Full definition
Mechanical device that maintains correct belt tension throughout the operating life, compensating for belt elongation (stretch) over time. Types: (1) Manual/fixed — adjustable bolt or screw mechanism, requires periodic retensioning, simplest and most economical. (2) Automatic spring-loaded — constant-force spring on a pivoting arm, self-adjusting, used in automotive serpentine drives and critical industrial applications. (3) Gravity/counterweight — weighted carriage on a guided track, for long conveyors and heavy-duty drives. Best practice: install on the slack side, as close as possible to the smaller pulley, on the outside of the belt (flat idler for V-belts, grooved for Poly-V). An automatic tensioner eliminates the need for periodic retensioning and maintains optimal tension as the belt wears. Per ISO 1081 and CEMA guidelines for conveyors. Brands: Gates, Dayco, Fenner.