Improved Safety Appliance for Boilers, Heaters, and the like.
Year: 1895

page_text: PROVISIONAL SPECIFICATION.
Improved Safety Appliance for Boilers, Heaters, and the like.
I, FRANCIS WILLIAM GREENGRASS, of Church Street, Epsom, in the County
of Surrey, Hot Water Engineer, do hereby declare the nature of this invention to
be as follows:-
My invention relates to a safety appliance for steam and circulating boilers,
heaters, and such like pressure vessels of the kind wherein a metallic diaphragm is
used to stop a pipe in connection with the vessel and adapted to withstand a given
pressure and to rupture when that is reached or exceeded.
The object of my improvement is to provide a cheap, simple and reliable
restraining device which will relieve the pressure without the danger, noise and
violent consequences attending the rupture of flat metal diaphragms of uniform
thickness such as have hitherto been used, and without risk of injury to the vessel
itself. I may also arrange for my improved appliance to give audible notice of
its action.
According to my improvements I employ a semi-spherical or dome-shaped
pressure restraining device made of lead or alloy, and of graduating thickness
decreasing from the maximum at the base to a minimum at the crown or apex,
whereat the thickness of the material is such as will withstand the required
pressure, which may be determined by simple experiment. Around the periphery
of the base of the dome is cast, pressed or formed a flange of suitable width by
which the appliance is fixed with its concave side in communication with the
pressure vessel by a suitable form of screwed union joint.
The effect of the graduated thickness of metal attaining a minimum at the apex
is that when the given pressure is reached a simple puncture results, and not any
violent tearing action on rupture, as is the case with discs of uniform thickness
above referred to.
In combination with the above described appliance I may use a metal whistle
device fixed above the dome so that on escape of pressure an alarm will be
given.
Dated this 6th day of September 1895.
I, FRANCIS WILLIAM GREENGRASS, of Church Street, Epsom, Hot Water
Engineer, do hereby declare the nature of this invention and in what manner the
same is to be performed to be particularly described and ascertained in and by the
following statement:―
This invention relates to a safety appliance for steam and circulating
boilers, heaters and such like pressure vessel, of the class or type wherein a
metallic diaphragm is used to stop a pipe in connection with the vessel and is

page_text: adapted to withstand a given pressure and to rupture when that pressure is
exceeded.
The object of my invention is to provide a cheap, simple and reliable restraining
device which will relieve the pressure without the danger, noise and violent
consequences attending the rupture of flat metal diaphragms of uniform thickness
such as have hitherto been used, and without risk to the vessel itself; I may also
arrange for my improved appliance to give audible notice of its action.
According to my invention, I employ a semi-spherical or dome-shaped pressure
restraining device made of lead or alloy and of graduated thickness decreasing
from the maximum at the base to a minimum at the crown or apex whereat the
thickness of the material is such as will just withstand the given pressure, which
may be simply determined by experiment. Around the periphery of the base of
the dome is cast, pressed, or otherwise formed, a flange of suitable width, by which
the appliance is fixed with its concave side in communication with the pressure
vessel by a suitable form of screwed union joint.
The effect of the graduated thickness of metal attaining a minimum at the
crown or apex is that when the given pressure is exceeded a simple puncture
results and there is no violent tearing action on rupture as is the case with discs of
uniform thickness above referred to. Further, the pressure being relieved in the
manner above explained, the necessity for a lead away pipe open to the atmosphere
through external walls or otherwise is obviated. This is another advantage, since
a pipe of this description is liable to be sealed by frost acting upon the condensed
vapours within it, or by corrosion.
In combination with the above described safety appliance I may use a metal
whistle device fixed above the dome so that on the escape of pressure an alarm
will be given.
In the accompanying drawings in which similar letters refer to like parts in both
figures:-
Fig. 1 is an elevation and Fig. 2 is a vertical section of a safety appliance
constructed in accordance with my invention.
is the semi-spherical or dome-shaped restraining device composed of lead or
alloy and gradually decreasing in thickness from the base to the crown or apex.
bis the flange formed around the periphery of the base. c is the screwed union.
joint for connection with the pressure vessel, to the upper end of which joint the
restraining device a is fixed by the screw collar d so that its concave side is in
communication with the pressure vessel, as shewn clearly in Fig. 2.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, I declare that what I
claim is
1. In a safety appliance for boilers, heaters and the like, the employment of a
semi-spherical or dome-shaped restraining device of graduated thickness,
substantially in the manner described and for the purpose set forth.
2. For the purpose set forth, a safety appliance constructed, arranged and
combined substantially as described and as illustrated in the annexed drawings.
Dated this 5th day of Nov 1896
E. P. ALEXANDER & SON,
Chartered Patent Agents,
19 Southampton Buildings, Chancery Lane, London, W.C., Agents.