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.