Improvements in Rotary Slide Valves and Valve Gear for Steam Engines.
Year: 1887

page_text: Date of Application, 23rd July, 1887.
Specification Accepted, 23rd Aug., 1887.
COMPLETE SPECIFICATION.
Improvements in Rotary Slide Valves and Valve Gear for Steam
Engines.
I, CARL PFAFF, of IX Währinger Strasse No. 59, Vienna, Austria, Professor, 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 construction of valves and valve gear for
steam engines, having for their object, firstly, to afford variation in the cut off between
the widest possible limits; secondly, to render the compression independent of the
motion of the inlet slides; thirdly, to enable the compression to be regulated ;
fourthly, to afford a very easy motion; fifthly, to prevent all jerky motion at the end
of the slide's stroke; and, sixthly, to obtain a very simple construction.
For effecting these purposes, the inlet and exhaust are effected at each cylinder end
by separate rotating slides receiving a step by step motion, and which are made
either cylindrical or conical, and have on their periphery a certain number of equi-
distant openings.
These rotating slides may either work with a portion of their periphery upon a
correspondingly formed slide face with a single opening, or they may be fitted in or
upon slide casings having the same number of openings as the slides. In both cases
the regulation of the expansion and compression may be effected by auxiliary slides
which can be moved over the openings of the slide valve or of the valve face or casing
either by the governor or by hand, or the slide valves may be moved quicker or slower
over the openings for that purpose. The step by step motion of the slides has the
advantage that the movement of the valve gear only consumes a small amount of work,
and that the regulation of the expansion and compression can be effected by alteration
of the speed at which the slide openings are led past the openings of the slide face or
casing. Continuously rotating slides, with which the regulation can only be effected
by means of auxiliary slides, may however also be used for fulfilling the above-
mentioned independent regulation of the compression and expansion.
For fulfiling the condition of easy motion, conical rotary slides are best employed,
which work in or upon corresponding slide casings, and in which the pressure with
which the steam presses them against the casing or face is reduced to the desired
extent by means of balancing pistons on the slide rods.

page_text: For easing the motion of the valve gear it is also preferable to effect the regulation
of the expansion and compression by varying the speed at which the slides pass the
openings of the casing rather than to do this by means of auxiliary slides. For
effecting such step by step rotary motion with variable speed, ratchet wheels are
employed the pawls of which are carried by sliding pieces with variable rectilinear
motion.
The course of the acting part of the pawl forms a chord of unvarying position
within the circumference of the ratchet wheel, so that the alteration of the stroke of
the sliding piece either by hand or by the governor has no influence on the extent of
the angle through which the valve is turned, but only varies the speed of motion.
With these conical rotary valves it is necessary to use a stop which prevents the
valve from being lifted off its seat by the pressure on the balancing piston when in
the position in which the steam ports are open.
It is also necessary to apply a braking action at the end of each angular motion in
order to arrest the valve accurately in the required position in consequence of its
acquired momentum owing to the reduction of the frictional resistance.
The construction of the improved valves and valve gear will be readily understood
on reference to the accompanying drawings in which Fig. 1 shews a cross section and
Fig. 2 a part longitudinal section of a steam cylinder, the inlet and exhaust slide
valves of which revolve on horizontal axes. Fig. 3 shews a cross section of a cylinder
the rotary slide valves of which slide on vertical axes. Fig. 4 shews an enlarged
section of the ratchet mechanism for actuating the spindle of an inlet slide valve.
Figs. 5 and 7 shew respectively a longitudinal section and sectional plan and Fig. 6 shews
an end view. Fig. 8 shews a vertical section of another form of the brake device for
the slide valve in which the sliding piece carrying the pawl is caused to rotate a screw
nut. Fig. 9 shews a longitudinal section of the end of a steam cylinder with rotary
inlet and exhaust slides which revolve with step by step motion upon a concave slide
face, the inlet slide being provided with an adjustable expansion slide.
