IMPROVEMENTS IN APPARATUS FOR RELIEVING SAFETY VALVES AND FOR INDICATING LOW WATER IN STEAM BOILERS, ALSO PARTLY APPLICABLE AS A SAFETY VALVE FOR DOMESTIC HOT WATER BOILERS
Year: 1876

page_text: PROVISIONAL SPECIFICATION left by Thomas Mitchell and Martin Mitchell
at the Oflice of the Commissioners of Patents on the 8th May 1876.
THOMAS MITCHELL, of Todmorden, in the County of Lancaster, and MARTIN
MITCHELL, of Bacup, in the same County. "IMPROVEMENTS IN APPARATUS FOR
RELIEVING SAFETY VALVES AND FOR INDICATING LOW WATER IN STEAM BOILERS,
ALSO PARTLY APPLICABLE AS A SAFETY VALVE FOR DOMESTIC HOT WATER BOILERS."
The object of this Invention is the construction of an apparatus which shall
self-actingly relieve a safety valve when the blowing off pressure is reached, and
which shall under all circumstances ensure the safety valve blowing off at the
desired pressure, notwithstanding that extra weight may have been applied to the
lever of the valve, and thus to effectually obviate the evil effects of tampering with
a safety valve, the same apparatus being useful for indicating lowness of water.
Now this Invention consists of a chamber, herein-after called the water chamber,
communicating with the steain and water space of the boiler, so that the level of
the water shall constantly be the same in such chainber as it is in the boiler. This
chamber communicates at the top with a small cistern containing mercury, herein-
after called the mercurial chamber, and from the lowest point of this chamber a
pipe is carried upwards and opens into an enlargement which is open to the
atmosphere at the top. Another pipe branches off the side of the mercurial
chamber, and is also extended upwards and opens into an enclosed compartment,
herein-after called the steam compartiment, which communicates with an india-
rubber diaphragm working in a suitable box containing water, and which diaphragm
is connected by means of a spindle to the lever of the safety valve.
The action of this apparatus is as follows:-The enlargement in the pipe herein-
before mentioned is set at the desired height to allow a quantity of mercury to
leave the mercurial chamber and to rise in the intermediate pipe without entering
the enlargement, thus constituting a column of mercury exactly corresponding to
the desired working pressure. The quantity of mercury in the apparatus is so
regulated that the end of the pipe leading upwards to the steam compartment
is sealed with mercury so long as the mercury does not rise into the enlargement.
In case the pressure in the boiler now rises beyond the working pressure the
column of mercury is caused to rise still higher, and coming into the enlargement
rapid diminution of the quantity of mercury in the mercurial chamber ensues,
the pipe leading to the steam compartment becomes unsealed, and steam thus finds
[Price 2d.

page_text: its way into the steam compartment, and is then free to raise the india-rubber
diaphragm, and so relieves the safety valve. In the water chamber we also arrange
a cylindrical compartiment in which a loosely fitting plunger is capable of rising
and falling, being connected at one extremity of a counterbalance lever, the counter-
balance weight of which is submerged in the water; the bottom of this cylindrical
compartment communicates with the mercurial chamber, and thus when the water
lowers in this compartiment and leaves the counterbalance weight it becomes more
powerful, and accordingly lifts the plunger when the mercury from the mercurial
chamber enters beneath the plunger in large quantity and has the same effect in
opening the end of the scaled pipe, as is herein-before described with reference to
over pressure of steam.
A single apparatus constructed according to this Invention is applicable for
several boilers working at the same pressure, and a modification of this Invention
is useful as a relief apparatus acting as a safety valve for domestic hot water
boilers.