IMPROVE- MENTS IN VARIABLE-EXPANSION VALVE GEAR FOR STEAM AND OTHER MOTIVE POWER ENGINES
Year: 1881

page_text: PROVISIONAL SPECIFICATION left by the said James McFarlane and
Thomas Templeton Mackie Lumsden at the Office of the Commissioners of
Patents on the 7th April 1881.
JAMES MCFARLANE and THOMAS TEMPLETON MACKIE LUMSDEN, both of
Edinburgh, in the County of Mid Lothian, North Britain, Engineers. "IMPROVE-
MENTS IN VARIABLE-EXPANSION VALVE GEAR FOR STEAM AND OTHER MOTIVE
POWER ENGINES."
This Invention relates principally to engines, the speed of which is regulated by
varying the cut-off or grade of expansion, and the improved gear has been
designed for adjusting more or less apart a pair of cut-off plates arranged to work
on the back of an ordinary slide valve. The improved gear is also applicable in
connection with valves of various other constructions.
In carrying out the Invention, a speed governor of the ordinary centrifugal or
any other suitable kind is used to determine the adjustments of the valves or cut-off
plates, but no power is derived from the governor for effecting the adjustments,
and whenever the governor has acted in bringing about an adjustment the return
of the governor to its normal position does not reverse the adjustment as in
ordinary governor arrangements, but simply stops it on the speed being brought
to its normal rate.
In one modification of the improved gear, a lever or lever frame centered on a
stud or shaft is made to vibrate by means of an eccentric, or crank pin, or cam on
the engine shaft, or on a shaft geared thereto. On a pin or spindle fitted to turn
in eyes in the two sides of the lever frame there are fixed two concentric ratchet
wheels with reversed teeth, and also two eccentrics, these last being in diametrically
opposite positions. Rods strapped or otherwise jointed on the eccentrics extend
from them through stuffing boxes to the cut-off plates, and are by the movement
imparted to the lever frame made to impart the ordinary reciprocating motion to
the cut-off plates. The adjustments of the cut-off plates are effected by turning
the ratchet wheels, which action shifts the eccentrics in opposite directions. For
acting on the ratchet wheels pawls are provided, being jointed to the lever frame,
and being formed with heels, spurs, or points, which rest against a guard so as to
be both held out of action when the engine is running at its proper speed. The

page_text: guard is upon a lever connected to the governor sleeve, and when the speed becomes
either too high or too low, the consequent action of the governor moves the guard,
so that the spur of one of the pawls becomes free to move over the end of the
guard. This allows the pawl to engage with its ratchet wheel, and the vibrating
motion of the lever frame then makes it turn the wheel, and with it the eccentrics,
and the necessary adjustment is thereby effected. When the governor recovers
its proper position it returns the guard to its central position and thereby stops the
action of the pawls in either direction. The guard may be made in two pieces,
which can be adjusted so as to require more or less shifting by the governor in
order to set the pawls in action. The pawls may be centered between the ratchet
wheels and the guard, or the guard may be between the ratchet wheels and the
centres of the pawls. In the latter case the pawls are made with projections
between their points and their centres to be acted on by the guard, and the guard
is by preference moved or turned by means of teeth on it in gear with a toothed
sector on a lever connected to the governor. Where a comparatively quick correcting
´action is required, two pairs of pawls may be arranged so that the ratchet wheel
will be moved twice instead of once for each double stroke of the lever frame.