IMPROVEMENTS IN AIR-SPRING PRESSURE GAUGES
Year: 1885

page_text: I, ALEXANDER ALLAN, of Glen House, the Valley, Scarborough, in the County
of York, Engineer, do hereby declare the nature of my said invention for
"IMPROVEMENTS IN AIR-SPRING PRESSURE GAUGES," and in what manner the same
is to be performed, to be particularly described and ascertained in and by the
following statement, that is to say:―
My said Invention relates to pressure gauges of the kind in which a confined
quantity of air is used as a spring to be acted upon by the pressure which it
wished to indicate. Gauges of the kind referred to are described in the
Specifications of British Patents N° 2332 of 1858 granted to myself and others,
and N° 1405 of 1876 granted to Alexander Allan, Junior; and my present
improvements relate to minor details and have for their object to overcome various
objections and to render the gauges more accurate and reliable.
An air-spring pressure gauge as made with my improvements is shown on the
accompanying sheet of explanatory drawings, of which figure, 1, is a front
elevation, figure, 2, a side elevation, figure, 3, a vertical section, figure, 4, an
inverted plan, and figure, 5, a vertical section of the lower part of the gauge as at
right-angles to figure, 3. In these drawings the same reference numerals are used
to mark the same or like parts wherever they are repeated.
The gauge comprises a chamber forming the interior of a metal vessel or
tube, 10, which is in communication at top and bottom with a glass tube, 11, and
the air confined in these parts is acted on from below by water or other suitable
liquid which has access through a pipe, 12. This pipe is, as usual, made with a
siphon bend to retain water and its other end is connected to the steam boiler or
to the apparatus containing the steam or other fluid the pressure of which it is
wished to indicate. Pressure acting through the pipe, 12, causes the water or
liquid to rise equally in the vessel, 10, and glass tube, 11, the air being compressed
towards the upper part of the gauge; and whilst the level to which the water or
liquid rises in the glass tube, 11, indicates the pressure on a scale, the shape of the
vessel, 10, is made such that the divisions on the scale may be made equal or
nearly equal for equal increments of pressure. The top of the metal vessel, 10, is
shown as closed by a screw plug, 13, but might be made without such plug, or in
other words quite solid; whilst if the plug arrangement is used for convenience in
making the gauge it is afterwards hermetically closed by brazing by means of a

page_text: blow pipe, it being important to completely prevent any leakage of the air which is
used as a spring. A lateral enlargement, 14, is formed near the top of the metal
vessel, 10, for holding and forming a communication with the top of the glass
tube, 11; and an airtight joint is made between this enlargement, 14, and the
glass tube, 11, by means of a rubber ring placed in an annular groove formed for it. I
The lower end of the glass tube, 11, is held in a lateral enlargement, 15, formed at
the lower part of the metal vessel, 10, this enlargement having a hole bored
completely through it so that the glass tube, 11, can be passed from below through
this hole and into its place. The hole in the enlargement, 15, is internally screwed
to receive a bottom closing plug, 16, and also to receive a disk, 17, having a screw
thread formed round its edge, for tightening up and fixing the glass tube, 11, the
disk being made with a cross groove on its underside for the application of a screw
driver. Between the disk, 17, and the bottom of the glass tube, 11, there are
placed a number of annular rubber washers with an annular metal washer between
them, and a flanged nipple, 37, which rests on the disk, 17, projects up through the
washers and prevents them from spreading inwards and insures their outer edges
being in close contact with the internal screw threads of the hole thus forming an
airtight joint. With these arrangements leakage of air is prevented as completely
as possible, the joints at the top and bottom of the glass tube, 11, being capable of
being made quite airtight; whilst if there should be any leakage past the bottom
plug, 16, it must be of water or liquid and will be visible, whilst it will not
interfere with the accuracy of the indications.
In former gauges of the kind to which the present Invention relates the scale
was marked upon the outside of the metal vessel, 10, but as this vessel is at
unequal distances from the glass tube, 11, there was a liability of inaccurate
reading especially if the gauge happened to be placed so that it must be inspected
in an upwardly or downwardly inclined direction. By my present Invention the
scale is marked upon a separate plate, 18, which is placed between the glass
tube, 11, and the metal vessel, 10. The plate, 18, is however curved away at the
sides so as to assist the reading by allowing light reflected from the sides to pass
through the glass tube, 11, and a small space is left between it and the tube to
allow of the tube and it being properly cleaned.
A single stopcock, 19, is provided for admitting the pressure to the gauge or for
shutting it off and at the same time allowing any water that may be in the gauge
to run out, and be replaced by air, thus remeasuring the quantity of air that is
confined in the gauge to act as a spring. Three separate passages are formed
through the plug, 19, one, 20, forming a communication between the pipe, 12, and
the interior of the gauge, when the plug is turned so as to make this passage
vertical, as shown in figure, 3. This is termed the "open" position of the plug, 19;
and a handle, 21, fixed on the plug has an index projection, 22, formed on it which
in this position of the plug points to the word "OPEN" marked on the outside of
the gauge. When the plug, 19, is in the "SHUT" position as shown in figure, 5,
a second passage,, 23, through it, puts in communication passages, 24, 25, formed
vertically through the bottom of the metal vessel, 10, so as to let any water then
in that vessel to drain out. At the same time the passage, 20, of the plug puts in
communication two parts, 26, 27, of an inclined passage the upper end of which
communicates with the space under the disk, 17, and by the central passage in
the disk and nipple, with the lower end of the glass tube, 11. This inclined
passage, 26, 27, also communicates by a short passage, 28, with. the bottom of the
metal vessel, 10, so that there are two outlets downwards from this vessel, and
there is consequently no risk of water hanging or remaining in it. A third small
passage, 29, is formed in the plug, 19, as shown in figure, 5, and a screw valve, 30,
is fitted into the end of the plug for closing this passage, the purpose of which is to
let out any air that may be in the pipe, 12, above the water retained by the siphon
bend.
The body of the gauge is formed with flanges, 31, at its back by means of which
the gauge, can be fixed against a vertical surface; and another of my present

page_text: improvements consists in placing the stopcock plug, 19, transversely, this is,
parallel to the back of the gauge or to the surface against which the gauge is
fixed, instead of being at right angles thereto as formerly. This improvement
allows of the plug, 19, being got out for examination and of its being reground
without taking down the gauge.
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed 1 declare that what
I claim is
1. The combination of parts forming my improved air-spring pressure gauge
substantially as herein before described.
2. The improved mode of constructing and putting together the parts of the
gauge without movable screw plugs in connection with the internal air space,
substantially as hereinbefore described.
3. The improved construction for entering and fixing the glass tube in its place
substantially as hereinbefore described.
4. The marking of the scale on a separate plate instead of on the metal vessel
substantially as herein before described.
5.-The improved construction or arrangement of the passages in and connected
with the stopcock plug substantially as herein before described.
6. The placing of the stopcock plug transversely substantially as and for the
purposes hereinbefore described.
Dated this fourteenth day of September 1885.
EDMUND HUNTI
Applicant's Agent.