To supply clean fuel, which is free from vapor, at the proper pressures and flow rates to the engine under all operating conditions is the primary function of an aircraft fuel system. On the jet aircraft, the fuel system has fuel tanks which are located in the center fuselage area and wings. The fuselage is the place where the center tank is located, while the wings are the places where the inner tanks and outer tanks are located. These fuel tanks are replenished with fuel through a filter cap on top of the wing. In this process, a fuel nozzle and a hose are employed. The hose is similar to the one which is used to refuel an automobile. With airplanes, however, we should take special attention not to allow the fuel nozzle spout to project very far into the fuel tank, since the tank can be damaged by it. In the center tank, two fuel pumps are installed. And two fuel pumps are installed in each inner tank. The fuel is allowed to be transferred from the outer tanks to the inner tanks through two transfer valves. Each inner tank feeds its respective engine. The fuel is cut off to the engines by two engine low pressure valves. The engines are also fed by the center tank. A cross feed valve is fitted to isolate or connect the left and right sides. The fuel system also feeds the APU. A low pressure valve is fitted to cut off fuel to the APU. From the aircraft fuel tanks, fuel is supplied, and the fuel will go through the necessary filters boost pump as well as valves, arriving at the engine driven fuel pump at last. From the pump, the fuel is delivered. The fuel control meters the fuel to the engine in proper quantities. Excess fuel is bypassed back to the pump.