IMPROVEMENTS IN SAFETY VALVES
Year: 1876

page_text: LETTERS PATENT to Alexander Turnbull, of Glasgow, in the County of Lanark,
North Britain, Engineer, for the Invention of "IMPROVEMENTS IN SAFETY
VALVES."
Sealed the 27th February 1877, and dated the 18th October 1876.
PROVISIONAL SPECIFICATION left by the said Alexander Turnbull at the
Office of the Commissioners of Patents on the 18th October 1876.
ALEXANDER TURNBULL, of Glasgow, in the County of Lanark, North Britain,
Engineer. "IMPROVEMENTS IN SAFETY VALVES."
This Invention, which relates to improvements in safety valves, has for its object
to enable such valves when lifted to be acted upon by a greater pressure than that
due to the steam in the immediate region of the escape. This object may be carried
out in different ways.
According to the first modification the improved safety valve is formed with a
long stem of small diameter at the upper part, which carries at its lower end a disc
having an area about equal to or greater than the area of the valve itself, the
arrangement being such that the stem connects the safety valve and disc rigidly
together. The effect of this arrangement is that the pressures on the upper side of
the disc and the under side of the safety valve being equal and opposite, and
therefore in equilibrium, the effectual area for lifting the valve when the areas of
the valve and disc are equal is that of the under side of the disc, but when the area
of the disc is less than the area of the valve, then the supporting or lifting area so
soon as the valve is opened is less than that due to the area of the valve itself.
The two preceding arrangements apply to safety valves loaded with dead weights,
but when loaded with a spring an intermediate disc of an area greater than the area
of the valve and near the escaping orifice is applied to the rigid stem, the effect of
which is that so soon as the valve is opened, the second disc being situated in the
region of diminished pressure, a greater difference of effective pressure acting upon
the under side of the bottom disc, which is also equal in area to the upper disc, and
therefore greater than the area of the valve, becomes available for lifting the valve
in opposition to the increasing tension of the spring in proportion to the extent of
the rising of the valve.

page_text: In lieu of placing a second disc on the spindle as now last described, the second
disc and the bottom disc may be substituted by a cylindrical or prismatic body of
equal area throughout. These two discs or prismatic body may be applied to the
valve without a guide, or a guide tube suspended from the valve seat or otherwise
rigidly supported may be used.
In place of connecting the safety valve rigidly to the discs or prismatic body, as
herein-before described, it may be connected thereto loosely, that is to say, with a
small amount of vertical play, so that in the event of the discs, cylindrical body, or
prism sticking in the guide tube, the valve may act independently of the discs,
cylindrical body, or prism, that is to say, after the manner of an ordinary safety
valve.
Under a second arrangement the valve consists of a short hollow cylinder, the
lower part of which rests on the valve seat. From the valve seat there passes down
into the lower part of the boiler a tube whose upper part rises above the valve seat,
and upon which a flanch is provided for supporting a loose piston free to work
either upon the interior of the hollow cylindrical valve or upon the central pro-
jecting part of the tube. The area of the hollow cylindrical valve may be equal to
that of the steam orifice or valve seat, and in the case of spring loaded safety valves
it is preferably larger. The action of this valve is as follows:-So soon as the valve
is lifted, the pressure in the neighbourhood of the escaping orifice being diminished,
and the full pressure acting up through the tube from the lower part of the boiler
upon the upper side of the piston is effected during all the time the valve is open
for lifting it.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Alexander Turnbull in the Great Seal Patent Office on the 5th
March 1877.
ALEXANDER TURNBULL, of Glasgow, in the County of Lanark, North Britain,
Engineer. "IMPROVEMENTS IN SAFETY VALVES."
My said Invention has for its object to construct a safety valve so that when it
opens in consequence of the steam or other fluid in the boiler or pipe, or other
apparatus to which it is applied being in excess of that to which it is loaded, the
action of the steam or fluid in escaping shall not diminish the effect of the steam in
opening the valve or keeping it open to its full capacity as long as the internal
pressure continues in such excess.
My improved safety valves may be loaded in any of the ways in which existing
safety valves are loaded, and when loaded by springs they can be proportioned so
as to compensate for the increasing pressure of the springs as they become strained
by the opening of the valves.
My improved safety safety valve will open freely so as to give a peripheral discharge
area equal to the total area for the passage of the steam or other fluid through the
seat of the valve, and as this exceeds the effective discharge area of ordinary safety
valves it follows that my improved valve may for a given discharge be made cor-
respondingly smaller than ordinary safety valves.
My Invention consists in part in making the valve in the form of an inverted
cup or hollow cylinder, and in some modifications the lifting pressure acting on it is
maintained by the centre of the column of steam or fluid rushing upwards or out-
wards, and is not affected by the reduction of pressure in the immediate vicinity of
the escape.
In other modifications the pressure bearing up the valve acts on a
surface situated below the region of the diminution of pressure due to the escape of
the steam.
And in order that my said Invention and the manner of performing the same
may be properly understood, I hereunto append a Sheet of explanatory Drawings

