IMPROVEMENTS IN SAFETY VALVE APPARATUS
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by Arthur William Lovell Reddie at
the Office of the Commissioners of Patents on the 12th September 1882.
ARTHUR WILLIAM LOVELL REDDIE of the Office for Patents 66 Chancery Lane
in the County of Middlesex, Patent Agent, "IMPROVEMENTS IN SAFETY VALVE
APPARATUS
11
This invention relates to the employment of hydraulic pressure for closing safety
valves, the object in view being to ensure their perfect tightness their operation and
their gradual complete opening and also to render them insensible to the vibrations
or variable waves of motion to which fixed and movable boilers are subject.
The invention is well adapted to the safety valves of marine engine boilers which
are liable to sudden alterations of pressure as the vessel pitches or rolls, but it may
be easily adapted to safety valves of any ordinary description.
In carrying out the invention the safety valve is held to its seat by a solid piston
or plunger moving freely but water tight within a cylindrical box or casing, the
space within the said box and above the said piston being filled with water. This
water chamber communicates by a small channel or duct with a central passage
in the top of a smaller chamber also filled with water, situate preferably above the
larger one.
The water in the upper chamber is in permanent communication with the water
in the boiler, preferably taken from the lower part of the water level gauge tube.
Fitted centrally within the small water chamber is a plunger of bronze, or other
suitable metal, carefully gauged to move freely but water tight in a vertical direction
within the said water chamber, its vertical movements being restricted by suitable
collars or stops. The upper part of this plunger passes through a hollow plug or
casting screwed into and forming the top of the small water chamber. This hollow
plug or casting is in connection with the outer air, and the lower part thereof
which is screwed into the small water chamber is grooved on a level with the
channel or duct, above referred to as serving to connect the smaller water chamber
with the larger one. Radial holes in the lower part of the hollow plug connect the
groove around it with the vertical cylindrical passage in the plug through which
the plunger works. The lower part of the plunger is filed away in such a manner
that when it rises communication is established between the channel leading from
Dion 971

page_text: the large water chamber, and the hollow part of the plug in connection with the
outer air.
The upper end of the plunger is loaded to the required extent by a ball or its
equivalent fitting thereon. The plunger remains normally at its lowest position,
and the cut away portions of its stem are partially within the small water chamber,
and connect that chamber with the channel leading to the lower water chamber.
Thus the water in the latter is subject to the pressure of the steam in the boiler,
and being of larger area than the safety valve which it is tending to seat, will
prevent the said safety valve rising until the pressure in the boiler exceeds the
load on the regulating slide or plunger. So soon as that takes place the plunger
will be lifted, cutting off the connection between the two water chambers, and thus
removing the steam pressure from the lower or larger one. The further rise of the
plunger then places the channel from the larger water vessel in connection with
the air chamber in the top of the hollow plug, and allows the water in the lower
chamber to escape freely, whereupon the safety valve forces up the solid piston
above it which it is then able to do having only the weight of the water above it,
without the pressure of steam in addition, to contend with. The safety valve thus
rises steadily and allows the steam to blow off until the normal pressure is reached,
when the weighted plunger will descend, putting the water space over the larger
piston in connection with the smaller water space, and subjecting it to the same
steam pressure, whereby the safety valve will be quickly forced down by the piston,
and held tightly to its seat.
The large piston may be provided with a washer of leather, or with suitable
packing, to render it water tight while allowing its free rise and fall. The stem of
the regulator plunger is filed or cut away in such a manner that the communication
with the atmosphere is small, and but a small fraction of that which exists between
the two chambers, so that the rise of the piston may be less rapid than its descent.
As a modification of the above, the pressure piston may form one with the safety
valve it tends to keep seated, instead of merely resting upon it as above described.
In this case the piston moves quite freely in its cylinder or casing so as to seat itself
exactly. Should any water pass by it will merely return to the boiler-but should
the normal pressure be exceeded the water will only seek to escape by the regulator.
The lower part of this balanced safety valve piston is grooved circumferentially
and it is against this part that the steam pressure acts to lift it off its seat.
It will be understood that the lifting of the valve will be progressive, and
complete, if the limit of pressure continues to be exceeded.
This hydraulic safety valve apparatus may be readily applied to spring, lever, or
dead weight valves, and by simply removing the ball, or by a cock for placing the
water supply pipe in communication with the air, the valve may be opened by
hand without requiring any special tools.