IMPROVEMENTS IN VARIABLE EXPANSION GEAR FOR LINK MOTION REVERSING ENGINES
Year: 1881

page_text: LETTERS PATENT to Thomas English, of Hawley, near Dartford, in the
County of Kent, and David Greig, of the Steam Plough Works, Leeds, in the
County of York. Eng ear. for an Invention of "IMPROVEMENTS IN
VARIABLE EXPANSION GEAR FOR LINK MOTION REVERSING ENGINES,”
PROVISIONAL SPECIFICATION left by the said Thomas English and David
Greig at the Office of the Commissioners of Patents on the 13th June 1881.
THOMAS ENGLISH, of Hawley, near Dartford, in the County of Kent, and DAVID
GREIG, of the Steam Plough Works, Leeds, in the County of York, Engineer.
"IMPROVEMENTS IN VARIABLE EXPANSION GEAR FOR LINK MOTION REVERSING
ENGINES."
This Invention has for its object improvements in variable expansion gear for
link motion reversing engines, and applies especially to a link motion of the type
in which the travel of the slide valve is regulated by shifting the slide block,
The central point of the link is supported between two guides parallel to the valve
rod, and the reciprocating motion of the central point of the link when thus
supported, which is due to the lead of the eccentrics, is employed to actuate the
rod of a separate expansion valve mounted on the back of the main slide valve.
The slide block is kept at one or other end of the link, thus allowing the main
alide valve its full travel and the cut off can be varied by causing the bars of the
expansion valve to approach or recede from each other either by hand or auto+
matically through the action of a governor.
For cutting off later than an expansion valve will allow, the link motion is
employed in the ordinary manner; the bars of the expansion valve are in this case
drawn together until they are inoperative, and the slide block is shifted along the
link to the point required.
J

page_text: Bear
A is the crank shaft; B, the crank; C, D, the forward and backward eccentrics,
shewn as of equal throw and set at equal angles with the crank; E, F, the eccentric
rods; G, G, the link; H, the alider; K, the radius rod; L, M, levers keyed to the
rocking shaft N; O, a connecting rod; P, the spindle of the main slide valve Q,
in which are ports opened and closed by the expansion valve R, R. The link G, G,
is restrained near its centre S between parallel guides T, T, which allow the
centre point of the link to receive the reciprocating motion due to the angular
advance or lead of the eccentrics C, D, beyond a right angle in advance of the
crank.
The valve spindle U of the expansion valve R, R, mounted on the back of the
main slide valve Q is jointed to the link near the centre S, and receives the reci-
procating movement of this point.
The spindle of the main slide valve may be jointed directly to the end of the
radius rod K, but by preference it is actuated as represented in the Drawings
through unequal levers L, M.
The lengths of these levers L, M, are preferably in the proportion of two to one;
and when this is the case, the effect of the combination is to make the relative
movement of the expansion valve R, R, on the back of the main valve Qalways
approximately equal to that of the main valve on its seat.
The steam ports in the main valve Q will be closed at a period of the stroke
which may be varied either by varying the lap of the expansion valve R., B, or
by varying the position of the slider H in the link G, G, or by the combined action
of both these means.
The lap of the expansion valve R, R, may be varied by well known suitable
means, as represented in the Drawing, by the rotation of part of the spindle U,
either automatically by a governor within its limits of action, and by hand beyond
these limits, or by hand throughout.

page_text: The variation by hand is by preference made capable of drawing the edges of
the expansion valve R, R, into such positions that either the steam will be cut off
at the commencement of the stroke (thus doing away with the necessity for a
separate regulating valve), or that the ports in the main valve will not be closed
at all by the expansion valve when the mechanism can be used as an ordinary link
motion.
The position of the slider H in the link G, G, is varied in the ordinary way, as
indicated in the Drawing, by connecting it to a reversing lever working in a
quadrant provided with notches..
If the engine is required to be used as a non-reversing one with a variable cut
off, the backward eccentric D may be made capable of being shifted round the
shaft, and of being then held in any desired position relatively to the crank by
well known means, either automatically by the action of a governor, or by hand.
In this case if the lengths of the levers L, M, be as two to one, the amount of
movement of the expansion valve R, R, on the back of the main valve Q will
remain approximately uniform, whatever may be the position of the eccentric D,
but the point of cut off will travel round relatively to the crank exactly as the
eccentric D is shifted, and there will be no necessity either to vary the lap of the
expansion valve or to shift the slider from the end of the link.
For the purposes of this mechanism the eccentrics need not necessarily be
attached to the link at equal distances from its centre if their throws and positions
relatively to the crank are so adjusted as to give a movement to the point of the
link at which the expansion valve spindle is attached, approximately the same as
would be given to it, as above described.
Having now described the nature of our Invention, and the manner of performing
the same, we would have it understood that we claim,-
First. Our improved variable expansion gear for link motion reversing engines,
substantially as described and illustrated by the annexed Drawings.
Second. In a link motion controlling the link at its centre or point of least
movement in a rectilinear course by stationary guides, and there connecting with
the link the spindle of an expansion valve on the back of the main slide valve,
substantially as described.
Third. In a link motion the connection of the link at its centre or point of least
movement where it is controlled in a rectilinear course, with an expansion valve
on the back of the main valve, such expansion valve being adjustable in respect to
the distance between its bars or ends, substantially as described.
In witness whereof, I, the said Thomas English, have hereunto set my hand
and seal, this Eighth day of December, in the year of our Lord One
thousand eight hundred and eighty one.
THOMAS ENGLI38. (L8)