IMPROVEMENTS IN SAFETY VALVES FOR STEAM BOILERS
Year: 1872

page_text: PROVISIONAL SPECIFICATION left by Edward Thomas Hughes at the
Office of the Commissioners of Patents, with his Petition, on the
31st May 1872.—A communication from abroad by Charles Augustus
Trowbridge, of New York, United States of America.
I, EDWARD THOMAS HUGHES, of the Firm of Hughes and Son, Patent
Agents, 123, Chancery Lane, London, do hereby declare the nature of
the said Invention for "IMPROVEMENTS IN SAFETY VALVES FOR STEAM BOILERS,"
a communication to me from abroad by Charles Augustus Trowbridge, of
New York, United States of America, to be as follows:-
This Invention relates to an improved construction for the escape of
steam from steam boilers when the steam shall have attained a certain
predetermined pressure. In the use of the common safety valve for this
purpose, the object is accomplished only in theory, for it is now a well
established fact that the common valve set at a certain weight will not
be raised to allow the escape of any material quantity of steam until the
pressure below the valve is very much greater than the weight set
upon the valve, and that the relief which is thus afforded being in the

page_text: 33
immediate vicinity of the valve, so soon as the pressure is there relieved
by a slight escape of steam so soon must the valve return to its seat;
and further, that the opening of the valve to allow the escape of steam
will be extremely slight, having been demonstrated under a largely
increased pressure not to exceed ½ of an inch, and this reduced or
closed so soon as the pressure at that point is reduced, hence the valve
although commonly termed a safety valve, can inspire but little re-
liability to such a result, any further than that it acts as a warning or
alarm. To overcome this difficulty and produce an arrangement which
will be reliable as a safety valve is the object of this Invention, and the
first part of the Invention consists in opening or actuating a valve at
one point of a boiler by means of pressure at another point, that is to
say, so that the steam which actuated the valve will not escape at that
point, but will cause an opening at another where the steam will escape,
and so continue until the pressure within the boiler is reduced to the
previously determined point.
"
4 a central section of the second part of this Invention; and
Fig. 5 a longitudinal section of the third part of this Invention.
In Fig. 1A is the boiler, B a chamber opening directly into the
boiler so that steam is always present in the said chamber; in this a
puppet or balance valve a is arranged upon a rod C, so that when these
valves are open steam will there escape and pass out to the atmosphere
through the conductor D or otherwise. At another point in the boiler
I arrange a cylinder E within which is a piston F, this cylinder com-
municating directly with the boiler through a coupling f, so that steam
will be always present in the said cylinder behind the piston maintaining
a pressure upon the piston equal to the pressure in the boiler, or nearly
SO. The other end of the cylinder is open to the atmosphere, so that the
pressure upon the piston tends to force it toward the open end of the
cylinder. The valve rod C is connected directly or indirectly to the said
piston, so that the moving of the said piston toward the open end of the
said cylinder will cause the valve a also to open; therefore when the
pressure upon the piston from the boiler overcomes the resistance placed

page_text: upon the said piston, the piston will move in the cylinder accordingly,
and open the valve a corresponding distance to allow the escape of steam
therefrom.
Resistance is here represented as produced by a weight L hung upon.
a lever P, the tendency of the weight being to hold the valves closed
and the piston against the steam, consequently the weight L adjusted
proportionately to the area of the piston will hold the valve closed until
the pressure on the piston from the boiler exceeds that weight, then the
pressure will cause the piston to move and open the valve and hold
them open until the pressure is reduced to the point indicated by the
adjustment of the weight, then the piston will return closing the valve.
The distance at which this piston is arranged from the valve is immaterial,
and several such pistons may be arranged at different points in the
boiler, so that if the pressure under any circumstance be greater at one
point than another, it would be relieved by the piston at that point.
As thus far described, the arrangement of the piston has been in
connection with the steam chamber or to be actuated directly by the
steam. The same result is obtained by placing the piston below the
water-mark, as denoted in Fig. 2, so that the cylinder will be filled below
the piston with water from the boiler instead of from steam, the result
being quite as satisfactory from water as from direct steam. Again, the
piston may be placed below or at a distance from the boiler but in
communication therewith, as in Fig. 3, so that the water in the boiler
would be cold or a very low temperature, the result in all cases being
the same, that is, the valve at one point will be positively open by means
of the pressure at another point, and remain open until the pressure is
reduced to the defined point.
Instead of a weight, which is here shewn as a means of illustration, a
spring may be employed, so that when the pressure on the piston attains
a certain point its movement will commence and open the valve and
continue increasing the opening of the valve as the pressure on the
piston increases, so that the greater the pressure the greater the opening
of the valves for the escape of steam, and in many cases this arrange-
ment would be preferable to a fixed weight.
The second part or modification of this Invention, which is illustrated
in Fig. 4, consists in a valve arranged in a seat in substantially the usual
manner, constructed with a central projection extending downward into

