AN IMPROVED DIFFERENTIAL VALVE GEAR."
Year: 1881

page_text: LETTERS PATENT to Hamilton Weldon Pendred, of Manchester, in the
County of Lancashire, for an Invention of "AN IMPROVED DIFFERENTIAL
VALVE GEAR."
PROVISIONAL SPECIFICATION left by the said Hamilton Weldon Pendred
at the Office of the Commissioners of Patents on the 12th August 1881.
HAMILTON WELDON PENDRED, of Manchester, in the County of Lancashire,
"AN IMPROVED DIFFERENTIAL VALVE GEAR."
The object of this Invention is to adjust the supply of steam, water, air, or gas
to the working piston of an engine in such a manner that the power shall increase
or diminish in equal ratio with the varying load or resistance to be overcome, and
more especially in pumping engines, whether for draining mines, pumping water
for town supply, town drainage, or for other like purposes.
The accompanying Drawing shows that it consists of an ordinary steam cylinder
and slide valve, and the piston rod is continued to and works a pump at one end of
the cylinder; the piston rod is also taken out behind the cylinder, and is supported
on a sliding shoe moving on a plate beneath in the ordinary way.
On the piston rod between the cylinder and the pumps is fixed an arm A which
can be adjusted in any required position. The outer end of this is forked and
embraces a nut B, which rides on a screwed rod C₁ having a screw of one or more
threads. This rod is carried in bearings D, D, and its end E is square or polygonal,
or is fitted with a rib at the place where the wheel F is placed in the bearing G,
so that the rod C can slide longitudinally within the wheel F.
On this rod C two collars H, H, are fixed so as to be adjustable, and between
them the forked end of a lever I engages, the other end of which lever acts at J
on the spindle of the slide valve K of the cylinder. The lever I pivots at L.
The screwed rod C is rotated by any suitable power contrivance, but for con-
venience of explanation a three cylinder rotary engine a on Mess™. Brotherhood
& Hardingham's Patent is shown, but other motors may be used.
The steam is conveyed to this engine a by the pipe M, which is fitted with two
cocks N and O.
The cock N is under the control of the engine driver, while O is to regulate the
expansion, and is kept always open by the weight P, except when the tappets Q. Q,
in passing close or partly close it for a second or two. The tannets Q. Q. are carried

