Iм- PROVEMENTS IN SAFETY VALVES
Year: 1873

page_text: 66
LETTERS PATENT to George Cockburn, of Glasgow, in the County of
Lanark, North Britain, Pattern Maker, for the Invention of “Iм-
PROVEMENTS IN SAFETY VALVES."
'
PROVISIONAL SPECIFICATION left by the said George Cockburn at
the Office of the Commissioners of Patents, with his Petition, on
the 2nd June 1873.
. I, GEORGE COCKBURN, of Glasgow, in the County of Lanark, North
Britain, Pattern Maker, do hereby declare the nature of the said
Invention of "IMPROVEMENTS IN Safety Valves," to be as follows, that is
to say :-
This Invention, which relates to improvements in the arrangement
and construction of safety valves for steam boilers or other apparatus
containing fluids or liquids under pressure, consists of a movable chamber
attached to the valve spindle. Below the chamber a cavity is preferably
formed to confine the steam, and between its circumference and the

page_text: casing in which the valve is contained is an annular space. A series of
openings are formed round the movable chamber so that the steam may
pass into it, and at the upper part of the chamber the valve proper
resting on its valve seat is situated. The areas of the different parts of
the valve are so adjusted that the extent of opening is always regulated
by the difference of pressure of steam in the outer chamber in which
the valve proper is contained, and that on the boiler side of the valve.
Under a modified form of the valve the movable chamber is substi-
tuted by a plate fixed on the lower part of the valve spindle, having an
annular space around it, through which the steam passes, and the outer
chamber is provided with adjustable openings by which to regulate the
escape of steam, and so vary or regulate the pressure. Weights or
springs may be used for loading the valves to any required extent.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said George Cockburn in the Great Seal Patent Office
on the 2nd December 1873.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, GEORGE
COCKBURN, of Glasgow, in the County of Lanark, North Britain, Pattern
Maker, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her:
Letters Patent, bearing date the Second day of June, in the year of
our Lord One thousand eight hundred and seventy-three, in the 36th
year of Her reign, did, for Herself, Her heirs and successors, give
and grant unto me, the said George Cockburn, Her special license that
I, the said George Cockburn, my executors, administrators, and assigns,
or such others as I, the said George Cockburn, my executors, adminis-
trators, or assigns, should at any time agree with, and no others, from
time to time and at all times thereafter during the term therein expressed,
should and lawfully might make, use, exercise, and vend, within the
United Kingdom of Great Britain and Ireland, the Channel Islands, and ;
Isle of Man, an Invention for "IMPROVEMENTS IN SAFETY VALVES," upon
the condition (amongst others) that I, the said George Cockburn, by
an instrument in writing under my hand and seal, should particularly
describe and ascertain the nature of the said Invention, and in what

page_text: manner the same was to be performed, and cause the same to be filed
in the Great Seal Patent Office within six calender months next and
immediately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said George Cockburn, do hereby declare
the nature of my said Invention, and in what manner the same is
to be performed, to be particularly described and ascertained in and
by the following statement, reference being had to the accompanying
Drawings and to the letters and figures marked thereon, that is to
Bay :-
My said Invention relates to improvements in the arrangement and
construction of safety valves for steam boilers or other apparatus con-
taining fluids or liquids under pressure.
And in order that my said Invention may be properly understood I
now proceed more particularly to set forth the system, mode, or manner
in or under which the same is or may be used or practically carried into
effect, that is to say :-
On the Sheet of Drawings hereunto appended Figure 1 is a vertical
section of the improved safety valve constructed in accordance with the
first modification of my Invention, namely, with a movable chamber A
situated below the valve B. Holes C are formed all round the lower
part of the chamber A, as shewn, through which the steam passes to the
interior of the chamber A. Orifices D are formed around the upper
part of the chamber A just below the valve B, through which the steam
escapes when the valve A is raised from its seat. A stop E is provided
at the upper part of the valve spindle by which the extent of spring of
the valve B is fixed. Weights or springs may be applied to the valve
spindle in order to load the valve.
The action of the valve is as follows:-When shut the steam acts
with equal pressure on all parts of the interior and exterior of the
chamber A so that it is in equilibrium, but when the pressure is sufficient
to lift the valve B the valve on being lifted immediately releases the
steam in the chamber A, and thereby breaks the balance or equilibrum
of pressure.
This momentary release allows the steam of full pressure
acting below the chamber A, (whose area is much greater than the area
of the valve), to exert a corresponding preponderating influence to lift
the valve, and thus the valve B is lifted higher than what is due to the
pressure on the under side of the valve B alone, thereby producing a

