IMPROVEMENTS IN PRESSURE AND VACUUM GAUGES
Year: 1876

page_text: LETTERS PATENT to Alexander Allan, junior, of Scarborough, in the County of
«
York, Engineer, for the Invention of IMPROVEMENTS IN PRESSURE AND
VACUUM GAUGES."
Sealed the 23rd September 1876, and dated the 1st April 1876.
PROVISIONAL SPECIFICATION left by the said Alexander Allan at the Office
of the Commissioners of Patents on the 1st April 1876.
ALEXANDER ALLAN, junior, of Scarborough, in the County of York, Engineer.
"IMPROVEMENTS IN PRESSURE AND VACUUM GAUGES."
This Invention comprises improvements in pressure and vacuum gauges of the
kind described in the Specification of Letters Patent granted to Alexander Allan,
Thomas Whimster, and Robert Gray, and dated 19 October 1858 (No. 2332).
In pressure gauges of the kind referred to a quantity of air is confined in a
vessel which or part of which is conical or conoidal, and it is by the extent to
which the air is compressed in such vessel that the pressure to be indicated is ascer-
tained, the pressure being applied to the confined air through the medium of water
or other suitable liquid. The conoidal part of the vessel may be of glass or metal,
but when of metal there must be fitted in connection with it a glass tube, or glass
must be fitted in an opening in it to admit of the height of the liquid being seen.
A scale of pounds or other suitable measure of pressure is marked or otherwise
applied close beside the part where the indications of the liquid level are visible,
and when the conoidal vessel is properly shaped the divisions on the scale may be
at equal distances apart for equal differences of pressure per square inch or other
unit.
One of the present improvements consists in forming an enlargement at or in
connection with the smaller end of the conoidal space, a plug being provided which
is adjustable in an opening in such enlargement so as to vary the internal capacity.
With such enlargement and plug small variations in different gauges can be cor-
rected so that the actual pressures may accurately agree with the equal divisions of
the scale. The scale being thus always the same (for the same range of pressures)
the divisions can be marked permanently on the glass by moulding or by incor-
porating white or colored marks in the glass, or by stamping or moulding on the
metal of the vessel or on a separate metal plate. The glass may also be made with

page_text: the back part white or of some tint that will make the level of the liquid or tho
divisions of the scale more easily discernible.
When a separate indicating glass tube is used it is entered down into its place
through a hole made for the purpose through the head of the metal part of the
instrument. The joints at the bottom and top of the glass tube are rendered tight
by rings of rubber or other suitable compressible material. Two plugs are screwed
into the hole in the head of the instrument, one to press down the upper rubber
ring on the tube end and the other to close the top opening, whilst the inner plug
is bored to allow the top of the glass tube to cominunicate by the passage in the
head with the top of the conoidal vessel.
Below the conoidal vessel and indicating tube a conical stop-cock plug is fitted,
being made with one way through it to put the bottom of the conoidal vessel in
communication with the pipe by which the pressure to be indicated is transmitted
from a boiler or other vessel. At a different part of the plug there is formed
through it a way at right angles to the other one, and when the plug is turned so
as to make the second way vertical it allows any liquid in the instrument to run
out by passages provided for the purpose and leading from the bottoms of both the
conoidal vessel and indicating tube. At the same time a small groove in the plug
puts an air hole in communication with the internal passages, and this air hole
being higher than the outlet for the liquid facilitates the complete discharge of the
liquid. Whenever the liquid runs out in this way the interior of the instrument
is refilled with air, being thereby as it were provided with a new spring, and this
renewal of the air can be effected in a few seconds at any time whenever the
observer feels the least doubt as to the indications of pressure. Stops are fitted on
the instrument so that the stop-cock cannot be turned too far, and the words
"open" and "shut" or other suitable words are marked on the stops so as to
prevent mistake.
"
When the instrument is to be used for indicating the pressure in a steam boiler
the pressure pipe is made to communicate with the water and not the steam space,
and where the water is liable to be muddy a quantity of sponge or other filtering
material is placed in an enlargement of the communicating pipe. By this arrange-
ment the necessary interposition of a liquid between the steam and the air of the
gauge is secured in a simple manner, and without causing the least trouble..
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by the
said Alexander Allan in the Great Seal Patent Office on the 28th September
1876.
ALEXANDER ALLAN, junior, of Scarborough, in the County of York, Engineer.
IMPROVEMENTS IN PRESSURE AND VACUUM GAUGES."
My said Invention comprises improvements in pressure and vacuum gauges of
the kind described in the Specification of Letters Patent granted to Alexander
Allan, Thomas Whimster, and Robert Gray, and dated 19 October 1858 (No.
2332).
In pressure gauges of the kind referred to a quantity of air is confined in a
vessel which or part of which is conical or conoidal, and it is by the extent to
which the air is compressed in such vessel that the pressure to be indicated is
ascertained, the pressure being applied to the confined air through the medium of
water or other suitable liquid. The conoidal part of the vessel may be of glass or
metal, but when it is of metal there must be fitted in connection with it a glass
tube, or glass must be fitted in an opening in it to admit of the height of the liquid
being seen. A scale of pounds or other suitable measure of pressure is marked or
otherwise applied close beside the part where the indications of the liquid level are

