IMPROVEMENTS IN EXPANSION VALVE GEAR
Year: 1875

page_text: PROVISIONAL SPECIFICATION left by Charles Frederick Amos and
Henry Wilson Ringrose Smith at the Office of the Commissioners
of Patents, with their Petition, on the 1st June 1875.
We, CHARLES FREDERICK AMOS and HENRY WILSON RINGROSE
SMITH, both of Kingston-upon-Hull, Engineers, do hereby declare the
nature of the said Invention for "IMPROVEMENTS IN EXPANSION VALVE
GEAR," to be as follows:-
:-
The object of this Invention is to vary the cut off of steam in steam
engines by varying the position (on its shaft) of the excentric which
works the slide of the expansion valve.
The Invention is especially applicable to engines which have an
expansion valve or slide on the back of the main slide.
In carrying out our Invention the main excentric is keyed fast on the
shaft as usual, but the excentric for working the expansion slide is
mounted loosely on it so that it can be turned round thereon, in order
that its angular position with respect to the crank may be altered when
required. On the side of this loose excentric is cast a bevil toothed
wheel so that the two are made to turn or rotate together on the shaft.

page_text: This bevil wheel gears into an intermediate wheel which gears into and
is controlled by a third bevil wheel which is keyed fast on the crank
shaft. The intermediate wheel is a mere dummy wheel, and is mounted
on an hand lever on which it turns when the crank shaft is rotating.
The hand lever is attached to a sleeve mounted on the crank shaft between
the fast and loose bevil wheels, so that the shaft forms a fulcrum for the
hand lever which is capable of being moved through a few degrees of an
arc and secured in any given position.
Instead of bevil wheels we sometimes use ordinary toothed wheels
or spur gearing, but in this instance (as in the former) one wheel is cast
or fixed on the side of the loose excentric, and consequently the two
must always move together while another toothed wheel is fixed or
keyed on to the crank shaft, and therefore rotates therewith. A hand
lever mounted on the crank shaft as its fulcrum (as in the other
instance) carries intermediate toothed wheels, whereby the fast and
loose wheels on the crank shaft are put in communication with each
other. This arrangement of spur gear will be found more compact than
the bevil gear, and is more applicable than the latter to the existing
engines.
Other arrangements of wheels may be employed without departing
from the nature of the Invention, but to effect the desired object it is
essential (in our opinion) that the number and arrangement of the
wheels should be such that the loose or expansion excentric should move
in the reverse direction to the main one.
It will be found that on moving the hand lever of either of the above
arrangements the position of the loose or expansion excentric on the
shaft will be altered as regards the crank, and this alteration of the
position of the excentric on the crank shaft will (by altering the position
of the slide of the expansion valve) effect a corresponding alteration in
the cut-off point of the steam. It should be understood that the
expansion excentric runs in the opposite direction to the other excentric,
and to the crank shaft on which it is mounted.