Year: 1894

page_text: Date of Application, 8th Dec., 1894-Accepted, 19th Jan., 1895

page_text: Assuming the piston b to be situated in the extreme or outermost position shown
in Fig. 1 then steam will pass through the port g (which is uncovered in this
position) of the slide valve m behind the piston 6 this taking place at the
commencement of the expansion period. As soon as the piston is at half stroke
that is to say has assumed the middle position above-mentioned (as shown in Fig. 3)
the port k of the slide valve is also opened simultaneously so that the steam behind
the piston instead of driving the piston onwards exhausts through this port k
and the cavity of the slide valve m to the passage n. This slide valve m at the same
moment closes the port k.
.
The piston which by these means had remained stationary in the central
position at half stroke now receives a fresh impulse from the fact that a suitable
movement of the main slide valve d causes steam to pass through the port p behind
the piston (see Figs. 3 and 4) so that the piston is impelled to the opposite end of
the cylinder a. This position is illustrated in Fig. 4.
.
5"
Now as the expansion period commences on the return stroke steam is admitted
to the steam cylinder a through the port h by suitable operation of the slide valve !
and such steam entering behind the piston 6 moves the latter again into its central.
or half-stroke position. The steam then exhausts (in a corresponding manner-35
before described) through the port i and the passage o-see Fig. 5.
Then after the port i is covered by a suitable movement of the slide valve / the
piston bis returned into its initial position by the steam admitted by the main slide
valve d through the port g-see Fig. 6.
The herein described sequence of operations is now repeated as will be readily
understood.
A particular advantage of this arrangement and construction consists in the fact
that the engine can be extremely easily stopped and kept in its middle position.
This is effected in the following manner :-
Let it be assumed that the piston has been moved from the position shown in
Fig. 1 into the mid-stroke position by the operation of the slide valve 'm. At this
instant the motion is automatically arrested and in order to stop the engine
altogether it is merely necessary by any suitable means or arrangement such as
would readily occur to any person conversant with the art to prevent the main
slide valve d from admitting steam through the port p.
If the engine is to be reversed this is effected in the following manner :-
Starting again from the position shown in Fig. 1 the piston has been moved by
means of the auxiliary slide valve m into the mid-stroke position and in the
ordinary further operation of the engine the piston would be moved by steam
entering through the port p up to the opposite end of the cylinder a. Now if this
is not to take place but it be desired to reverse the direction of motion of the engine
for any reason the main slide valve must be caused as shown in Fig. 6 to admit
steam through the port a whereby the piston is impelled back again into the
position shown in Fig. 1 thereby reversing the direction of motion of the engine.
*Fig. 7. illustrates a modification in which two auxiliary exhaust ports and s are
provided in the main slide valve. These ports serve to stop the piston instanta-
neously at the end of its stroke even in the absence of air-buffers because as soon as
the piston has moved past one of the ports and s an equilibrium or equalization of
pressure is instantaneously effected through the said port.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed 1 declare that what I
claim is
1.
1. Valve gear for steam engines which causes exhaust every time the piston
reaches the mid-stroke position. as well as at the end of the stroke of said piston.
2 valve gear for steam engines the use of auxiliary valves adapted to admit
steam only from the beginning of each stroke of the piston up to half-stroke of the
latter and then exhaust and again close the exhaust in combination and acting in
conjunction with an ordinary main valve adapted to only admit steam after the

page_text: piston is at half stroke arranged and acting substantially in the manner and for the
purposes herein before described.
3. In valve gear for steam engines the combination with the ordinary main valve
of two auxiliary valves such as land m adapted to uncover exhaust ports such as 2
and respectively when the piston is in the mid-stroke position in the cylinder
substantially as and for the purposes set forth.
4. The improved valve gear arranged constructed combined and acting sub-
stantially in the manner and for the purposes bereinbefore described and
illustrated in the drawings hereunto annexed.
Dated this 8th day of December 1894.
TONGUE & BIRKBECK,
Southampton Buildings, Chancery Lane, London, W.C.,
Agents for the Applicant.