IMPROVEMENTS IN SAFETY VALVES
Year: 1878

page_text: LETTERS PATENT to Robert Gill, of Sidcup, in the County of Kent, for the In-
vention of "IMPROVEMENTS IN SAFETY VALVES,"
PROVISIONAL SPECIFICATION left by the said Robert Gill at the Office of
the Commissioners of Patents on the 14th August 1878.
ROBERT GILL, of Sidcup, in the County of Kent. "IMPROVEMENTS IN SAFETY
VALVES."
The lift of a common safety valve acted on by steam pressure is known practi-
cally to be very limited, and the chief object of my improvements is to extend its
range, so as to increase the efficiency of the valve, and thus allow a reduction of its
size.
Experiment shews that steam, particularly at high pressure, rushing out from
under a safety valve of ordinary construction loses rapidly the power of supporting
the valve as its lift increases; but in endeavouring to improve the safety valve it
does not seem to have been considered that while the upward pressure of the
escaping steam on the valve diminishes as its lift increases, the downward pressure
of the same steam on the vessel from which it is escaping remains constant, on the
principal known as re-action, exemplified in the flight of a rocket, or the motion of
a steam turbine or Barker's mill. Thus a boiler discharging steam upwards through
a valve full open, or without any valve at all over the aperture, is pressed down-
wards with a force equal to the statical pressure, of the steam on an area equal to
that aperture; and my improvements are based on the application of this power of
re-action in the escaping steam to increase the lift of safety valves, not by utilizing
its reduced pressure after it has passed the valve proper, but by using the re-active
power directly on the valve itself, as described in what follows:-A valve like an
inverted cup, preferably a short cylinder closed above, rests on a solid seat, on which
its lower edge fits steam-tight. Steam is admitted under it through a lateral nozzle
projecting from its upper end and jointed to a flexible or hinged pipe communi-
Din's

page_text: cating with the boiler. Like safety valves generally, this valve begins to rise when
the steam pressure exceeds the load, but in rising it does not loose support like an
ordinary valve, as the steam rushing out of the cup affords an efficient fulcrum
to the mass of steam inside, and with a slight increase of pressure the valve
opens to its full area, or to that of the pipe which admits the steam if this is
smaller.
In another arrangement steam is admitted under the cup valve through a short
vertical tube fixed centrally in the seat, forming a free passage from the boiler to
the upper part of the cup, which is guided by feathers on the tube. The annular
space between this tube and the cup forms the outlet passage for the escaping steam,
and its area is rather smaller than the inlet passage through the tube. When the
valve opens the steam rushing downwards through the annular passage to the
aperture of efflux furnishes a fulcrum to the general mass of steam under the valve,
which thus, with a small increase of pressure, opens to the full area of the annular
passage. This opening however with the most efficient proportions is only about
half the area of the valve.
With a modification of the preceeding arrangement a useful opening equal to the
whole area of the valve is obtained by making the aperture in the seat of the full
diameter of the valve, and fixing by wings or some equivalent in its centre a
vertical tube, as described, of the preceeding arrangement, but leaving an open
passage round it, and projecting downwards somewhat below the seat. Here the
valve rises, and is supported as in the preceding case, but the discharge is approxi-
mately doubled, as the steam is free to escape also through the annular opening in
_ the seat round the central tube.