page_text: to be herein-after referred to, and representing various modifications of my improved
safety valves. In these Drawings the same reference numerals are used to mark
the same or like parts wherever they are repeated.
Figures 1 and 2 are respectively a plan and a vertical section of one modification
of my improved safety valves. In this example the valve seat 3 is fitted into a
hole in the bottom part 4 of a casting 4, 5, 6, which can be fixed to a boiler, or pipe,
or other apparatus containing steam or fluid, the pressure of which is to be limited
by means of the valve; this casting is in the form of a circular base 4, connected
by pillars 5 to an upper annular part 6, which last is bored to act as a guide for the
valve 7; this valve 7 is a hollow cylinder, the upper end of which is closed by or
terminates in a cup 8 to receive the bottom of a helical steel spring 9. The spring 9
is held down by an upper plate 10, fixed by screw nuts on the upper ends of rods 11
screwed into the casting 4, 5, 6. The bottom end of the valve 7 is contracted, so
that the annular part, which bears on the seat 3, may be slightly less in diameter
than the interior of the valve. The contact surfaces of the seat 3 and valve 7 are
shown flat, but they may be conical or spherical. The valve seat 3 has attached to it
by radial feathers a central tube 12, which projects up into the hollow valve 7, and
has a collar formed on it near its upper end. An annular block 13 rests loosely on
the collar on the central tube 12, and serves to check the communication between
the upper part of the hollow valve 7 and the lower part thereof near the outlet ;
this block 13, whilst nearly as large in diameter as the interior of the hollow
valve 7, is not in any sense a close fitting piston, whould be liable to stick and get
out of order, besides it is not at all necessary for the action of the valve that it
should fit like a piston. On the other hand, should the block 13 under any circum-
stances ever tend to move up or outwards with the hollow valve 7, it would be
quite free to do so, as it is not fixed to the central tube 12. With the spring 9, applied
as shown in Figure 2, its pressure down on the valve 7 will be greater the higher
the valve is lifted, owing to its being thereby more compressed; this increased
pressure of the spring will however be compensated for by action due to the interior
of the valve 7, being larger in diameter than the inner edge of the contact surfaces
of the valve and seat. When the valve is shut the excess of pressure over that cor-
responding to the effective area of the seat, and acting inside the valve on its upper
end, will be balanced by the downward pressure on the inside of the contraction 14
at the bottom of the valve; but when the valve is opened the pressure downwards
on the contraction 14 will be diminished in consequence of the vicinity of the con-
traction to the outlet, whilst the full pressure, or at least a greater pressure than
that acting on the contraction 14 will be maintained against the upper end of the
valve, and will continue to bear up the valve against the increased pressure of the
spring.
When the valve is loaded by a dead weight or by any known arrangement of
weights or springs applying a uniform pressure to the valve in any of its positions,
it may be made without the contraction 14. In other wo. ds, it may be made with
an internal diameter about the same as that of the effective area of the valve seat.
The annular block 13 and the central tube 12 are not absolutely essential to the
practical efficiency of my improved safety valve, as it may be proportioned so that
it will act in the desired manner without the annular block 13, and even without
the central tube 12. The central tube 12 serves to separate the centre of the column
of steam from the outer parts of that column, which latter parts rush towards the
outlet when the valve opens, and become diminished in pressure; and to make such
separation more certain and complete, the tube 12 may be continued downwards to
any reasonable extent. On the other hand, a greater pressure will be maintained
in the centre of the column of steam when the valve is open than at the outer parts,
even without any separating tube 12, and if without that tube the pressure of the
centre of the column of steam is not sufficient on a certain internal area of the
valve 7, that internal area has simply to be made a little larger.
When the central tube 12 is used without the annular block 13 it may be
attached to the valve 7 instead of to the valve seat 3; or the tube 12 and annular

