IMPROVEMENTS IN THE CONSTRUCTION OF MOTIVE-POWER ENGINES
Year: 1869

page_text: PROVISIONAL SPECIFICATION left by John Davey at the Office
of the Commissioners of Patents, with his Petition, on the 19th
February 1869.
I, JOHN DAVEY, of Wisbeach, in the County of Cambridge, Mechanical
Engineer, do hereby declare the nature of the said. Invention for
"IMPROVEMENTS IN THE CONSTRUCTION OF MOTIVE-POWER ENGINES," to be as
follows:
The main object of this Invention is to economise the use of
steam or other source of motive power in motive-power engines by
admitting it at such part of the stroke of the piston as will enable it
to perform its work most efficiently.
It is well known that when the crank is at the dead point steam
admitted to the cylinder will have no effect in moving the piston,
but that before it can act the piston must be started by the
momentum of a fly wheel or its equivalent applied to the crank
shaft. When, however, the piston has moved forward some distance
the steam will have power to act, and its energy will be applied
with the greatest advantage when the piston has performed about

page_text: one-third of its stroke. To this end it is, however, necessary to
fill the large space vacated by the piston in reaching what may
be termed the initial point for action, and thus a large amount of
steam is wasted. Now in order to avoid this waste I cause what
may be considered the cylinder head to travel with the piston until
it approaches this initial point; it will then rest, and steam being
admitted between it and the piston the piston will be caused to act
in the ordinary manner. This principle of causing the cylinder
head to travel with the piston admits of being carried out in several
ways; for example, I may use a cylinder with open ends and fitted
with two pistons which are connected together by cross heads and
guide rods, and which alternately work up to a movable head or
division plate formed and fitted like a piston, and situated near the
middle of the cylinder. The traverse of this head is limited to the
distance between the two steam ports, and it receives its motion
from a cam on the crank shaft of the engine working in a bridle
carried by the rod of the division plate. This rod passes through
the rod of the piston that lies between it and the crank shaft, and
the cam which actuates the division plate is so adjusted that it
will cause the division plate to follow each piston alternately as they
severally make their outward stroke. When, however, the piston
and division plate have travelled together to the required distance
which I term the initial point the division plate will stop, and
steam being now admitted to the cylinder the piston will be
impelled with the full energy of the steam and while the crank
is in a proper position to receive and utilise the impulse. The expan-
sion or cut-off valve will be worked by a rod attached directly to the
cross head.
The like result to that above described may also be obtained by
closing the cylinder ends with two moveable heads and having but
one travelling piston, the heads each in turn moving with the piston
up to the steam port; or the cylinder may have fixed heads and
the whole move, following the piston to the initial point at cach
stroke.