Pro-Grid DE comes with the new stronger PermaGlass XL, an improved glass reinforced copolymer, providing the ultimate strength, durability, and long life. Pro-Grid filters also combine high technology features with a "service-ease" design for dependable operation and low maintenance.. Incorporates vertical curved grids to maximize square footage. This filter incorporates an internal air relief and Noryl bulkhead fittings. Valves sold separately.