page_text: corresponding increase in the capability of the valve to relieve the
pressure in the boiler or other vessel to which it is applied. That portion
of the apparatus below the chamber A is shewn in the form of an
inverted cup in Figure 1.
This form is not however essential, as a flat
plate may be used in lieu thereof.
Figure 2 is a vertical section and Figure 3 a horizontal section on the
line b, b, Figure 2, of a "lock up" safety valve constructed in accord-
ance with the second modification of my Invention. A plate or disc A
is secured to the lower part of the safety valve B by means of a nut C,
which is screwed on a thread D formed at the lower part of the valve B.
Between the circumference of the plate or disc A and the lower part of
the chamber E is an annular space x, through which steam passes from
the boiler into the chamber E. The downward load or weight upon the
valve B is exerted by a helical spring F which surrounds the spindle G
of the valve B, and when the pressure of steam or other fluid or liquid
upon the under side of the valve B exceeds the pressure of the spring F,
and the valve begins to rise from its seat, the steam escapes from the
chamber E, and by so doing the pressure of steam within the chamber E
is reduced, that is to say, the pressure on the upper side of the plate or
disc A becomes less than the pressure on the under side thereof. This
sudden reduction of pressure above the disc or plate A momentarily
gives the steam acting on the under side of the disc or plate a prepon-
derating influence to raise the valve B further from its seat, thus
imparting to the valve a greater relieving effect than would be due to it
without the plate or disc A. Stops a are situated on the valve spindle G,
thus limiting the extent of the lift thereof. The periphery of the disc
or plate A is curved or bevelled to a greater or less extent, as indicated
by the dotted lines at Figure 2, so that as the valve is lifted to a greater
or less extent; the difference of pressure above and below the disc or
plate A is variable. A weight.or weights may be employed to exert the
downward pressure on the safety valve, as shewn at A, Figure 4.
Instead of forming the periphery of the disc or plate curved or bevelled,
as shewn at Figures 3 and 4 of the Drawings, the curved or bevelled
surface may be formed in the annular opening surrounding the disc, as
shewn in vertical section at b, Figure 5.
Under another arrangement, shewn in vertical section at Figure 6, the
safety valve A is constructed with the equivalent of the disc or plate,
namely, the projection or flanch B at its upper end, beneath which an

page_text: annular chamber a is formed in the valve casing. Around the periphery
of the flanch or projection an annular opening c is made in the valve
casing, the side of which is curved or bevelled as shewn, or the bevelled
or curved surface may be formed on the periphery of the flanch or pro-
jection B. When the pressure of steam on the under side of the valve A
exceeds the downward pressure of the spring C, and the valve rises from
its seat, the steam escapes into the chamber a, and thence passes out-
wards through the annular space c, and according as the outward passage
of the steam is retarded by a greater or less extent of curvature or bevel
on the side of the space c, or periphery of the flanch or projection B, or
the extent of opening permitted by the position of the flanch B in
relation to the surrounding position of the valve casing, so does the
steam after escaping over the valve seat act upon the under side of the
projection or flanch B, thus enabling the steam to exercise an additional
or preponderating influence in lifting the valve over and above that
which is due to the area of the valve proper.
Figure 7 of the Drawings is a vertical section of a safety valve wherein
the features of the valves herein-before described are combined.
Having now described and particularly ascertained the nature of my
said Invention, and the system, mode, or manner in or under which the
same is or may be used or practically carried into effect, I would observe
in conclusion that what I consider to be novel and original and therefore
claim as the Invention secured to me by the herein-before in part recited
Letters Patent is, the arrangement and construction of safety valves
with a plate or disc, or its equivalent, attached to the under or upper
side, or both, and having a bevelled or curved edge, or with parallel
edges, situated in a curved or bevelled opening or openings in the valve
casing, as herein-before described and shewn on the Sheet of Drawings
hereunto appended.
In witness whereof, I, the said George Cockburn, have hereunto
set my hand and seal, this Twenty-ninth day of November, One
thousand eight hundred and seventy-three.