AN IMPROVED VALVE MOTION
Year: 1871

page_text: PROVISIONAL SPECIFICATION left by Alexander Melville Clark at
the Office of the Commissioners of Patents, with his Petition, on
the 23rd September 1871.-A communication from abroad by
William Livingstone, of Brooklyn, County of Kings, and State of
New York, United States of America:
I, ALEXANDER MELVILLE CLARK, of 53, Chancery Lanc, in the
County of Middlesex, Patent Agent, do hereby declare the nature of
the said Invention for "AN IMPROVED VALVE MOTION," to be as
follows:-
The nature of this Invention consists in an apparatus for producing
from the alternate motion of the piston an alternate motion of the
slide valve, to all intents and purposes the same as produced by an
eccentric, and consists in a curvilinear groove arranged to act upon and
move the valve by means of the piston rod as herein-after described.
The form and design of this curvilinear groove will depend on the
manner in which it is made to perform its intermediate action upon the
valve. The groove plate may be fastened to the piston rod and travel
back and forth with it. In this groove works a friction roller on a pin
fixed at the extremity of the long arm of a bell crank rod or lever, the

page_text: short arm of which is connected to the valve rod. The horizontal
distance from one extremity of the curve to the other is made equal to
the length of stroke of piston, and the perpendicular distance between
one half the groove and the other is equal to an arc to be described by
the long arm of the lever, which shall produce a throw of the short arm
equal to the throw of the valve. The connection of the rock lever with
the groove plate being made as above described, the alternate motion. of
the groove plate will therefore give a regular vibrating motion to the
rock lever, and a horizontal throw to the valve.
For the purpose of giving the valve the necessary lead when the
piston is at the end of the stroke, the one extreme of the groove is
situated above and the other below the horizontal centre line, so that
the roller arriving at the horizontal extremity will find a space in
which to rise or to drop, which may be effected by means of a small
fly wheel mounted on a vertical shaft passing through the steam chest
cover, and having at its lower end an eccentrical pin which works in a
transverse slot of the valve. This wheel receiving motion from the
slide valve will accumulate power for the whole revolution, and when
the friction roller shall arrive at the extremity, bearing against the
bottom side of the groove, the action of the wheel will raise it to the
upper bearing. In case a very slow speed of the engine shall be
required the weight at the end of the rock lever will make it pass the
centre at the one extremity, and a spring may be applied in the groove
to drive it past the centre at the other. The curvilinear groove plate
may be fastened to the cylinder head, in which case the piston rod
carries a slotted arm in which a square block is fitted to move up and
down. This block carries two rollers, one to move in the groove and
the other in a slot in the rock lever, and as the slotted arm moves back
and forth the roller following the curved groove will make the block
rise or fall in the slotted arm, and likewise raise or lower the slotted
rock lever and thereby work the valve. The curvature of the groove in
this arrangement is flatter, and the position of its extremities is not
equidistant from the horizontal centre line as the rock lever when being
acted upon by the roller near the fulcrum will travel less to produce
the necessary lead motion than when acted upon at the other end of
the stroke. Or the long arm of the rock lever may form or carry the
groove plate. To the piston rod is fastened an arm as before but not
slotted, which carries a friction roller working in the groove, and as the
".

page_text: roller will move back and forth in a line parallel to the piston rod the
groove accommodating itself to the position of the roller will rise and
fall, and thereby effect a movement of the valve. Springs are placed in
the curvilinear groove to aid the friction roller at the extremity of the
groove, one or two springs may be so employed as may be found
necessary. One spring will probably be necessary to raise the end of
the rack lever, but where the end is weighted it will drop by its own
gravity, or a spring attached to the piston rod for raising the rock
lever may be used instead of the spring placed in the groove as before
mentioned.