IMPROVEMENTS IN ELECTRIC LOW-WATER ALARMS FOR STEAM-BOILERS, APPLICABLE ALSO AS A THERMO- ELECTRIC ALARM
Year: 1883

page_text: LETTERS PATENT to Alexander Melville Clark of the firm of A M and
W Clark, of 53 Chancery Lane in the County of Middlesex, Fellow of the
Institute of Patent Agents for an Invention of IMPROVEMENTS IN ELECTRIC
LOW-WATER ALARMS FOR STEAM-BOILERS, APPLICABLE ALSO AS A THERMO-
ELECTRIC ALARM communicated to him from abroad by Thomas McKenna
and Harvey Carley, both of Long Branch in the County of Monmouth and
State of New Jersey, United States of America
COMPLETE SPECIFICATION filed by the said Alexander Melville Clark at
the Office of the Commissioners of Patents on the 12th December 1883.
ALEXANDER MELVILLE CLARK of the firm of A. M. and W. Clark of 53 Chancery
Lane, in the County of Middlesex, Fellow of the Institute of Patent Agents
"IMPROVEMENTS IN ELECTRIC LOW-WATER ALARMS FOR STEAM-BOILERS, APPLICABLE
ALSO AS A THERMO-ELECTRIC ALARM "
communicated to me from abroad by
Thomas McKenna and Harvey Carley both of Long Branch in the County of
Monmouth and State of New Jersey, United States of America
The object of this Invention is to provide an electric alarm apparatus more
especially intended for use as a low water indicator for steam boilers in which
apparatus mercury is used for completing the electric circuit when the alarm should
be given.
The apparatus is also applicable to ovens, furnaces, and other contrivances where
the heat within has need to be watched.
When applied to steam boilers the action of the apparatus depends upon the
fact that the steam in the boiler is always of a higher temperature than the
water.
+
In the accompanying drawing forming part of this specification the figure

page_text: represents a sectional elevation of the invention as it appears when applied to a
steam boiler.
A represents a thermometer like device, the mercury bulb a of which is enclosed
in the sectional globe B, which forms the chamber b around the mercury bulb as
shown. This chamber b, communicates with the interior of the boiler C, through
the valve stem D, to which the globe B is attached, and which stem is screwed
into a suitable screw-tap made in the boiler at the low water line.
In the plate F, which closes the upper end of the tube d of the thermometer-like
device A, is fitted the thumb-nut f, through which passes the insulated arm e of
the bent wire or rod E, and the insulating material c, on said arm e is screwthreaded
to match the screw threads of the nut f, so that by turning the said nut f, the
bent rod E, may be raised or lowered to suit the temperature at which it is desired
to have the alarm given. The arm e' of the bent wire E, is of the same length as
the arm e, and reaches down in front of the graduated plate G, attached to the
thermometer tube a, and thus serves as an indicator for setting the rod E, with
reference to the degree marks on the plate G.
H, J, represent respectively the connected electric alarm and battery which are
connected respectively to the bent rod E, and the mercury tube d, by the wires h
and j.
a,
The action of the device is as follows: When the water in the boiler stands
above the low water line, the water entering the chamber b, through the stem D,
will prevent the entrance of steam to the said chamber and the mercury in the
bulb will have the same temperature as the water causing it to stand in the
tube d, somewhat below the lower end of the wire. e. But when the water in
the boiler falls below the low water line the steam in the boiler will enter the
chamber b, and being of a much higher temperature than the water, will cause
the mercury to rise in the tube d in contact with the lower end of the arm e, (the
rod E, having been previously properly adjusted), and thus complete the electric
circuit, and cause the alarm to be given.
In the spindle D is fitted the screw plug k for cutting off communication
between the chamber b and boiler C in case it should be desired to unscrew the
bulb B, from the tube D or to unscrew the upper section 61 from the lower
section 6 of the bulb for repairs; and to adapt the spindle D, to serve also as a
test cock, I provide it with the faucet sleeve l, and plug , as shown in the drawing.
The mercury tube d, is enlarged upon the inside at a point above the lower end
of the arm e, as shown at d¹ to prevent all danger of overflow of the mercury in
case of excessive heat.
Constructed in this manner, the alarm is reliable and cheap and by adjusting the
rod E, it may be applied to a variety of uses
Having described the nature of the said Invention and the manner of performing
the same I declare that what I claim as new and desire to secure by Letters
Patent is
1st An electric low water alarm for steam boilers employing mercury to complete
the electric circuit, the apparatus being attached to the boiler in such manner that
steam will reach the mercury-containing bulb only when the water in the boiler
falls below low water mark.
2nd The combination with the boiler C, provided with the tube D, of the globe B,
enclosing the water and steam chamber b mercury bulb a provided with mercury
tube d, adjustable insulated wire c, e, projecting into the bulb tube, alarm H,
battery J, and connecting wires h, j, substantially as described and for the purpose
set forth.
3rdly In an electric alarm the combination with a mercury bulb enclosed within
a chamber a, and provided with a tube d, and plate F, at its upper end and adapted
to be placed in communication with a boiler C, of the thumb nut f, bent wire E
having adjustable insulated wire c, e, and graduated plate G, substantially as
described and for the purpose set forth.

page_text: 4thly In an electric alarm the combination with the globe B, of the mercury
tube a, suspended within said globe, the tube d, provided with the thumb but f
and the insulated threaded wire, c, e, substantially as herein shown and
described.
In witness whereof I the said Alexander Melville Clark, have hereunto set my
hand and seal this tenth day of December A.D. 1883.
AM CLARK (L.S.)