As well known, in every well-constructed injection pump, there is a
system of gearing which acts upon the suction valve and stops the
operation of the pump as soon as the requisite pressure is reached;
but the piston, for all that, continues its motion, and, besides the
resistant work of the pump has passed through different degrees of
intensity, seeing that at every moment of its operation the piston
has preserved the same stroke and velocity. We are speaking, be it
understood, of pumps that are controlled mechanically. In the one that
we are about to describe, things take place far otherwise. In measure as
the pressure increases, the stroke of the piston diminishes, and when it
has reached its maximum, the motion of the piston ceases entirely. If,
during the operation progression undergoes more or less variation,
that is, for example, if it diminishes at a given moment to afterwards
increase, the stroke of the piston undergoes all the influences of it.
The pump of which we speak is shown in Figs. 16 to 21, and is the
invention of Messrs. Laurent Bros. & Collot. It may be described briefly
as follows:
The apparatus, as a whole, has for base a cast-iron reservoir; A, to the
top of which is fixed the pump properly so-called, B, as well as the
clack box, A, and safety valve. The pump is placed opposite an upright,
D, whose top serves as a guide to the prolongation, E, of the piston
rod. This latter is traversed by a pivot, a (Fig 19), on which is
mounted a lever, F, whose outer extremity is articulated with a
connecting rod, G, which is itself connected with the cranked shaft,
G¹. This shaft has for its bearings two supports, b, attached to the
reservoir, and carries the driving pulleys and a fly wheel. The beam, F,
having to give motion to the piston in describing an arc of a circle at
the extremity attached to the connecting rod, must, for that reason,
have a fixed point of oscillation, or one that we must consider as such
for the instant. Now, such point is selected on a piece, H, having the
shape of the letter C, and which plays an important part in the working
of the pump. This piece is really a two-armed lever, having its center
of oscillation in two brackets, c, at the base of the reservoir. Fig. 17
shows the relation of the beam, F, and lever, H. The upper extremity of
this latter is forked, and embraces the beam, F, whose external surfaces
are provided with two slots, d, in which to move slides, e, attached to
studs, f, which are perfectly stationary on the extremities of the forks
of the lever, H. One of the slots is shown in section on the line 1--2
in Fig. 20, and on the line 3--4 in Fig. 21.
Things thus arranged, if we suppose the piece, H, absolutely stationary,
it is clear that, as the oscillation of the beam, F, is effected on the
studs, f, as centers, the piston of the pump will perform an invariable
travel whose extent will be dependent upon its position between such
point of oscillation and the point of articulation of the connecting
rod, G. But we must observe that even according to such a hypothesis,
the point, f, would not be entirely stationary, because the point
of articulation, a, upon the piston rod being obliged to follow an
invariably straight line, the slots, d, will have to undergo an
alternate sliding motion on the slides, e, save, be it understood,
when the latter are brought to coincide exactly with the center of
articulation, a. Now we shall, in fact, see that the point, f, can move
forward in following the slots, d, and that it may even reach the point
of articulation, a, of the beam, F, on the rod, E, that is to say,
occupy the position shown in Fig. 18, where the oscillation of the beam,
F, being effected according to the point, a, the stroke of the piston
has become absolutely null.
The position of the piece, H, is, in effect, variable with the pressures
that are manifested in the pump. It will be seen that the latter has a
tubular appendage, g, in whose interior there plays what is called
a "starting rod," h, which is constantly submitted to the pressures
existing in the interior of the pump, and which rests against the lower
arm, H¹, of the piece, H. But this latter is also loaded at the opposite
side with heavy counterpoises, i, which counterbalance, within a
determinate limit, the action of the rod, h, that tends constantly to
cause the lever, H, to oscillate around its pivot, in the brackets, c.
To sum up, then, as long as the pressure in the pump has not reached a
determinate limit, the lever, H, held by its counterpoises, _i_,
will keep the position shown in Fig. 16, and for which the center of
oscillation, f, corresponds with the maximum stroke of the pump piston.
But as soon as such limit is exceeded, the equilibrium being broken, the
action of the rod, h, predominates, the piece, H, reverses from right to
left, the point of oscillation, f, moves forward in the slots, d, and
the stroke of the piston is reduced just so much. If, finally, the
pressure continues to increase, the motion of the piece, H, will
continue, and the point of oscillation, f, will reach the position for
which the motion of the piston ceases completely (Fig. 18).
But it results further, therefrom, that if when such position is
reached, the pressure diminishes, the lever, H, will, under the
influence of its counterpoise, tend to return to its first position and
thus set the piston in motion. As we remarked in the beginning, the
automatism of these functions is absolutely complete.
It will be remarked that the piece, H, is provided with an appendage,
H², whose interior forms a rack. This rack engages with a pinion, I,
mounted on an axle, J, which carries externally a fly wheel, K. This
axle, J, moves with the various displacements of the lever, and its fly
wheel overcomes by its inertia all backward and forward shocks resulting
from the thrusts due to the sliding of the steel slides in the different
positions of the connecting rods. Such shocks would make themselves
especially felt while the dead centers were being passed.
The velocity with which this pump runs varies from 75 to 80 revolutions
per minute. It easily gives a pressure of 200 atmospheres. With a
hydraulic press having a piston O.27 of a meter in diameter, it
permits of effecting in ten minutes the extraction of the oil from 25
kilogrammes of colza seeds. Referring to the drawings, the scales for
Figures 16, 17, 18 are one-fifteenth actual size, and Figures 19, 20,
21, one-tenth.--_Machines, Outils et Appareils_.
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