(218) A necessary corollary to the process of doubling slivers is the provision of means whereby the passage of all the combined slivers is ensured throughout their entire length. Assuming, for instance, that eight ends were being passed through the machine, and one of them from some cause failed, it is clear that the delivered sliver would be diminished in thickness one-eighth. Of course the attendant would rectify this at the earliest moment, but, in the interim, a large amount of the thin sliver might have been produced. In order to avoid this serious evil, it is the practice to fit all machines of this class with a detector motion, which operates on the failure of any of the ends. Referring now to Fig. 123, it will be seen that, after passing through the guide-plate =F=, the sliver is conducted over the end of the short lever =G=, which oscillates on a knife-edge bearing. The end over which the sliver passes is hollowed out, and is highly polished, while the other end—which is slightly heavier—is beneath a curved guide-plate, shown in section. The lever =G= is balanced so that the pressure of the sliver during its passage is sufficient to keep the spoon-shaped end down, while, on the breakage or failure of the sliver, the lever oscillates on its bearing. A reference to Fig. 124 will show that a shaft =H=, driven from the main shaft, as shown, has on it an eccentric, to which the rod =I= is attached. This rod is attached to a bell crank lever =J=, on the shaft =K=, which is oscillated, and thus gives a reciprocal movement to the levers =L=, carrying a square bar. A bell crank lever =M= is also placed upon the shaft =H=, and ordinarily engages with a snug on the stop rod =N=. The latter has a helical spring attached, which always tends to pull it longitudinally, and when it is released, to throw over the strap from the fast to the loose pulley.
(219) Assuming now that one of the slivers has failed, its spoon lever will oscillate and its weighted end will fall. It thus comes in the path of the reciprocating bar in the lever =L=, which is prevented from completing its traverse. The result is that the lever =M= is oscillated and the stop rod =N= released, so that the spring named at once throws the strap on to the loose pulley and stops the machine. As the reciprocations of =L= are very rapid, no considerable length of the sliver can pass without causing the stoppage of the machine. The attendant is compelled to piece up the broken end, and “single” is thus prevented.