A gravity-fed fuel delivery system is provided. A central storage tank holds fuel to re-supply a number of pump trucks or other mechanized equipment, such as on a hydraulic fracturing location, and can be selectively raised or lowered. Hoses or other conduits extend from the central storage tank to individual fuel tanks of the equipment to be refueled. Adapters allow connection of the distal end of each hose or conduit to an inlet opening of a fuel tank. A float valve assembly senses when fuel inside an individual fuel tank is below a predetermined level, thereby mechanically opening a valve assembly to permit fluid to flow from the central storage tank, through a conduit, through the float valve assembly and into the fuel tank.