Page:The Kinematics of Machinery.djvu/381

 SIMPSON AND SHIP TON, KNOTT. 359

no way was known of throwing light on the matter, because the methods hitherto used for describing such motions have to a great extent failed in reaching their real underlying principles.

What we have before us is simply a reduced swinging block, the link d omitted and a and c made respectively piston and chamber, the former being the driving link. The formula for the mechanism is (C'^P-^i d, and for the chambering ( F") = a, c. Disregarding the latter and also the reduction, the chain is simply that shown in Fig. 226 (ante}. Kelatively to c, a describes similar oscillations to those of the piston d in Figs. 2 and 3, PL XVI., from which it differs only in having rotation as well as oscillation. In the machine itself a suitable valve gear was used to control the admission and exhaust of the steam just as in the former cases. It is obvious, however, that the reduction of the chain, which has necessitated the use of a higher instead of a lower pairing between c and a, has made it extremely difficult to keep the piston steam- tight. I may add that the same mechanism, (CgP- 1 -); d } has been employed also by an American Broughton* as a pump. He uses trunnion valves arranged upon the shaft 2 of the piston a.

Fig. 3. PL XVII. Pump patented by Knottf in England 1863. Here the link d has become piston and I chamber, the chain is not reduced. The prism 4 of the link d, -which is placed within 3 as in our schematic Fig. 242, makes a water-tight joint with the block c, as does the periphery of the open cylinder 1 with the cylindrical wall of the chamber. In the upper position of d there is for an instant free communication between the suction and delivery pipes as in Pattison's pump ; apart from this, however, the fluid is drawn in continuously, without the necessity of valve gear, upon one side of the piston, and discharged continuously from the other, by the rotation of a. This link is therefore given as the driving link in the formula. According to our former definition Knott's pump is single-acting, while the four other arrangements of the same mechanism which we have mentioned are double-acting.

Fig. 4. PL XVII. Blowing machine, patented in Prussia by Wedding in 1868. The chain (C^P 1 -) is here reduced by the

\ Newton, London Journal of Arts, &c. New series, vol. xix., 1864; also Konig, Pumpen (Jena 1869), p. 103, where, however, there is an inaccuracy in the figure.
 * Propagation Industrielh, iv. 1869, p. 145. The French patent is dated 1856.