AN IMPROVED PRESSURE GAUGE
Year: 1884

page_text: I, JAMES MURRIE, of 206 Gallowgate, Glasgow, in the County of Lanark, North
Britain, Engineer, do hereby declare the nature of the said invention for AN
IMPROVED PRESSURE GAUGE to be as follows:-
This Invention, which relates to an improved pressure gauge, is so constructed.
that, when used in connection with a thermometer of the type described in the
Provisional Specification of the said James Murrie Number 9393, A.D. 1884, it
always shows the pressure within the apparatus corresponding to the temperature
to which the said apparatus is subjected. The apparatus consists of a chamber in
which there is contained a bulb of less diameter than the interior of the said
chamber itself and having a hollow stem dipping down through the liquid in the
tube extending from the said chamber, this hollow stem being of such length that it
reaches, or very nearly reaches, or is slightly immersed in mercury or other suitable
liquid contained in the lower part of the instrument.-As the chamber and tube
forming the upper part of the instrument as well as the bulb and hollow stem
contained therein are both filled with a liquid, and as this liquid in both cases is
constantly opposed to the pressure of the mercury or other liquid in the lower part
of the instrument, and as pressure is generated therein either mechanically as in the
case of an Hydraulic Press or by the heating of the mercury or other liquid, it
follows that the bulb and hollow stem are at all times subjected to exactly opposite
and equal pressures at all points internally and externally. As the pressure to be
measured causes the mercury or other liquid to rise against the pressure of the
liquid in the other parts of the apparatus which it compresses, the amount of that
compression or the pressure due thereto is indicated by the extent to which the
mercury or other liquid is forced into the stem attached to the bulb contained in
the upper chamber and this is a constant true indication of pressure. When used
with the aforesaid thermometer of the said James Murrie, the pressure indicated is
at all times true irrespective of whether there be leakage in the outer parts of the
apparatus or not. Should there be leakage in the outer parts of the apparatus in
such wise that the liquid opposed to the mercury does not quite fill the parts of the
apparatus proper to it, then the mercury on becoming heated generates vapour
from the opposing liquid, of pressure sufficient to substitute the loss of liquid by

page_text: leakage; but as the interior bulb and its hollow stem are without joints and of
homogeneous structure and are at all times charged with a constant amount of
liquid, it results that leakage therefrom cannot take place so that the amount
of pressure generated in the said liquid is always constantly and without error
indicated by the length to which the mercury has expanded in the stem of the 5
inner bulb.
In place of filling the bulb and stem with a liquid the instrument may be made
more sensitive by partly or wholly charging it with air or gas.

page_text: JAMES MURRIE, 206 Gallowgate Street, Glasgow, Lanarkshire North Britain,
Engineer do hereby declare the nature of my invention for AN IMPROVED PRESSURE
GAUGE and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
This Invention, which relates to an improved pressure gauge, is so constructed
that, when used in connection with a thermometer of the type described in the
Provisional Specification of the said James Murrie Number 9393, A.D. 1884, it
always shows the pressure within the apparatus corresponding to the temperature
to which the said apparatus is subjected. The apparatus consists of a chamber in
which there is contained a bulb of less diameter than the interior of the said
chamber itself and having a hollow stem dipping down through the liquid in the
tube extending from the said chamber, this hollow stem being of such length that
it reaches, or very nearly reaches or is slightly immersed in mercury or other
suitable liquid contained in the lower part of the instrument. As the chamber and.
tube forming the upper part of the instrument as well as the bulb and hollow' stem
contained therein are both filled with a liquid, and as this liquid in both cases is
constantly opposed to the pressure of the mercury or other liquid in the lower part
of the instrument, and as pressure is generated therein either mechanically as in
the case of an Hydraulic Press or by the heating of the mercury or other liquid,
it follows that the bulb and hollow stem are at all times subjected to exactly
opposite and equal pressures at all points internally and externally. As the
pressure to be measured causes the mercury or other liquid to rise against the
pressure of the liquid in the other parts of the apparatus which it compresses,
the amount of that compression or the pressure due thereto is indicated by the
extent to which the mercury or other liquid is forced into the stem attached to
the bulb contained in the upper chamber and this is a constant true indication of
pressure. When used with the aforesaid thermometer of the said James Murrie
the pressure indicated is at all times true irrespective of whether there be,leakage
in the outer parts of the apparatus or not. Should there be leakage in the outer
parts of the apparatus in such wise that the liquid opposed to the mercury does
not quite fill the parts of the apparatus proper to it, then the mercury on becoming
heated generates vapour from the opposing liquid, of pressure sufficient to sub-
stitute the loss of liquid by leakage; but as the interior bulb and hollow stem are
without joints and of homogeneous structure and are at all times charged with a
constant amount of liquid, it results that leakage therefrom cannot take place so
that the amount of pressure generated in the said liquid is always constantly and
without error indicated by the length to which the mercury has expanded in the
stem of the inner bulb:
In place of filling the bulb and stem with a liquid the instrument may be made
more sensitive by partly or wholly charging it with air or gas.
In order that my said Invention be clearly understood and readily carried into
effect I will describe the accompanying drawing.

