IMPROVEMENTS IN PRESSURE GUAGES
Year: 1859

page_text: LETTERS PATENT to George Allcraft, of Upper Thames Street, in the
City of London, for the Invention of "IMPROVEMENTS IN PRESSURE
GUAGES." A communication from abroad by John Allcraft, of Bedford
Street, New York.
Sealed the 15th November 1859, and dated the 16th May 1859.
PROVISIONAL SPECIFICATION left by the said George Allcraft at the
Office of the Commissioners of Patents, with his Petition, on the
16th May 1859.
I, GEORGE ALLCRAFT, of Upper Thames Street, in the City of London, do
hereby declare the nature of the Invention for "IMPROVEMENTS IN PRESSURE
GUAGES," to be as follows:-
This Invention has for its object improvements in pressure guages. For
these purposes two corrugated plates of metal are used; the projecting corru-
gations of one plate fit into the undulations of the other, and the corrugations
in both consist of a series of concentric circles. These corrugated plates have a
sheet of vulcanized india-rubber between them and the two corrugated plates
or discs are fixed at their circumference to a cylindrical chamber into which
the steam or other fluid passes. There is also a disc or sheet of vulcanized
india-rubber introduced between the corrugated metal discs, and the interior
of the cylindrical chamber, so that the joint all round may be made fluid-tight
and steam or other fluid be also prevented from coming directly in contact
with the corrugated metal. The pressure of the steam or other fluid acts on

page_text: the corrugated plates with a tendency to press them outwards, and as they
are pressed outwards, they act on one end of a bell-crank lever; the other
end of such bell-crank lever is attached by a connecting rod or link to a
toothed quadrant, the teeth of which gear with a toothed pinion on the axis of
the pointing band of the instrument. In order to keep the toothed quadrant
and pointing hand steady, a coiled spring is used, one end of which is attached
to the quadrant, and the other end thereof is attached to the frame of the
apparatus.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said George Allcraft in the Great Seal Patent Office on the
16th November 1859.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, GEORGE
ALLCROFT, of Upper Thames Street, in the City of London, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Sixteenth day of May, in the year of our Lord
One thousand eight hundred and fifty-nine, in the twenty-second year of
Her reign, did, for Herself, Her heirs and successors, give and grant unto
me, the said George Allcroft, Her special licence that I, the said George
Allcroft, my executors, administrators, and assigns, or such others as I,
the said George Allcroft, 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 PRESSURE GUAGES," upon the condition (amongst others)
that I, the said George Allcroft, 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 calendar months next
and immediately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said George Allcroft, 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 pressure guages. For these

page_text: purposes two corrugated plates of metal are used, the projecting corrugations
of one plate fit into the undulations of the other, and the corrugations in both
consist of a series of concentric circles. These corrugated plates have a sheet
of vulcanized india-rubber between them and the two corrugated plates or
discs are fixed at their circumference to a cylindrical chamber into which the
steam or other fluid passes. There is also a sheet or disc of vulcanized india-
rubber introduced between the corrugated metal discs, and the interior of
cylindrical chamber, so that the joint all round may be made fluid-tight, and
steam or other fluid be also prevented from coming directly in contact with
the corrugated metal. The pressure of the steam or other fluid acts on the
corrugated plates with a tendency to press them outwards, and as they are
pressed outwards, they act on one end of a bell-cranked lever; the other end of
such bell-cranked lever is attached by a connecting rod or link to a toothed
quadrant, the teeth of which gear with a toothed pinion on the axis of the
pointing hand of the instrument. In order to keep the toothed quadrant and
pointing hand steady, a coiled spring is used, one end of which is attached
to the quadrant, and the other end thereof is attached to the frame of the
apparatus.
In order to explain my said Invention as completely as possible, I now pro-
ceed to describe the best means I am acquainted with for carrying the same
into practical effect, and having attached to these Presents a Sheet of Drawings
illustrative of the construction thereof, and have marked thereon numeral,
figures and letters of reference, as follows:-
DESCRIPTION OF THE DRAWING.
Figure 1 is a front elevation of a pressure guage constructed according to
my said Invention; Figure 2 exhibits the said guage without the dial plate-
and outer case; Figure 3, the guage without the mechanism exhibited at
Figure 2; Figure 4, section through the line A, B, at Figure 3, shewing
corrugated plates and india-rubber packing. At each of the foregoing Figures
I employ similar letters of reference to denote corresponding parts in so far
as such parts appear or can be seen at each of said Figures respectively.
A, A, is a casting formed with a cylindrical chamber B open at front, and
communicating with a hole C for the admission of steam or other. fluid into
said chamber; D, D', are plates of metal formed with concentric projections
and undulations, the said projections of one plate coinciding with the projections
and undulations of the other plate, so as to fit into each other; y is a double
headed rivet, the inner end of which coming into contact with the plate D'
causes the plate D to be acted upon at the same time as the plate D¹; E is a.

