IMPROVEMENTS IN VALVES AND VALVE GEAR FOR MOTIVE-POWER ENGINES
Year: 1883

page_text: PROVISIONAL SPECIFICATION left by Archibald Fulton Craig, Robert
Fulton Craig, and Robert Motion at the Office of the Commissioners of
Patents on the 27th June 1883.
ARCHIBALD FULTON CRAIG, ROBERT FULTON CRAIG, and ROBERT MOTION, all
of Paisley, in the County of Renfrew, "IMPROVEMENTS IN VALVES AND VALVE
GEAR FOR MOTIVE-POWER ENGINES,"
This Invention relates to improvements in the arrangement of admission and
exhaust valves of motive-power engines, and in the construction of valve-gear for
operating the admission valves or expansion valves of such engines to cut off the
steam or motive fluid at any part of the stroke.
According to this Invention an admission and an eduction valve are provided at
each end of the engine cylinder, and are made in the form of long flat faced or
gridiron slide valves bearing upon seats of corresponding form. The valves and
valve seats are fitted within covered recesses or casings at the ends of the cylinder,
and the valves are by preference placed transversely so that they operate vertically
in horizontal engines, and horizontally in vertical engines. Between each induction
and eduction valve is formed a port leading directly into the corresponding end of
the cylinder, and the steam which enters the port through the induction valve
exhausts through the same port, and out by the eduction valve while the inlet
valve is closed. The steam from the boiler is admitted to both induction valves
by a common port or passage which may partially surround the cylinder as a steam
jacket, and the valves aro so placed in relation to their seats that the steam
pressure is on the back and tends to keep each valve tight.
The improved valve gear for cutting off the admission of steam, comprises a
long lever arm to which is connected the rod of the admission valve or cut-off
valve or plate. Onc. end of this lever is pivotted to a fixed centre which may
conveniently be formed on a bracket over the cylinder, and the opposite end is
actuated, against the power of a spring or dash pot, by a rod from an eccentric on
a rotating shaft, such as the shaft from which the governor spindle is operated.
The eccentric rod is not directly connected to the end of the lever arm working
the cut-off valve, but has a projecting edge on it which fits a corresponding edge
or step on a catch piece which is hung on the end of the lever arm, and which is

page_text: fitted to slide in a parallel-motion guide. The eccentric rod is kept in line by the
friction on its straps, aided if need be by a spring or weight, to bear on this sliding
catch piece, and raise the valve lever to its full extent to give steam for the whole
stroke if required. To cut off the steam before the end of the stroke, the eccentric
rod is pressed over out of contact with the catch piece, by means of an oscillating
finger or cam lever acted on by the governor, so that the valve lover is brought
down by the dash pot or spring and suddenly closes the valve. The finger or
cam lever which disengages the eccentric rod and catch piece is connected to the
sliding collar of the governor by means of levers which are arranged to move the
disengaging finger the nearer or further from the path of the eccentric rod, and 1
throw it the carlier-or-later-out-of-action, according-as-the-speed-of-tho-engine
increases or diminishes. The position of the disengaging finger and consequently
the point at which the actuating eccentric rod is disengaged from the valve lever
and allows the valve to be-closed is thus regulated by the governor; and as the
action of the governor is to cut off the steam earlier or later according as the 1
speed of the engine rises or falls, an approximately uniform speed can be regularly
maintained.
'
This arrangement of cut-off valvo gear is applicable not only with the valves of
the kind herein described, but also to operate other forms of valves, such as Corliss,
conical, piston, or slide valves, and the cut off plates of rotating valves.
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