Page:The Kinematics of Machinery.djvu/497

 VALVES AS CLICK-TRAINS.

475

FIG. 344.

clicks, which must be p aced in and removed from their fixing position by external means.

The common pump- clack, Fig. 344, corresponds to the free click- train with the common pawl, Fig. 345. The valve b is the pawl, which prevents the click-rack a, the water, from moving downwards. The tube c, which carries also the joint for the valve, corresponds to the frame c of the click-train. It is merely accidental that the hinge of the valve is made of a flectional element, leather; valves with cylinder-pair joints are of course quite usual. The fluidity of the pressure organ which forms the click-rod makes the click teeth unnecessary. The cock, Fig. 346, corresponds to a fast-click, such, for example, as that in Fig. 323. The train shown in Fig. 347, which is used in Thomas' calculating machine, is also exactly ana- logous to the cock, a is the click-piece (here a wheel turning about a fixed centre) corresponding to the water in Fig. 346 ; if 6 be turned through a certain angle it interposes no obstacle to the

motion of a, in the position shown it prevents it from turning in either direction. The frame c contains two elements, one for carrying a, the other for carrying 6, exactly as in Fig. 346. The sluice-valve used in water or steam-pipes, Fig. 349, corresponds to the fast click in Fig. 349 ; a click rod, I valve or click, c frame carrying both. Balanced valves of all kinds represent clicks so arranged that the fluid pressure affects their engagement and disengagement to the smallest possible extent. The reader can find a multitude of other analogies, for we have here an actual correspondence to deal with, and not a mere fanciful parallel.

If a valve be opened only a small distance, so that the pressure organ encounters great resistance in passing through it, the click-train acts as a brake. These two classes of mechanisms, therefore, pass here one into the other, exactly as we have already found ( 122) to be the case with trains composed of rigid ele- ments only.

FIG. 345.