IMPROVEMENTS IN RAILWAY CARRIAGE ROOF LAMPS
Year: 1879

page_text: LETTERS PATENT to Osgood Gee Pritchard, of Crutchedfriars, in the City of
London, for the Invention of " IMPROVEMENTS IN RAILWAY CARRIAGE ROOF
LAMPS."
Sealed the 18th May 1880, and dated the 9th December 1879.
PROVISIONAL SPECIFICATION left by the said Osgood Gee Pritchard at
the Office of the Commissioners of Patents on the 9th December 1879.
OSGOOD GEE PRITCHARD, of Crutchedfriars, in the City of London.
MENTS IN RAILWAY CARRIAGE ROOF LAMPS."
"IMPROVE-
My Invention relates to an improvement in railway carriage roof lamps having
for its object to enable such lamps to be extinguished and relighted repeatedly
without causing an overflow of the oil into the globe or lantern, or otherwise
affecting the supply of oil to the burner.
Experience has shown that when such lamps are first lighted, the oil reservoir
being full, the supply of oil to the wick or burner may, if the lamp be of proper
construction, be made to correspond exactly to the rate of consumption by the
flame, the gravity of the oil being balanced by the atmospheric pressure. No
overflow of the oil therefore occurs, provided that the lamp is kept burning
continuously, but if the lamp be extinguished and relighted after a time it is found
that the conditions are entirely different, the result of which is an excessive supply
of oil to the wick or burner, and consequently an overflow of oil into the globe or
lantern, due probably to the expansion by heat of the air drawn into the oil
reservoir on cooling.
My Invention consists in a means of ensuring that the oil chamber from which
the wick is fed shall always be quite filled when the lamp is first lighted, so that
the conditions necessary to ensure the proper working of the lamp and avoid
overflow shall always be fulfilled.
According to my Invention the oil chamber is filled from a reserve of oil at a
higher level than that in the chamber each time the lamp is lighted, the oil
chamber being then closed liquid and air tight, with the exception of course of the
tube by which oil is conveyed to the wick tube.
One way of carrying my Invention out in practice is to divide the oil reservoir
of the lamp as at present constructed into two chambers by a horizontal

page_text: partition having an opening in it provided with a screw down or other cap, plug,
or valve by which it is closed liquid and air tight. The wick would be fed in the
usual way from the lower chamber, which would be only large enough to contain
oil for a consumption of say 2 hours or any period for which the lamp is required
to burn continuously. This lower chamber would be filled from the upper and
larger chamber or reservoir whenever the lamp is lighted by opening the cap, plug,
or valve by means of a handle or key rising through and above the top of the
upper chamber or reservoir. The outlet of the oil tube from the lower chamber
may also be provided with a small valve so arranged in connection with the cap,
plug, or valve that when the latter is opened the former will be closed to prevent
the oil flowing to the wick whilst the lower chamber is being filled and opened
when the cap, plug, or valve is closed.
Instead of being operated by a handle or key the plug or valve by which the
aperturo connecting the two chambers is closed might be operated by a cam, lever,
or other mechanical movement in connection with the hinged cover of the lamp so
as to be opened by the act of raising the lid to light the lamp, and closed by the
act of shutting it down.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Osgood Gee Pritchard in the Great Seal Patent Office on the
9th June 1880.
OSGOOD GEE PRITCHARD, of Crutchedfriars, in the City of London. " IMPROVE-
MENTS IN RAILWAY CARRIAGE ROOF LAMPS."
My Invention has for its object to enable railway carriage roof lamps to be
extinguished and relighted repeatedly without causing an overflow of the oil from
the wick tubo or burner into the glass globe or bowl at the second or subsequent
time of lighting.
Experience has shown that in railway carriage roof lamps as ordinarily con-
structed during the burning which immediately follows the first lighting after the
oil chamber has been filled with oil, the flow of oil to the wick or burner corre-
sponds (if the lamp be properly constructed) to the rate of consumption by the
flame, as the gravity of the column of oil, plus the pressure of the heated and
rarefied air entering the oil chamber to replace the oil consumed is constantly
balanced by the atmospheric pressure at the burner. Therefore usually no overflow
of the oil occurs provided the lamp is kept burning continuously, but if after
burning some time the flame be extinguished, and there be a relighting after the
oil chamber has become cool, an excessive supply of oil to the burner occurs, due
probably to the presence and expansion in the oil chamber above the oil, of an
additional quantity of air that has entered in an unexpanded state during the
contraction by cooling of the air that was present in an expanded state whilst the
lamp remained alight.

