AN IMPROVED APPARATUS FOR IN- DICATING THE SPEED OF ENGINES
Year: 1871

page_text: LETTERS PATENT to John Prossor Allen, of Devonport, in the County
of Devon, for the Invention of "AN IMPROVED APPARATUS FOR IN-
DICATING THE SPEED OF ENGINES."
Sealed the 5th September 1871, and dated the 10th June 1871.
PROVISIONAL SPECIFICATION left by the said John Prossor Allen
at the Office of the Commissioners of Patents, with his Petition, on
the 10th June 1871.
I, JOHN PROSSOR ALLEN, of Devonport, in the County of Devon, do
hereby declare the nature of the said Invention for "AN IMPROVED
APPARATUS FOR INDICATING THE SPEED OF ENGINES," to be as follows:-
This apparatus consists of a cylindrical case in which is mounted
a central axle that is intended to be driven by the engine shaft whose
rotations are desired to be indicated. This central axle carries a pair
of curved elastic arms weighted at their extremities and made sensitive
to centrifugal action. Fitted to the axle but capable of sliding freely

page_text: thereon is a collar embraced by a ring to which is pivotted the pendent
end of a bell-crank lever carried by a fixed bracket. This sliding collar
is connected by chains (led over guide rollers) with the weights carried
by the elastic arms in order that their movement outwards from their
centre of motion may slide the collar on its axle and thus rock the
bell-crank lever.
•
The motion of the bell-crank lever is transmitted in the following
manner to an indicator arm placed in front of a graduated dial plate
over which it travels to show the speed of the engine:-The indicator
is mounted on an arbor in line with the central axle, and it is fitted
with a small pinion into which gears a segment rack working on a
pivot pin. By means of a connecting rod the segment rack and bell-
crank lever are connected and thus the oscillation of the latter will cause
the rack to drive the pinion and work the indicator. The return motion
of the bell-crank lever is obtained from a spring which has a tendency 1
to lift the horizontal arm of the lever.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said John Prossor Allen in the Great Seal Patent
Office on the 9th December 1871.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOHN
PROSSOR ALLEN, of Devonport, in the County of Devon, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Tenth day of June, in the year of
our Lord One thousand eight hundred and seventy-one, in the thirty-
fourth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said John Prossor Allan, Her special
licence that I, the said John Prossor Allen, my executors, adminis-
trators, and assigns, or such others as I, the said John Prossor Allen,
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
"AN IMPROVED APPARATUS FOR INDICATING THE SPEED OF ENGINES," upon

page_text: the condition (amongst others) that I, the said John Prossor Allen,
my executors or administrators, by an instrument in writing under
my, or their, or one of their hands and seal, 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 calendar months next and
immediately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said John Prossor Allen, do hereby
declare the nature of my said Invention, and in 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 Drawing here-
unto annexed, and to the letters and figures marked thereon (that is
to say) :-
The object of this Invention is to shew by the traverse of an index
hand or pointer over a graduated dial the speed at which motive power
and other engines are being driven, and also in the case, for example,
of a marine engine, the direction in which the engine is working.
In the accompanying Drawing Fig. 1 represents in front elevation
the improved indicating apparatus; Fig. 2 is a vertical section of the
same taken in the line 1, 2, of Fig. 1; Fig. 3 is a back view; Fig. 4
is a sectional plan view taken in the line 3, 4, of Fig. 1; and Fig. 5
is a front view of the apparatus with the dial and indicator removed..
By referring to these Figures it will be seen that the apparatus
consists of a cylindrical case A, A, fitted with an open dial plate A',
which carries a glazed cover. This dial plate forms with the back of the
case the framing of the instrument, and the two parts are braced
together by means of cross pieces A³. In this case A a. central axle B is..
mounted. The rear end of this axle passes through the back of the
case, and is carried by a strap piece A* bolted to the back of the case,
while the forward end of the axle fits in a bearing formed for it on a
strap piece A' affixed to the back of the open dial plate A'. This central
axle carries a boss, from which projects a pair of curved elastic arms C, C,
which are weighted at their extremities, and made sensitive to centri-
fugal action. Fitted to a squared portion of the axle B, but capable of
sliding freely thereon, is a collar D, which is embraced by a ring D', to
which is pivotted the forked end of a bell-crank lever D³, having its
fulcrum on a bracket affixed to the dial plate A'. The sliding collar D
is connected by chains C¹ (led over guide rollers mounted in the boss of
.

page_text: the elastic arms C) with the weights carried by the elastic arms, in order
that their movement outwards from their centre of motion may slide the
collar on its axle, and thus rock the bell-crank lever. The motion of
the bell-crank lever D² is transmitted in the following manner to an
indicator arm or pointer E mounted centrally in front of the graduated
dial plate A', over which it travels to show the speed of the engine :-
The indicator is fitted to an arbor E¹ mounted in bearings in a line with
the central axle B (see Fig. 2), and it is fitted with a small pinion
which gears into a sector rack F working on a pivot pin F" carried by
the plate A¹ and strap piece A5. By means of a rod F³ the sector rack
and bell-crank lever are connected, and thus the oscillation of the latter
will cause the rack to drive the pinion and work the indicator. The
return motion of the bell-crank lever is obtained from a spring G, which
has a tendency to.draw back the horizontal arm of the lever. To the
rear end of the axle B and within the strap A' is keyed a pinion B¹, and
in gear with this pinion is a spur wheel H keyed to a short axle H¹
which carries a band pulley H³. In order to set the indicator in action
the pulley H³ is connected by a band with a pulley of the same diameter
on the engine shaft, and rotary motion being given thereto the elastic
arms C will be caused to revolve, and by their centrifugal action (the
amount of which will depend on the speed maintained by the engine)
the bell-crank lever D³ will be caused to actuate the pointer E and drive
it round to the graduation on the dial corresponding to the number of
revolutions per minute of the engine shaft. The dial plate being open
the revolving arms will be presented to view, and their direction of
motion will indicate the direction in which the engine is being driven.
The dial may be marked with the words “ahead” and “astern,” and
with arrows to explain the direction of the motion of the revolving
arms.
The only difference required in the apparatus to adapt it to fast
or to slow engines is, that for an engine making a great number of
revolutions the number of teeth in the pinion B' should be increased,
and for very slow engines the teeth of the spur wheel H should be in
like manner increased.
Having now set forth the nature of my Invention of "An Improved
Apparatus for Indicating the. Speed of Engines," and explained the
manner of carrying the same into effect, I wish it to be understood that
under the above in part recited Letters Patent I claim, the arrangement

page_text: of apparatus above described whereby through the action of centrifugal
force the speed of engines may be indicated.
In witness whereof, I, the said John Prossor Allen, have hereunto
set my hand and seal, the Sixth day of December, in the year of
our Lord One thousand eight hundred and seventy-one.
JOHN PROSSOR ALLEN. (L.S.)