Improvements in Steam Engine Indicators.
Year: 1898

page_text: Date of Application, 14th May, 1898
1000
1000
Improvements in Steam Engine Indicators.
I, JOHN CLARK DOBBIE, of 45, Clyde Place, in the City of Glasgow, Nautical
Instrument Maker, do hereby declare the nature of this invention to be as
follows:-
This invention has for its object to simplify and improve the construction of
steam engine indicators of the kind described in the Specification of Letters
Patent No. 16258 of 1887.
In order to obviate overhanging of the arm carrying the indicator pencil to
clear the upright bracket on which the radius link, connecting the arm to the
piston rod, is centred, the said arm is, according to the present invention, formed
with a downwardly projecting knee or branch to the lower end of which the
radius link is jointed, and the outer end of the indicator arm is curved or bent
downwards over the upright bracket so that its extremity carrying the pencil
may reach to the bottom of the card drum when the piston rod is at its lowest
point and traverse the length of the drum in a vertical line as the piston rod
rises.
The helical spring which is provided to counterbalance the steam pressure and
is usually placed within the upper end of the cylinder containing the moving
piston of the indicator is rendered more readily accessible for removal and inter-
changing by cutting out the upper part of the cylinder or connecting its upper
end to the base or framing of the indicator by open brackets which leave the
spring exposed to view. The piston rod where it is enclosed by the spring is
divided and one length is screwed into the other whilst a vulcanite or other non-
conducting ferrule or collar on which the spring bears, is secured on the piston
rod to provide for unscrewing one part of the rod from the other. By separating
the meeting ends of the divided piston rod the spring can be withdrawn and
replaced.
The barrel on which the indicating card or paper is wound is secured upon the
upper end of the cord bed which is formed with a cylindrical flange portions of
which are cut out to form a pronged gallery upon which the drum is fitted and
held by the spring pressure of the flange whose normal diameter is greater than
that of the drum fitted on it but is allowed to contract owing to its prong like
formation. The indicator card is secured to the druin and the latter held down
on its seat on the cord bed by a blade spring attached at its lower end to the cord
bed extending up the side of the drum and terminated at its upper end in a
catch which engages with a notch in the upper end of the drum."
The cord clip may be of the usual form wherein ne cord is threaded through
holes in a small metal plate, but by preference the plate is made with a hinged
door held by a spring catch and the cord is led through eyes formed on one side
of the plate and under the door which firmly clips it to the plate.
The drum spring is fitted with a head having an internal screw thread the

page_text: convolutions of which are left handed when those of the spring are right handed
and which is screwed on to a screw threaded stem in the centre of the cord bed.
Dated this 13th day of May 1898.
WALLACE FAIRWEATHER,
Of the Firm of Cruikshank & Fairweather,
Chartered Patent Agents,
Saint Vincent Street, Glasgow, Agent for the Appl
Improvements in Steam Engine Indicators.
I, JOHN CLARK DOBBIE, of 45, Clyde Place, in the City of Glasgow, Nautical
Instrument Maker, do hereby declare the nature of this invention and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement:―
This invention has for its object to simplify and improve the construction of
steam engine indicators of the kind described in the Specification of Letters
Patent No. 16258 of 1887.
a
The invention is illustrated by the accompanying drawings, Figure 1 being
vertical section, and Figure 2 a plan of a steam engine indicator as constructed
under my invention. Figures 3 to 9 are details of the indicator hereinafter
particularly referred to.
Referring to Figures 1 and 2, in order to obviate overhanging of the arm A
carrying the indicator pencil A to clear the upright bracket B on which the
radius link C, connecting the arm A to the piston rod F, is centred, the said
arm A is, according to the present invention, formed with a downwardly project-
ing knee or branch A2 to the lower end of which the radius link C is jointed,
and the outer end of the indicator arm is curved or bent downwards over the
upright bracket B so that its extremity carrying the pencil may reach to the
bottom of the card drum E when the piston rod F of the piston F1 is at its
lowest point and traverse the length of the drum E in a vertical line as the
piston rod Frises. The radius link C is connected to a link which is in turn
connected to a jaw F on the upper end of the piston rod F, said jaw F being
constructed as shewn to enlarged scale at Figures 3 and 4 and screwed into the
tubular piston rod F.
The helical spring G which is provided to counterbalance the steam pressure
and is usually placed within the upper end of the cylinder H containing the
moving piston of the indicator is rendered more readily accessible for removal
and interchanging by cutting out the upper part of the cylinder or connecting
its upper end to the base of framing I of the indicator by open brackets on the
cylinder, or by a bracket I carrying or formed integral with the framing I and
open as shown at 12 in order to leave the spring G exposed to view. The piston
rod F where it is enclosed by the spring G is divided and one length is screwed
into the other or joined thereto by a screwed piece F whilst a vulcanite or other
non-conducting ferrule or collar 13 on which the spring G bears, is secured on
the piston rod F to provide for unscrewing one part of the rod F from the other.
By separating the meeting ends of the divided piston rod F the spring G can be
withdrawn and replaced.
The barrel or drum E on which the indicating card or paper J is wound, is
carried by a cylindrical flange formed integral with or attached to the cord bed
or pulley I, which latter is centred on the framing I. Portions of the flange 1³

