Improved Duplex Pressure Gauges.
Year: 1894

page_text: PROVISIONAL SPECIFICATION.
Improved Duplex Pressure Gauges.
I, JAMES THOMAS, of The "Argus" Pressure-gauge Works, Chippenham,
Wilts. Gauge Maker, do hereby declare the nature of this invention to be as
follows:-
My invention relates to improvements in duplex pressure gauges, for indicating
steam, water, vacuum and other pressure; and bas for its object to provide a meaus
whereby a single dial will show two separate indications of the pressure in the neck
or inlet of the gauge, each obtained by totally different appliances from a tube or
tubes under different conditions, such indications being a check one on the other;
and when they agree, will afford conclusive proof that the gauge is in proper
working order.
With the duplex gauges at present in operation, the dual indication is obtained
by setting the two pointers to work in opposite directions, the conditions of the
operating tubes and the mechanism for actuating the pointers being practically
identical; by my invention, one half the tube or tubes containing the fluid under
pressure is made very much lighter than the other, consequently will be more
sensitive; one half of the tube is made to actuate a central and the other an
eccentric pointer, each pointer covering its respective scale, arranged according to
the usual method.
In carrying my invention into effect, I provide the ordinary drum shaped frame
or case to hold the mechanism, with a neck or inlet to connect the gauge to the
steam or other pipe conveying the pressure; within the drum and connected
to the neck and to each other, I place two tubes, one considerably stouter
than the other, each bent to a semi-circle, and lying on either side the drum near
its periphery, the outer ends being closed; these bent tubes being of different
thickness, will be expanded in different degrees by the pressure, the closed end of
one tube is attached by rods and levers to a rack and pinion which operate a
central spindle extending through the dial to receive a pointer; the end of the
other tube or part of tube is also connected by levers to an adjustable slide
attached to another spindle which is eccentric, this spindle also extends through
the dial to receive a pointer; each pointer works over its scale arranged and
imprinted on the dial according to the usual requirements; each scale may
conveniently differ in colour from the other to facilitate comparison; the frame is
covered with glass for protection in the usual manner.
With a gauge made as described, it is evident that the indication of the pressure
on the stout tube operating a pinion and central pointer, will be obtained by
different means and under different conditions from that obtained from a lighter
tube operating an eccentric pointer, and by my invention, these different means of
arriving at the same result are so adjusted, that when in proper order, the
indications of each pointer (when the gauge is used) will be identical, and while
this is the case, each proves that the other registers correctly, and whenever they
show any material divergence, it will serve as a warning to the engine driver or
attendant that the gauge is unreliable and out of order, requiring repairs or
re-adjustment, without having to be periodically tested as is necessary with gauges.
made according to the existing method.
Dated this 7th day of June 1894.

page_text: Improved Duplex Pressure Gauges.
I, JAMES THOMAS, formerly of Chippenham, Wilts, now residing at Salisbury
Street, Barton Hill, Bristol, Gauge Maker, do hereby declare the nature of this
invention and in what manner the same is to be performed, to be particularly
described and ascertained-in-and-by-the following statement :-
My invention relates to improvements in duplex gauges for indicating steam,
vacuum, water, and other pressures, and has for its object to provide a means
whereby two indications of the pressure on the neck or inlet of the gauge will be
exhibited on the face of a single dial, each indication being separate and distinct,
and each obtained by differing appliances from resistance tubes, coils, or springs of
different lengths, textures, and strength, thus providing a double check, so that the
periodical removal of gauges from boilers and the like for purposes of testing will
be rendered unnecessary, as when the two indications are identical, it will be the
best possible proof of their accuracy, each being obtained by differing mechanical
appliances from resistance tubes or springs under different conditions.
With the duplex gauges at present in operation, the dual indication is obtained
from two pointers, each slightly eccentric, moving in opposite directions, connected
with resistance tubes or springs of identical strength and operating under identical
conditions, therefore any improper disturbing element would influence each tube or
spring and the pointers connected thereto in exactly the same degree, and if one
pointer was incorrect, the other, being equally affected, would give the same
indication, thereby apparently verifying the false reading of the two pointers.
According to this invention, the two bent tubes or springs are of different sizes,
lengths, and strength, consequently one will be much more sensitive than the other,
and any accident, rough usage, or decay, will affect one tube or spring to a greater
extent than the other; the actuating appliances are so adjusted, that when in
working order, each pointer will indicate the same pressure on its respective scale,
and any material discrepancy between the two readings will serve as a warning to
the engineer or attendant that the gauge is unreliable.
The nature of this invention, and suitable means for carrying the same into
effect, will be more fully described in connection with the accompanying sheet of
drawings, in which Fig. 1 represents a steam pressure gauge complete, with the
two pointers and scales, and Fig. 2 is a view of the interior of the same, the dial
and pointers being removed to show the resistance tubes and operating mechanism.
A is the neck or inlet for the steam, attached thereto on one side is a piece of
flattened tubing B, bent to a semicircle or thereabout, the other end being closed
and connected by levers to a rack and pinion which actuate the central spindle D
on which the pointer d is fixed, to move over its circular scale when the spindle is
rotated. C is a similarly formed and bent tube of a lighter texture, attached
(conveniently) on the other side of the neck, also closed at the end, and connected
by a lever and cam to an eccentric spindle E on which the pointer e is fixed to
travel over the eccentric scale when the spindle is rotated. The movements in the
interior of the gauge thus described are identical with those now in common use
for gauges with central and eccentric single pointers respectively, and the essential
feature of this invention consists in combining these two dissimilar sets of
movements with tubes or springs of different degrees of resistance, and so
regulating and adjusting them that the amount of pressure on each will be
correctly indicated by the pointers.
The foregoing description and drawings refer to gauges for steam boilers, but
the modifications necessary to adapt the invention to gauges for other purposes are
so obvious that any maker will be able to apply the mechanical equivalents without
any alternative description or directions.

page_text: To enable the indications on the dial to be more readily seen, the scales may be
printed in two different and contrasting colours; e.g. the central scale may be red
and the eccentric black, or any other suitable variation may be adopted.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. In duplex pressure gauges, making the resistance tubes or springs in differing
sizes and strengths, so that any permauently disturbing influence, accident, or
decay, acting on the gauge will affect the tubes or springs to a different relative
extent, and cause the pointers to indicate unequal pressure, and thus show that the
gauge is unreliable, substantially as set forth and described.
2. In duplex pressure gauges as described fitted with resistance tubes or the like
of differing textures and strengths, the employment of dissimilar sets of movements
for actuating the pointers, by which they can be accurately adjusted to correctly
indicate the pressure on their respective tubes, substantially as set forth and
described.
3. In the construction of duplex pressure gauges, the combination of dissimilar
and unequal tubes or coils, movements, and scales as herein described and shown to
secure a reliable gauge, in which the indication of each of the pointers will be a
check on the other, substantially as and for the purposes herein set forth and
illustrated in the accompanying drawings.
Dated this 6th day of March 1895.
J. G. WESTLAKE,
2, John Street, Bristol, Applicant's Agent.