IMPROVEMENTS IN SAFETY VALVES
Year: 1876

page_text: PROVISIONAL SPECIFICATION left by Martyn John Roberts at the Office of
the Commissioners of Patents on the 17th March 1876.
MARTYN JOHN ROBERTS, of the City of Bath, Esquire. ." IMPROVEMENTS IN
SAFETY VALVES."
The objections to steam boiler relief or safety valves as at present constructed are
well known. When they rise from their seats to allow of the escape of steam they
do so in such a slight degree that they fail to relieve the boiler from excessive
pressure; they require to be held down by heavy weights or by strong springs, the
former of which are cumbrous and strain their spindles, and for marine boilers are
comparatively useless by reason of their varying pressure consequent upon the ship's
rolling, while the latter do not give way easily, and their power increases as the
valve rises, although the pressure of the steam decreases. Further, seated safety
valves are liable to stick to their seats.
Now, according to my Invention, I construct a steam relief valve, which is a true
safety valve. It will afford any desired amount of opening for the escape of steam;
it requires no weight or metallic spring to keep it shut, and being constantly in
motion it cannot stick to its scat; it can also be set so as to open at any desired
pressure of steam, a property which is valuable for marine engines.
My valve is constructed as follows:-A pipe is fitted preferably outside the
boiler; it extends downwards about two feet more or less, and is in connection at
its top with the steam space of the boiler, and it may also be in connection with the
water in the boiler. The downward extension of the pipe is for the purposo of
maintaining the water in it at a moderate heat, so as not to injuriously affect the
flexible dise herein-after mentioned. At the bottom of this pipe is a chamber or
enlargement in which is fitted a disc of india rubber, or other suitable flexible
material, and to this disc is fixed a rod extending up to the steam space, where it is
fixed to a small slide valve, which when open gives passage for the steam into the
open air. Below the disc is a water space in which is a hollow ball or bag of india-
rubber or other flexible and air-tight material, and this bag (there may be one or
several) is surrounded by water. From that portion of the pipe which is above
the disc to the portion below the disc there is a communicating pipe provided with
a tap or cock, which can be shut or opened at pleasure.
The action is as follows:-The tap being opened the
enlargement at the bottom thereof are filled with water.
A
pipe and the chamber or
Steam is then raised in

page_text: the boiler until the maximum pressure desired is obtained; this presses on the
surface of the water in the pipe, and thus compresses the air in the bag to a corre-
sponding degree. While the boiler steam is being raised to the desired pressure
with the tap open the flexible disc remains unmoved, because the pressure is equal
on each of its surfaces. The tap is now shut, and the safety valve is ready to act.
Any difference between the pressure upon the top surface of the disc and that on its
bottom surface will immediately cause the disc to inove.
An increase in pressure
causes it to descend, and in its descent it pulls the valve rod and slides the valve
open, thereby allowing steam to escape. As the pressure in the boiler and on the
flexible disc falls below its normal degree the higher pressure in the bag acts upon
the under surface of the disc, raising it and thereby sliding the valve shut. If at
any time it be required to reduce or increase the working steam pressure in the
boiler, and at the same time adjust the safety valve to a proper action at that altered
pressure, it is only necessary to open the tap to keep it open until the desired
pressure is obtained, and then to shut it.
In a modified arrangement of my valve I dispense with the bag, and connect a
vertical pipe to the chamber or enlargement before described, so that when the tap
is opened water fills the enlargement, and rises in the vertical pipe until the air in
its head becomes so compressed that it balances the steam pressure. The tap is
then closed, and the flexible disc comes into action as before. In order to reduce
the absorption of the air by the water I diminish as much as possible the extent of
water surface in contact with the air by placing a float thereon.