The Hankison E3-28 (official part number 3211137) is a Grade 3 high-efficiency cohesive fine oil removal filter element designed specifically for compressed air systems. It is commonly installed as a pre-filter at the front end of adsorption dryers and membrane dryers, or at the rear end of refrigerated dryers, to remove fine solid particles and suspended oil droplets from the air, preventing contamination of downstream equipment.