WaterWorker HT-4B Water Worker Vertical Pre-Charged Well Tank, 4 Gal, 3/4 in Mnpt, 100 Psi, Steel, 4-Gallon, Blue Designed to meet the requirements of, and are listed by the National Sanitation Foundation (NSF) under ANSI/NSF Std 61 The Butyl diaphragm has seamless construction and is designed to flex rather than stretch and crease like bladder tanks The polypropylene liner for the water reservoir will not flake, chip, crack or peel and does not impart taste and odor to the water Diaphragm, liner isolate water from contact with deep drawn steel domed shell - twice as strong as rolled steel shell of same thickness A high gloss enamel finish protects tank from the elements Pre-charged to 25psi: please refer to product manual for proper pre-charge setting