AN IMPROVED EQUILIBRIUM SLIDE VALVE FOR STEAM ENGINES
Year: 1858

page_text: LETTERS PATENT to George Davies, of No. 1, Serle Street, Lincoln's Inn,
in the County of Middlesex, and No. 28, St. Enoch Square, in the City
of Glasgow, Civil Engineer and Patent Agent, for the Invention of
"AN IMPROVED EQUILIBRIUM SLIDE VALVE FOR STEAM ENGINES."-A com-
munication.
Sealed the 23rd November 1858, and dated the 16th June 1858.
PROVISIONAL SPECIFICATION left by the said George Davies at the
Office of the Commissioners of Patents, with his Petition, on the
16th June 1858.
I, GEORGE DAVIES, of No. 1, Serle Street, Lincoln's Inn, in the County of
Middlesex, and No. 28, St. Enoch Square, in the City of Glasgow, Civil
Engineer and Patent Agent, do hereby declare the nature of the said Inven
tion for "AN IMPROVED EQUILIBRIUM SLIDE VALVE FOR STEAM ENGINES," (a
communication from a foreigner residing abroad), to be as follows:-
The object of the present Invention is to obviate in a great measure the
expense and delay of converting an ordinary slide valve into an equilibrium
slide valve by retaining the ordinary valve face, the steam induction & eduction
passages, and the valve rod, so that only the valve itself and its casing require
alteration. The form of the valve employed is prismatic, and it is enclosed in
a well-fitting case or cap, which serves as a guide to its longitudinal movement.
This casing is A shaped, and the cylinder facing containing the steam ports

page_text: forms its third side. In order to poise the middle portion of the valve, the
steam is allowed to escape round the outside of the valve, by means of a
groove passing round the valve. The steam communicates to both ends of the
box cither by passing along an exterior passage or through a longitudinal
opening or canal formed through the valve, in order that there may be the
same pressure at each end of the valve.
And in order further to counterbalance the outward pressure of the steam
in the cylinder, the sides of the above-named longitudinal canal are perforated,
so as to admit steam between the upper sides of the valve and the casing or
cap. In order to compensate for the wear produced by the friction of the
surfaces in contact, one of the sides of the casing is recessed, and is fitted with
a moveable face or plate, which is kept up to its work by means of a wedge
or wedges at the back, which is or are advanced, when necessary, by means of
a screw or other contrivance placed outside the valve box.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said George Davies in the Great Seal Patent Office on the
16th December 1858.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, GEORGE
DAVIES, of No. 1, Serle Street, Lincoln's Inn, in the County Middlesex,
and No. 28, St. Enoch Square, in the City of Glasgow, Civil Engineer and
Patent Agent, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Sixteenth day of June, in the year of our Lord
One thousand eight hundred and fifty-eight, in the twenty-first year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me, the
said George Davies, Her special licence that I, the said George Davies,
my executors, administrators, and assigns, or such others as I, the said
George Davies, my executors, administrators, and assigns, should at any
time agree with, and no others, from time to time and at all times thereafter
during the term therein expressed, should and lawfully might make, use,
exercise, and vend, within the United Kingdom of Great Britain and Ireland,
the Channel Islands and Isle of Man, an Invention for "AN IMPROVED
EQUILIBRIUM SLIDE VALVE FOR STEAM ENGINES," (being a coinmunication from
a foreigner residing abroad,) upon the condition (amongst others) that I, the
said George Davies, my executors or administrators, by an instrument in
writing under my, or their, or one of their hands and seals, should particularly