page_text: the said Robert Gill in the Great Seal Patent Office on the 13th February
1879.
ROBERT GILL, of Sidcup, in the County of Kent. "IMPROVEMENTS IN SAFETY
VALVES."
The lift of a common safety valve acted on by steam pressure is known practi-
cally to be very limited, and the object of my improvements is to extend its
range, so as to increase the efficiency of the valve, and thus allow a reduction of its
size.
Experiment shows that steam, particularly at high pressures, rushing out from
under a safety valve of ordinary construction loses rapidly the power of supporting
the valve as the lift increases, and various means have been used to effect a larger
opening of the valve.
In some cases the escaping steam meets in its outward passage to the atmosphere
an external lip or appendage attached to the valve and of larger area, on which it
acts at a reduced pressure, and thus assists in raising the valve.
In other cases the valve is lifted by the quiet statical pressure in the boiler acting
by means of a cylinder and piston independent of the escaping steam; but in
attempting to improve the safety valve it does not seem to have been considered
that while the upward pressure of the escaping steam diminishes on a common
valve as its lift increases, the downward pressure of the same steam on the vessel
from which it is escaping continues constant, or nearly so, on the principle known
as re-action, exemplified in the flight of a rocket, or the motion of a steam turbine
or Barker's mill. Thus a boiler discharging steain upwards through a valve full
open, or without any valve at all, over the aperture of efflux, is pressed downwards
with a force equal to the statical pressure of the steam on an area equal to that
aperture; and my improvements are based on the direct application of this power
of re-action in the escaping steam to the lift of safety valves, as will be explained
in what follows:-The valve A, Figure 1 of the accompanying Sheet of Drawings,
is an inverted cup, preferably a short cylinder closed above, its lower edge fitting
steam-tight on the solid seat B on which it rests. Steam is admitted under it
through a lateral nozzle projecting from its upper end, and jointed to a flexible or
hinged tube C communicating with the boiler. This valve begins to lift as soon as
the regulated load which holds it down is exceeded by the steam pressure, and as in
this arrangement the cup A represents the boiler as a steam vessel, but moveable,
while the solid seat represents the common valve, but fixed and inverted, the
pressure on the seat diminishes as the escape aperture widens, just as the pressure
under a common valve diminishes with the increase of its lift; but at the same
time the upward pressure of the steam on the cup valve A from which it is escaping
remains constant, or nearly so, and the valve continues to rise with a small increase
of pressure until its opening is equal to the passage which admits the steam.
This form of valve is shown chiefly as an illustration of the manner in which a
valve lifts beyond the usual limits by re-action, but with the tube C of thin elastic
metal properly shaped and proportioned, and the seat B supported on a swivel joint
and adjustable, the arrangement is practical, the natural spring of the tube C forming
the load or part of the load on the valve.
In the construction shown by Figure 2 in sectional elevation the steam is admitted
under the valve A through a short vertical tube C fixed centrally in the seat B, and
forming a free passage between the boiler and the upper part of the cup, which is
guided by feathers projecting from the tube or by other equivalent arrangement.
The annular space between the cup and the tube C forms the outlet passage for the
escaping steam, and its area is preferably rather smaller than the inlet passage
through the tube. This valve, like safety valves in general, begins to rise as soon
as the steam pressure exceeds the load; but, unlike the common valve, it does not

page_text: lose the initial support of the steam as it rises, because on the principle of re-action
the steam which is escaping downwards to the orifice of efflux affords a fulcrum to the
general mass of steam under the valve, causing it to be efficiently supported, and it
would still be thus supported even if the obstacle of the seat were removed altogether,
and the annular passage of efflux were perfectly free, in which circumstance the
statical pressure of the steam on the roof of the cup valve would cease altogether,
but would be replaced by an equal upward pressure, occasioned by the impact of the
outrushing steam, and by its re-action consequent upon the downward direction
given to it by the valve. With a slight increase of pressure the valve thus opens
to the full area of the annular outlet passage, which however in this arrangement is
limited to about half the area of the valve, i.e., to the area of the inlet tube C.
With the arrangement shown by Figure 3 in sectional elevation a useful opening
is obtained equal or nearly equal to the whole area of the valve. The central aper-
ture in the seat B is of the full diameter of the valve, and in its centre stands the
tube C firmly attached to the seat by the wings D. This tube extends downwards
somewhat below the seat and upwards into the cup, which is guided by the
spindle E and pivot on the lever G. When this valve rises things are in the same
condition as described of Figure 2, the valve being equally supported, but rising
higher with a slight increase of pressure the discharge is approximately doubled, as
the steam is free to escape also through the annular opening in the seat round the
tube C.
In loading the improved safety valve by means of a spring, I prefer to interpose
between the valve and the spring a bent lever so arranged that the motion caused
by the opening of the valve will virtually shorten the arm on which the spring
acts, at the same time that it increases the tension of the spring. Figure 4 shows
one manner of obtaining this effect. The spring balance being attached to a hinge
at its lower extremity will follow at the other the circular path described by the
end of the lever. As the latter rises the tension of the spring increases, but at the
same time the efficient arm of the lever becomes shorter, so that the load upon the
valve may remain constant or diminish, notwithstanding the increase of tension of
the spring.
The peculiarity of the Invention which I claim consists in causing the re-active
power of the steam escaping from a safety valve to raise or assist in raising the
valve beyond the ordinary lift, not by utilizing its reduced pressure after it has
passed the valve proper, but by its direct application to the valve itself, substantially
by the means shown in the foregoing description and the annexed Sheet of
Drawings, without confining myself to the particulars therein specified.
In witness whereof, I, the said Robert Gill, have hereunto set my hand and
seal, this 22d day of January, in the year of our Lord One thousand
eight hundred and seventy-nine.