Belt tighteners are sometimes used to give intermittent motion, as in the case of trip hammers; the belt being vertical is made long enough to run loose, until the tightening pulley closes the belt upon the pulley, taking up its slack and increasing the arc of contact.
"Modern Machine-Shop Practice, Volumes I and II"
Joshua Rose
The resistance offered by the introduction of carrying pulleys and tighteners is appreciable, and depends upon the pressure brought to bear against their journals.
"Modern Machine-Shop Practice, Volumes I and II"
Joshua Rose
The patent described thread tighteners above and below the work and an adjustment to vary the stitches for different kinds of material.
"The Invention of the Sewing Machine"
Grace Rogers Cooper