page_text: describe and ascertain the nature of the said Invention, and in what manner-
the same was to be performed, and cause the same to be filed in the Great.
Seal Patent Office within six calendar months next and immediately after the:
date of the said Letters Patent.
· NOW KNOW YE, that I, the said George Davies, do hereby declare
the nature of the said Invention, and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement in writing, and on réference to the accompanying Drawings, that
is to say:
The object of the present Invention is to obviate in a great measure the
expense and delay of converting an ordinary slide valve into an equilibrium
slide valve by retaining the ordinary valve face, the steam induction and
eduction passages, and the valve rod, so that only the valve itself and its
casing require alteration. The form of the valve employed is prismatic, and it
is enclosed in a well-fitting case or cap, which serves as a guide to its longi-
tudinal movement. This casing is A shaped, forming two sides of the prism,
and the cylinder facing containing the steam ports forms its third side. In
order to poise the middle portion of the valve, the steam is allowed to escape
round the outside of the valve, by means of a groove passing round the valve.
The steam communicates to both ends of the box either by passing along an
exterior passage or through a longitudinal opening or canal formed through
the valve, in order that there may be the same pressure at each end of the
valve.
And in order further to counterbalance the outward pressure of the steam
in the cylinder, the sides of the above-mentioned longitudinal canal are
perforated, so as to admit steam between the upper sides of the valve and the
casing or cap. In order to compensate for the wear produced by the friction
of the surfaces in contact, one of the sides of the casing is recessed, and is
fitted with a moveable-face or plate, which is kept up to its work by means of
a wedge or wedges at the back, which is or are advanced when necessary by
means of a screw, or other contrivance placed outside the valve box.
Such being the nature and object of the said Invention for "An Improved
Equilibrium Slide Valve for Steam Engines," I will proceed to describe more
in detail the manner of carrying the same into practical effect; and in order
that the Invention may be perfectly understood; I have annexed hereunto a
Sheet of Drawings illustrative thereof, and have marked the same with figures
and letters of reference corresponding with those in the following explanation
thereof.
Figure 1 represents a side view, and Figure 2 a transverse section of the

page_text: prismatic valve, which is formed by adding to the ordinary valve C, C¹, C", a
top or cap, having two sloping sides D, E. Figure 4 is a longitudinal section
of the valve, casing, and cylinder; and Figure 5 is a transverse section of the
same. This valve is covered by a box F, F', F, (see Figures 4 and 5), which
is fixed on the cylinder facing, and forms the casing of the valve, guiding it in
its longitudinal movement imparted to it by the rod T. This casing may either
be employed by itself, or it may be enclosed in the ordinary square valve box.
It will be observed that in order to compensate for the wear of the surfaces
occasioned by the friction and movement of the valve, one of the interior sides
of the casing is made moveable by means of a wedge, which is placed between
it and the casing. This moveable side is shewn at E', E", (Figures 2 and 5),
in section, and at Figure 3 in elevation and side view, and the wedge which
'moves it is shown in section at e, e, (Figure 2), and in elevation at e¹ in
Figure 8, in which it will be seen that it is provided with a screwed rod e¹¹,
which passes through one end of the valve box, where it is furnished with a
screw nut for working or tightening the wedge in the interior, as required.
The steam from the boiler which enters the box, either by the steam pipe I or
by lateral openings made in the part H, H, passes through the passage or
canal A, A, and presses equally upon both ends of the valve, in order to
balance it in a longitudinal direction. The steam contained in the cylinder
pressing against the under side of the valve which covers the ports L, L, tends
to raise the valve and to press it too forcibly against the casing F. In order
to obviate this defect there are grooves 1, 1, made in the casing, and in the
moveable side. These grooves, although opposite to the ports L, L, do not
communicate therewith, as will be distinctly seen in Figures 2 and 3. The
steam which escapes by the eduction port M also exerts a pressure against the
valve, and tends to lift it. In order to obviate this a small quantity of steam
is admitted between the valve and the casing, by means of the holes J, J,
pierced in the top of the valve. These holes, of which a few only are repre-
'sented in the Drawing, are to be of a sufficient number and size for the surface
which it is desired to place "in equilibrio," and it is even necessary to give an
excess of pressure, in order to cause that side of the valve which touches the
cylinder facing to press slightly thereon. Instead of these holes, or in addition
thereto, longitudinal grooves may be made either in the outer surface of the
valve or the inner surface of the casing, both in the fixed and moveable
sides.
In cases where it is desirable to vary the length of the stroke of the slide
valve, it is advisable to hollow out the part marked H, H, in order to prevent
the formation of ridges of dirt, which might cause the ends of the valve to

page_text: stick or bind when the length of the stroke is increased. The Drawings
represent the valve and its casing as applied to a cylinder constructed for the
purpose with short steam passages, but it is evident that in cases where this
valve is intended to replace an old one, the relative dimensions of the various
parts will depend upon those of the valve previously employed. It will be
evident also that in some cases, for want of space between the cylinder facing
and the other parts of the engine, it will not be practicable to use a valve
completely prismatic; in which case the upper part must be truncated, but
the principle of the valve and the means of poising or balancing the same will
remain unchanged.
In witness whereof, I, the,said George Davies, have hereunto set my
hand and seal, this Sixteenth day of December, in the year of our
Lord One thousand eight hundred and fifty-eight.
GEORGE DAVIES. (L.S.)