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Page 2
20 � 30 = 600 kilogrammeters.
In the case of a pressure of 80 millimeters, we have:
20 � 80 = 1,600 kilogrammeters.
If we admit a product of 50 per cent., we shall have in the two cases,
for the power actually necessary:
600
---- = 1,200 kilogrammeters, or 16 H.P.
0.05
1,600
----- = 3,200 kilogrammeters, or 43 H.P.
0.05
Such are the limits within which the power of the motor should be able
to vary.
After successively examining all the different systems of engines now
in existence, and finding none which, in a plain form, was capable of
fulfilling the conditions imposed, Mr. E.D. Farcot decided to study
out one for himself. Almost from the very beginning of his researches
in this direction, he adopted the Woolf system, which is one that
permits of great variation in the expansion, and one in which the
steam under full pressure acts only upon the small piston. There are
many types of this engine in use, all of which present marked defects.
In one of them, the large cylinder is arranged directly over the small
one so as to have but a single rod for the two pistons; and the two
cylinders have then one bottom in common, which is furnished with a
stuffing-box in which the rod moves. With this arrangement we have but
a single connecting rod and a single crank for the shaft; but, the
stuffing-box not being accessible so that it can be kept in a clean
state, there occur after a time both leakages of steam and entrances
of air.
Mr. Farcot has further simplified this last named type by suppressing
the intermediate partition, and consequently the stuffing-box. The
engine thus becomes direct acting, that is to say, the steam acts
first upon the lower surface of the small piston during its ascent,
and afterward expands in the large cylinder and exerts its pressure
upon the upper surface of the large piston during its descent.
Moreover, the expansion may be begun in the small cylinder, thanks to
the use of a slide plate distributing valve, devised by the elder
Farcot and slightly modified by the son.
As the volume comprised between the two pistons varies with the
position of the latter, annoying counter-pressures might result
therefrom had not care been taken to put the chamber in communication
with a reservoir of ten times greater capacity, and which is formed by
the interior of the frame. This brings about an almost constant
counter-pressure.
The type of motor under consideration, which we represent in the
accompanying plate, is possessed of remarkable simplicity. The number
of parts is reduced to the extremest limits; it works at high speed
without perceptible wear; it does not require those frequent repairs
that many other cheap engines do; and the expansion of the steam is
utilized without occasioning violent shocks in the parts which
transmit motion. Finally, the plainness of the whole apparatus is
perfectly in accordance with the uses for which it was devised.
[Illustration: FARCOT'S IMPROVED WOOLF COMPOUND ENGINE.]
_Details of Construction._--Figs. 1 and 2 represent the motor in
vertical section made in the direction of two planes at right angles.
Figs. 3 and 4 are horizontal sections made respectively in the
direction of the lines 1-2 and 3-4.
The frame, which is of cast iron and entirely hollow, consists of two
uprights, B, connected at their upper part by a sort of cap, B�, which
is cast in a piece with the two cylinders, C and _c_. The whole rests
upon a base, B�, which is itself bolted to the masonry foundation.
Each of the uprights is provided internally with projecting pieces for
receiving the guides between which slides the cross-head, _g_, of the
piston rod. The slides terminate in two lubricating cups designed for
oiling the surfaces submitted to friction.
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