page_text: visible, and when the conoidal vessel is properly shaped the divisions on the scale
may be at equal distances apart for equal differences of pressuro per square inch or
other unit.
One of my present improvements consists in forming an enlargement at or in
connection with the smaller end of the couoidal space, a plug being provided which
is adjustable in an opening in such enlargement so as to vary the internal
capacity.
When a separate indicating glass tube is used I enter it down into its place
through a hole made for the purpose through the head of the metal parts of tho
instrument.
Below the conoidal vessel and indicating tube I fit a conical stop-cock plug, and
contrive it to answer the purposes of clearing the gauge and renewing the air
spring.
When the instrument is to be used for indicating the pressure in a steam boiler
I make the pressure pipe communicate with the water and not the steam space,
and where the water is liable to be muddy I place a quantity of spongo or other
filtering material in an enlargement of the communicating pipe.
And in order that my said Invention, and the manner of performing the same,
may be properly understood I hereunto append a Sheet of explanatory Drawings
to be herein-after referred to, and representing pressure and vacuum gauges as
made with my improvements. In these Drawings the same reference numerals are
used to mark the same or like parts wherever they are repeated.
Figure 1 of the Drawings is a vertical section, and Figure 2 is a front elevation
of a pressure gauge as made with my improvements, the section Figure 1 being as
at right angles to Figure 2. The conoidal vessel 1 is in this example of metal, and
has a glass tube 2 in connection with it. An enlargement 3 is formed at the top
of the conoidal vessel 1, and is fitted with a screw plug 4, admitting of the
capacity of the enlargement being varied either by screwing the plug 4 in more or
less or by changing it for one of a different size. With such enlargement 3 and
plug 4 small variations in different gauges can be corrected so that the actual
pressures may accurately agree with the equal divisions of the scale. The scale
being thus always the same (for the same range of pressures) the divisions can bo
marked permanently on the glass by moulding or by incorporating white or colored
marks in the glass, or by stamping or moulding on the metal of the vessel 1 or on
a separate metal plate. The glass tube 2 may also be made with the back part
white, or of some tint that will make the level of the liquid or the divisions of the
scale more easily discernible.
The glass tube 2 is entered down into its place through a hole made through the
head 5. The bottom of the tube 2 enters an annular recess formed for it in the
base 6 of the instrument, and the joints at the bottom and top of the tube 2 are
rendered tight by interposed rings of rubber or other suitable compressible
material. Two plugs, 7, 8, are screwed into the hole in the head 5, one 7 to press
down the upper rubber ring on the tube end, and the other 8 to close the top
opening, whilst the inner plug 7 is bored to allow the top of the glass tube 2 to
communicate by the passage 9 in the head with the top of the conoidal vessel 1.
A conical stop-cock plug 10 is fitted into the base 6, and is made with one way,
11, through it to put the bottom of the conoidal vessel 1 in cominunication with
the pipe 12, by which the pressure to be indicated is transmitted from a boiler or
other vessol, such pipe being connected to the base G of the instrument by a
coupling 13.
At a different part of the plug 10 there is formed through it a way
14 at right angles to the other one 11, and when the plug is turned so as to make
the second way 14 vertical it allows any liquid in the instrument to run out by
passages 15, 16, provided for the purpose and loading from the bottoms of both the
conoidal vessel 1 and indicating tube 2. At the same time the plug puts an air
hole 17 in communication with the interior, and this air hole 17 being higher than
the outlet 16 for liquid, facilitatos the complete discharge of the liquid. Whenever
the liquid runs out in this way the interior of the instrument is rofilled with air,

