CL 50021A 17hp Kawasaki Engine Pre-Filter for Nilfisk Advance, Clarke High Speed Burnishers. Foam engine pre-filter for high speed burnishers equipped with the 17hp Kawasaki engines. Protects the CL 50005A air filter found on these engines. Commonly found on Nilfisk Advance, Clarke PBU high speed burnishers equipped with the 17hp engines (will not fit 13hp Kawasaki models -- use CL 53590A Pre-Filter, CL 53574A Filter). Replace your used dirty filter with a new engine air filter. Use our CL 50005A. One pre-filter required per unit. Priced Each. Replaces Nilfisk Advance, Clarke 50021A, Kawasaki 11013-7001. Our Part Number CL 50021A