IMPROVEMENTS IN OR APPLICABLE TO THE MAIN SLIDE OR OTHER SLIDING DISTRIBUTING VALVES OF STEAM HYDRAULIC OR OTHER LIKE MOTIVE POWER ENGINES OR MACHINES
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by Joseph Hopwood at the Office of the
Commissioners of Patents on the 4th May 1882.
JOSEPH HOPWOOD of the Cottage Clevelys Poulton-le-Fylde in the County of
Lancaster Engineer "IMPROVEMENTS IN OR APPLICABLE TO THE MAIN SLIDE OR
OTHER SLIDING DISTRIBUTING VALVES OF STEAM HYDRAULIC OR OTHER LIKE
MOTIVE POWER ENGINES OR MACHINES."
This Invention relates to an extended application of the system or mode of
remedying certain imperfections in sliding expansion or "cut off" valves of steam
or other like motive power engines by rendering the fluid pressures upon them
nugatory for which provisional protection was granted to me bearing date the
14th of March 1882 No 1244 and has for its object the removal of the back pressure
from the main slide or other distributing valve of the sliding or non lifting class of
steam hydraulic or other like motive power engines or machines such back pressure
being intermittent not only in loading and liberating the valve once every stroke
of the piston and varying only in amount and the period of its duration but also in
preponderating at each end or on each side of the middle line of the main slide
valve alternately at every revolution of the crank. My present invention consists
in applying a separate balance ring severally to the central or exhaust or exit port
and to each of the end ports or of the two end ports conjointly (where double ported
main slide valves are employed) and in placing the cylinder port spaces permanently
in free and separate communication with the spaces enclosed by the balance rings
situated opposite to them at the back of the main slide valve such communication
being effected and maintained as regards the exhaust or exit port by a direct
passage through the main slide valve or by a passage through the door of the casing
of such valve into the balance ring enclosure in conjunction with a pipe fitted with
a stop cock leading therefrom into the exhaust or exit port of the cylinder. The
communication between the end ports and their balance ring enclosures is effected
either by one or more enclosed passages or pipes through the main slide valve at
each end or as in the exhaust by passages through the slide casing door into the
enclosures and pipes fitted with stop cocks leading therefrom into the port spaces
of the cylinder as most convenient the balance rings being fitted and carried in
grooves or on projections formed on the inside of the slide casing door and held in
contact with the back of the main slide by springs as usual. The enclosures opposite
D

page_text: the end ports are made of sufficient depth only to permit of expansive and vibratory
movements arising from changes of temperature and tremor in working in order to
avoid objectionable enlargement of port spaces and the area of the space enclosed
by each balance ring or their collective area when more than one ring is employed
at each end or for the exhaust as may be expedient when it is desired to retain the
advantages of the circular form is made equal to the area of the cylinder port or
ports to which it is opposite and its centre is in the same line or perpendicular to
the plane of motion as the centre or effective centre of the said port or ports and
the area of the space enclosed by the balance ring or rings located opposite the
exhaust port (which when one only is employed will most conveniently but not
necessarily be made oblong and rectangular) is by preference made equal to the
area of that port added to the area of one of the bridges interposing between it and
the end ports and their centres are in the same line or perpendicular to the plane
of motion. In single ported or small sized main slide valves the balance rings may
be formed of one piece containing the several openings proportioned as to the area
or collective area and centre or effective centre of each as hereinbefore specified.
The back plate of the main slide is surfaced and made in shape and dimensions
suitable to the form of balance ring or rings adopted the balance ring enclosures at
the ends are simultaneously with their opposite port spaces placed in communication
alternately with the exhaust and with the interior of the main slide or casing
accordingly as the steam enters through the valve or direct from the slide casing
or steam chest, by the motion of the valve itself and the entrance and exit of steam
or other fluid through the end ports or variations of pressure within them do not
impair the balance of the valve the end to end movement of unbalanced pressure
together with the initial imposition of that varying load are therefore avoided there
remains only a small preponderance of pressure on the back of the valve, due to the
difference between the area of the exhaust opening in the valve itself and the area.
specified herein as preferably to be enclosed by its balance ring or rings or its.
portion of the whole when all are included in one piece which is of trifling amount.
diminishing as the bridges between the exhaust and end ports are narrowed down
only affecting the valve fully at its midstroke and disappearing at the extremes of
its throw