Improvements in and relating to Compound Steam Engines.
Year: 1894

page_text: Date of Application, 14th Aug., 1894-Accepted, 22nd Sept., 1894
COMPLETE SPECIFICATION.
Improvements in and relating to Compound Steam Engines.
I, WILHELM SCHMIDT, of Villa Henkel, Wilhelmshöhe near Cassel, Province
of Hesse-Nassau, German Empire, Engineer 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 compound steam engine, the manner of working of
which is similar to that of a compound-engine with receiver. There are, however,
the differences, that one side of the low-pressure piston is constantly under the
influence of the low-pressure steam, and that the space between that side of the
low-pressure piston and the opposite cylinder cover (Fig. 1), or the opposite side of
the high-pressure piston respectively (Fig. 2), forms part of the receiver, the
capacity of the latter being, therefore, a variable one.
The objects of my invention are, first, to provide an engine, which is specially
adapted for use with superheated steam, and, second, to cause in such engine the
high-pressure cylinder to be cooled by the low-pressure steam, and the low-
pressure cylinder to be heated by the receiver-steam, as is hereinafter more fully
described.
In order to make my invention more clear, I refer, first, to Fig. 1 of the accom-
panying drawing, in which is shown a longitudinal section through a double-acting
engine constructed according to my invention. In this fig. a is the high-pressure
cylinder, within which works the hollow high-pressure piston a³ of plunger-like
configuration. This piston extends into the low-pressure cylinder, and carries at
its end the low-pressure piston 3, by which latter the said cylinder is divided
into two compartments or chambers b¹².
Chamber extends, as a matter of course, up into the hollow plunger, and
constitutes the variable receiver-part mentioned in the preamble. This part is in
constant communication with the receiver proper c by a port d, whilst the high-
pressure cylinder a and the annular chamber of the low-pressure cylinder are
alternately brought into communication with the receiver proper c by the piston
valves e and f. These valves are made integrally, and are simultaneously operated
by one and the same valve-rod 9.
Supposing, the valves to be in their highest position, the high-pressure steam
entering the engine at will flow into cylinder a through the groove around the
contracted portion of valve e, and through the channel i. During this time, the
low-pressure steam contained within the receiver will flow into the annular
chamber b, acting therein on a piston surface of a size equal to the difference
between the working-surfaces of the two pistons. As, now, also chamber b² is
(constantly) filled with the low-pressure steam, there is consequently a pressure
counteracting the pressure of the high-pressure steam, the said counteracting
pressure being produced by the influence of the low-pressure steam upon the lower
side of the high-pressure piston.
During the expansion-period the valves e fare in their middle position, as shown
in the drawing. If, thereafter, the valves are lowered, the high-pressure cylinder
will come into communication with the receiver proper c, whilst chamber 61 of the
low-pressure cylinder communicates through the outlet k either with the atmosphere,
or with a condenser.
The chambers a and b, as well as the receiver, are, thus, filled with steam of
equal pressure, and the piston on its return stroke is acted on by a pressure
constituted by the influence of the low-pressure steam on a piston-surface of a

page_text: size equal to that of the difference between the working-surface of the two
pistons.
Besides the chamber 62 of the low-pressure cylinder, also the annular space c
around the high-pressure cylinder forms part of the receiver. Therefore, the
latter cylinder as well as the small piston is constantly cooled by the low-pressure
steam present within said space c', whilst the low-pressure steam present within
chamber 62 constantly heats the low-pressure cylinder as well as the large piston.
By reason of these functions of said spaces, the engine is specially adapted to be
driven by superheated steam; there is, then, the further advantage that stuffing
boxes between the high and low pressure cylinders may entirely be dispensed with.
The same advantages may be attained by the modified form of construction,
shown in Fig. 2, in which is represented a single-acting engine, the two cylinders of
which are open on their neighbouring sides. The space 62 between the high-
pressure piston a³ and the low-pressure piston 63 is the one, which constantly
communicates with the receiver proper c, and forms the variable portion of
the same.
The co-operation of the two hollow slide-valves e and with regard to the high-
pressure cylinder a and the low-pressure cylinder b¹ is similar to that described
with regard to Fig. 1. If the pistons are in their highest position, the valves will
be in their lowest one, and live steam will flow through the groove around the
contracted portion of valve e, and through channel i, into the small cylinder a. At
the same time, communication has been established by valve f between chamber 61
and the atmosphere, or a condenser respectively, so that the low-pressure steam
present within said chamber may escape. The low-pressure steam present within
chamber 6 thus contributes to the down-stroke of the pistons with a pressure on a
surface equal to the difference between the working-surfaces of the two pistons, as
said steam is then acting on the upper side of the larger piston, as well as on the
lower side of the small one.
If, thereafter, the position of the valves is the reverse one, i.e. if they are in their
highest position, the variable receiver portion 62, as well as the cylinder-chambers a
and will be in communication with the receiver proper c, that is to say, all
compartments of the engine will be filled with steam of the same tension.
The pistons are at this time moving upwards, which is performed by the vis viva
of the rotating parts (not shown) of the engine, as the pressure of the steam on the
two surfaces of each piston is the same. This comes, however, not wholly to pass,
as there will arise during the upstroke of the pistons a slight compression in
chamber a, and a slight expansion in chamber 61, both on account of the throttling
action of the steam ports. In consequence thereof, there is always a certain
pressure tending to act on the pistons in the direction of the working-stroke of the
latter. By reason of this pressure, the caps of the bearings are perfectly relieved
from any upward pressure, as any change in the direction of the pressure of the
crank-axle on its bearings is effectively prevented.
Having now particularly described and ascertained the nature of this inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
1. A compound steam engine with a differential piston, in which the larger side
of the latter constantly communicates with a receiver, and the annular side of said
piston is alternately communicating also with said receiver and with the exhaust
port of the engine, for the purpose of first, obtaining a double acting engine by
effecting the return-stroke of the differential piston by the excess pressure acting
on the larger side of the same, and secondly heating by means of the receiver steam
the cylinder and piston walls forming the annular space from which the steam is
escaping, substantially as described.
2. A compound steam engine with two co-axial pistons in which the neighbouring
sides of the two pistons constantly communicate with a receiver, and the other side
of the larger piston is in alternate communication with the said receiver and with

page_text: the exhaust port of the engine, for the purpose of heating by means of the receiver
steam the cylinder and piston walls forming the space between the two pistons,
substantially as described.
Datel L 141 1
CA
1004
WILHELM SCHMIDT,
By Thos. Ernest Halford,
11, Furnival Street, London, E.C., Agent for the Applicant.