page_text: My Invention relates to means whereby the oil chamber from which the wick is
fed, may be readily and completely refilled with oil prior to each relighting of the
lamp, so that overflow may be avoided. According to my Invention a reserve of
oil is provided at a higher level than, and in connection with the oil chamber from
which the wick or burner is fed, so that the oil chamber may be refilled therefrom
each time the lamp is to be relighted, all communication between the oil
chamber and the reserve of oil being cut off except during the act of refilling the
oil chamber.
My Invention may be conveniently carried out in practice by dividing the oil
reservoir of the lamp as at present usually constructed into two chambers, an upper
and a lower one, by a horizontal partition having an opening, which is closed fluid
tight by a valve or its equivalent at all times except whilst the lower chamber is
being refilled. The wick or burner is fed in the usual way from the lower chamber,
which need be only large enough to contain oil for a consumption of say two hours,
or the longest period for which the lamp is usually required to burn continuously.
This lower chamber is to be completely refilled with oil from the upper chainber
or reservoir (which may be larger than the lower one) whenever the lamp is to be
relighted by opening the valve, and so putting the two chambers temporarily into
communication. Air contained in the lower chamber is displaced by the inflowing
oil, and rises into the upper chamber. The oil tube conveying oil from the lower
chamber to the wick or burner is also provided with a small valve, so arranged in
connection with the valve above mentioned that so long as the one valve is kept
closed the other will remain open, and when the communication between the upper
and lower chambers has been opened to refill the lower chamber the passage or
way leading from the lower chamber to the wick tube or burner will be closed to
temporarily stop the flow of oil to the wick, and prevent any overflow occurring
by the access of the atmospheric pressure to the lower chamber whilst it is being
refilled. These valves may be connected, and might be raised by hand or by a
spring, and pressed down by a screw, can, lever, or other mechanical contrivance
operated by hand, or they might be acted on by the hinged cover of the lamp, so
that the communication between the two chambers will be established by the act
of raising the cover, and cut off by the act of shutting it down.
In order that the Invention may be more readily understood I have illustrated
one example of the way it may be carried out in practice in the accompanying
Drawings, in which Figure 1 represents a vertical section of a railway carriage
roof lamp showing the valves in their normal position; Figure 2 is a part vertical
section of the same with the lid of the lantern thrown back, and the valves raised ;
Figure 3 is a similar section showing the valves pressed down by the lid. The
same letters of reference indicate the same parts in all the Figures.
A is the oil reservoir situated above the level of the burner as usual and of the
ordinary annular construction, but divided into two chambers a, b, one above the
other, by a horizontal partition c. Instead of these two chambers being contained
in the same box, and merely separated by a partition, it will be evident that the same
result will be obtained if they are made quite separate and placed the one above
the other, and connected by a pipe, in which case the valve which I will now
describe would be placed in the said pipe, or over the orifice thereof, in the upper
reservoir. Such an arrangement is therefore comprised in my Invention, but the
construction shown in the Drawings is the most compact, and is therefore
preferred.
d is a conical or bonnet valve opening upwards, and fitted in a corresponding
conical seat e, fixed either directly in the horizontal partition c or in a vertical
tube of a diameter to fit between the inner and outer walls of the annular
reservoir, said tube passing through and being soldered in a corresponding opening
in the partition c. The tube has perforations g in its sides, above and below the
valve seat e, by which the upper and lower chambers communicate freely with the
interior of the tube. The valve d is carried on a spindle h, working in guides i at
top and bottom, fixed in the tube f. The top of the tube frises through the top of

page_text: the upper chamber a, and is screwthreaded to receive a screw cap k, which may be
lined with a washer or pad of leather to ensure a tight joint and prevent any oil
oozing out when the upper reservoir is filled quite full, and the oil expands by the
heat. The valve spindle h is preferably of such a height that its top end is pressed
upon by the soft pad within the screw cap k, so that when the latter is screwed
down the valve d will be forced down tightly into its seat c, thus cutting off all
communication between the upper and lower chambers a, b. B is the tube by which
cil is conveyed from the lower chamber b to the burner C; D is the usual chimney,
and E the reflector; F is the outer case or lantern; G, the glass globe or bowl;
and H, the hinged lid or cover, all constructed as usual. The valve spindle h is
prolonged downwards, and upon its lower end is fixed another smaller conical
valve ĭ, opening downwards within the tube B. This valve 7 fits in a seat m in
the tube B when raised to temporarily stop the flow of oil to the burner whilst
the lower chamber is being filled. When the lamp is to be relighted after it has
been already in use, and a portion of oil in the lower chamber b has been
consumed, this chamber is refilled from the upper chamber a by merely unscrewing
cap k and raising the valve spindle, or allowing it to rise so as to open valve d and
close valve . A spiral spring n may be applied on spindle so as to raise valve d
and close valve immediately the screw cap k is removed. If the valve d is to be
kept close by the weight of the lid or cover of the lantern, as shown in
Figure 3, the valve rod h must pass through a hole in the screw cap k and be
pressed down by a spring p, fixed to the cover H. In this case the spiral spring n
is necessary to open the valve & when the cover is raised.
Having described the nature of the said Invention, and explained in what manner
it is to be performed or carried into practical effect, I would have it understood
that I do not claim generally a lamp with two oil chambers, or the arranging two
valves on one stem or spindle in a lamp, but what I consider to be novel and
original, and therefore claim as the Invention secured to me under the Letters
Patent hereinbefore in part recited is,-
1st. The combination of parts forming the improved lamp, constructed, arranged,
and operating as herein before described and shown in the accompanying Drawings,
Figures 1 and 2.
2nd. Combining with the oil chamber that communicates directly with and is
arranged above the level of the wick tube or burner, a reservoir of oil connected
with that oil chamber in such manner that it may (without causing overflow at
the wick tube or burner) be completely filled with oil from the reservoir, thus
expelling air and obviating overflow at the wick tube or burner during the
subsequent burning, substantially as hereinbefore described.
In witness whereof, I, the said Osgood Gee Pritchard, have hereunto set my
hand and seal, this Eighth day of June, in the year of our Lord One
thousand eight hundred and eighty.