IMPROVE- MENTS IN BALANCED SLIDE VALVES OF STEAM AND OTHER ENGINES
Year: 1883

page_text: PROVISIONAL SPECIFICATION left by John William Hall at the Office of the
Commissioners of Patents on the 19th May 1883.
JOHN WILLIAM HALL of Kentish Town in the County of Middlesex, " IMPROVE-
MENTS IN BALANCED SLIDE VALVES OF STEAM AND OTHER ENGINES."
"
This Invention has for its object to balance the slide valves of steam and other
engines in such a manner that they shall not be subject to pressures varying in
amount and in point of application during the travel of the valve to which most
other so called balanced valves are exposed, and which causes unequal wear of the
working surfaces and entails loss of power.
At
I carry out my Invention as follows:-The valve has a working face on the back
as usual in balanced valves and works against an abutment plate of a length equal
to that of the valve less the extent of its travel, so that no portion of the working
face of the abutment plate is ever exposed to the pressure of the live steam.
the back of this abutment plate is fixed a shallow ring cylindrical or otherwise
which fits steam tight like a piston into a corresponding shallow cylinder or box
fixed upon the valve chest cover or upon a mid partition in the valve chest in the
case of an inside cylinder locomotive. This cylinder or box is of an internal area
as much less than the area of the abutment plate as it may be desired to leave the
back of this plate exposed to a constant pressure of steam to keep it up to the
valve, or preferably the cylinder may be exactly equal area to the said plate
provided a spring be applied to effect the same result. This abutment plate has
shallow recesses in its working face corresponding in shape and size to and
opposite to the steam ports of the cylinder face in order to admit steam pressure
to the portions of the back of the valve opposite and equal to the steam ports in
the cylinder face in order to balance the pressure tending to force the valve from
its seat. At the back of the abutment plate and corresponding to these recesses
are fixed small shallow rings or cylinders within the larger one before referred to
and of areas equal to the areas of the said recesses in the face of the plate, and
in these cylinders fit steam tight corresponding pistons which abut against the
unyielding valve chest cover. Openings lead from the recesses in the abutment
plate into these cylinders to admit steam to the latter to counterbalance the
pressure of steam in the said recesses which would otherwise tend to force the
D....1l

page_text: abutment plate away from the valve. These cylinders are kept in constant com-
munication with the steam ports of the cylinder by holes through the valve, or by
pipes passing outside the valve chest or otherwise, so that the pressure within
these small cylinders and recesses shall at all times correspond to that in the
cylinder ports, so as to ensure the varying pressure therein against the valve being
always exactly balanced, and prevent any tendency of the said pressure to force
the valve off the cylinder face.
The slide valve has ports leading through it from its ends to its working face,
through which ports the steam passes to the cylinder ports instead of going past
the ends of the valve as usual. The extra length thus given to the valve is for the
purpose of always keeping the face of the abutment plate covered so as to prevent
the steam forcing it off the valve, and the length of the working face of the
cylinder exceeds that of the abutment plate by the width of the two steam ports
in the valve, so that after the valve begins to cut off steam, the pressure in the
valve port tending to force the valve off its working face, shall be counteracted by
pressure at the back of the exposed end of the valve.
The exhaust cavity of the valve opens at the back and the abutment plate has a
recess sunk in its face corresponding in shape and size to, and opposite to, the
exhaust port in the cylinder, and from this recess an aperture leads into the large
cylinder on the back of the abutment plate to admit exhaust steam thereto.
The Invention may be carried out in various ways, for instance, instead of
pistons fitting in cylinders I may use flexible metal diaphragms to close the
cylinders or steam chambers and connect the abutment plate to the valve chest
cover. In this case the exhaust port can also have a balancing arrangement.