page_text: block 13 may be in one piece or attached together, the bottom of the tube being
then separate from the valve seat 3, but resting on catches attached to that seat.
Figure 3 is a vertical section of a safety valve embodying some of the modifi-
cations herein-before referred to and comprised in my Invention. This valve is well
suited for a marine boiler, although not exclusively so. The valve seat 3 is fitted
in the bottom of a casing 19 formed with a flanged outlet 20 for the attachment of
an escape pipe, and having fixed on the top of it a cylinder 21 enclosing the
spring 9. The upper plate 10, which confines the spring 9, is screwed into the
upper part of the cylinder 21, and a cap 22 covers the upper part. The valve 7 is
formed with a spindle 23 projecting up a central cavity in the cap, and a key 24 is
entered through slots in the cap and in the spindle. The key 24 may be secured by
a padlock, and serves the purpose of securing the parts so as to prevent tampering
with the spring, and at the same time of connecting the valve 7 with the cap 22, so
that by means of handles formed on the cap the valve can be turned on its seat,
whilst it can be eased by means of a forked lever 25 acting on the bottom edges of
the cap. The valve 7 is in this example guided by a bush 26, which may be of
brass, and which is fitted into a conical seat formed for it in the upper part of the
casing 19. The bush 26 is formed with three or other number of guide surfaces
fitted so that the valve works freely on them, and it is held down in its seat by
light springs, so that it can rise with the valve if from any tendency to stick the
valve does not move quite freely through it. This guide bush 26 serves to prevent
the access of steam to the spring 9.
Figure 4 is a vertical section of a modification of my improved safety valves as
loaded with a dead weight 27, the weight being arranged in a pendulous manner as
is done with some existing valves of the ordinary kind. The valve seat 3 is fitted
in the upper end of a vertical pipe 28, and the contact surfaces of the seat 3 and
valve 7 are made spherical to allow of the pendulous action of the weight 27, and to
admit of guides being dispensed with.
I prefer to have the opening in the valve seat in the common circular form, but
my improved cup-like or hollow chambered valve may be modified in shape to suit
any form of opening that may be found usable in practice.
Figure 5 is a vertical section of a modification of my improved safety valves, in
which the pressure bearing up the valve acts on a surface situated below the region
of diminution of pressure due to the escape of the steam. In this example the
valve 7 is by preference made in the form of an inverted cup or hollow cylinder,
having its upper end closed, as in the first modification; it may however be of the
ordinary form. The valve seat 3 is made with a tube or shell 15 extending down
from it into the boiler, and within this shell and extending down some distance
beneath its lower end there is a cylinder 16, having a closed bottom end 17 of about
the same area as that bounded by the inner edge of the contact surfaces of the
valve 7 and seat 3; this cylinder 16 is attached to the valve 7 by a rod 18, or it
may be made in the same piece as the valve. The bottom 17 of the cylinder 16 is
acted on by the full boiler pressure even when the valve is open, and is unaffected
by the diminution of pressure in the vicinity of the outlet. Whatever diminution
takes place (from the valve being opened) in the pressure of the steam acting imme-
diately on the valve 7 also affects the top of the cylinder 16 and thereby counteracts
the effect of the diminution on the valve, so that an internal pressure that will open
the valve will keep it open until the pressure below the cylinder bottom 17, or, in
other words, the general boiler pressure, becomes lower than that for which the
valve is loaded. I prefer to make the top of the cylinder 16 open, as shewn, in
order that the current of steam rushing towards the outlet when the valve is open
may induce the exit of some steam from within the cylinder, and thus reduce the
downward pressure that in the cylinder is opposed to the upward pressure acting
against the bottom 17 of it. A small hole is provided at the bottom of the
cylinder 16 for the exit of any water that may get into it.
In the case of a spring loaded valve it will be advantageous to make the
bylinder 16 a little larger in area than that bounded by the inner edge of the

page_text: contact surfaces of the valve 7 and seat 3, in order that there may be a little extra
upward pressure when the valve opens to compensate for the increased force of the
spring.
Having thus particularly described my said Invention, and the manner of per-
forming the same, I have to state that I do not restrict myself to the precise details
herein described or delineated, but that what I believe to be novel and original, and
claim as the Invention secured to me by the herein-before in part recited Letters
Patent is,
1. The safety valve (7) in the form of an inverted cup or hollow vessel, the
central tube (12), and the annular block (13), all combined substantially in the
manner and for the purposes herein-before set forth.
2. The safety valve (7) in the form of an inverted cup or hollow vessel com-
bined with the central tube (12), substantially as and for the purposes herein-before
set forth.
3. The safety valve (7) made in the form of an inverted cup or hollow vessel with
or without a contraction at the bottom, substantially as and for the purposes hercin-
before set forth.
4. The cylinder (16) attached to the safety valve (7) with its bottom end down
away from the region of escaping steam, substantially as and for the purposes
herein-before set forth.
5. The cylinder (16) attached to the safety valve (7), and made with its upper
end open, substantially as and for the purposes herein-before set forth.
In witness whereof, I, the said Alexander Turnbull, have hereunto set my
hand and seal, this Third day of March, in the year of our Lord One
thousand eight hundred and seventy-seven.
ALEXANDER TURNBULL. (LS.)