IMPROVEMENTS IN STEAM ENGINE INDI- CATORS
Year: 1879

page_text: LETTERS PATENT to Michael Longridge, of Manchester, in the County of
Lancaster, for the Invention of "IMPROVEMENTS IN STEAM ENGINE INDI-
CATORS."
Sealed the 10th October 1879, and dated the 27th May 1879.
PROVISIONAL SPECIFICATION left by the said Michael Longridge at the
Office of the Commissioners of Patents on the 27th May 1879.
MICHAEL LONGRIDGE, of Manchester, in the County of Lancaster.
MENTS IN STEAM ENGINE INDICATORS."
" IMPROVE-
Steam engine indicators as hitherto constructed consist of a piston working in a
cylinder, below which the steam and vacuum act alternately. This piston is con-
nected with a spiral spring, and it carries a pencil which marks a curved line on a
paper attached to a revolving cylinder.
According to my Invention I employ in lieu of a cylinder, piston, and spiral
spring of the ordinary steam engine indicator, a spring consisting of a steel bar
firmly attached by one end to the frame of the instrument, and having attached to
its other end a cylindrical boss carrying two radial wings or pistons placed diame-
trically opposite each other, and fitting accurately in a cylindrical casing.
This cylinder is divided into two chambers by fitting pieces firmly attached to its
circular sides, one wing or piston being in each chamber. The steam is admitted to
the wings on opposite sides, so that it causes them and the boss to revolve. The
boss being firmly attached to the free end of the steel bar, whose other end is fixed,
a strain of torsion is set up in the bar, and the amount of strain is measured by its
degree of torsion.
A pencil is connected with the end of the bar next the winged piston, the point
of which pencil describes an are dependent on the degree of torsion. A sheet of
paper is clamped upon a concave surface curved to the radius of the pencil, and is
made to traverse backwards and forwards in a direction parallel to the axis of the
instrument, this to and fro motion being given from some reciprocating part of the
engine by means of a cord, drum rack, and spring box.
Instead of a steel bar acting by torsion, in some cases I attach a spiral spring of
the form of a watch spring to the axis of the winged piston (the plane of the spring
being at right angles to the axis of the winged piston), the pencil, also attached to
the same axis, vibrating through an arc, and marking the course upon the paper
traversing to and fro, as before.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Michael Longridge in the Great Seal Patent Office on the 27th
November 1879.
MICHAEL LONGRIDGE, of Manchester, in the County of Lancaster.
MENTS IN STEAM ENGINE INDICATORS."
"IMPROVE-
The principal object of my Invention is to reduce the momentum of those moving
parts of the instrument to which the steam pressure is applied and transmitted to
the recording pencil, and for this purpose I have abandoned the use of the cylinder
and piston as used in ordinary indicators, and I employ instead thereof a winged
boss caused to revolve on its axis by the steam pressure acting against the elastic
force of a spring, so that the intensity of the pressure acting on the winged boss is
'measured by the angle through which the boss revolves.
In some cases I employ a spring consisting of a bar of steel acting by torsion.
One end of this bar is firmly fixed to the frame of the instrument, and the other end
is attached to a cylindrical boss carrying one or two radial wings placed, if there be
two, diametrically opposite to each other, and forming a surface or surfaces on which
the steam pressure acts. This winged boss fits accurately in a cylindrical casing,
which is divided internally by one or more filling pieces accurately fitted and firmly
attached to the sides of the cylindrical case. In the case of only one wing there is
only one of these filling pieces and one chamber in which the wing revolves. The
steam is admitted on one side of the wing, and the chamber on the other side is
open to the atmosphere.
In the case of two wings there are two filling pieces dividing the cylinder into
two equal chambers, one wing being in each chamber, and the steam is admitted to
one side of the wings, the chambers at the other sides of the wings being open to
the atinosphere.
In either case the action of the steam is to causo the winged boss to partially
revolve, and the end of the steel bar with it, and as the other end of the bar
is fixed, a strain of torsion is set up which balances the force upon the winged
pistons.
A pencil holder is rigidly connected with the end of the steel bar next to the
boss, and the pencil point describes an arc corresponding to the degree of torsion.
This pencil marks upon a sheet of paper carried on a moving frame curved to the
radius of the pencil, and which is made to travel backwards and forwards parallel
to the axis of the instrument by means of a spring and of a cord attached to some
reciprocating part of the engine in the usual manner.
Thus a diagram is obtained similar in form to the ordinary indicator diagrams,
the ordinates representing the pressures as indicated by the degree of torsion, and
the abscissae the corresponding motion of the engine piston. The action of the
vacuum side in condensing engines is precisely similar, vacuum being substituted
for pressure, and the ordinates being marked on the paper on the opposite side of
the zero line.
In some cases the sheet of paper is carried on a cylinder made to revolve in the
ordinary way. In this case the axis of the cylinder is placed at right angles to the
axis of the instrument, and the pencil is made to take a lineal direction in the line
of the axis of the cylinder by means of a toothed sector attached to the axis of the
boss (in place of the radial pencil arm above described) and a rack attached to the
pencil.
In soine cases, instead of the steel bar acting by torsion, I employ one or more
spiral springs of the form of a watch spring, the same being attached by the outer
end to the frame of the instrument, and by the inner end to the axis of the winged
boss, which for that purpose projects out through the side of the cylindrical casing,
the plane of the spring or springs being thus at right angles to the axis of the boss.
In this case the pencil is connected with the boss in either of the manners above

