IMPROVEMENTS IN STEAM ENGINE SLIDE VALVES, VALVE GEAR, AND GOVERNORS, PARTS OF WHICH ARE APPLICABLE. TO. OTHER: PURPOSES
Year: 1868

page_text: PROVISIONAL SPECIFICATION left by George Alfred Bridgett at tho
Office of the Commissioners of Patents, with his Petition, on the
21st February 1868.
I, GEORGE ALFRED BRIDGETT, of Rose Bank, Fallowfield, near
Manchester, in the County of Lancaster, do hereby declare the nature
of the said Invention for "IMPROVEMENTS IN STEAM ENGINE SLIDE VALVES,
VALVE GEAR, AND GOVERNORS, PARTS OF WHICH ARE APPLICABLE. TO. OTHER:
PURPOSES," to be as follows:-
My Invention relates, firstly; to two novel forms of slide valve. The
object of both is to uncover the full area of a port by a valve movement*
of only half its width, they being at the same time in equilibrium and'
of light weight. By combining both forms of valve in one, and making
the cylinder face double ported, the full area may be uncovered by a
valve motion of one-quarter of the total width of port. The two valves
and the one formed by their combination require to work steam-tight
against the valve chest cover as well as against the cylinder face. One
of my improved valves, as adapted to control the flow of steam to and
from one end of the cylinder only, consists of a sort of frame formed
by two sides and three cross bars, one at each end of the valve and

page_text: one between the other two. Instead of preventing the steam in the
valve chest from entering the port by means of a bar as wide or wider
than the port, as is usual, I do so by surrounding it with a frame
formed by two of the cross bars and the portion of the valve sides
between them. The other portion of the valve is employed to surround
the exhaust port. The steam port in the cylinder face is wider than
the passage from it to the cylinder end by the width of one of the
cross bars of the valve. By the working of the valve the bars on each
side of the steam port alternately arrive at its centre. When the
outside bar is there the steam rushes into the steam port both outside
of the bar, and by means of a passage formed in the valve chest cover
for the purpose between the two bars. When the inside bar is at the
centre of the steam port the steam escapes into the exhaust port
directly, and also indirectly between the two bars, and through the
aforesaid passage in the valve cliest cover. When the same valve is
required to regulate the flow of steam to and from both ends of an
engine cylinder, four cross bars in the valve are necessary, the two
steam ports being one on each side of the exhaust port. The other of
my improved valves as adapted to control the flow of steam to and from
one end of an engine cylinder only, consists also of a sort of frame
formed by two sides and three cross bars. The steam port is also closed
at the proper times by being surrounded with a frame formed by two
cross bars and the portion of the valve sides between them. The cross
bars on each side of the steam port are placed further apart than in
the former valve, and the steam port is not wider than the passage
from it to the end of the cylinder, by which means the outside cross
bar is made to slide beyond the cylinder face and that on the valve
chest cover, and the steam rushes into the port both under and over
it. The bar on the other side of the steam port or the inside bar
slides over the exhaust port and permits the steam to escape both over
and under it. By placing four cross bars in this valve it may be made
to control the flow of steam to and from both ends of the cylinder.
In both of the foregoing valves when a bar on one side of the steam
port opens a passage in one direction the bar on the other side keeps
the passage in the opposite direction closed. The combined valve is
adapted to control the flow of steam to and from one end of an engine
cylinder only, though of course two of them may be connected together
so as that one cannot be moved without the other. It has four bars
across, two at one end arranged according to the first method, and

page_text: two at the other end arranged according to the second method. The
passage from the cylinder end terminates in two ports, one on each
side of the exhaust port, which latter if preferred may be conducted
through the valve chest cover. Engines with valves of the foregoing
description may be conveniently reversed by providing suitable valves
to reverse the position of the exits of the exhaust and steam pipes in
the valve chest. In connection with slide valves my Invention also
includes two novel, simple, and efficient methods of causing the back
of a valve to work steam-tight against the valve chest cover, or its
equivalent. The first method consists in making the face and back
inclined to one another in a direction at right angles to its traverse;
the cylinder face and a face on the valve chest cover or its equivalent
being similarly inclined, so that the valve may be caused to work
steam-tight between them by means of adjustable guides. A good
method of carrying the guides is by means of hollow screws with
bolts through them. It is sometimes preferable to provide such wedge-
shaped valves with side bearings forced outwards by means of springs,
india-rubber, or other elastic material; the springs at its widest side
being in stronger compression than the others, keep it constantly in
contact with both the cylinder face & the valve chest cover. An
additional casing door is provided at the widest side of the valve in
order that it may be removed for examination, repair, &c., without dis-
turbing the casing door or valve chest cover, against which its back bears.
My second method of causing both sides of a slide valve to work
in steam-tight contact, consists of an improved method of applying
india-rubber or other suitable material to prevent leakage through the
joint when the valve is made in two portions. According to this
method the valve is made in two similar or ucarly similar halves,
upper and under, the one steadied on the other by means of pins similar
to those in moulding boxes or other suitable device. A groove or
channel is formed all round cach half of the valve, and also along the
bars of the same, if any, in such a manner that when the two halves
of the valve are placed on each other the groove in each will coincide
with that in the other. A piece of india-rubber or other suitable
material of the form requisite to fill the grooves is placed in the same
between the tivo halves of the valve, previous to finally placing the
valve in the valve box. The groove may be cut out of the solid, or
it may be cast in and merely cleaned out by means of a slotting drill
or other suitable tool. The advantages of this method are that it is

