Improved Positive Motion Valve Apparatus for Steam Engines and the like.
Year: 1899

page_text: Date of Application, 7th Nov,, 1899-Accepted, 13th Jan., 1900
COMPLETE SPECIFICATION.
Improved Positive Motion Valve Apparatus for Steam Engines and
the like.
I, CHARLES DENTON ABEL, of Birkbeck Bank Chambers, Southampton Build-
ings, in the County of London, Consulting Engineer and Chartered Patent
Agent, do hereby declare the nature of this invention (as communicated to
me from abroad by Gebrüder Sulzer, of Winterthur, Switzerland, Manufacturers,)
and in what manner the same is to be performed, to be particularly described aud
ascertained in and by the following statement:-
-
This invention relates to an improved construction of valve apparatus with
positive or prescribed motion, for tubular lift valves having two or more seats
and a comparatively small lift, the construction being more particularly suited
for quick speed steam engines.
The object of the invention is mainly in view of a high rate of piston-speed,
to transmit the positive motion of an excentric or crank connecting rod in such
manner to the valve, that this is rapidly opened to the full extent of its lift,
then maintained as long as possible in that position, and, lastly, rapidly closed
again, but without concussion.
The positive motion valve mechanisms heretofore proposed all require a more
or less large extent of lift if, with large and medium cut offs the valve is to
be sufficiently opened, and the maximum lift of the valve only occurs with the
smallest amount of cut off. But with rapid opening and closing motions, com-
bined with large valve lifts, there necessarily occur considerable pressures due
to accelerations, such as occur with all valve mechanisms, and which requiro
strong closing springs, which in their turn produce, at the closing of the valve,
in combination with the acceleration-pressure and the suction action of the steam,
too high an impact velocity between the valve and its scat.
In the valve mechanism forming the subject of the present invention, there-
fore, the closing springs are entirely done away with, and the free masses are
reduced to a minimum. By avoiding the use of the usual closing springs the
object is also attained of doing away as much as possible with the back pressure
upon the governor, which in most cases of positive motion valve gear, exercises
a detrimental influence upon the regulation.
This back pressure is, according to the present invention, only slightly exercised
both by the cam mechanism at the moment of lifting the valve off its seat, and
again at the closing down, as the velocities at which the opening and closing
are effected are kept as low as possible.
The actual valve motion consists according to this invention, of the combination
of that of an excentric and that of a cam. If the former were alone in operation
and were transmitted in the usual manner through an equal armed double lever,
the lifting diagram would appear about as indicated by the dotted line at Fig. 2
of the accompanying drawings. The assumed comparatively lurge total valve
lift, is however in the present instance reduced to about from rd to fih, such as
indicated by the full line at Fig. 2, by means of an interpolated cam device, the

page_text: dimensions of the valve being of course so chosen that only moderate speeds of
the steam current occur even with this reduced lift.
Figs. 1 and 3 of the accompanying drawings shew vertical sections of two
arrangements of the valve mechanism according to the present invention. Fig. 4
shews a cross section on line A B Fig. 3.
a is a two-armed lever, one arm of which operates as a cam b, formed with a
lifting curve and counter curve.
The radii of the area c―d e-f, gh and -, have their centre in the pivot
centre of the lever a or in the immediate neighbourhood thereof. The centre /
itself is situated somewhat outside the valve spindle and cam either be arranged
above as at Fig. 1 or below as at Fig. 3. The difference between the two
inner radii Fig. 1 or the two outer radii Fig. 3 corresponds to the lift of the
valve. The bridge shaped guide m for the valve spindle is formed with a
cylindrical bore in its upper part which serves as guide for two cylindrical
alides n and o in which are fixed the pins of rollers P and 1-
These rollers are kept in continuous contact with the two curves of the cam
by means of the two screws r and s which are connected together at their upper
and lower ends by cross pieces t and u. Between these cross pieces and the
slides and are provided strong springs and, by means of which tho
rollers can be pressed with any required degree of strength against the cams.
The lower slide also embraces by means of a spherical surface in a screw nutr
adjustable upon the valve spindle, by means of which the valve can be accurately
adiusted to the correct position relatively to the cam b.
The lifting or closing curve of the cam, and its counter ourve can be co
constructed. that the lifting motion of the upper roller, of which motion a
part is emoloved in compressing the upper spring. is effected quite gradually, the
counter roller following at the same distance. As soon as the upper roller has
arrived on the arc of smaller radius, the further forward motion of the cam, as
also the return motion thereof to the same point is such that the stroke of
the valve remains the same.
On the closing motion of the valve taking place, the valve is accelerated
downwards towards its seat by the counter curve of the cam and the counter
roller, these parts having previously, during the opening motion, taken up
by means of the disc springs we, the acceleration pressure of the free masses,
as also any existing excess steam pressure exercised on the section of the valve
spindle, the closure of the valve being effected under the reaction of the upper
spring with a speed almost reduced to zero.
The two circular arcs of the cam, which act on the rollers during the idle
motion of the valve gear, can also be so formed that the upper spring is gradually
freed from strnin, while the lower one is strained to a somewhat greater degree,
by which means a tight closure of the valve can be insured during the idle
motion of the gear.
For the exhaust valve motion, the com lever is preferably directly actunted
by the excentric, while for the supply valve motion there may be advantageously
interposed between the eccentric and the cam lever a toggle-lever motion, in
order to reduce the idle motion of the latter as much as possible. For the
supply valve motion controlled by the governor, if an adjustable link motion
or equivalent device be employed for fulfilling the conditions as to constant
lead, the greatest resistance occurring in the valve mechanism at the commence-
ment of opening motion of the valve, can be prevented from reacting upon the
governor, the only remaining perceptible re-action occurring at the moment of
the closing of the valve. The steam charge of the cylinders can easily be
varied between 0 and 60 per cent.
The above described invention possesses the following advantages, as com-
pared with known valve apparatus.
1. Avoidance of surfaces that roll or slide upon each other, which, during

page_text: the idle motion of the valve mechanism move away from each other, and,
at the commencement of the lift motion, come in contact with a certain speed.
2. Doing away with the air buffer and the valve closing spring which impedes
the governor.
3. Greatest possible reduction of the free parts connected to the valve, and,
consequently of the momentum thereof.
4. Small amount of motion, or work performed by the springs which effect a
gradual closing of the valve and absorb the momentum.
5. Slight lateral shifting of the point of contact between rollers and cam,
and therefore a less lateral guiding pressure than heretofore.
6. A full lift for the valve maintained for some time for medium and large
degrees of filling, that is, good utilisation of the steam passages, small dimensions
for the ralve and small dead spaces.
7. Attainment of a tight closure of the valves not controlled by the governor
by pressing the same upon their seats during the closing period.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed, I declare that what
I claim is:-
:―
In positive motion valve apparatus, an oscillating cam device such as b
against which bear rollers such as p, q, that are connected to the valve stem by
springs, which cam device is actuated either directly or indirectly by an excentric
so as to transmit motion in such manner to the valve that the opening and the
closing of the valve is effected gently even with quick action engines while at
the same time the valve is opened and closed rapidly and held open as long
as possible to the full extent of its lift, substantially as described.
Dated this 7th day of November 1899.
ABEL & IMRAY,
Agents for the Applicant.