Full definition
A specialized pulley with movable flanks (conical halves) that can be adjusted axially relative to each other, changing the effective pitch diameter where the belt rides. As the flanks move closer, the belt rides higher (larger effective diameter, higher speed); as they separate, the belt drops lower (smaller effective diameter, lower speed). Requires a matching wide-section variable-speed belt (e.g., 1422V, 1922V, 2322V). Speed range typically 3:1 to 10:1 in a single stage. Two types: (1) manually adjustable (screw mechanism, adjusted while stopped), and (2) automatic (spring-loaded or motor-actuated, adjusts under load). Used in drill presses, milling machines, HVAC fans, agricultural equipment, and textile machines. The driven pulley typically has a spring-loaded mechanism that compensates for belt length as the driver pulley diameter changes. Per DIN 7719. Brands: TB Woods, Lenze, Reeves.