page_text: the water or very near the surface, the area of the said projection being
a little less than the area of the valve, so that the pressure upon the
water or in the immediate vicinity is exerted upon the lower end of this
projection to raise the valve.
A' represents the shell of a common boiler at the point where the
valve case B¹ is attached; C₁ the valve: D₁ the lever; E' the weight;
all of substantially the common constructing and arrangement, the area
of the valve proportioned to the boiler to which it is to be applied upon
the usual calculation. Upon the under side of the valve I attach or form
a downward projecting cylinder F, the area of the said cylinder in
transverse section being a little less than the area of the valve, so that
when the valve is raised from its seat there will be sufficient space
between this seat and the cylinder for the escape of steam. This pro-
jection I extend, by preference, below the water-line G', hence at the
pressure within the boiler upon the surface of the water is affected
equally even if the pressure upon the boiler be more at one point than
another, therefore it may be relied upon that the upward pressure upon
the lower end of the cylinder will be exerted from the whole extent of
the boiler, hence, so soon as the pressure upon the water has become
greater than that for which the valve is sct, the valve will be raised by
the pressure upon the lower end of the cylinder and held open until the
pressure is removed from the whole boiler, and increasing the pressure
will open the valve to a greater extent, and the valve will not return to
its seat so soon as the pressure is reduced in its immediate vicinity, as in
the case without the cylinder, but will be held open until the pressure
is equally reduced throughout the boiler.
The cylinder may be made hollow or solid; if the latter less weight of
course will be required upon the valve.
While the most satisfactory results are attained by extending the cylinder
below the surface of the water this desired result will be approached
by its extension down to near the surface of the water, I therefore do not
confine myself to submerging the lower end of the cylinder.
While I have termed the downward projection F¹ a cylinder, it is not
intended to confine the form of the projection to that of a cylinder, as it
may be any other form, it only be essential that its area should be a
little less than the valve, sufficient to allow the free escape of steam at
the valve seat.

page_text: Another modification whereby the object of this Invention is accom-
plished is illustrated in Fig. 5. A³ is the boiler; B² an opening over
which the safety valve C³ is arranged resting upon a seat D². From the
valve downward extends a tube E', and this may run down into the
water, as denoted in broken lines, or to some other part of the boiler
above the water-line, as denoted by the tube F2. The valve C³ is con-
nected to this tube by a flexible or elastic device so as to form an
expansive chamber H2 below the valve, and upon the upper side of the
valve a pressure is brought to bear by a spring or weight to the extent
desired for the boiler to carry. In use, the steam or water, as the case
may be, fills the chamber H2 beneath the valve, and so soon as the
pressure within the boiler bears upon the valve greater than the external
pressure, then the valve C³ will rise, the sides of the chamber H2 allowing
it so to do, and permit the escape of steam through the valve opening, a
pressure beneath the valve being maintained by the pressure within the
boiler distant from the opening and uninfluenced by the opening.
It should be observed that the tube E' is firmly or rigidly supported
by a connection with the boiler or case of the valve, so that the operation
of the valve in no way affects the tube E' below the chamber H³.