of suitable diameter
similar to that of the ordinary planimeter. To any desired point of the lever, say
midway between its two ends, I attach the top of the piston rod of the indicator by
means of two short links so that the rise and fall of the said piston rod will cause
the rise and fall of the measuring wheel, the motion of the latter being greater or
less in proportion to the leverage employed. The perimeter of the measuring wheel
is lightly pressed by means of a spring (or when the instrument is used temporarily
the said wheel may be supported by hand) against the side of the ordinary paper
cylinder of the indicator. The breadth of face of the measuring wheel is such as
will ensure the wheel touching the cylinder on the same vertical line notwithstanding
the circular arc in which the measuring wheel necessarily rises and falls.
The measuring wheel is fixed upon one end of a very light spindle which extends
from end to end of the lever, which spindle rises and falls with the lever, and by
means of a pair of bevil wheels and a suitable counter having several dials, registers
the number of revolutions of the measuring wheel. The fractions of a revolution
are read off from a finely divided rim attached directly to the spindle and a vernier
scale fixed to the lever.
F
Instead of the ordinary paper cylinder before referred to a flat vertical plate may
be used, properly guided and moved to and fro by the same arrangement of cord or
wire as is commonly used to actuate the paper cylinder.
The action of the apparatus is as follows:-A piece of smooth paper is wrapped
around the paper cylinder, or is applied to the flat plate, as the case may be, not
for the purpose of receiving a drawn diagram, but to render the action of the
measuring wheel smooth and certain. The paper is caused to reciprocate syn-
chronously with the piston of the steam engine, and upon the indicator tap being
opened the measuring wheel rises and falls at every stroke proportionately with the
pressure of steam within the cylinder of the engine.
The measuring wheel describes, but does not delineate, upon the paper a diagram,
and in the action of doing so receives a permanent amount of rotation, exactly propor-
tionate to the area of the diagram described. As one diagram succeeds another it
gives further rotation to the wheel, and the cumulative or total amount of rotation
is recorded upon the dials and vernier, and the total area of all the diagrams de-
scribed is consequently ascertainable by mere inspection. The said total area being
divided by the number of minutes occupied in obtaining the said total, gives a
mean area for one minute, which can be reduced to mean pressure, as herein-before
described, to be employed as a factor in an ordinary calculation in order to obtain
the mean indicated horse power per minute.
I make the hands or pointers of the counter dials sufficiently loose upon their

page_text: spindles to be adjustable to zero by hand before the indicator is set to make its
record.
My improvements may be constructed so as to be easily connected to and discon-
nected from the indicator, in which latter case the ordinary pencil apparatus can be
applied and used in the ordinary manner.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Henry Lea in the Great Seal Patent Office on the 21st August
1877.
HENRY LEA, of Birmingham, in the County of Warwick, Consulting Engineer.
IMPROVEMENTS IN OR ADDITIONS TO STEAM ENGINE INDICATORS."
In ordinary steam engine indicators the pencil of the instrument is made to
describe on a surface of paper a figure or diagram, from which may be ascertained
amongst other things the mean pressure per square inch of the steain upon the
piston of the steam engine throughout the stroke of the said piston. The said
mean pressure per square inch and the area and speed of the piston being known, a
simple calculation shows the indicated horse power which the piston received, from
the steam when the particular diagram in question was taken.
The work done by the engine is sometimes so regular that a single diagram will
represent with sufficient accuracy the power exerted by the steam during a period
of several minutes or hours; but in most cases the action of the steam is very
irregular, and in such cases the diagrams may vary so rapidly that it becomes im-
possible to ascertain correctly what total power the steam has exerted for any
period other than that during which any particular diagram or diagrams was or
were taken.
One method of ascertaining the mean pressure per square inch from a diagram
drawn by the indicator is to measure by means of the planimeter the area in square
inches contained within the outline of the diagram, and then to divide the area
thus found by the length of the diagram in inches. The result gives the mean
height of the diagram in inches, and the mean height may be converted into the
mean pressure by muliplying it by the pressure of steam in pounds per square inch
required to raise or depress the pencil of the indicator one inch above or below its
normal position.
