IMPROVEMENTS IN REGULATING APPARATUS FOR AIR REFRIGERATING MACHINES
Year: 1881

page_text: LETTERS PATENT to Thomas Bell Lightfoot, of the Dartford Iron Works,
Deptford, in the County of Kent, for an Invention of "IMPROVEMENTS IN
REGULATING APPARATUS FOR AIR REFRIGERATING MACHINES."
(Void by reason of the Patentee having neglected to file a Specification in
pursuance of the conditions of the Letters Patent.)
PROVISIONAL SPECIFICATION left by Thomas Bell Lightfoot at the Office
of the Commissioners of Patents on the 11th April 1881.
THOMAS BELL LIGHTFOOT, of the Dartford Iron works, Dartford, in the County
"IMPROVEMENTS IN REGULATING APPARATUS FOR AIR REFRIGERATING
of Kent.
MACHINES."
My Invention relates to regulating apparatus for machines in which air is
refrigerated by compressing it, cooling it, and then permitting it to expand while
performing work. In such machines the air heated by compression is usually
cooled by bringing it in contact with water, or with tubes or other extended
surfaces which are cooled by circulation of water, but as the temperature of the
water so employed, and consequently of the air cooled by it, is subject to considerable
variation, it is necessary to vary the extent to which the cooled air is expanded,
in order to obtain an approximately uniform temperature of the air after expansion.
The object of my Invention is to render the regulation of the expansion automatic,
which I effect in the following manner :-I place in contact with the cooling water
or with the cooled compressed air a thermometric instrument which may be of any
known kind in which movement is produced by change of temperature. It may,
for example, be a vessel containing liquid with a flexible diaphragm, as in an
aneroid barometer, or it may be a bent pipe, as in Bourdon gauge, or it may be a
bent bar or set of bent bars consisting of two metals that have different degrees of
expansion. The moving part of the thermometric instrument is connected through
a differential lever to the slide of a subsidiary cylinder fitted with a piston, which
according as the slide is moved in the one direction or the other is subjected to the
Dine 211

page_text: pressure of the compressed air on the one or the other of its sides, and so caused to
move in the one or the other direction. The piston rod has a rack gearing with a
pinion on the rod of an expansion slide which is fitted on the back of the main
slide of the cylinder in which the compressed air expands. This slide rod has on
it a screw thread working in a nut on the expansion slide, so that according as the
rod is turned in the one direction or the other, the expansion slide is moved length-
wise over the main slide, so as to cut off sooner or later the admission of the
compressed air to the cylinder in which it has to expand. The piston rod of the
subsidiary cylinder is connected to the differential lever of its own slide, so that
when that slide is moved from its middle position by the action of the thermometric
instrument, and the subsidiary piston moves in obedience to the pressure thus
brought to act upon it, this movement of the piston transmitted through the
differential lever causes the slide to return to its middle position, and the piston
consequently remains in the position to which it had been moved. Thus a change
of temperature of the cooling water, or of the air cooled by it, by causing move-
ment of the thermometric instrument shifts the subsidiary slide, and the subsidiary
piston being thus caused to move its rack giving revolution to the rod of the
expansion slide, shifts that slide, so as to cut off the supply of air to be expanded at
an earlier or later period of the stroke, and the expansion of the air being thus
varied in accordance with the cooling temperature, the temperature of the air after
expansion is rendered constant or nearly so. The regulator above described is
applicable generally to air refrigerating machines of the kind referred to. It is
also applicable to refrigerating machines constructed and operating as described in
the Specification to Letters Patent granted to me on the 6th October 1880,
No. 4065, in which the cooled compressed air is expanded by successive stages, the
regulator being in this case applied to govern the cut off for the first stage of
expansion which is intended to effect only such an amount of cooling as to cause
deposit of moisture from the air in liquid form without freezing it.