IMPROVEMENTS IN STEAM GAUGES AND APPLICABLE TO OTHER PRESSURE INDICATORS
Year: 1866

page_text: LETTERS PATENT to Robert William Thomson, of Edinburgh, in the
County of Mid Lothian, North Britain, Civil Engineer, for the Invention
of "IMPROVEMENTS IN STEAM GAUGES AND APPLICABLE TO OTHER PRESSURE
INDICATORS."
PROVISIONAL SPECIFICATION left by the said Robert William Thomson
at the Office of the Commissioners of Patents, with his Petition, on the
9th April 1866.
I, ROBERT WILLIAM THOMSON, of Edinburgh, in the County of Mid Lothian,
North Britain, Civil Engineer, do hereby declare the nature of the said
Invention for "IMPROVEMENTS IN STEAM GAUGES AND APPLICABLE TO OTHER
PRESSURE INDICATORS," to be as follows, that is to say :-
This Invention has for its object the constructing of steam gauges and other
pressure indicators in an improved and simplified manner, and so as to obtain
a very direct action on the index or pointer with sufficient amplitude or range
In one simple modification embodying the improvements the part of the
instrument to be acted upon by the steam (or other fluid), the pressure of
which relatively to the atmosphere or to a vacuum is to be indicated, consists
of a hollow ribband of metal, glass, or other suitable material, which is twisted
so as to present a helical configuration about its longitudinal axis. The steam

page_text: is admitted into one end of this hollow twisted ribband, and this end is fixed;
the other end is left free to turn the index, being fitted in connection with it,
and the action of the internal pressure causes the hollow ribband to untwist
or straighten itself to an extent depending on the pressure, and which is shown
by the index. It is a peculiarity of the twisted form that the outer parts are
necessarily longer than the more central parts, the pressure forces out the
more central parts so as to make them more nearly equal in length to the
outer parts, hence the untwisting action, the limit of which would be the com-
plete untwisting of the ribband when the central and outer parts would
become of equal length. Instead of the cross section being that of a flat
ribband it may be of other forms, having, for example, three or more lobes or
hollow flanges projecting from the centre, the twisted or helical form being
retained in all cases.
In other modifications the gauge consists of two or more tubes of a circular
or other cross section, and twisted helically round a longitudinal centre line,
being fixed at one end and having the index or pointer fitted in connection
with the other end.
All the modifications of the instrument may be arranged to have the
greater pressure outside when the action will be to cause the tube or tubes
to collapse or become more twisted in proportion as the external pressure is
greater.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Robert William Thomson in the Great Seal Patent Office ou
the 9th October 1866.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ROBERT
WILLIAM THOMSON, of Edinburgh, in the County of Mid Lothian, North
Britain, Civil Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters.
Patent, bearing date the Ninth day of April, in the year of our Lord One
thousand eight hundred and sixty-six, in the twenty-ninth year of Her reign,
did, for Herself, Her heirs and successors, give and grant unto me, the said
Robert William Thomson, Her special licence that I, the said Robert
William Thomson, my executors, administrators, and assigns, or such others
as 1, the said Robert William Thomson, 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

page_text: lawfully might make, use, exercise, and vend, within the United Kingdom of
Great Britain and Ireland, the Channel Islands, and Isle of Man, an Inven-
tion for "IMPROVEMENTS IN STEAM GAUGES AND APPLICABLE TO OTHER PRESSURE
INDICATORS," upon the condition (amongst others) that I, the said Robert William
Thomson, 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 Robert William Thomson, 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 in writing, reference being had to the accompanying
Drawings, that is to say:-
My said Invention has for its object the construction of steam gauges and
other pressure indicators in an improved and simplified manner, and so as to
obtain a very direct action on the index or pointer with sufficient amplitude or
range.
And in order that my said Invention and the manner of performing the
same may be properly understood I have hereunto appended a Sheet of
explanatory Drawings to be herein-after referred to, and representing examples
of the various modifications of gauges or pressure indicators that may be made
with my improvements.
A simple modification is shown in side view in Figure 1, with the casing in
section, and in front view in Figure 2, the gauge being represented as fitted
in connection with the end of a steam boiler B. The casing consists of the
usual circular box C with index dial and glass front, and from the centre of
the back of this casing there projects backwards a tube T, which contains the
part of the instrument to be acted upon by the steam (or other fluid), the
pressure of which (relatively to the atmosphere or to a vacuum) is to be
indicated. This consists of a hollow ribband G of brass or other suitable
metal or material, which is twisted so as to present a helical configuration.
about its longitudinal axis, being of the cross section shown at S before it is
twisted. The back end of this twisted gauge tube G is fixed in the back end
of the casing tube T, and on the end of the steam pipe P by soldering and
rivetting or otherwise, and the steam, or by preference water, retained by a
siphon bend and pressed on by the steam has access by the pipe P to the
interior of the twisted gauge tube G. The other or front end of the twisted

page_text: gauge tube G is closed and is left free to turn, the index 1 being fixed upon
it, and the action of the internal pressure causes the tube to untwist or
straighten itself to an extent depending on the pressure, and which is shown
by the index. It is a peculiarity of the twisted form that the outer parts are
necessarily longer than the more central parts; the pressure forces out the more
central parts and stretches them, so as to make them more nearly equal in
length to the outer parts, hence the untwisting action, the limit of which would
be the complete untwisting of the ribband when all its parts would become of
equal length. The elasticity of the material of the tube causes it to recover
its more twisted form on the reduction or removal of the pressure.
Figures 3 and 4 are a sectional and face view of a modification in which to
obtain a greater range of the index I it has a pinion fixed on its axis in gear
with a toothed segment fixed on the free end of the twisted gauge tube G.
Figures 5 and 6 are horizontal and vertical sections of a modification in
which the gauge tube G and dial casing C are both vertical, the index pinion
being acted on by a crown-toothed segment fixed on the top end of the gauge
tube G. The connection of the gauge tube with the index may be made
in a variety of other ways. Any reasonable range can also be obtained with
the index fixed directly on the gauge tube G by simply increasing the length
of that tube. Instead of the cross section of the gauge tube G being that of
a flat hollow ribband it may be of other forms, having, for example, three
lobes or hollow flanges projecting from the centre, as shown in side and end
view in Figures 7 and 8, or four lobes, as in Figures 9 and 10, the twisted or
helical form being retained in all cases.
In other modifications the gauge consists of two or more tubes of a circular
or other cross section, and twisted helically round a longitudinal centre line,
being fixed at one end and having the index or pointer fitted in connection
with the other end. An example of such modification is shown in Figures
11 and 12.
All the modifications of the instrument may be arranged to have the
greater pressure outside, when the action will be to cause the tube or tubes
to collapse or become more twisted in proportion as the external pressure is
greater. In some cases the tube or tubes (G) may be made of glass, as, for
example, for making barometers.
Having thus particularly described my said Invention, and the manner in
which the same is to be performed, I have to state that I do not restrict
myself to the precise details herein described or delineated, but that what I.
believe to be novel and original, and claim as the Invention secured to me
by the herein-before in part recited Letters Patent is, the applying of a single

page_text: twisted tube, or of two or more tubes twisted together, for indicating pressure
by untwisting or twisting, substantially as herein-before described.
In witness whereof, I, the said Robert William Thomson, have hereunto
set my hand and seal, this Fifth day of October, in the year of
our Lord One thousand eight hundred and sixty-six.
Witness,
EDMUND HUNT,
Patent Agent,
Glasgow.
R. W. THOMSON. (L.S.)