page_text: on the rod R, which is worked to and fro by the arm A. R is supported on the
porter wheels S, S, and in the guide S'. The screwed rod C is supported at its
outer end in the eye T bolted to the pump. The screwed rod C has also tappets
U, U, fixed on it.
The back end of the piston rod V has an eye on its sliding shoe W which acts
on tappets on the rod X, which as it is shifted to and fro reverses the engine
rotating C by the belt wheels G', as shown, or by other well known means.
rotating C by the belt wheels G', as shown, or by other well known means.
THE ACTION OF THE GEAR.
The screwed rod C by its rotation always tends either to push the nut B from
the cylinder, or if the engine rotating it is reversed, tends to draw it to the
cylinder. The rod C is always rotated so as to drive the nut B along with the
motion of the main piston, but the nut can only travel at the speed due to the
pitch of the screw and the speed of rotation.
Now supposing the main piston to be at the back end of the cylinder, as shown
on Drawing, and ready to move forward, the slide valve is not yet moved to open
the supply port, but the engine rotating C is started by opening the cock N, and
the immediate result is that the nut B being fixed C is caused to move backwards,
and thus it moves the slide valve forwards and admits steam to start the main
piston. When the piston moves, the arm A embracing B moves also, and tends
to close the supply port, but the rod C is rotating and tending to open it.
Then as long as the main piston moves as fast as the rod tends to move in the
nut B the steam supply is constant and the slide valve is stationary, but should
anything diminish or remove the load opposing the main piston it would tend to
rush forward, but in so doing it would over run the speed of the screw on C, and
it would pull C bodily with it and instantly shut off the steam supply, and if con-
tinuing to move in the same direction it would so move C as to reverse the steam
supply and let steam in against itself, so that if a main or water pipe burst
or broke down the engine by means of the screw traverse would simply stop
itself.
On the other hand if the load on which the piston had to act increased then the
piston would slacken its speed, and the screw on C would overrun it and open the
supply port more and increase the supply of steam. In fact, the main piston is
absolutely controlled by the speed of O.
The lever Y is actuated by tappet gear on the trailing or back end of the piston
rod, and reverses the movement of the engine a, which rotates C at each end of the
stroke, while tappets u on C itself are acted on by the arm A, so that the main
piston has a double reversing gear.
The rod R is intended to cut off the steam supply at any required point of the
stroke of the main piston, which it does thus:-It is moved by the arm A and has
tappets Q, Q, which at the right points in the stroke move the handle of the
cock O and close it, thus for a second or so stopping the engine rotating C, during
which time the arm A overruns C and pulls it with it, closing the steam supply;
but when the tappet is past the weight P opens O and C begins to rotate again,
the slide simply remaining now at rest so long as speed of screw on C and of main
piston are equal, but if main piston moves slower then more steam is given it by C
overrunning it, and if it moves faster then it overruns C and moves the slide
valve so as to open the exhaust and let steam in against main piston.
The action of the rotating engine a working C being reversed at each end of the
stroke, C of course moves in the proper direction for each stroke.
The screwed rod C may have a right hand screw at its point of connection with
the lever A, and a left hand one at the portion acting on or with the lever I.
This arrangement will halve the speed of rotation of the said traverse rod C.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Hamilton Weldon Pendred in the Great Seal Patent Office on the
10th February 1882.
HAMILTON WELDON PENDRED, of Manchester, in the County of Lancashire.
"AN IMPROVED DIFFERENTIAL VALVE GEAR."
The object of this Invention is to adjust the supply of steam, water, air, or gas
to the working piston of an engine in such a manner that the power shall increase
or diminish in equal ratio with the varying load or resistance to be overcome, and
more especially in pumping engines, whether for draining mines, pumping water
for town supply, town drainage, or for other like purposes.
The accompanying Drawings show an ordinary steam cylinder and slide valve.
The piston rod is continued and works a pump at one end of the cylinder; the
piston rod may also be taken out behind the cylinder and supported on a sliding
shoe moving on a plate beneath in the ordinary way.
On the piston rod, between the cylinder and the pump, is fixed an arm A which
can be adjusted in any required position. The outer end of this is forked and
embraces a nut B which rides on a screwed rod C¹ having a screw of one or more
threads. This rod is carried in bearings D, D. On this rod C two collars H, H,
are fixed so as to be adjustable, and between them the forked end of a lever I
engages, the other end of which lever acts at J on the spindle of the slide valve K
of the cylinder. The lever I pivots at L.
The screwed rod C₁ may be rotated by any suitable power contrivance. In the
Drawing it is shown rotated by a rotary water motor a. A¹, A¹, are loose or dead
pullies; B' is a pulley to rotate the traverse screw C. A cross belt and a straight
belt shown by dotted lines are alternately thrown on to the centre driving pulley B'
by the tappet rod R. T is a tappet collar to alter length of engine stroke. The
screwed rod C¹ has also tappets U, U, fixed on it.
Figure 5 shows a double slide with cross ports, so that the arm or lever
be dispensed with and the screw traverse connected direct.
ACTION OF THE GEAR.
may
The screwed rod C¹ by its rotation always tends either to push the nut B from
the cylinder, or if the engine rotating it is reversed, tends to draw it to the
cylinder. The rod C¹ is always rotated so as to drive the nut B along with the
motion of the main piston ; but the nut can only travel at the speed due to the
pitch of the screw and the speed of rotation.
Now supposing the main piston to be at the back end of the cylinder, as shown
on the Drawing, and ready to move forward, the slide valve is not yet moved to
open the supply port, but the engine rotating 0¹ is started by opening the cock W,
and the immediate result is that the nut B being fixed C¹ is caused to move back-
wards, and thus it moves the slide valve forwards and admits steam to start the
main piston.
When the piston moves the arm A embracing B moves also, and
tends to close the supply port, but the rod C¹ is rotating and tending to open it.
Then as long as the main piston moves as fast or the rod tends to move in the nut B,
the steam supply is constant, and the slide valve is stationary, but should anything
diminish or remove the load opposing the main piston it would tend to rush
forward, but in so doing it would overrun the speed of the screw on C¹, and it
would pull C' bodily with it and instantly shut off the steam supply, and if con-
tinuing to move in the same direction it would so move C¹ as to reverse the steam
supply and let steam in against itself, so that if a main or water pipe burst

page_text: or broke down, the engine, by means of the screw traverse, would simply stop
itself.
On the other hand if the load on which the piston had to act increased, then
the piston would slacken its speed, and the screw on C' would overrun it and open
the supply port more and increase. the supply of steam. In fact, the main piston
is absolutely controlled by the speed of C².
The movement of the rod R can be arranged to cut off the steam supply at any
required point of the stroke of the main piston. The arm A has tappets which at
the right points in the stroke move the handle of a cock and close it for a second
or so, preventing the rotation of the shaft C, during which time the arm A over-
runs C and pulls it with it, closing the steam supply, but when the tappet is past
a fixed point the shaft C begins again to rotate, the slide simply remaining at rest.
This "rest" continues so long as the speed of the screw C² and main piston are
equal, but if main piston moves slower then more steam is given it by Cover-
running it; and if it moves faster then it overruns C and moves the slide valve
so as to open the exhaust and let steam in against the main piston.
The action of the rotating engine a working C₁ being reversed at each end of
the stroke, C of course moves in the proper direction for each stroke.
The screwed rod C¹ may have a right hand screw at its point of connection with
the lever A, and a left hand one at the portion acting on or with the lever I.
This arrangement will halve the speed of rotation of the said traverse rod C¹.
Having now described the nature of my said Invention, and in what manner the
same is to be performed, I declare that I claim,—
The improved differential valve gear shown in the annexed Drawings, and its
method of action as described for the purposes set forth.
In witness whereof, I, the said Hamilton Weldon Pendred, have hereunto
set my hand and seal, this Fourth day of February, in the year of our
Lord One thousand eight hundred and eighty two.
HAMILTON WELDON PENDRED.
(L.S.)