AD 56478720 Primary Engine Air Filter for Nilfisk Advance Power Sweepers and Scrubbers. A cylindrical engine air filter. This filter measures 14" x 4" with a 2-1/2" inside diameter. Works in conjunction with the inner secondary air filter, AD 56478722. Priced Each. Replaces Nilfisk Advance 482720, 56482720. Our Part Number AD 56482720