Pulley

Collier's New Encyclopedia (1921)

in mechanics, one of the six simple machines or mechanical powers. It consists of a small circular plate or wheel which can turn round an axis passing through the centers of its faces, and having its ends supported by a framework which is called the block. The circular plate has a groove cut in its edge to prevent a string from slipping pulley. off when it is put round the pull With a single fixed pulley (that is one in which the block in which the pulley turns is fixed), there is neither gain nor loss of power; for, as the tension in every part of the cord is the same, if a weight be suspended at one extremity, per cent. over the amount contained in an equal weight must be applied at the pure air. A valve mechanism causes alother to maintain equilibrium. Hence, ternate pressure and suction to be apthe effect of a fixed pulley is simply to change the direction of a force. By means of movable pulleys one can gain mechanical advantage, greater or less, according to the number and mode of combination of the pulleys. Fast pulley, a pulley firmly attached to the shaft from which it receives or to which it communicates motion. Loose pulley, a pulley running free on the shaft, to receive the belt and allow it still to traverse without being affected by, or affecting the motion of, the shafting. Sliding pulley, a kind of coupling in which the band-pulley is slipped into or out of engagement with an arm freely attached to the shaft and rotating therewith.