page_text: being thereby provided with a new spring; and this renewal of the air can be
effected in a few seconds at any time whenever the observer feels the least doubt
as to the indications of pressure. Stops 18, 19, are formed or fitted on the front
of the base 6 of the instrument, so that the handle 20 of the stop-cock 10 cannot
be turned too far, and the words "open" and "shut" or other suitable words are
marked on the stops with the view of preventing mistakes.
Figure 3 is a vertical section of a simplified modification of my improved pressure
gauges suitable for moderate pressures such as a maximum of thirty pounds above
the atmosphere. The conoidal vessel 1 is of glass so that a separate indicating tube
is not required, and the enlargement 3 is formed on the upper smaller end. The
glass vessel 1 is secured to the base 6 of the instrument by a flanged ring 21 screwed
upon the base, rubber rings being interposed on both sides of a flange formed on to
the bottom of the glass vessel 1.
.
A modification for indicating vacuum is shown in Figures 4 and 5, which are
respectively a side elevation and a sectional front elevation. In this case a tubular
metal column 1 is connected by a head 5 and base 6 with a glass indicating tube 2,
which last is secured as herein-before described with reference to Figures 1 and 2.
The glass tube 2 has united to its bottom end a glass vessel 22, there being a
capillary communication between the bottom of the vessel 22 and the bore of the
tube 2, whilst the otherwise open top of the vessel 22 is with an interposed rubber
ring pressed tightly up to a bearing in the base 6, being secured by a bottom piece
23 screwed upon the base 6.
A stop-cock 10 introduced between the bottom of the metal column 1 and the top
of the glass vessel 22 is made with two ways, one 24 of which puts the vessel 22, and
the column 1, and through the latter, the top of the glass tube 2 in communication
with the atmosphere, whilst the other 25 puts the bottom of the column 1 in com-
munication with the passage 26, by which the instrument is made to communicate
with a condenser or other vessel, the degree of vacuum in which is to be indicated.
A certain quantity of mercury or other suitable liquid is put into the vessel 22, and
when the top of that vessel and the top of the tube 2 are open to the atmosphere
the mercury stands at the same level in the vessel 22 and in the tube 2; but when
the stop-cock 10 is turned into the position in which it is shown in Figure 5 the
top of the vessel 22 is closed, and the top of the tube 2 being then subjected by the
passages 25, 26, to the vacuum to be indicated the air confined in the upper part of
the vessel 22 expands and causes the mercury to rise in the tube 2 and thus
indicates the degree of vacuum. A scale is marked on the tube 2 or on the metal
column 1, or it may be marked on a separate plate which can at any time be adjusted
to the exact zero position of the mercury.
Figure 6 of the Drawings is a partially sectioned end elevation of a steam boiler,
and showing the mode in which I connect my improved pressure gauges thereto; I
either connect the gauge pipe 12 by a stop-cock 27 fitted below the water level, or
by a stop-cock fitted in the steam space but having an internal pipe 28 dipping
below the water level so as to make sure of the gauge pipe 12 being filled with
And when the water is muddy I put sponge or other filtering material in
an enlargement 29 on the pipe 12 so as to render the water actually reaching the
gauge free from suspended impurities.
water.
Having thus particularly described my said Invention and the manner of
performing the same, I have to state 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,―
1. The forming of an adjustable enlargement or space (3) in connection with the
small end of the conoidal gauge vessel (1), as and for the purposes herein-before
described.
2. The improved mode herein-before described of fixing the glass indicating tube
2 in its place.
3. The improved arrangement of the passages through and in connection with the
stop-cock (10) as herein-before described.

page_text: 4. The combination of parts constituting the vacuum gauge, herein-before
described with reference to Figures 4 and 5 of the accompanying Drawings.
5. The connecting of the pressure gauge pipe (12) so as to communicate with
the water and not the steam space of a boiler as and for the purpose herein-beforo
described.
In witness whereof, I, the said Alexander Allan, junior, have hereunto set my
hand and seal, this Twenty-seventh day of September, in the year of our
Lord One thousand eight hundred and seventy-six.
ALEXANDER ALLAN, JUNIOR. (L.S.)