Truestar Air Systems The purpose of sand trap louvres for fresh air intake is to lessen excessive dust loading on traditional stage filters and to stop sand particles from entering at low air velocity. It is designed specifically to be used in sandy locations, allowing clean air to enter while draining away the particles of sand. It comes with a typical setup for a 25mm filter (filter supplied separately). With its working mechanism accessible from the interior of the structure, an optional Opposed Blade Damper can be installed on the rear of the Louvre.