Improvements in Direct Acting Steam Engines.
Year: 1897

page_text: Date of Application, 9th Nov., 1897-Accepted, 15th Jan., 1898
COMPLETE SPECIFICATION.
Improvements in Direct Acting Steam Engines.
I, AUGUST MISCH, of 43, St. Michaelstrasse, Magdeburg-Sudenburg, Head Foreman
of Works, 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 a slide valve gear which is specially designed to be
employed in steam engines which are coupled direct to pumps having no fly
wheels. This gear can be constructed to produce any desired degree of expansion.
The invention is illustrated in the accompanying drawings in which:-
Figure 1 shows a slide valve gear applied to a steam cylinder. Figure 2 shows
a modified form of construction of this apparatus, and Figure 3 illustrates the
steam engine fitted with this valve gear in combination with a pump having no
fly wheel.
C
As shown in Figures 1 and 3, the slide valve A in the valve chest B is operated
by means of the rods a b c. The rod c is connected to the lever b (pivotted at b¹)
and also connected to the levers d and d. Upon the axles of these levers d
and , or formed in one with these levers, are arranged two straps e e¹ in such a
manner that they project into the path of the roller f¹ which is mounted in the
cross head f. These straps are positively connected together by means of the
rod c.
When the engine is in operation, and the cross head is moving accord-
ingly out of the position shown in Figure 1, it, after moving through a certain
distance, will strike against the strap e and force it upwards. The lever d and
consequently the rods ba follow this movement of the strap e so that the slide
valve is moved over into the opposite position to that shown in Figure 1. In this
movement of the strap e the strap e moves down so that when the piston has
reached its lower dead point the strap e' will have moved down with its long
end and the roller f' will have forced up the short end e². The determination of
the cut-off with which the engine is to work is effected by the shape of the
straps e e'. If the roller f' meets the straps only after having moved through a
considerable distance, the cut-off will consequently be so much later. In Figure 1
the straps e c are so formed as to cause the engine to work with a cut-off or
degree of expansion of 0.3.
Figure 2 shows one arrangement of this apparatus in which instead of the two
straps e e¹ there is employed a single strap g which is suspended pivotally at its
centre and is also connected with a slide valve by means of the rods a b c engaging
with a projection situated over its pivot. This strap is also arranged to be turned
over by means of the roller f¹ as is clearly shown in the Figure. This arrange-
ment of gear is suitable for engines which work with a degree of expansion
greater than 0.5, because the strap is so situated that the shaft f¹ will meet and
consequently operate the strap only behind its pivot, that is to say, only in the
second half of its length. In other respects the strap operates exactly as the
two straps of the first arrangement. It is advisable to accelerate as much as
ossible the motion of the slide valve at the end of its travel. For this purpose

page_text: there is employed the usual inclined surfaces in the slide valve cavity upon which
the steam acts; and an auxiliary pushing device shown in Figure 1 also serves
for this purpose. This device consists of two rollers h which are under spring
pressure and which are adapted to roll along on the surface of the slide valve.
These rollers are each embraced from above by a suitably recessed plunger i which
is capable of moving in a casing that is cast on the slide valve chest or is other-
wise connected therewith. Each plunger is guided by means of a rod which is
fixed to it and which is capable of sliding in a suitable hole in the cover of the
chest, and further by means of a plate-shaped extension which is exactly equal
to the inside diameter of the casing. Upon these plungers there act spiral
springs which have some play in the casing. The surface of the slide valve
is somewhat recessed as shown in Figure 1 for the purpose of allowing the rollers /
to roll. This path of the roller is sharply bevelled towards both ends of the
slide valve and terminates in a slightly hollowed-out part, in the hollow of which
the roller is capable of entering when in its end position. The operation of this
apparatus is as follows:-On moving the slide valve by means of the reversal
of one of the straps e e¹, one of the rollers runs on the straight portion of its path,
whilst the other roller commences to move on the inclined portion. Towards the
end of the path, one of the rollers, after overcoming the inclined portion, has
reached the straight portion. In the same instant the other roller begins to roll
downward along the inclined portion of its path, and the pressure of the corre-
sponding spring commences to act upon the plunger i. This spring pressure
aided by the inclined surface of the slide valve produces a considerable accelera-
tion of the motion of the slide valve. Instead of the spring pressure, steam may
also be caused to act directly upon the plungers, or instead of the whole apparatus,
drag-springs may be employed.
The slide valve is preferably a cylindrical or round slide valve which is turned
to fit accurately in the distributing chest. It receives steam from the inside
only, so as not to exert any pressure upon the port face. The pressure which is
produced by the spiral springs is balanced by the steam from underneath.
The slide valve is thus capable of moving very easily so that the wear and
tear thereon is only very slight.
When the engine as shown in Figure 3 is coupled directly to a pump having
no fly wheel, then cushioning valves must be provided on the cylinder in
combination with the slide valve gear hereinbefore described, because there is a
great risk of the pistons striking against the cylinder covers as soon as the pump
runs without any load, or receives a little more steam than is necessary for the
ordinary number of revolutions.
It frequently happens when such pumps suddenly loose the water to be sucked
up, and steam is not shut off at once, that the piston and covers get broken. This
drawback is obviated by the arrangement of the cushioning valves at both ends
of the steam cylinder. By this means an absolutely certain and safe compression
is produced, and the striking of the piston against the cylinder covers is rendered
impossible.
These cushioning valves operate as follows:
On opening the exhaust port, the exhaust steam moves the valve plug m along
with it and closes the valve. The piston moves on, covers the ports and com-
pression begins. By this means the piston is forced back until the pressure of
the live steam presses down the valve plug, and the steam passes through the
valve into the cylinder. There thus always remains between the piston and the 5
cylinder cover a cushion formed by the steam which has again been compressed.
The valves may also be arranged in the cylinder covers.
Having now particularly described and ascertained the natur of my said
invention and in what manner the same is to be performed, I decla
claim is:-
(1\ A
77
that what

page_text: is arranged to be reversed by means of the straps e e¹ or of the strap g, through
the medium of the rods a be, which straps project with a portion of the same
into the path of the roller mounted in the cross head f to an extent corresponding
to the desired expansion or cut-off, and are operated by said roller, the slide valve
experiencing an acceleration at the end of its travel by means of the spring-
pressed rollers which roll on the bevelled end portions of the paths of the slide
valve as set forth.
(2) In a slide valve gear as specified in Claim 1, an arrangement for preventing
the engine from racing, consisting of two cushioning valves arranged at both ends
of the cylinder, the plugs m of said valves being pressed upon their seats during
the exhaust and thus producing compression after the exhaust port has been
covered, said compression lasting until the pressure of the freshly admitted steam
raises the valve plugs m again, as set forth.
(3) The improvements in direct acting steam engines as herein before described
and shown.
9th day of November 1897.
ROBERT E. PHILLIPS, Assoc. M. Inst. C.E., M.I. Mech. E.,
Consulting Engineer and Patent Agent,
70, Chancery Lane, London, W.C., Associate Agent.