Full definition
An auxiliary (non-powered) pulley introduced into a belt drive layout to redirect the belt path around obstacles, increase the wrap angle on the driver or driven pulley, or accommodate spatial constraints in the machine frame. Also called a snub pulley when positioned close to a drive pulley specifically to increase wrap angle. The deflection pulley adds two additional bending cycles per revolution, increasing flex fatigue — so its diameter must meet or exceed the minimum for the belt profile. Located on the slack side whenever possible to minimize bearing loads. Bearing selection must account for belt tension and pulley weight. For timing belts, a flat (non-toothed) back-side idler is used when the belt wraps on the smooth back; a toothed idler is used for inside (tooth-side) contact. Per ISO 1081 design guidelines. Adding a snub pulley near the drive pulley can increase wrap from 150° to 210°, boosting capacity by 20-30%.