page_text: easy of construction, and that leakage is prevented by the steam tending
to force the india-rubber out of the grooves on the opposite side to
that on which the steam acts. Of course the groove in each half must
be deep enough to prevent its doing this. It will at once be apparent
that my improved slide valves, besides being applicable to all kinds of
steam engines, may be used in connection with other motive-power
engines, steam hammers, hydraulic presses, and other apparatus wherein
slide valves are required.
The second part of my Invention refers to mechanism for actuating
steam or other motive-power engine valves. My improvements are
better suited for working slide valves having short traverses, such as
those herein-after described. The advantages attained by my improved
gear are, first, that the cut-off may be varied from a mere sip, or even
from no steam at all, up to full steam the whole stroke; second, the
suddenness with which the valve is worked prevents wire-drawing the
steam and relieves back pressure on the piston; third, the same handle
that varies the expansion may by a further movement be made to
reverse the engine; fourth, the absence of complication and separate
expansion valves saves power, repairs, and oil.
My improved valve gear may be thus described:-A cam formed like
a broad pulley with its rim all on one side of its arms or plate is driven
by the engine at the same speed as the crank shaft. A U-shaped or
double-armed lever having a bowl. spherical, or partialy spherical, by
preference on each of its extremities is keyed or otherwise secured on
to a rocking shaft. The bowls on the ends of the U-shaped lever aro
arranged to run, one on the outside and the other on the inside of the rim.
the cam, which is not in all parts equally distant from its centre of
rotation. The revolution of the cam consequently causes the U-shaped
lever to impart a vibratory motion to the rocking shaft, from which
motion is communicated to the valve by means of a lever arm.
The cam
is capable of being moved endways along its axis of rotation either by
hand or by governor, so as that the outside portion of its rim furthest from
the arms or plate, or the inside portion of its rim nearest to its arms
or plate, or any intermediate part of its rim may be made to act on
the bowls. The exact conformation of the cam rim is dependent upon,
first, the speed of the engine; the quicker the engine runs the greater
the portion of the rim of the cam devoted to moving the valve, and
the less the portion which passes the bowls without imparting motion

page_text: to the valve. Second, the points in the stroke of the piston, between
which it is desired to vary the cut-off. One edge (either the inside or
outside edge) is of the conformation requisite to cause the valve to cut
off the steam at the earliest required portion of the stroke. By the
cudways motion of the cam the further the portion of the rim which
acts on the bowls from this edge the greater the portion of the stroke
accomplished before the cam causes the valve to cut off the steam,
that is to say, the curved portions of the rim which act to cause the
valve to supply steam and to open and close the exhaust, run across
the rim in a direction parallel to its axis of rotation; and the endways
motion of the cam does not alter these movements of the valve. But
the curved portion of the rim which causes the valve to stop the supply
of steam winds in the portion of a spiral round it, so as that the steam
is cut off sooner or later according to the endways position of the cams
Third, whether the engine is required to be reversible by shifting the
cam endways beyond the limits between which the expansion is varied.
When such is the case it may be accomplished by casting two additional
portions on to the rim, one of the correct shape and in the correct
position to operate the valve for going backwards, and the other inter-
mediate between this latter and the forward portion of the cam so as
to enable the bowls to slip from one to the other. Instead of reversing
an engine by means of additions to its cam or cams, it may be done
by the use of catches, such as are now used in connection with the
eccentrics of those marine engines not fitted with link motion. When
a separate valve is used for, cach end of an engine cylinder it is pre-
ferable to have a cam rocking shaft, &c., for each. The best method
of arranging the cams is to place them on a shaft parallel to the piston
rod. The same cam or cams may be made to operate the valves of
two coupled engines. Instead of running a bowl both on the outside
and on the inside of the cam rim by means of a U-shaped lever, it is
sometimes preferable to use a single-armed lever having a bowl on its
extremity running on the outside only, the bowl being kept in constant
contact with the cam by means of a spring or its equivalent. When
this latter method is adopted, thero being a separate valve to each end
of the cylinder, and a separate cam rocking shaft, &c. to cach valve,
it is preferable to place a spring between the two valves, onc end of
the spring acting on one valve, and the other end on the other valve.
The spherical bowls may with advantage be made partly of india-
rubber. In very small engines they may be made spherical nobs.