page_text: described, and the diagram is obtained on a sheet of paper, to which the motion is
given in either of the methods above described.
In further explanation I proceed to describe the annexed Drawings.
Figure 1 represents a longitudinal section of the instrument passing through the
steam spaces of the cylindrical case, the spring in this case being a torsion rod, as
above described; Figure 2 is a section of the same at right angles to Figure 1,
the section being taken through the cylindrical casing; Figure 3 is an elevation of
the opposite end of the instrument. The same letters refer to the same parts in
all the Figures.
A is the main frame, having at one end a branch pipe with screw coupling for attach-
ment to the indicator cock, and at the other a pedestal a, into which the fixed end
of the steel torsion rod is secured. C is the cylindrical casing, which contains the
winged boss B, hereinafter described; this cylindrical casing is fixed firmly to the
frame A, its axis being parallel to that of the said frame; it is divided into two
chambers c, c, by filling pieces c', c¹, when, as in the instrument illustrated, the boss
has two wings. B is the boss and b, b, the wings, which fit accurately in the
chambers c. d, d, are the passages connecting the spaces c at one side of the wings
b with the cylinder of the engine, and e, e, are holes by which the said chambers c
at the opposite side of the wings communicate freely with the atmosphere. F, F,
are two arms projecting from the frame A, one at or near each end of it; these
arms support the guide rods f, f, which extend the full length of the instrument,
and are parallel with the axis thereof; these rods serve as guides for the paper
carrier G, which is curved to the radius of the pencil, and is provided with four
legs g, g, two at top and two at bottom, through which pass the guide rods f, f;
this paper carrier is provided with a rack h, which gears with a toothed wheel i.
On the same axis i¹ as this toothed wheel is a druin j, to which is attached a cord
that passes round said drum, and is led, as shown in the dotted lines in Figure 1, to
the swivel pulley k, and thence to some reciprocating part of the engine. On the
same axis as and preferably within the drum j is a spiral spring to bring back the
cord and paper carrier; this axis is firmly attached to the frame A at any con-
venient part, and so that the toothed wheel gears into the rack on the paper
carrier f.,, is the steel rod or bar which constitutes the torsion spring; it is
firmly fixed at one end to the pedestal u, so as to be incapable of turning, and
attached at the other to the boss B, so as to turn with it. m is a thin tube of
light material, which in some cases is used in order to bring the pencil near to the
centre of the instrument, and thus shorten the latter. At one end this tube is fixed
to the steel bar close to the boss B, or to the journal of the boss itself, which pro-
jects through the end of the cylindrical case; at the other end it moves freely in a
guide n fixed to the frame A, the guide serving simply to steady the tube. To the
end of the tube adjoining the guide is fixed the pencil carrier o by means of a set
screw. It is thus evident that the pencil will describe the same are as if it were
attached direct to the boss or to the steel bar close to the cylindrical caso.
action therefore is this -The point of the pencil describes a certain are in a plane
at right angles to the axis, whilst the paper carrier curved to the same radius travels
to and fro in a plane parallel to the same axis.
The
Figure 4 is an elevation of a similar instrument, except that the boss is placed at
the middle of a torsion rod fixed by both its ends. The tube m is not used, tho
pencil holder being attached directly to the spring close to the boss, but the remainder
of the instrument is like that just described.
When a spiral spring (or springs) is used instead of the steel torsion bar, it is
applied as shown in Figures 5 and 6. m is the tube, as before described, and on it
at the end next the cylindrical casing C is fixed one end of the spiral spring p, p
the other end of which is firmly fixed to a small pedestal a' attached to the frame A;
or the axis of the boss may be prolonged through the opposite end of the cylindrical
casing, and the spiral spring be attached to such prolongation.
The remaining parts of the instrument remain similar to those above described,
except that the torsion bar is not used.

page_text: Having described the nature of my Invention and the manner of performing
the same,
I declare that what I claim as my Invention to be protected by the herein-
before in part recited Letters Patent is,-
1st. A steam engine indicator in which a winged boss is caused by the steam
pressure acting against the elastic force of a, spring to rotate on its axis, so that
the intensity of the pressure acting on the wing or wings of the boss is measured
by the angular motion of the boss, as specified.
2nd. The employment in combination with a winged boss moving on an axis in
a cylinder, and actuated as described, of a steel bar applied to act by torsion for the
purpose
of counterbalancing and thus measuring the intensity of the pressure acting
on the wing or wings of the boss, as set forth.
3rd. The employment in combination with a winged boss moving on an axis in
a cylinder, and actuated as described, of a spiral spring like a watch spring, applied
as and for the purpose herein set forth.
4th. The combination with a winged boss caused to rotate on its axis by the
steam pressure acting against the elastic force of a spring, as specified, of a radial
arm carrying or actuating a pencil and participating in the angular motion of the
boss, whereby the travel of the pencil is considerably increased without largely in-
creasing the inertia of the moving parts.
5th. The combination with a winged boss actuated as specified, a spring applied
as described, and a radial pencil arm connected with the boss, of a paper carrier
curved to the radius of the pencil, and traversed to and fro in a plane parallel to the
axis of the boss, substantially as shown and described.
In witness whereof, I, tho said Michael Longridge, have hereunto set my
hand and seal, this Twenty sixth day of November, in the year of our Lord
One thousand eight hundred and seventy nine.
MICHAEL LONGRIDGE. (L.S.)