IMPROVEMENTS IN STEAM ENGINES
Year: 1864

page_text: PROVISIONAL SPECIFICATION left by Henry Davey at the Office of
the Commissioners of Patents, with his Petition, on the 17th December
1864.
I, HENRY DAVEY, of Gunnislake, in the County of Cornwall, Engineer, do
hereby declare the nature of the said Invention for "IMPROVEMENTS IN STEAM
ENGINES," to be as follows:-
The first part of my Invention relates to a particular arrangement of the
valves; I make the valve face of a circular form with four openings (of a
quadrant form) if for two cylinders, and with two only if for one ;.these openings
radiate from the centre; on this face is placed a circular valve with two
openings of a similar form to those in the face, one opening for the exhaust
and the other for steam, this valve is caused to revolve with its centre coin-
ciding with the centre of the said face by any convenient means, one revolution
of the valve being produced in the same time as that of the crank shaft; the
revolution of the valve causes the openings in it which are placed diametrically
opposite to each other, to pass alternately over the openings in the face which
are in communication with the respective steam passages of the cylinder or
cylinders; they are designed to supply permitting induction and eduction at
proper times. If required to work expansively, another valve is placed over
this valve with a plate or plates of metal between, the valves being provided
with two openings (one on either side of the centre) this plate (or plates) remains
stationary whilst the two valves revolve, any suitable means of moving the top
valve is provided by which it can be fixed with its opening at any degree in
advance of the opening for the admission of steam in the bottom valve, thereby

page_text: causing the steam to be cut off before it otherwise would, and consequently
producing the expansion required; or the face may be so constructed that the
openings in it can be expanded or contracted, thereby causing the first or under
valve to cut off steam at any degree before the end of the stroke, consequently
producing expansion without the top valve, each valve consists of two discs or
circular plates tied together by feathers or ribs stretched between them. In
the latter case the openings communicating with the cylinder ports are in the
periphery and not directly through as before. By this valve or valves the
engine can be reversed simply by pulling round the valve or valves half a
revolution, thereby causing the steam to be admitted at the opposite port, the
valve or valves run loose on the spindle which drives them, and which passes
through the centre of the said valve or valves, a driver being fixed on the said
spindle, and a corresponding projection being provided on the boss of the wheel
affixed to the said under valve, and by which the valve can be pulled round
half a revolution when it is desired to reverse the engine, the expansion can
be adjusted when the top valve is used by a wheel being affixed to it and
placed under the first named wheel, any means being provided for fastening the
two wheels together so that the valves may rotate together when the degree of
expansion is determined; when expansion is produced by adjusting the openings
in the face, any convenient means of adjustment and fixing may be used. I
give these circular valves together with their axis an excentric motion simul-
taneously with their rotary motion to prevent nuts wearing in their faces.
The second part of my Invention consists in forming the condenser with a
cold water cistern in the top, the bottom of which cistern is provided with
holes to allow the water to descend into the condenser in the form of a shower,
the said cold water cistern to be supplied with water by means of the air pump
which is to be made double acting; at one end of the air pump an opening is
provided in communication with the said cold water cistern, in or on which is
placed a valve to prevent the return of water from the said cold water cistern
to the air pump; at the same end is also provided another opening in commu-
nication with any convenient supply having the pressure of the atmosphere
upon it, a valve is also placed in or on this opening to prevent the return of
water from the air pump to the said supply; at the opposite end of the air
pump an opening is also provided in communication with the bottom of the
condenser, a valve being also placed in or on this opening to prevent the
return of hot water from the air pump to the condenser, at this end is also
provided another opening in communication with the hot well or any other
desirable place, a valve is also provided in or on this opening to prevent the
return of water from the hot well or any place into which the water shall be

page_text: forced to the air pump, the end of the air pump in which the opening leading
to the cold water cistern is placed to be the end through which the piston rod
comes, and as there is more water to be withdrawn from the condenser than is
supplied to the cold water cistern, the piston rod may be made of any size to suit
this inequality; by this arrangement the great atmospheric resistance to which
the ordinary air pump is subjected, is obviated or partially so.
The third part of my Invention relates to slide valves, and consists in a
particular arrangement whereby the greatest part of the back pressure of the
steam is removed. The valve is made with two faces, and in cross section
somewhat like the double beat valve; the back of the valve proper is subject
to the pressure of the steam as usual, while the face of the other additional
part is also subject to such pressure, but being rather less in area allows a
preponderance of pressure on the back of valve to keep it on its face. The
upper and additional valve surface is enclosed by a cover in which any steam
that may escape through the faces of the upper valve condenses, or a small
opening may be provided for the escape of any steam that may accumulate
above the upper valve.
The fourth part relates to the reversing gear of steam engines. I extend
the breadth of or bifurcate the eccentric rod at the point where it is connected
with the pin of the rocking shaft, and form a gab on each side the eccentric
rod facing in opposite directions and opposite to two studs or pins disposed on
opposite sides of the rocking shaft or axis, into one of which pins the gabs take
as may be required when the engine is required to move in one direction, the
rod by its gab is in connection with the pin on one side of the rocking axis, and
when traversed that gab is removed and the opposite one placed in gear with
the pin on the other side of the rocking axis.
In order to move the eccentric rod and change its connection as described,
I extend a double hand lever from the rocking axis, the main lever being fixed
thereto, while the second one is pivotted to the main lever, and at the opposite
end operates on the eccentric rod so as to produce the changes required which
are effected by hand by means of these levers. The main lever has notches in a
segmental piece into which the secondary lever slips to keep it in position when
changed, or it may be fixed by a binding screw. The eccentric rod may be
held by same means midway between the two rocking pins, and not in gear
with either.