It was once customary to refuel an airplane by pulling a tank vehicle up alongside the plane, and pumping fuel from the vehicle tanks into the fuel tanks of an aircraft.
Today, at large airports a different system is used. Pipes from storage tanks, located on the perimeter of the airport, carry fuel to various locations on the runway apron. At each of these locations, a manhole contains underground connection points or hydrants located just beneath the surface. When an airplane arrives at the position for refueling, a hydrant refueler pulls up alongside the airplane. The driver raises the lid on the manhole, and connects one end of a hose-located on his truck-to a hydrant. The other end is connected to equipment on the hydrant truck which separates any water from the fuel that may be present, filters the fuel,and meters the fuel delivery. After it has been filtered and metered, the fuel flows through a second hose connected to the airplane fuel tank.
An second connection from the vehicle to the hydrant controls the pressure of the system. The pumping source for hydrant systems is not on the refueler itself. Rather, pumping pressure on the entire system is provided by stationary pumps that may be located on the perimeter of the airport, as far as 2 or 3 miles away.
