Amtrol Well-X-trol Pressure Tank Steel Blue 4.4 gal.. Amtrol invented the first pre-pressurized well tank over 50 years ago as a better solution to traditional air-over-water tanks. This revolutionary product featured an innovative design that uses a hoop ring and groove to lock the diaphragm, liner and shell together. Today, Well-X-Trol is still the standard of the industry with many unique features including high strength steel to deliver 150 PSIG working pressure, patented Turbulator water circulator device and patent pending antimicrobial liner that neutralizes bacteria on contact.