page_text: Fig. 1. is a sectional elevation of the form of instrument for indicating com-
paratively high pressures. Fig. 2. is a sectional elevation of an instrument wherein
the inside chamber is charged with a gas. Fig. 3. is a sectional elevation of an
instrument for indicating comparatively low pressures.
In the aforesaid drawing the letter A represents the outside chamber or casing;
B, the inside bulb with hollow stem; C, the packing glands; D, transparent tube
forming part of the outside vessel; E, Indicator plate; F, bottom chamber; G, com-
municating passage, H. opaque liquid; I, pet cock or valve. K combined washer
and suspender for inside bulb & stem. L, outside casing. M, stopper or plug.
When the present invention is used in conjunction with the aforesaid thermo-
meter patent No 9393 and 15947 A.D. 1884, the pet cock I or inlet G. is connected
to the stem of the thermometer by ground couplings or other mechanical means for
making a perfect joint. The internal vessel B. being filled with an elastic fluid,
the opaque fluid H, being placed at the lower part of the hollow stem and the
remaining part of the gauge filled with water or other transparent liquid, it follows
that when the instrument is connected with the thermometer stem, the liquid. in
said stem is brought into direct communication with the fluids in the aforesaid
apparatus.
On the mercury or other liquid in the thermometer expansion chamber being
subjected to heat, a pressure is generated which re-acts equally or nearly equally
throughout the entire fluid contained in the combined apparatus. The pressure
acting on the surface of the water or other liquid in the pressure gauge at the pet
cock I or inlet G, it follows that the confined fluids will be subjected to an equal
and uniform pressure; the water or other liquid surrounding the inner vessel 'B'
being practically incompressible and the fluid in the interior chamber B. being
compressible, it necessarily follows that the elastic fluid contained therein will be
compressed, or take up less space until the internal pressure corresponds to the
external pressure, the reduced space being occupied by the opaque liquid H; an
equivalent quantity of water or other liquid being supplied by the connecting tube,
the extent of the contraction of the confined elastic fluid will therefore be shewn
by the height or ascent of the opaque liquid H, and the pressure and temperature
corresponding to the degree of contraction will be read off from the graduated
scale E, placed alongside the stem of the inner vessel B. It thus follows that any-
leakage in the connecting tubes or intermediary parts will not affect the accuracy
of the readings so long as sufficient mercury remains in the expansion chamber of
the thermometer to compensate for any waste: The inner vessel B, forming the
spring of the gauge, and being without joints, any leakage can only take place out-
side of the indicator proper. When this invention is employed to indicate pressure
on steam boilers, hydraulic presses and other pressure apparatus, the pet cock I is
connected to an intermediate tube or syphon charged with a liquid, in communi-
cation with the source of pressure in an analogous manner to the foregoing.
The aforesaid apparatus may also be employed as a means of testing the elasticity
of fluids: the fluid being placed in the inner vessel B. as shewn Fig. 1. and the
contents subjected to hydrostatic pressure by means of a thermometer or pump in
the same way as hereinbefore described, the extent of compression being shewn by
the ascent of the coloured liquid H. The capacity of the bulb as well as the
hollow stem being known, the degree of elasticity of the confined fluid is easily
determined with great accuracy: To guard against different results being obtained
thro' variation in the thermometric conditions, the chamber A, surrounding the
globe B, may have an external vessel as shewn in Fig. 1. which can be charged with
water or other liquid, and a thermometer placed inside to shew the temperature of
the confined fluids.
The aforesaid apparatus may be modified in construction to a certain extent. In
Fig. 1 the inlet or passage G. may be placed at the top or extreme base of the
instrument as found most advantageous, the chamber A, may be constructed of
gun metal or other metal, joined in two halves as shewn by means of a screw or

