AN IMPROVED EQUILIBRIUM EXPANSION VALVE FOR STEAM ENGINES
Year: 1883

page_text: PROVISIONAL SPECIFICATION left by John Brooks at the Office of the
Commissioners of Patents on the 26th September 1883.
JOHN BROOKS of N° 22 Bristol Street, Hulme, Manchester, in the County of
Lancaster, Mechanical Engineer. "AN IMPROVED EQUILIBRIUM EXPANSION VALVE
FOR STEAM ENGINES."
The object of my invention is to reduce the friction that takes place during the
working of an ordinary slide valve between the face of such valve and the
corresponding surface of the Engine Cylinder.
It may be advantageously applied to the cylinders of both high and low pressure
Engines, to Locomotives of any design and with either inside or outside Cylinders,
and generally to steam Engines whether stationary or portable
Instead of as heretofore inclosing the slide valve of an engine in a steam chest
that is in communication with the boiler and covers the surface of the cylinder
whereon such valve is caused to slide under the full working pressure of the steam,
which is constantly pressing upon the back of the valve-I, in accordance with
my invention, form in the body of the cylinder two cavities wherein the steam
at its working pressure is admitted from the Boiler by a regulator or steam valve
in the usual manner.
These cavities or steam chests are located between the cylinder valve-surface and
the steam ways that alternately conduct the steam to the cylinder ends; they
communicate one with the other by means of side passages, and each has a suitable
opening made through the cylinder valve-surface which forms their roof or cover,
and through these openings the working steam finds access to beneath the face of
the slide valve, which is cast hollow and may be termed a box valve. It comprises
in one piece a slide valve of the usual form combined with what is actually a
movable steam chest, having suitable openings through its under side or face,
which openings as the valve slides to-and-fro come into coincidence with the
openings in the cylinder valve-surface, and at such times they open a clear passage
for the working steam to pass from the cavities or steam chests beneath the valve-
surface of the cylinder, into the interior of the valve chest that slides upon it, and
which is thereby kept supplied with steam, and in this way all the steam that
works the engine passes through the sliding valve chest.

page_text: There is no difference in the form of the under face of the central portion of the
valve chest that constitutes the slide valve, the ends whereof regulate the admission
and cut off the steam in the usual manner, and the exhaust is governed as
heretofore.
The upward pressure of the working steam acting through the steam openings
against the under face of the sliding valve chest and the valve surface of the
cylinder, has a constant tendency to lift the valve, and to counteract this I so
construct and attach to the cylinder a low pressure steam chest that it completely
envelops the sliding valve chest and the Cylinder valve-surface. Into this
steam chest, which also forms a steam jacket to the sliding valve, I, by means of
a reducing steam valve placed upon or connected with the boiler, admit low
pressure steam possessing sufficient expansive power to overcome the upward
pressure and prevent the slide lifting, but not to produce any appreciable amount
of friction between the face of the slide valve chest and the valve-surface of the
cylinder.
The reducing valve I work either simultaneously with the steam regulator
handle or separately, and in connection with the reducing valve I arrange an
outlet pipe to allow the steam to escape from the low pressure steam chest when
required. I also mount on the chest a steam gauge to indicate the pressure, and a
relief valve to permit at a certain fixed pressure of the discharge of either steam
or water,