PRX 48sqft SMBW 4000 Series DE Filter Our SMBW 4000 Series Filters remove the tiniest of contaminants, so your water truly sparkles. In addition to exceptional filtration, they feature sheet molded fiberglass tanks and Noryl?® rotary backwash valves for long life, dependable performance and easy maintenance. Features Maximum Operating Pressure 50 psi Corrosion-resistant 20 in. diameter fiberglass filter tank for strength and durability Unique Spiro-Mite grid design provides high efficiency filtration and longer filter cycles Exclusive clamp ring design is proven to be safe, strong and reliable. It allows for quick and easy access to internal components 2 in. plumbing connections provide maximum flow