Amtrol designed and patented the first Extrol diaphragm expansion tank in 1954 to control system pressure and help reduce energy consumption in heating and chilled water systems. Over six decades later, Extrol is still the world's leading expansion tank brand, setting the standard for quality, reliability and innovation. All Extrol tanks are made in the USA at our ISO registered facilities by American workers dedicated to producing the highest quality expansion tanks in the world.