The invention of pressure engines brought to light a _new_ mode of
employing water as a motive agent: and also the means of applying
it in locations where it could not otherwise be used; with pressure
engines the motive agent may be taken to the machine itself. In valleys
or lowlands, having no natural fall of water, but where that liquid
can be conveyed in tubes from a sufficient elevation (no matter how
distant the source may be), such water, by these machines, may be
made to propel others; unlike the steam engine, a pressure engine is
inexpensive, and simple in construction—it requires neither chimneys,
furnaces nor fuel; neither firemen nor engineers, nor is there any
danger of explosions. It may be placed in the comer of a room, or be
concealed under a counter or a table. It may be set in operation in a
moment, by opening a cock, and the instant the work is done, it may be
stopped by shutting the same, and thus prevent waste of power.
Pressure engines afford an illustration of the variety of purposes to
which a _piston and cylinder_ may be applied. These were probably first
used in piston bellows; next in the syringe; subsequently in pumps
of every variety; and then in water-pressure and steam engines. _The
moving piston is the nucleus or elemental part that gives efficiency to
them all_; and the apparatus that surround it in some of them, are but
its parts.
The history of machines composed of pistons and cylinders also
illustrates the process by which some simple inventions have become
applied to purposes, foreign to those for which they were originally
designed—each application opening the way for a different one.
In another form hydraulic motors have been adopted, in favorable
locations, as first movers of machinery, and when thus used, _they
exhibit a very striking resemblance to high pressure steam engines_.
Indeed, the elemental features of steam and pressure engines are
the same, and the modes of employing the motive agents in both are
identical—it is the different properties of the agents that induces a
slight variation in the machines—_one being an elastic fluid, the other
a non-elastic liquid_.
[Illustration: FIG. 131.]
[Illustration: FIG. 132.]
In steam engines a piston is alternately pushed forward and back in
its cylinder by steam; and by means of the rod to which the piston is
secured, motion is communicated to a crank and fly-wheel, and through
these to the machinery to be driven: it is the same with pressure
engines when used to move other machines, except that instead of the
elastic vapor of water, a column of that liquid drives the pistons to
and fro.
NOTE.—“The hydraulic engine of Huelgoat, in Brittany, is used to
drain a mine; is single-acting, and acts directly to lift the piston
of the pump. It makes five and a half strokes per minute, the stroke
being a little more than eight feet in length. The piston-rod is 767
feet long, and it weighs 16 tons. The power of the engine is derived
from a source at a height 370 feet above its own level.”—KNIGHT.
In default of a natural head of sufficient pressure, the head is
sometimes established in _an accumulator_ of power; this is a body
of water driven into a reservoir under heavy pressure, by forcing
pumps worked by power. In cities where the water distribution is from
elevated reservoirs, and in which the water supply is sufficiently
abundant to justify the application of a portion of it to industrial
uses, the water-engine or motor is recommended.
The following description of a water engine of world-wide adaptation
will, if attentively studied, show the working of an approved type of
this machine:
Ramsbottom’s hydraulic engine (Figs. 129 and 130), is oscillating,
and employs two cylinders _b_, _l_, operating one crank-shaft, _a_,
by means of two cranks at right angles to each other. In one of the
accompanying figures the channels of induction are marked _j_ and are
cast on the cylinders; the dotted circle _c_ shows the position of
the supply and discharge pipes; in the other figure these pipes are
indicated by arrows. The two views are vertical cross-sections at right
angles to each other, one being through the axis of the cylinders and
the other through the middle post in which the inner trunnions of the
cylinders are journaled. The apertures of induction are seen at _h_
and those of eduction at _i_, and have the form of truncated circular
sectors, whose center is the center of motion.
The induction and eduction spaces are divided by a sectoral partition;
the apertures of admission and discharge on the sides of the cylinders
are of similar construction. The surfaces of contact between the
cylinders _b_, _l_ and the support _d_ are planed and polished and
are made water-tight by the adjusting screws _m_ _m_ of the pivots.
When the piston _p_ is at the end of its course in either direction
the cylinder and crank are vertical, and the valves all momentarily
closed, the openings by which the channels _j_ _j_ communicate with the
discharge and supply pipes presenting themselves exactly opposite the
solid sectors which separate _h_ from _i_.
In the next moment the flow of water will recommence, the cylinder
discharging itself from the full side of the piston, and filling anew
from the opposite side. Air chambers and relief-valves are used as a
provision against counter-pressure and hydraulic shocks.
The Brotherhood three-cylinder reciprocating engine is an appliance for
producing rotary motion by water-pressure.
The working parts of the Brotherhood three-cylinder hydraulic engine
consist only of the three pistons and connecting rods, one crank and
one rotating balanced valve and spindle which fits into the driver and
is turned direct from the crank-pin; there are no glands, stuffing
boxes, or oscillating joints.
It is shown by Figs. 131, 132. The three cylinders, A (made in one
casting) are always open at their inner ends, and are attached to a
central chamber, B. They contain three pistons, P, which transmit
motion to the crank-pin through the rods, C. The water is admitted and
exhausted by means of the circular disc valve, V, having a lignum-vitæ
seat. The valve is rotated by the eccentric pin, E. A face view of this
valve is shown above the steam chest. It has segmental ports which, in
rotating, pass over apertures in the valve seat. There being no dead
centers, the engine will start from all positions of the crank-pin, and
a uniform motion of the shaft is produced without a flywheel.
The pressure is always on the outer end of the piston, so that the
rods, C, are in compression, and take up their own wear. This engine is
well adapted for transmitting pressure to appliances which are worked
intermittently, as, owing to the great speed at which it can be run, it
will not only save the loss from friction (where gearing is employed),
but will also reduce the friction in the machine itself by enabling
the gearing for increasing speed to be dispensed with. The production
of this simple hydraulic rotary engine led to its wide application to
capstans.
Fig. 133 represents a small hydraulic engine—The Compton Hydraulic
Motor—attached to and operating a gas-compressor. It shows a style
of water motor in large use in connection with city water-mains. A
pressure of 15 to 20 lbs. per square inch is sufficient to operate it;
the motor here illustrated occupies a floor space of 9 x 23 inches; it
will supply gas burners to the extent of 6,000 candle-power.
[Illustration: FIG. 133.]
The valve motion on the motor is unique in this, the outlets and inlets
have a positive motion by which they are simultaneously opened and
closed by the motion of the piston; this valve motion is designed to
overcome the back pressure; it has a governor, incorporated in the
valve-motion for the purpose of maintaining uniform pressure on the
main pipes.