By my Invention the process of drawing separate diagrams to be afterwards
measured in detail is dispensed with, and instead thereof the indicator is caused to
measure the area of every diagram during its formation, and to add that area to the
sum of the areas already recorded. A cumulative result is thus obtained, extending
over any desired length of time, and far more accurate than can be had from
separate diagrams, be they ever so numerous.
My Invention has for its object to construct and arrange the parts of the said
instruments for indicating and registering, so that they shall register continuously
the areas of the diagrams.
My said Invention consists essentially in combining, in the manner herein-after
described, registering or recording mechanism with the indicator so as to obtain
without calculation a direct delineation of the work performed by the steam engine.
To the cylinder of an ordinary indicator I attach a lever pivotted at one end upon
a fixed stud so as to be moved in a vertical arc by the piston rod of the indicator.
The said lever has at its free or moving end a measuring wheel of suitable diameter
similar to that of the ordinary planimeter. To any desired point of the lever, say
midway between its two ends, I attach the top of the piston rod of the indicator by
means of two short links, so that the rise and fall of the said piston rod will cause
the rise and fall of the measuring wheel, the motion of the latter being greater or

page_text: less in proportion to the leverage employed. The perimeter of the measuring wheel
is lightly pressed by means of a spring (or when the instrument is used temporarily
the said wheel may be supported by hand) against the side of the ordinary paper
cylinder of the indicator. The breadth of face of the measuring wheel is such as
will ensure the wheel touching the cylinder on the same vertical line, notwithstand-
ing the circular are in which the measuring wheel necessarily rises and falls.
The measuring wheel is fixed upon one end of a very light spindle which extends
froin end to end of the lever, which spindle rises and falls with the lever, and by
means of a pair of bevil wheels and a suitable counter having several dials, registers
the number of revolutions of the measuring wheel. The fractions of a revolution
are read off from a finely divided rim attached directly to the spindle and a vernier
scale fixed to the lever.
Instead of the ordinary paper cylinder before referred to a flat vertical plate may
be used, properly guided and moved to and fro by the same arrangement of cord
or wire as is commonly used to actuate the paper cylinder.
The action of the apparatus is as follows:-A piece of smooth paper is wrapped
around the paper cylinder or is applied to the flat plate, as the case may be, not for
the purpose of receiving a drawn diagram but to render the action of the measuring
wheel smooth and certain. The paper is caused to reciprocate synchronously with
the piston of the steam engine; and upon the indicator tap being opened the
measuring wheel rises and falls at every stroke proportionately with the pressure
of steam within the cylinder of the engine. The measuring wheel describes but
does not delineate upon the paper a diagram, and in the act of doing so receives
a permanent amount of rotation exactly proportionate to the area of the diagram
described.
As one diagram succeeds another it gives further rotation to the wheel, and the
cumulative or total amount of rotation is recorded upon the dials and vernier, and
the total area of all the diagrams described is consequently ascertainable by mere
inspection. The said total area being divided by the number of minutes occupied
in obtaining the said total gives a mean area for one minute, which can be reduced
to mean pressure, as berein-before described, to be employed as a factor in an
ordinary calculation in order to obtain the mean indicated horse power per
minute.
I make the hands or pointers of the counter dials sufficiently loose upon their
spindles to be adjustable to zero by hand before the indicator is set to make its
record.
My improvements may be constructed so as to be easily connected to and dis-
connected from the indicator, in which latter case the ordinary pencil apparatus
can be applied and used in the ordinary manner.
Having explained the nature of my Invention I will proceed to describe, with
reference to the accompanying Drawing, the manner in which the same may be
performed.
Figure 1 is a side elevation, partly in section, and Figure 2 is a plan, also partly
in section, of a steam engine indicator containing the improvements or additions
constituting my Invention. The Figures are drawn about twice the actual size in
order that the small parts may be more readily seen.
The same letters of reference indicate the same parts in both Figures.
