Improvements in Valve Gear for Steam Engines.
Year: 1896

page_text: Date of Application, 21st July, 1896-Accepted, 3rd Oct., 1896
COMPLETE SPECIFICATION.
Improvements in Valve Gear for Steam Engines.
1, FRANÇOIS PANOUX of Estacion del Norte, Madrid, in the Kingdom of
Spain, Sub-Manager of Traction, do hereby declare the nature of this invention
and in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement:-
This invention relates to an improved steam distributing and reversing valve
gear, in which the use of cams and pawls is dispensed with; and which is mainly
applicable to locomotives, marine and other steain engines working at high speeds
while subjected to frequent vibrations and concussions. The conditions under
which these engines work do not admit of the employment of cams and pawls
in the engine mechanism, which must consist exclusively of simple and compact
parts.
My improved valve gear, while insuring a far higher degree of expansion than
that obtained with the means generally employed in engines of the kind herein-
before referred to, reduces considerably the wire drawing or throttling of the
steam for high expansions, by affording larger openings and a more rapid closing
of the admission-ports and obviates the undue protraction of the pre-release or
period preceding the exhaust and of the period of compression, usual in the case
of ordinary distributing methods when it is desired to extend the expansion to a
higher degree than that equal to three or four times the initial volume.
The variation of the degree of admission, of expansion and of compression, the
reversing motion and likewise the motion when working against the steam are
obtained by the operation of one single piece of mechanism, namely the reversing
lever or screw.
Thus a great economy in steam consumption is effected when this simple and
compact device is employed.
The steam distributing device in question is represented in the accompanying
drawing, in which
Figure 1 is a longitudinal section illustrating the whole mechanism.
Figure 2 a distribution diagram and
Figure 3 shows a modification of the slide-valve.
The distributing mechanism substantially consists of a slide valve A and of an
expansion valve or plate B (Figures 1, 2 and 3) the particular relative movements
of which, as hereinafter explained, deterinine all phases of the distribution.
The slide-valve A provided with an orifice or port a, a' at each of its extremities
for the admission of steam, is guided in the ordinary way by a reversing link G H
which imparts to it a variable travel, according to the position of the head I of the
rod 1 J connecting the slide valve to the reversing link.
The expansion valve or plate B sliding on the back of the slide valve A, in
order to alternately close each of the admission ports a, a', is guided through the
connecting rod L M by a fixed pin L at the centre of the reversing link I I',
so that the said expansion plate receives a motion opposite in direction to that of
the slide valve during the first half of the travel of this latter.
The minimum admission corresponds to the maximum travel of the slide valve;
in order to increase the admission, the travel must be diminished by approaching

page_text: the slide block situated in I, toward the centre of the reversing link, in order to
retard the arrival of the admission ports a al of the slide valve A beneath the
expansion plate B. The variation of the travel of the slide valve is such that the
period of admission may be varied from 5 per cent. up to about 30 per cent. of
the piston stroke, without undue protraction of the period preceding the exhaust
and the period of compression.
By continuing to diminish the travel of the slide valve a point will be arrived at,
when the outer edges of the ports a and a respectively no longer reach the
expansion plate B, the admission can still take place by the proper movement of
the slide valve, although the opening of the ports is partly covered by the plate B;
in this manner the admission is extended to about 60 per cent. of the piston stroke,
and permits of starting a double cylinder engine irrespective of the position of the
pistons.
The diagram represented in Figure 2, shows the positions occupied by the slide
valve A, the plate B and the ports from the moment of the maximum admission
to the moment of the minimum admission; the point in the reversing link which
corresponds to the maximum admission, lies about midway of the length of the
effective or working portion of half the reversing link; this is likewise the point
suitable for the slide valve during the motion with closed regulator.
The central portion of the connecting link only serves for reversing the motion
and for working the engine against the steam.
In Figure 1 this steam distribution gear is shown as applied by way of example,
to a locomotive, in which the principal proportions are as follows:
Stroke of the piston
Length of the motive connecting rod
Length of the eccentric rods
Length of the reversing link
Angle at which the eccentric rods are mounted-
Radius of the eccentrics
-
Outer lap of the slide valve (total)
Inner lap of the slide valve (total)
0-610 metres.
1-690
33
1.200
0.450
"
27 degrees.
دو
0085 metres.
"
0.036
0.017 "
In Figure 1, C is the centre of the driving shaft; D is the centre of the driving
crank; E is the eccentric for the forward motion; F the eccentric for the back-
ward motion; E G is the eccentric rod for the forward motion (in the illustration
the rods are crossed); F H is the eccentric rod for the backward motion; N G is
the suspension rod for the reversing link; O P is the suspension rod for the
actuation of the slide valve connecting rod; Q is the centre of the reversing shaft
and S R is the reversing rod.
The table hereinafter given, indicates, with regard to the forward motion; the
phases of distribution in the example illustrated in Figure 1, the dimensions of the
slide valve and of the expansion valve being indicated in Figure 3.
The differences existing between the admissions at the "front "and at the "back"
of the piston laces, result from the obliquity of the eccentric rods and of the motive
connecting rod.
The phases for the backward motion are symmetrical and analogous, apart from
the differences due to the obliquity of the connecting rods for the suspension of the
reversing link and of the slide valve connecting rod."

