IMPROVEMENTS IN SAFETY AND RELIEF VALVES
Year: 1873

page_text: PROVISIONAL SPECIFICATION left by John William Melling at the
Office of the Commissioners of Patents, with his Petition, on the
4th June 1873.
I, JOHN WILLIAM MELLING, of Birkett Bank, Wigan, in the County
of Lancaster, Engineer, do hereby declare the nature of the said In-
vention for "IMPROVEMENTS IN SAFETY AND RELIEF VALVES," to be as
follows:-
These improvements are for the purpose of increasing the efficiency
of safety and relief valves. In ordinary safety valves the lift and
consequently the orifice for the escape of the steam is very limited, more
particularly with high pressures. Now my Invention consists in
obviating the above defects by maintaining, when the steam is escaping,
a constant and in some arrangements, an increased pressure to raise and
keep open the valve. This I accomplish in one way by exposing to the
pressure of the steam or air in the boiler or reservoir a flexible
diaphragm or a plate connected to a flexible diaphragm, instead of
exposing the whole or nearly the whole of the under side of the valve,
and only exposing so much of the valve as shall cover one or more
annular orifices in the seating, through which the steam or air escapes

page_text: WHICH THE VALVE IS Tased; eve is also by having its spiauit resting
on or in connection with the plate exposed to the steam or air. Also in
one modification the plates are so arranged that a part of their surface
is exposed to pressure, both upwards and downwards, so that when the
valve is closed that part is neutral, but when the steam begins to blow
off the pressure on the upper part next the orifices is diminished, and
consequently the valve is raised and held open by the steam underneath
with less resistance than heretofore. Or in place of the valve spindle
bearing directly on one of the plates the valve may be acted upon by a
lever that is raised by the steam acting on a flexible plate.
The second part consists in increasing the efficiency of the ordinary
form of safety valve, by enlarging the under part of the seat to
accomodate a hollow cylinder or cylindrical boss that is formed on or
attached to the valve, in such a manner as shall allow just sufficient
space between the top of the boss and the seat for the steam to escape
freely when the valve is raised to the full height required. The lower part
of the valve seat is enlarged to allow the steam to pass up the outside of
the boss, or the steam may pass up at the outside of the seat, and
through orifices at the side to reach the upper part of the boss, and
thus escape.
When the valve is closed the pressure on the upper part of the boss
exposed to the steam is the same as that on the lower part; but when
steam begins to escape the pressure on the upper side will be reduced,
and as the pressure underneath remains constant, or nearly so, the valve
may be made to rise to any extent required against the increasing force
of a spring or springs, by suitably proportioning the difference between
the area of the boss or cylinder, and the area of the opening in the seat,
and the space between the boss and the seat. When the valve is loaded
by means of a lever and weight, or dead weight, the boss may be of the
same or nearly the same diameter as the opening in the seat, and have
a groove or space cut in the side to allow the steam to pass from under
the seat and up to the face. The ribs for guiding the valve are in the
seat. Or instead of enlarging the seat a boss or a stem may be carried
down and terminate in a flange, which projects under the valve seat at
such a distance from it as shall allow the steam to pass when the valve
is full open. The size of the flange will be proportioned in the same way
as that of the cylinder or boss before mentioned,

page_text: The same means may also be employed to raise that kind of valve
where steam is carried up a central tube to the top of a flange that fits
up in the head of the valve.
My improvement consists in enlarging the head, so as to accomodate
a flange of greater diameter than the orifice; the steam at the under
side of this flange will be reduced in pressure, when the valve commences
to blow off as is the case in the before-mentioned designs.