page_text: The third part of my Invention has for its object improvements in
governors chiefly applicable to marine engines, by means of which
improvements the throttle valve is suddenly shut the instant the
engines exceed a certain speed; it remains shut until they return to
that speed, when it suddenly opens wide.
My improvements are as follows:-I cause the centrifugal action of
a ball governor, which it is preferred should run horizontally and at a
good speed, to force one part of a conical clutch box into the other,
the one part of the clutch being driven round, and the other part being
secured on to the throttle valve spindle. The half of the clutch box which
is driven round is kept out of contact with the other half by means
of a spring, except at such times as the speed of the engines is excessive,
when the action of the governor overcomes the power of the spring.
Two stops, which may be padded to prevent concussion, prevent the
throttle valve from turning more than one quarter of a revolution, i.c.,
from open to shut and from shut to open. A spiral or other spring
keeps the throttle valve wide open, except at such times as its action
is overcome by that of the clutch box. Of course the one part of the
conical clutch slips in the other as soon as it has shut the valve, it
being prevented from moving it further. Instead of a centrifugal
governor, inclined blades similar to those of a screw propeller may be
used to force in opposition to a spring by the excessive speed of the
ongine the cone which is driven into contact with the cone on the
throttle valve spindle. It is not necessary that the throttle valve bc
a butterfly valve, as one half of the conical clutch may be secured to
a spindle, from which a lover arm may be attached to a double beat
or other valve. Instead of a conical clutch box, any other kind, one
half of which will slip round in contact with the other, may be used.
:
In order that the nature of my improved valves and valve gear may
be more readily understood, I have hereunto annexed a Sheet of
Drawings.
In all the Diagrams, except Figures 10 and 11, A indicates the
valve chest cover; ba passage in the valve chest cover; c, cross bars
of the valve; d, sides of the valve; e; exhaust port; f, the steam port;
g, the cylinder..
Figure 1 is a longitudinal section of part of a steam engine cylinder
and valve chest containg one of my improved valves, it being in the
position at which the steam port is closed; Figures 2 and 3 show the

page_text: same as Figure 1, except that in Figure 2 the port is open to steam,
and in Figure 3 to exhaust. The arrows indicate the direction of the
flow of steam; Figure 4 is a plan of the valves shown in Figures 1, 2,
and 3. The sole use of the bar 1, Figures 1, 2, and 3, is to shield the
scraped surfaces of the cross bars of the valve from being worn by the
rush of steam. It may appropriately be termed a shield bar, and may be
dispensed with when the valve is made of a metal not liable to be
worn by steam. A shield bar may, if preferred, be placed along the
steam port, as shown by the dotted lines in Figure 3. Figure 5 is a
longitudinal section of part of a steam engine cylinder and valve-chest
containing the other of my improved valves, it being in the position at
which the steam port is closed. Figure 6 is a plan of the valve shown
in Figure 5. Shield bars may be used in connection with this valve,
if preferred. Figure 7 is a view showing the valves in Figures 1 and 5
combined for the purpose of still further shortening the traverse of the
valve. Figure 8 shows the valve in Figure 1 made double-ended for
the purpose of regulating the flow of steam to and from both ends of
an engine cylinder. Figure 9 shows the valve in Figure 5 made double-
ended for the same purpose. Figure 10 is a front view of a deep rimmed
cam forming part of my improved valve gear. Figure 11 shows a
longitudinal section of the same; also the U-shaped lever b with its
bowls a, a; also the rocking shaft c, and the lever arm d, to commu-
nicate motion to the valve. The rim of the cam shown is designed to
actuate a single-ended valve, such as those shown in Figures 1, 5,
and 7. By modifying its conformation it may be made to actuate a
double-ended valve, such as those shown in Figures 8 and 9. The cam
shown in Figures 10 and 11 is designed to cut off the steam at from
one-tenth to two-thirds of the stroke.