IMPROVEMENTS IN CONNECTION WITH SLIDE VALVES
Year: 1883

page_text: LETTERS PATENT to John Forsyth Johnstone of Belvedere in the County of
Kent Chemical and Manure Manufacturer for an Invention of IMPROVEMENTS
IN CONNECTION WITH SLIDE VALVES
PROVISIONAL SPECIFICATION left by the said John Forsyth Johnstone at
the Office of the Commissioners of Patents on the 18th April 1883.
JOHN FORSYTH JOHNSTONE of Belvedere in the County of Kent Chemical and
Manure Manufacturer IMPROVEMENTS IN CONNECTION WITH "SLIDE VALVES"
.
This invention has for its object improvements in connection with Slide Valves.
In Order to compensate for the steam or other fluid pressure upon the back of a
slide valve which pressure tends to produce friction by forcing the valve with
unnecessary violence against the valve seat-I close the valve chest behind the
valve with a flexible steel diaphragm and I couple the centre of the diaphragm by a
link with the back of the valve
The pressure in the valve chest tends to bulge the diaphragm outwards and this
tendency is restricted by the link connecting the diaphragm with the valve
The flexibility and play of the diaphragm is sufficient to allow all the freedom
of movement which the valve requires
5 SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said John Forsyth. Johnstone in the Great Seal Patent Office on the
18th October 1883.
JOHN FORSYTH JOHNSTONE of Belvedere in the County of Kent Chemical and
Manure Manufacturer "IMPROVEMENTS IN CONNECTION WITH SLIDE VALVES
S
This Invention has for its object improvements in connection with slide valves.
In order to compensate for the steam or other fluid pressure upon the back of a
Dusion ART

page_text: slide valve which pressure tends to produce friction by forcing the valve with
unnecessary violence against the valve seat. I close the valve chest behind the
valve with a flexible steel diaphragm and I couple the centre of the diaphragm by
a link with the back of the valve.
The pressure in the valve chest tends to bulge the diaphragm outwards and
this tendency is resisted by the link connecting the diaphragm with the valve.
The flexibility and play of the diaphragm is sufficient to allow all the freedom
of movement which the valve requires.
In order that my said Invention may be most fully understood and readily
carried into effect I will proceed to describe the Drawings hereunto annexed.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a front elevation of a steam engine cylinder and slide case with my
improved compensating apparatus attached and Figure 2 is a vertical section of
the same taken through a vertical line on the centre of the ports. In these
figures A is the cylinder B the slide case CC the ports, D the slide valve. On
the back of the slide case is a chamber E closed at its outer end by a flexible
steel diaphragm F secured steam tight between the flange of the chamber E and
that of a hollow cover G. The slide valve D is connected to the flexible
diaphragm F by the link H. The position of the pin I on which the link rocks
is adjusted by the position of the nuts j, j, on the stem J.
On the side of the chamber E is a pipe through which steam is admitted at K,
the pressure of which acting on the slide valve D in one direction on the valve is
balanced more or less completely by the pressure in the contrary direction on the
flexible diaphragm. The valve D is worked in the usual way by a rod working
through a stuffing box.
Another arrangement I propose is in place of making the face of the valve, and
the corresponding face on the cylinder against which the valve slides, flat to make
them curved, the curvature being from the centre of the pin about which the
link turns. In this case in place of the link being jointed to the valve it would
be connected rigidly aud would form a radius arm on the back of the valve. In
this case the valve may be worked by a rod working through a stuffing box having
on its end a bridle to encircle the valve with sufficient freedom to allow it to slide
in and compensate for the curvature of the valve face on the cylinder or in any
other convenient manner.
A hole may be drilled in the outer end of the hollow cover G to prevent an
accumulation of pressure should the joint at the diaphragm leak.
What I claim is,-The means substantially as described relieving the slide valve
from a portion of the pressure upon its back by connecting the valve with a
metallic diaphragm on which also the pressure is exerted.
In witness whereof I the said John Forsyth Johnstone have hereunto set my
hand and seal this seventeenth day of October in the year of our Lord One thousand
eight hundred and eighty three.
TATHTT
JAHNSTONE