I will proceed to describe the construction which I consider best suited for the
purposes of this invention, shewn at Figs. 1, 2 and 3 of the drawings, in which rotary,
conical, inlet and exhaust valves are employed. These are either slides B surrounded
by the valve casing as shewn at Figs. 1 and 2, or slides B₁ which surround the
slide casing C, as shewn at Fig. 3. These slides have a considerable number of
narrow longitudinal slots 6 situated at equal distances from each other, and which
correspond to an equal number of slots c in the casing. The movement of these slides
is effected in such manner that before each change of stroke they are turned through
an angle comprising the width of one of the slits and the width of the space between,
the rotation being always in one and the same direction. At each such motion each
slot b is consequently made to pass over the contiguous slot c of the casing. The apex
angle of the conical valve is made somewhat greater than the angle at which it would
stick or jam when acted upon by the steam pressure. Such steam pressure, which,
when the ports are closed, is equal to the product of the pressure upon the unit of
surface in the projection of the slide surface upon a plane at right angles to its axis, is
reduced to the desired minimum by attaching to the valve spindle a piston 62 which
passes through a stuffing box D of the steam chest to the outside thereof so as to be
acted upon by the steam pressure on its inner surface in the contrary direction to that
of the pressure on the valve. During the time that the inlet or exhaust ports are
open, the steam pressure upon the slide ceases, and in order at that time to prevent
the pressure on the piston 62 from moving the valve from its seat, there is provided at
the end of the spindle a screw 63 the end of which is at a sufficient small distance
from the end of the spindle to allow for expansion by heat. This distance is best
regulated by introducing a piece of thin sheet metal between the spindle and screw,
and after setting the latter up to this and fixing it in position, removing the
metal strip.
For effecting the step by step rotary motion of the slide B or B', a ratchet wheel is
fixed to the spindle 6', and a sliding piece sliding in a guide F carries a pawl f
which is pressed in gear with the teeth of the ratchet wheel by a spring and is

page_text: adjusted by a screw f³ passing through a tail on the pawl and bearing upon a lug on
the sliding piece so as to regulate the extent to which the pawl gears with the
ratchet E, and consequently, the distance through which it imparts motion to the
latter.
The to and fro motion of the sliding piece f¹ for the inlet valve is effected by
means of a slotted crank lever G, and for the exhaust valve by means of a slotted
crank lever G. These levers are loose upon a shaft g and a second shaft g parallel
to g carries cranks; the pins g2 work with sliding blocks in the slots of the levers G G¹
according to the positions which the shafts g g¹ occupy relatively to the sliding
pieces, the connections of the other ends of the levers G G₁ with f¹ is effected
either directly by a simple connecting rod H as at Fig. 1 or, as shewn at Fig. 3,
through the connecting rod H and bell crank lever h h¹.
It will be evident that the means for imparting the motion to the sliding pieces fi
may be arranged in a variety of different ways, such means forming no part of my
present invention.
The regulation of the expansion and compression is effected in this case by causing
the slide openings 6 to pass quicker or slower over the openings c of the casing, this
being effected by increasing or decreasing the stroke of the sliding piece f. For
this purpose the pins connecting the rods H with the levers & G₁ are made
adjustable.
But the
The compression gear is adjusted before starting the engine and remains unaltered,
for which purpose the arm of G¹ connected to the rod H only has a slot in which the
joint pin is adjusted in position and then fixed in any suitable manner.
adjustment of the pin of rod H for regulating the expansion has to be effected by
the governor, for which purpose the following arrangement is employed. The arm
of G has a curved slot, the centre line of which is an arc struck from a centre
corresponding to the upper pivot of the rod H when in the position in which the
pawl carried by the sliding piece begins to gear with the ratchet wheel E, and the
lower end of the rod H is pivotted to a block 2 sliding in the slot of G. The shaft
on which the levers G G₁ are mounted loose is connected to the governor in such
manner as to be partially rotated thereby and an arm h³ fixed on this shaft is
connected to rod H by links h'. Thus on being turned the block h² is shifted in
one direction or the other in the slot of G by means of h³ 4, thereby increasing or
decreasing the stroke of f¹, and consequently increasing or decreasing the speed of
the pawl f.
