IMPROVEMENTS IN PRESSURE GAUGES
Year: 1878

page_text: PROVISIONAL SPECIFICATION left by Allan Stewart and Charles Stewart
at the Office of the Commissioners of Patents on the 10th October 1878.
ALLAN STEWART and CHARLES STEWART, both of Glasgow, in the County of
Lanark, North Britain. "IMPROVEMENTS IN PRESSURE GAUGES."
This Invention, which relates to improvements in pressure gauges, has for its
object to afford a double indication of the pressure, in such a manner that one
indication so acts as a check or tell-tale on the other, as to make it apparent at a
glance whether the gauge is or is not efficiently performing its duty. In the gaugo
constructed according to this Invention two curved spring tubes are employed at
one end; each of these tubes is connected to a pipe communicating between the
gauge and the steam boiler or other vessel, the pressure of the fluid or liquid
contained in which it is desired to indicate; at their other or upper ends the
spring tubes are closed, and they are each connected at the said ends by arins or
levers to toothed quadrants centred upon pins or studs carried on a plate screwed
or otherwise fixed to the back of the gauge casing. The two toothed quadrants
gear with corresponding pinions formed or fixed on two spindles, which are so
carried on the before-mentioned plate as to be capable of free rotation, and on the
outer end of each of the said spindles an indicating finger or pointer is fixed. The
dial of the gauge is divided off into the scales circunferentially, the zero and highest
pressure points of one scale being in close proximity to those of the other, and the
two indicating fingers or pointers, each actuated by its own spring tube (through
the intervention of the herein-before described mechanism) work round these
indicating scales. When both of the fingers or pointers indicate the same amount
of pressure upon their separate scales the gauge is in efficient working order;
otherwise it is not, and a double check is thus maintained not only upon the
pressure within the steam boiler or other source of pressure, but also upon the
working of the gauge itself. To enable communication between the gauge and the
source of pressure to be cut off when desired a three-way cock or its equivalent is
placed in the communicating pipe, and by turning the said cock in one direction
communication between the gauge and the atmosphere is established, and the

page_text: pressure within the spring tubes being thereby released, the two indicating fingers
or pointers are each enabled to return to their zero points.
Under modifications of this Invention instead of both fingers or pointers working
through an arc over separate scales on one dial the gauge may be provided with a
dial both at the back and front, in which case only one finger or pointer is provided
for each dial, and instead of securing the plate carrying the moving parts of the
mechanism to the back of the gauge casing, as herein-before described, the said
plate may be secured to the dial; or when two dials are provided the moving
mechanism for the pointer or finger of each may be carried by a plate secured to
the back thereof, or other equivalent arrangements may be adopted.