Pulley

a rotating part of a belt drive or a cable transmission, made in the form of a wheel around which a flexible link passes. Drive pulleys and driven pulleys, which transmit torque, are fastened to shafts by means of, for example, key or spline joints. Pulleys that do not transmit torque, such as idler and tension pulleys, turn freely on shafts or axles. Pulleys with grooved surfaces are sometimes called sheaves.

Pulleys are available in a wide variety of designs. Pulleys of small diameter are manufactured in one solid piece (Figure l,a). Pulleys of medium or large-diameter (Figure l,b) have a hub (1) and a rim (2) connected by a web (3) or by arms. Large pulleys are sometimes produced in two halves, which are bolted together. Pulleys may be made of cast iron, steel (Figure l,c), a light alloy, plastic, or—in some cases—wood.

Figure 1. Pulleys: (a) a one-piece pulley, (b) a pulley with a hub and rim, (c) a pressed-steel pulley, (d) a step pulley

Flat-belt pulleys (Figure 1,a) have a cylindrical or crowned peripheral surface to prevent the belt from being thrown off; flanges (4) are sometimes used for the same purpose. V-belt pulleys for single-belt or multiple-belt drives have grooves with a trapezoidal cross section (Figure l,b). Round-belt pulleys have a groove with a rounded bottom. Timing-belt pulleys have flanges and axial grooves for the teeth of the timing belt. Step pulleys (Figure 1,d) are used in drives in which the transmission ratio is adjusted by shifting the belt from one step to another. Doublecone pulleys in continuously variable transmissions with a wide V belt are produced with one or two springloaded movable cones; the displacement of one or both cones is forced.

(Russian, espander), a piece of athletic training equipment with springs or weights, used to create an additional load on specific muscle groups during various physical exercises, such as stretching and lifting weights. Both stationary and portable types are used.