page_text: flange. The stuffing glands consist of the cominon method of forming a joint
between glass and metal. The indicator plate E, can be attached to the shield L,
which encircles the outer glass tube D, or it can be attached to the instrument at
top and bottom. The vessel F, at base of the instrument must either be made of
iron, when mercury is employed, or if brass, or other metal, an inside cup con-
taining the mercury is placed therein. The internal bulb & hollow stem B, is
made of glass, the capacities depending upon the fluid employed, and the pressure
which it is desired to register; the vessel may be supported by a rubber ring as
shewn in Fig. 1. or suspended by a knob at the top as shewn in Figs. 2 and 3.
When the inner vessel B. is charged with air or gas, as in Figs. 2 and 3, the bulb
at the top serves as a means of obtaining comparatively distinct graduations of
pressure, the chamber being equivalent to employing a very long tube, while by
having enlargements at the lower end of the hollow stem, cr by making the bore
of the stem tapering towards the chamber at the top, comparatively high pressures
can be indicated with an approach to uniformity in the graduations. The capacities
of the respective enlargements and the hollow stem being proportioned to indicate
the desired scale of pressures. In this case the outside glass tube D, may be sealed
at the end as shewn in Figs. 2 and 3, and a stopper M, with some intermediate
elastic packing placed at the extremity of the casing to prevent the tube being
blown out when under pressure.
In Fig. 3 which is mainly intended to indicate comparatively low pressures,
below or above the atmospheric pressure, the internal tube may have the chamber
at the lower end, with the stem dipping through the air or gas into the mercury
placed therein, the opposite end of the stem being in communication with the
surrounding liquid-or, if preferred in practice the inner vessel B, may be sealed
at the top as in Fig. 2. but having the centre of the hollow stem carried down near
the base of the glass tube D, and thence curved upwards, the open end being near
the chamber, while the confined air is prevented from escaping from the inner leg,
by placing mercury in the base of the syphon.
The aforesaid apparatus may be constructed in such a way as to resemble the
circular thermometers in common use, in which case the internal vessel has its
hollow stem made circular, the extremity of the stem being returned to or near
to the enlargement on internal vessel, much in the same way as the spring of the
Bourdon gauge is made to take up a circular or nearly circular position. The bulb
or enlargement is placed at the lower part of the dial, as well as the open end of
the hollow tube, which dips into a vessel containing a coloured or opaque liquid
already described, the outer chamber is made circular and the transparent tube D
is made curved to embrace the hollow stem as before-on the elastic fluid being
subjected to pressure, the mercury follows the curved direction, being kept from
breaking or falling away by the compressed fluid.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed. I declare that what
I claim is
1. In an instrument for indicating pressure the use of an internal vessel charged
with an elastic fluid, or fluids, which vessel is wholly surrounded by or enveloped
in a liquid or liquids, confined in an external chamber, the internal vessel being
free from any tendency to distortion, by the external and internal pressures being
equal under all conditions of pressure, constructed substantially as hereinbefore
described.
2. In an instrument for indicating pressure the use of a vessel containing an
elastic fluid, which vessel has one or more enlargements at or near the extremities,
which enlargements enable a comparatively short vessel to be equivalent to
employing a comparatively long tube, constructed substantially as herein before
described.
3. The use of the pressure gauge herein before described in combination with the
thermometer referred to in specification: Patents N° 9393 and 15947 A.D. 1884,

page_text: wherein the pressure generated. in the expansion chamber of the thermometer
is accurately indicated by the aforesaid gauge, independently of leakage in the
connecting tubes, so long as any mercury remains in said expansion. chamber,
substantially as hereinbefore described..
4. The use of the apparatus hereinbefore described for testing the elasticity of
fluids.
5. The construction and arrangement of apparatus for indicating pressure,
substantially as herein before described...