IMPROVEMENTS IN SAFETY VALVES FOR STEAM AND OTHER PRESSURES
Year: 1879

page_text: LETTERS PATENT to John Guy Wilson, of the British & Foreign Patent
Office, 71, Market Street, in the City of Manchester, Mechanical Engineer
and Patent Agent, for the Invention of "IMPROVEMENTS IN SAFETY VALVES
FOR STEAM AND OTHER PRESSURES." A communication from abroad by
Frank B. Scovell, of the Town of Waterford, in the County of Norfolk and
Province of Ontario, Canada, Machinist.
Sealed the 18th May 1880, and dated the 21st November 1879.
PROVISIONAL SPECIFICATION left by the said John Guy Wilson at the
Office of the Commissioners of Patents on the 21st November 1879.
JOHN GUY WILSON, of the British & Foreign Patent Office, 71, Market Street,
in the City of Manchester, Mechanical Engineer and Patent Agent. " IMPROVE-
MENTS IN SAFETY VALVES FOR STEAM AND OTHER PRESSURES." A communication
from abroad by Frank B. Scovell, of the Town of Waterford, in the County of
Norfolk, and Province of Ontario, Canada, Machinist.
The object of the Invention is to provide a sensitive safety valve combining the
advantages of quick relief, durability, and compactness, and may be described in
brief as follows:-Two cylindrical valve chambers, one of which hereinafter called
the main chamber, is supplied with a piston valve seated on an elbow-pipe, so
arranged that the steam in the chamber cannot escape to the outside atmosphere
until the valve is raised from off its seat. The other cylinder is also provided with
a peculiarly made valve, consisting of a combined valve and piston, and is supplied
with steam from the boiler by a pipe passing preferably through the lower part of
the main chamber, thence into the boiler. This pipe should be conducted to some
part of the boiler remote from the opening into the main chamber. The duty of
this pipe is to supply the auxiliary valve with the actual boiler pressure, and not
with the pressure near the opening of the main chamber, which may fluctuate with
the opening and closing of the piston valve. These two chambers also communicate
together through a passage open at one end above the piston in the main chamber,
and at the other end between the auxiliary valve and its piston.

page_text: The valve referred to in the auxiliary valve chamber is loaded by a spring or
weight, which can be suitably adjusted to carry any desired pressure in the boiler.
When this pressure is exceeded the auxiliary valve raises from its seat, which
action opens communication between the atmosphere and the main chamber above
the piston valve.
As the steam cannot enter or leak through the auxiliary and piston valves to
the top of the piston valve as rapidly as it can escape into the atmosphere through
the seat of the auxiliary valve the consequence is that the opening of the auxiliary
valve causes the pressure on the piston valve to diminish, and the steam pressure
beneath the piston valve forces the valve away from its seat and allows the steam
to escape from the boiler into the atmosphere and relieve the boiler.
As soon as the pressure of the boiler is slightly diminished the spring or weight
again forces the auxiliary valve to its seat, thereby closing the escape of steam to
the atmosphere and causing it to again accumulate on the top of piston valve,
forcing it back to its seat on the top of the elbow pipe within the main chamber.
The top of piston valve has more surface exposed to the pressure of the boiler than
the surface beneath, as that portion of the lower surface which covers the elbow
pipe is mostly exposed only to the atmosphere. When the valves are closed the
pressure in both chambers is equal, and the same pressure as that of the boiler, but
as soon as the auxiliary valve opens the pressure will diminish above the piston
valve and the piston portion of the auxiliary valve.