Single deflection grille for ducts 0 OF CIRCULAR DUCT H mm 75 125 175 Selection table Product description Single deflection grille for circular ducts, KOOLAIR, model 21-SVC, of dimensions LxH, for supplying or returning air. It can incorporate volume control dampers (-RFS-05/06). Finished in steel sheet or any RAL colour upon request. Other models 21-SVR. Single deflection grille for rectangular ducts,. Mounting With screws. The grille is provided with holes for screwing. General dimensions The Selection Table shows a summary of dimensions. Other sizes available. Consult the Sales Department. LEGEND Q (m3/h): Air flow. Lwa [dB(A)]: Sound power level. APt (Pa): Total pressure loss. X (m): Throw for a maximum velocity of 0.25 m/s at the occupied zone AT = -10 °C (cold), installed at 2.7 m of height, with ceiling effect. Vk (m/s): Effective velocity.