IMPROVEMENTS IN SLIDE VALVES FOR STEAM AND OTHER ENGINES AND IN THE MEANS FOR HOLDING THE SAME TO THEIR WORK
Year: 1882

page_text: LETTERS PATENT to James Dunbar of the Town and County of Southampton
for an Invention of "IMPROVEMENTS IN SLIDE VALVES FOR STEAM AND OTHER
ENGINES AND IN THE MEANS FOR HOLDING THE SAME TO THEIR WORK
"
(Void by reason of the Patentee having neglected to file a Specification in
pursuance of the conditions of the Letters Patent.)
PROVISIONAL SPECIFICATION left by the said James Dunbar at the Office
of the Commissioners of Patents on the 21st October 1882.
IMPROVEMENTS IN
JAMES DUNBAR of the Town and County of Southampton,
SLIDE VALVES FOR STEAM AND OTHER ENGINES, AND IN THE MEANS FOR HOLDING
THE SAME TO THEIR WORK
"
The object of this invention is to prevent the cutting of slide valve faces, and
yet to ensure close contact between slide valves and their seats.
Many attempts have already been made to obtain a good balanced slide valve,
but the difficulty has been to maintain the balance when the face of the valve has
become worn.
In constructing a slide valve according to my invention I form it
hollow, or like a shell, giving it a flat face through which the ports are cut, and a
central recess for the passage of the exhaust steam. The ports which supply
steam to the opposite ends of the cylinder are parallel to the central recess and open
to the hollow back of the valve, and at a right angle to these ports, or in the line
of travel of the valve, I make a third steam port also opening into the hollow shell.
This third port is intended to receive steam from a port of about half its length
pierced in the cylinder face, and in connection with the steam boiler. The length
of this longitudinal port in the valve is such that in all positions of the valve,
steam will continue to be admitted thereto, the other ports of the valve being
arranged as usual with respect to the ports leading to the opposite ends of the
cylinder.
-
The steam entering by the longitudinal port will pass into the shell or hollow
back and make its exit from the valve by the right and left port alternately.

page_text: Connected with the chest in which the valve works is an arrangement of valves
and steam passages for admitting steam direct from the boiler to the back of the
valve and regulating the pressure of the steam thereon so as to provide for the
proper holding of the valve to its seat.
The supply of steam to the passage leading to the valve chest is governed by a
loaded valve which rises, under the boiler pressure, to supply steam to the valve chest,
and seats itself when the pressure in that chest has reached its desired maximum.
This is determined by adjusting the load on the valve; which load may conveniently
consist of a pressure spring adjusted by means of a nut or its equivalent on the
valve spindle. To facilitate this adjustment a pointer travelling over a graduated
scale may be used. At the back of this valve is a passage leading to the condenser
for the purpose of providing for the escape of any steam that may pass the valve
face and disturb the regulated pressure at the back of the valve. The passage to
the condenser will, like the steam passage, be controlled by a loaded valve adjusted
to yield to any excess of pressure that may occur at the back of the slide valve.
From the foregoing explanation it will be understood that the slide valve will
have a tendency to rise from its seat under the pressure of the steam passing to
the cylinder, and that to balance the valve a supply of steam will be automatically
admitted to the back of the valve, the pressure being automatically adjusted should
an excess of pressure in the valve chest occur.
This
To adapt my invention to steam cylinders of the ordinary pattern it will be
necessary to modify the construction of my valve. For this purpose I omit the
longitudinal port by which steam is introduced to the shell or hollow back, and
provide in place thereof a tube which leads from the slide valve through & stuffing
box in the valve chest into a steam chest communicating with the boiler.
tube is closed at its end and slotted longitudinally to allow the steam to pass
along it to the interior of the valve. In other respects the valve will be constructed
as already explained its ports corresponding to the supply and exhaust ports of the
cylinder to which it is to be fitted. The stuffing box is arranged about midway
between the end of the tubular extension of the slide valve and the farthest port
thereof, and the inlet and outlet ports of the valve and its tube, are arranged so as
to preserve the balance of the moving parts.
By the above described construction and arrangement of slide valves, they may
be readily adjusted to work under varying pressures of steam and yet retain their
seating.