Pressurized Valves: The Subterranean Mechanics of Fire Hydrants

Standing silently on city corners, fire hydrants represent the ultimate pressurized fail-safe of urban safety. In regions that experience freezing temperatures, these heavy cast-iron pillars harbor a brilliant thermodynamic secret: they are completely empty. To prevent water from freezing and violently expanding which would shatter the metal casing engineers developed the dry-barrel hydrant. The...