A is the body containing the steam cylinder A¹, the piston A³, the coiled
spring B, and the piston rod B¹, which latter works through the cylinder cover B².
The arm C carries the paper cylinder C¹, which turns upon a central fixed stud C²
and contains the usual coiled spring for turning the paper cylinder in the opposite
direction to that given by the cord which occupies the groove D. The whole of
the foregoing parts are old and well known. Upon the upper and cylindrical part
of the body A. I place a hollow cylinder or socket D¹, which turns freely but
steadily thereon in a horizontal plane, being held down by the cylinder cover B².
To the said cylinder D₁ is attached a pair of arms E, E¹, which serve to support

page_text: the planimeter arm and the registering apparatus herein-after described. The
planimeter arm consists for the greater part of its length of two thin side plates
E, E, rivetted at one end to the trunnion frame F and at the other end to the
semicircular arm F¹. Between the said side plates E is situated the spindle Fº, the
extreme ends of which are pointed and hardened and turn in hardened hollow
centres, of which the centre G is fixed to the semicircular arm F¹, and the centre G¹
is adjustable in the end. of the fulcrum frame F by means of the set screw G2 and
locking screw H. The links H₁ connect the planimeter arms E to the swivel
block H2, which is attached to the upper end of the piston rod B¹ by means of the
usual milled screw cap I; I is a short tube which preserves the proper distance
between the arms E2 at that point, and through which passes one of the connecting
pins I. Into the trunnion frame F are screwed two trunnions K, K', which turn
in bearings formed in the upper ends of the aforesaid arms E, E, and are held down
by the caps K² and screws L.
Upon one end of the spindle F is secured the measuring wheel L¹; upon the
other end of the said spindle F2 is secured the vernier wheel L², by means of which
and the corresponding fixed vernier M the fractional parts of a revolution of the
spindle F may be easily read off to the one-thousandth part of one revolution. In
order to register whole revolutions a bevil pinion M¹ of 12 teeth is secured to the
spindle F and gears into a bevil wheel M2, of 36 teeth, the axis N of which passes
through the hollow trunnion K. In consequence of the coincidence of the axes of
the trunnion and bevil toothed wheel the bevil wheel and pinion remain in gear
with each other, notwithstanding the vertical radial motion of the planimeter arm
about the axis of the trunnions K, K. Upon the outer end of the axis N is secured
a spur pinion N¹, of 12 teeth, which gears into a spur wheel N2, of 40 teeth, situated
below the pinion N¹, and secured upon the axis O, which carries the pointer 0¹ of
the first dial 0%. The aforesaid combination of wheels causes the pointer O' to
perform and register one revolution for each ten revolutions of the spindle F. The
axis Ohas a pinion P, of 6 teeth, which gear into a wheel P¹, of 60 teeth, the axis
of which carries the pointer P2 of the second dial R, and every revolution of the
pointer P³ registers 100 revolutions of the spindle F2. Five dials in all are shown
upon the Drawing, but a greater or less number may be employed if preferred.
The fifth dial would register during one revolution one million revolutions of the
spindle F. The whole of the wheel work is enclosed in a metallic case R¹ attached
to the arm D'; and the dial plate R³ is also protected by a light door S turning
upon hinges S¹, and secured by a spring catch S. The aforesaid pointers are sprung
upon their respective axes, so that they may be easily set to zero before the instru-
ment is used.