page_text: piece of vulcanized india-rubber placed between the plates D, D'; G is another
piece of vulcanized india-rubber placed underneath the plate D¹ to protect
said plate from being injuriously affected by the action of the steam or other
fluid in the chamber B, the plates D, D', and india-rubber E and G are all
firmly connected to the open front of the chamber B by screws a, a, passed
through a metal ring H into screw head holes formed at the part A' of the
casting A; I is a bell-cranked lever, the fulcrum whereof is a pin at b fixed
into the plate K, said plate being connected by screws c to the ring H; Lisa
toothed quadrant, the axis whereof is a pin at fixed into the plate K; M is
the pointing or index hand of the guage, said hand being fixed on an axis or
pivot e, fixed in the plate K¹; N is a toothed pinion fixed on the axis e, and
gearing into the teeth of the quadrant L; O is a convolute or coiled tempered
spring, one end of which is fixed to the piece f, and the other end of such said
spring is connected by a link P to the quadrant L, as at Figure 2; Qis a
rod or link for connecting the bell-cranked lever I to the quadrant L, the
extremity of the horizontal arm of the bell-cranked lever I rests upon the rivet
head at the centre of the metal plate D, and is kept in close contact therewith
by the elastic force of the spring O; R is an index plate having divisions
engraved thereon representing the pressure in pounds of the steam or other
fluid entering the chamber B; the proper adjustment of the guage may be
determined by the pressure of a column of mercury as commonly practised in
the manufacture of pressure guages, and also by altering the distance of the
fulcrum of the bell-cranked lever I from the end of the horizontal arm thereof;
I propose to form this arm very short, so that a trifling outward movement of
the plate D will produce considerable movement of the quadrant L; the
substance of the plates D and D', and also of the india-rubber E being such
as to register or indicate the true pressure of the steam or other fluid intended
to act thereon. In practice I have found the plates answer well when made
about 4th of an inch thick, and 2 inches diameter with five concentric
corrugations, and the india-rubber about th of an inch thick; S is a pin
fixed in the plate R, said pin being employed as a stop for the index hand to
press against when the said hand points to zero, when the guage is out of
cation.
The operations of this improved guage are as follows:-Suppose the guage
to be connected by the part C to a steam boiler or other generator of fluid
power, the fluid having entered the chamber B will exert pressure upon the
india-rubber disc G and plates D, D³, above it until such pressure overcomes
the resistance offered by the aforesaid spring plates, which, moving slightly
outwards, will impart motion to the horizontal arm of the bell-cranked lever I,

page_text: thereby pulling the quadrant Lin the direction of the arrow's flight at Figure 2,
and imparting motion to the index hand M, which will point steadily to the
divisions on the index plate, notwithstanding the guage may be affixed to a
locomotive engine or in a steamboat, or in any other situation wherein the
guage may be subjected to an oscillatory or shaking movement. And I
would here observe that this steady pointing of the index hand and true
method of indicating the pressure of the steam or other fluid effected by the
tension of the spring o forms a very important feature in this Invention, and
is a considerable improvement upon pressure guages as heretofore constructed,
as it renders the index hand a positive indicator instead of an approximative
indicator as heretofore.
Having now fully described and set forth the nature and object of my
said Invention of improvements in pressure guages, together with the best
means I am acquainted with for carrying the same into practical effect, I
would remark in conclusion that I hereby declare my Invention to consist in,
and I claim,
First, the combining of two or more corrugated plates or discs of
metal D, D¹, with india-rubber or other suitable elastic substance in the
manufacture of pressure guages in the manner and for the purposes above
described and represented.
Secondly, I claim the convolute or coiled spring O arranged as above
described and represented, for the purpose of preventing vibration of the index
hand of pressure guages as constituting improvements in these said instruments
as above stated.
In witness whereof, I, the said George Allcroft, have hereunto set my
hand and seal, this Sixteenth day of November, in the year of our
Lord One thousand eight hundred and fifty-nine.
GEORGE ALLCROFT.
(L.S.)