page_text: In the example represented in Figure 1, the slide valve A is provided at its back,
above the exhaust orifice, with a perforation b, nearly corresponding to the area of
the ports in the valve face, so as to partly balance the pressure of the steam acting
to force the slide valve upon the valve face. The said valve slides between the
face and the bottom of the expansion valve or plate B, which is protected from the
steam pressure by a compensating ring corresponding in diametral section to
the area of the orifice provided in the back of the slide valve; the compensating
ring, adjusted under slight friction in the expansion valve or plate, is surrounded
by packing rings c and its upper smooth part works against the bottom of the steam
chest cover which is adjusted parallel to the said expansion valve or plate and to
the slide valve face; a spring d resting upon the expansion plate B lifts the
compensating ring and maintains the same in contact with the bottom of the steam
chest cover; the space isolated by the ring is placed in communication with the
exhaust conduit by means of a small orifice e, which also traverses the expansion
valve or plate B, in order to prevent the accumulation of steam in the interior of
the compensator.
The compensator is not indispensable to this distributing device; the slide valve
may be of the ordinary three port kind, such as shown in Figure 3, but the
compensator is very necessary in order to diminish the friction and wear of the
constituent parts of the mechanism when high pressures are used.
This distributing device may be successfully employed in a compound engine
with two or more separate or tandem cylinders, for obtaining a very high degree of
expansion; while avoiding the protracted periods of compression usual in the high
pressure cylinders of such engines using ordinary distribution gear.
In the case of tandem cylinders being used, the slide valves of the two cylinders
may be actuated by the same rod, thus reducing the number of the constituent
parts of the device; the expansion valves or plates of both cylinders may also be
actuated by the same rod, where it is necessary to employ this mechanism for both
cylinders in order to obtain a very high expansion.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. The steam distributing device with reversing mechanism for expansion engines
comprising a reversing link which actuates a slide valve with a variable travel,
which slide valve determines or fixes all phases of the distribution, in co-operation
with an expansion valve or plate having a fixed travel, and actuated directly
by the centre of the connecting link, substantially as and for the purpose described
and illustrated.
2. As a steam distributing device with reversing mechanism for expansion engines,
the combination of a slide valve acting upon the valve face, of an expansion valve
or plate, acting upon the back of the slide valve, of a link with reversing mechanism,
suspended from a fixed point and actuated by the eccentric rods coupled to the axle
or driving shaft; of a rod connecting the slide valve to the reversing link; of a rod
connecting the expansion valve or plate to the centre of the said connecting link,
and of a transmission gear for operating the connecting rod of the slide valve
substantially as described.
3. In the steam distributing device referred to in the first claim, the particular
arrangement of the slide valve with two steam admission ports, placed one at each
side of the exhaust orifice, substantially as described.
4. In the steam distributing device referred to in the first claim, the use of
a compensating ring applied to the expansion valve or plate, for reducing the
friction of the said expansion valve or plate as well as that of the slide valve;
substantially as and for the purpose described and illustrated.
HASELTINE, LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicant.