IMPROVEMENTS IN REFRIGERATING MACHINES AND IN APPARATUS IN CONNECTION THEREWITH
Year: 1871

page_text: PROVISIONAL SPECIFICATION left by Hunter Henry Murdoch at the
Office of the Commissioners of Patents, with his Petition, on the
11th October 1871.-A communication from abroad. by Edward
Roettger,-of Lille, France, Civil Engineer.
I, HUNTER HENRY MURDOCH, of No. 7, Staple Inn, in the County of
Middlesex, Patent Agent, do hereby declare the nature of the said
Invention for "IMPROVEMENTS IN REFRIGERATING MACHINES AND IN APPARATUS
IN CONNECTION THEREWITH," to be as follows:-
This Invention relates to machines for the production of cold by
means of compressed air. It is well known that if compressed air be
cooled to, say, the temperature of the atmosphere and then allowed
to expand, cold will be produced. Hitherto in all applications of this
principle the expansion of the compressed air has taken place freely
without having to overcome any resisting pressure:
1

page_text: Now this Invention is based upon a series of experiments which liave
led to the discovery that in order to produce cold economically by means
of compressed air the expansion of the said compressed air must take
place under pressure equal to the expansive force of the said air.
According to this Invention an air pump provided with a double
casing, through which water is allowed to circulate, is connected by its
piston rod and a connecting rod with a crank upon a shaft supported
in suitable bearings in the frame of the machine. Upon the said
shaft at a suitable distance from the air pump crank is another crank
connected by means of a connecting rod with a piston rod, the piston
of which rod works in a cylinder, which may be termed the "expansion
cylinder," the said expansion cylinder being provided with ports for the
entry and outlet of air and also with a slide valve and variable expansion
gear such as would be fitted to an ordinary steam engine wherein the
steam is intended to work expansively. The air pump is made to draw
air from the vessel or apparatus in which refigeration is to be produced;
the said air is then forced by the said pump into an air-tight reservoir
or chamber in which water circulates through suitable pipes. From
the said reservoir or chamber the compressed air passes into a second
reservoir or holder so arranged that the communication between it and
the first-mentioned reservoir or chamber may be cut off when required.
From the said second reservoir or holder the compressed air passes into
the expansion cylinder, in which it acts as a motive power, giving a
feciprocal motion to the piston as in a steam engine, and giving rotatory
motion to the crank shaft and thereby working the air pump. The
relative positions of the cranks of the air pump and expansion cylinder
are such that when the compressed air is admitted to the expansion
cylinder the piston of the air pump will be exerting its greatest amount
of pressure upon the air. Thus if the air is to be compressed by the
air pump to a pressure, say of four atmospheres, it is when the piston
of the said air pump has completed three-fourths of its stroke that the
compressed air is admitted to the expansion cylinder, and the said com-
pressed air is fed into the said expansion cylinder till all the air in the
air pump is forced into the air-tight reservoir or chamber. During this
latter portion of the stroke of the air pump piston the communication
between the said air-tight reservoir or chamber and the second reservoir
or holder is cut off by means of a cam, or excentric, or other suitable

page_text: mechanical contrivance acting on a suitable valve or stop-cock. 'During
the first portion of the stroke of the air pump piston when the said
piston begins to compress the air, the compressed air in the expansion
cylinder is allowed to work expansively, the feed of compressed air tō
the said cylinder being cut off by the expansion gear: ':
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By this arrangement, the compressed air in the expansion cylinder
as it expands is opposed constantly by a pressure equal to its own
expansive power, the heat it still contains is converted into motive power,
and cold is produced. The length of stroke of the air, pump is equal
to that of the expansion cylinder, but the diameter of the said expansion
cylinder is somewhat larger than that of the air-pump in order to
compensate for the loss of power absorbed by friction and other causes;
and as the said expansion cylinder thus requires a larger supply of
compressed air than is forced into the reservoirs or holders by the air
pump a small extra air pump is used to force air into the said reservoir
to complete the necessary supply.
The difference in the quantity of air forced into the reservoir and
given out therefrom is compensated in all other machines of the kind
by driving belts and pulleys or extra steam power, but according to
this Invention it is made to produce extra refrigerating effect.
The air reservoir may be provided. with a regulator or valve, which
may consist of a weighted piston pressed upwards by the air in the
reservoir. The said piston communicates by means of suitable gearing
with the feed valve of the steam cylinder driving the-air pump. When
the pressure in the air reservoir falls the said piston also falls and opens
the feed valve of the steam cylinder, thereby causing the air pump 'to
pump air into the said air reservoir. When the required amount of
pressure in the said reservoir is attained the said piston rises and stops
the air pump, thus rendering the whole machine self-acting.
The working of the machine is as follows:-The air is compressed
and partially cooled in the air pump. It is then forced into the first
reservoir or chamber where it is further cooled by contact with the
water pipes. It then is admitted into the second reservoir or holder,
from which it passes at intervals as required into the expansion cylinder,

page_text: in which it expands and by its action on the piston of the said cylinder
it works the air pump, compressing therein a volume of air nearly equal
to its own volume, and forcing the said compressed air into the reservoir
herein-before described. The power thus exerted by the compressed air
during its expansion effectually deprives it of its remaining caloric, and
the cold expanded air thus produced is then discharged into the
refrigerating chamber or apparatus for use.