page_text: are cut out to form a pronged gallery upon which said drum E is fitted so as
to revolve with the cord pulley 1, the drum being held thereon by the spring
pressure of the flange 13 whose normal diameter is greater than that of the
drum E fitted on it but is allowed to contract owing to its prong like formation.
The indicator card J is secured to the drum E and the latter held down on its
seat on the cord bed or pulley I by a blade spring K attached at its lower end
to the cord bed or pulley I extending up the side of the drum E and terminated
at its upper end in a catch ' which engages with a notch E¹ in the upper end
of the drum E.
The drum spring M is fitted with a head M' having an internal screw thread
the convolutions of which are left handed when those of the spring M are right
handed and which is screwed on to a screw threaded stem M³ in the centre of
the framing I. A device for screwing the head M of the drum spring M on
to its spindle M2 is shown at Figures 7, 8 and 9 and consists of a bridge piece L
having notches L' at its lower end which engage projections M³ on the drum
head M, the actuating handles L3 of this bridge piece being carried through
to engage and raise the head M4 at the upper edge of the spring M from the
square portion M³ of the spindle M², the raising of the head M¹ being necessary
in order that it may be screwed upon the spindle without further coiling the
spring M.
The pencil arm A and also the radius link are constructed as shown at Figures 5
and 6 with bosses round their connecting eyes.
Having now particularly described and ascertained the nature of my said in-
vention, and in what manner the saune is to be performed, I declare that what
I claim is:
1. A steam indicator the parts of which are constructed, combined and arranged
to operate, substantially as described.
2. In a steam engine indicator, the combination of a pencil carrying arm
curved at its forward end and having a downwardly projecting kuce or branch,
a tubular piston made in two portions joined together and removed from each
other, that portion of the piston rod beyond the cylinder being surrounded by
the usual spring to which access can be had for removal through an open bracket,
and a pronged gallery upon which the card drum is fitted and held by a spring
catch substantially as and for the purpose set forth.
3. In a steam engine indicator a tubular piston made in two portions joined
together and removable from each other, a spring surrounding said piston rod
beyond the cylinder and accessible through an open bracket carrying or formed
integral with the framing substantially as and for the purpose set forth.
4. In a steam engine indicator a pronged gallery formed on the cord bed or
pulley upon which the card drum is fitted and held by a spring catch substan-
tially as described.
5. In a steam engine indicator a curved pencil carrying arm having a down-
wardly projecting branch connected to the radius link, said arm being adapted
to clear the stationary bracket on which the radius link is centred substantially
as described.