For the purpose of arresting the motion of the rotary slides at the end of each
movement, as before stated, the screw 63 which, as before stated, prevents the valve
from being moved away from its seat, is carried in a spring bearing and is pressed
inwards against the valve stem b¹. For this purpose the screw 63 is screwed into a
tube I passing through a second tube i containing a strong spring ¹, so that on
pressing inwards the tube i the tube I is also carried inwards by means of the spring i
acting on the shoulder and thus the screw ³ is pressed elastically against . In
order that the spring may not press continuously on the shoulder of I, it is
supported by a ring that rests upon a shoulder i of the tube i so that on pressing
inwards the tube the pressure of the spring is transmitted to I through ring 3.
The depression of the tube i is effected by a connection with the sliding piece;
Fig. 8 shews one arrangement suitable for this purpose and Figs. 4 to 7 shew another
arrangement. As shewn at Fig. 8, the tube is carried in a guide and has at its
inner end a quick screw thread on which is a screw nut, which is prevented from
shifting longitudinally of the spindle 6 by being confined between the wheel E and
the end of the guide, while the tube i is prevented from turning by a feather and
groove. The nut has an arm which is connected to an arm on the sliding
piece by a link.
In order to afford the screw b³ an abutment at its outer end to enable it to act as a
stop to the valve stem, a bridge piece K is fixed on the guide carrying an abutment
screw k.
In the arrangement shewn at Figs. 4 to 7 the tube also has quick screw threads

page_text: on its inner end, which take into a screw nut f combined with the guide F. For
effecting the inward and outward motion of the tube i, this is provided with an arm
which is connected by a link ƒ with the arm of the sliding piece f¹. As the
arm moves in and out with the tube i, the link is made with a fork, as shewn at
Figs. 5 and 7, of sufficient width to allow of the required lateral play of the arm
its pin, the latter being made to move in a guide L.
upon
The outward motion of the tube I is in this case limited by a shoulder on its
inner end. These braking devices gradually press the slide valve with gradually
increasing pressure against its seat shortly before the end of its motion, and thus
effect its arrest without any jerk.
The arrangement shewn at Fig. 9 also to a certain extent fulfils the conditions
herein before set forth; in this arrangement the valves 0 0¹, which bear on one side
only against a valve face, are also actuated by a pawl gearing with a ratchet wheel
on the valve spindle. The inlet slide valve O is provided with an expansion slide m
actuated by the governor, so that if it be turned by the latter in the contrary direction
to the rotation of the slide it will more or less close the openings of the latter and
thus reduce the duration of the steam supply. The exhaust slide, if it is not desired
to regulate the compression, may have the form shewn at O'; if the compression is to
be regulated, it is provided with an inner regulating slide like that of O.
Having now particularly described and ascertained the nature of my said invention
and in what manner the same is to be performed I declare that what I claim is :-
1. The construction of valves and valve gear for steam engines wherein separate
rotary inlet and exhaust valves for each end of the cylinder have a step by step
rotary motion in the same direction imparted to them, the said valves being arranged
either to fit against valve faces on one side thereof, or being formed conical and fitting
with their whole surface in or upon a correspondingly formed casing with openings,
and being partly balanced by means of pistons on their spindles, substantially as
herein described.
2. In rotary slide valves arranged and operating as set forth in the preceding
claim, the use of auxiliary slides m m¹ within the rotary slide valves adjusted either
by the governor or by hand for regulating the expansion and compression, substantially
as herein described.
3. In rotary slide valves arranged and operating as set forth in the first claim, the
method of effecting the step by step motion of the slide valve by means of a pawl
gearing with a ratchet wheel on the valve spindle and carried by a rectilineally
reciprocating slide piece f the stroke of which may be varied by hand or by the
governor, so as to cause the openings of the slide to pass quicker or slower over the
openings c of the valve casing or face, substantially as herein described.
4. The use in combination with conical balanced rotary slide valves such as are
referred to in claim No. 1, of screw stops and k at the end of the valve spindle for
preventing the valve from being drawn off from the slide face by the balance piston
when the steam ports are open, substantially as herein described.
5. The use in combination with conical balanced rotary slide valves such as are
referred to in the first claim, of a brake device for stopping the valve at the end of
each movement, consisting of a screw made to act with elastic pressure against the
end of the valve spindle by means of a tube i actuated by the sliding piece through
suitable mechanism substantially as herein described.
Dated this 23rd day of Julv 1887
ABEL & IMRAY,
Agents for the Applicant.