The action of the instrument is as follows:-The indicator cylinder A¹, having
been put into communication in the ordinary way with the cylinder of the steam
engine of which the indicated horse power is required to be known, and the paper
cylinder C¹ having been connected with the cross head or other suitable recipro-
cating part of the same steam engine by means well known and ordinarily used for
those purposes, a piece of paper having also been secured around the paper cylinder
C, and the socket D' having been turned, so as to bring the measuring wheel L'
lightly into contact with the said paper, the said measuring wheel L' will describe
a diagram upon the said paper, of which diagram the height at any given point
will be determined by the rise and fall of the piston rod B' under the influence
of the steam pressure in the indicator cylinder A³, while the length of the diagram
will be determined by the amount of rotation of the paper cylinder. The measuring
wheel L', after having described the outline of the said diagram, will have received
a certain amount of permanent rotation in one direction, which, according to tho
well-known principle of the planimeter, will bear a fixed relation to and will be a
correct indication of the area included in the said diagram. As one diagram suc
ceeds another the amount of permanent rotation of the measuring wheel L' will
increase, and will be registered as to whole revolutions by the aforesaid pointers

page_text: "
O, P2, and the pointers of the other dials, and as to fractions of a revolution by the
aforesaid vernier wheel L and vernier M. At the end of the experiment the pointers
will show the sum of the areas of all the diagrams which the measuring wheel has
described, no matter how they may have varied in area, and the said sum having
been divided by the number of diagrams described during the experiment the
quotient will be a mean area from which the mean pressure per square inch and
indicated horse power of the engine may be ascertained by the usual method of
calculation.
The registering apparatus herein-before described, and supported from the socket
D¹, can be removed as a whole by unscrewing the screw cap I, and the cylinder
cover B, and the ordinary Richards' parallel motion, or other kind of pencil holder
can then be attached instead thereof for the purpose of obtaining pencil diagrams
drawn in the ordinary manner.
The measuring wheel L₁ is made of such a diameter that the recording dials of
the registering apparatus will register the actual area in square inches of the
diagram, which would be drawn by the pencil, supposing the same piston spring to
be used in each instance, and supposing the extent of rotation of the paper
cylinder and the action of the steam in the indicator cylinder to be also identical
in both cases.
The side of the paper cylinder against which the measuring wheel L' works
being vertical, and the motion of the measuring wheel about the trunnions K, K',
being a radial motion, the distance from the centre of the trunnions to the point of
contact between the measuring wheel and the paper cylinder will be a variable
distance, increasing as the measuring wheel rises above or falls below the horizontal
position of the planimeter arm. The effect of this increase would be to cause the
measuring wheel to describe and to record larger areas than would be shown by
the Richards' pencil under the same conditions; and in order to correct this error I
make the measuring wheel slightly larger in diameter at one end than at the other,
so that the amount of rotation imparted to it by the paper cylinder shall decrease
in suitable proportion as the measuring wheel rises or falls below the horizontal
position of the planimeter arm aforesaid.
In order that the instrument may count the number of diagrams described I
sometimes add a counter T of six dials (more or less), so fixed upon the top of the
spring box within the paper cylinder C₁ that the paper cylinder shall through the
medium of a ratchet and pawl move the first pointer one division for each double
reciprocation. of the said paper cylinder, that is, for each diagram described. The
-pointers of this counter are also sprung upon their respective axes, so as to be readily
adjustable to zero by hand before using the instrument.
Instead of employing a paper cylinder turning upon a central stud, and neces-
sitating a comparatively long and conical measuring wheel for the purpose, herein-
before described, a flat plate sliding to and fro in suitable rectilinear guides may be
used, in which case the measuring wheel would have only a very narrow edge
touching the plane surface of the paper at a point whose distance from the axis of
the trunnions of the planimeter arm would remain unaltered by the radial motion
of the said arm.
Having now described the nature of my Invention, and the manner in which the
same is to be performed, I wish it to be understood that I claim as my Invention
of improvements in or additions to steam engine indicators,-
First. Combining with a steam engine indicator mechanism constructed and
worked, substantially as herein-before described and illustrated in the accompanying
.Drawing, for the purpose of measuring the area of each diagram described by the
indicator, and recording the sum of the areas of any desired number of consecutive
diagrams.
Secondly. Combining a steam engine indicator having the registering or recording
mechanism, herein-before. described and illustrated, with a second counter or regis-
tering apparatus connected with the paper cylinder, whereby the number of diagrams

page_text: described by the indicator during any experiment is recorded, as herein-before
described and illustrated in the accompanying Drawing.
In witness whereof, I, the said Henry Lea, have hereunto set my hand and
seal, this Twentieth day of August, in the year of our Lord One
thousand eight hundred and seventy-seven.